Xianchun Li

Interests

Teaching

Molecular Entomology

Research

Plant-insect interactions, gene regulation, transposable elements, Bt and insecticide resistance

Courses

Scholarly Contributions

Journals/Publications

• Deng, Z., Ren, Y., Guo, L., Xie, X., Wang, L., & Li, X. (2023). Genome-wide analysis of G-quadruplex in Spodoptera frugiperda. International journal of biological macromolecules, 226, 840-852.
  More info

  Spodoptera frugiperda (Lepidoptera: Noctuidae) is a globally distributed lepidopteran crop pest that has developed resistance to most insecticides. The G-quadruplex (G4) is a secondary structure in the genome enriched in the promoters for regulating gene expression. However, little is known about G4 in S. frugiperda, especially whether G4 is involved in insecticide resistance and pest control. In this study, 387,875 G4 motifs in the whole genome of S. frugiperda were identified by bioinformatics prediction. We found that 66.90 % of theseG4 structures were located in genic regions and highly enriched in the upstream regions of start codons. Functional and pathway analyses showed that the genes with G4 enriched in promoter regions participate in several metabolic processes. Further analyses showed that G4 structures occurred more frequently in the promoters of P450 and CarE gene families. It was also investigated that G4 ligand N-methyl mesoporphyrin IX (NMM) decreased P450 protein activity in larval midgut tissue. Cytotoxicity and bioassay results revealed that NMM and pesticides had synergistic effects on toxicity. In conclusion, our findings suggest that G4 motif could be a new potential target for pest control.
• Jia, B., Zhang, J., Hong, S., Chang, X., & Li, X. (2023). Sublethal effects of chlorfenapyr on Plutella xylostella (Lepidoptera: Plutellidae). Pest management science, 79(1), 88-96.
  More info

  The diamondback moth (DBM), Plutella xylostella (L.), is the most destructive pest of cruciferous vegetables worldwide. Chlorfenapyr is an important insecticide for controlling DBM. The impacts of three sublethal doses (LC , LC and LC ) of chlorfenapyr on the chlorfenapyr-exposed DBM individuals and their unexposed F and F offspring were investigated in order to reveal the non-lethal deleterious effects of chlorfenapyr and its potential hormetic effects.
• Benowitz, K. M., Allan, C. W., Degain, B. A., Li, X., Fabrick, J. A., Tabashnik, B. E., Carrière, Y., & Matzkin, L. M. (2022). Novel genetic basis of resistance to Bt toxin Cry1Ac in Helicoverpa zea. Genetics, 221(1).
  More info

  Crops genetically engineered to produce insecticidal proteins from the bacterium Bacillus thuringiensis have advanced pest management, but their benefits are diminished when pests evolve resistance. Elucidating the genetic basis of pest resistance to Bacillus thuringiensis toxins can improve resistance monitoring, resistance management, and the design of new insecticides. Here, we investigated the genetic basis of resistance to Bacillus thuringiensis toxin Cry1Ac in the lepidopteran Helicoverpa zea, one of the most damaging crop pests in the United States. To facilitate this research, we built the first chromosome-level genome assembly for this species, which has 31 chromosomes containing 375 Mb and 15,482 predicted proteins. Using a genome-wide association study, fine-scale mapping, and RNA-seq, we identified a 250-kb quantitative trait locus on chromosome 13 that was strongly associated with resistance in a strain of Helicoverpa zea that had been selected for resistance in the field and lab. The mutation in this quantitative trait locus contributed to but was not sufficient for resistance, which implies alleles in more than one gene contributed to resistance. This quantitative trait locus contains no genes with a previously reported role in resistance or susceptibility to Bacillus thuringiensis toxins. However, in resistant insects, this quantitative trait locus has a premature stop codon in a kinesin gene, which is a primary candidate as a mutation contributing to resistance. We found no changes in gene sequence or expression consistently associated with resistance for 11 genes previously implicated in lepidopteran resistance to Cry1Ac. Thus, the results reveal a novel and polygenic basis of resistance.
• Deng, Z., Zhang, Y., Gao, C., Shen, W., Wang, S., Ni, X., Liu, S., & Li, X. (2022). A transposon-introduced G-quadruplex motif is selectively retained and constrained to downregulate CYP321A1. Insect science, 29(6), 1629-1642.
  More info

  Insects utilize xenobiotic compounds to up- and downregulate cytochrome P450 monooxygenases (P450s) involved in detoxification of toxic xenobiotics including phytochemicals and pesticides. G-quadruplexes (G4)-forming DNA motifs are enriched in the promoter regions of transcription factors and function as cis-acting elements to regulate these genes. Whether and how P450s gain and keep G4 DNA motifs to regulate their expression still remain unexplored. Here, we show that CYP321A1, a xenobiotic-metabolizing P450 from Helicoverpa zea, a polyphagous insect of economic importance, has acquired and preserved a G4 DNA motif by selectively retaining a transposon known as HzIS1-3 that carries this G4 DNA motif in its promoter region. The HzIS1-3 G4 DNA motif acts as a silencer to suppress the constitutive and induced expression of CYP321A1 by plant allelochemicals flavone and xanthotoxin through folding into an intramolecular parallel or hybrid-1 conformation in the absence or presence of K . The G4 ligand N-methylmesoporphyrin IX (NMM) strengthens the silencing effect of HzIS1-3 G4 DNA motif by switching its structure from hybrid-1 to hybrid-2. The enrichment of transposons in P450s and other environment-adaptation genes implies that selective retention of G4 DNA motif-carrying transposons may be the main evolutionary route for these genes to obtain G4 DNA motifs.
• Fabrick, J. A., Heu, C. C., LeRoy, D. M., DeGain, B. A., Yelich, A. J., Unnithan, G. C., Wu, Y., Li, X., Carrière, Y., & Tabashnik, B. E. (2022). Knockout of ABC transporter gene ABCA2 confers resistance to Bt toxin Cry2Ab in Helicoverpa zea. Scientific reports, 12(1), 16706.
  More info

  Evolution of pest resistance reduces the benefits of widely cultivated genetically engineered crops that produce insecticidal proteins derived from Bacillus thuringiensis (Bt). Better understanding of the genetic basis of pest resistance to Bt crops is needed to monitor, manage, and counter resistance. Previous work shows that in several lepidopterans, resistance to Bt toxin Cry2Ab is associated with mutations in the gene encoding the ATP-binding cassette protein ABCA2. The results here show that mutations introduced by CRISPR/Cas9 gene editing in the Helicoverpa zea (corn earworm or bollworm) gene encoding ABCA2 (HzABCA2) can cause resistance to Cry2Ab. Disruptive mutations in HzABCA2 facilitated the creation of two Cry2Ab-resistant strains. A multiple concentration bioassay with one of these strains revealed it had > 200-fold resistance to Cry2Ab relative to its parental susceptible strain. All Cry2Ab-resistant individuals tested had disruptive mutations in HzABCA2. We identified five disruptive mutations in HzABCA2 gDNA. The most common mutation was a 4-bp deletion in the expected Cas9 guide RNA target site. The results here indicate that HzABCA2 is a leading candidate for monitoring Cry2Ab resistance in field populations of H. zea.
• Fang, L., Guo, L., Zhang, M., Li, X., & Deng, Z. (2022). Analysis of Polyadenylation Signal Usage with Full-Length Transcriptome in (Lepidoptera: Noctuidae). Insects, 13(9).
  More info

  During the messenger RNA (mRNA) maturation process, RNA polyadenylation is a key step, and is coupled to the termination of transcription. Various cis-acting elements near the cleavage site and their binding factors would affect the process of polyadenylation, and AAUAAA, a highly conserved hexamer, was the most important polyadenylation signal (PAS). PAS usage is one of the critical modification determinants targeted at mRNA post-transcription. The full-length transcriptome has recently generated a massive amount of sequencing data, revealing poly(A) variation and alternative polyadenylation (APA) in . We identified 50,616 polyadenylation signals in via analysis of full-length transcriptome combined with expression Sequence Tags Technology (EST). The polyadenylation signal usage in is conserved, and it is similar to that of flies and other animals. AAUAAA and AUUAAA are the most highly conserved polyadenylation signals of all polyadenylation signals we identified. Additionally, we found the U/GU-rich downstream sequence element (DSE) in the cleavage site. These results demonstrate that APA in plays a significant role in root growth and development. This is the first polyadenylation signal usage analysis in agricultural pests, which can deepen our understanding of and provide a theoretical basis for pest control.
• Zhao, R., Wang, H. H., Gao, J., Zhang, Y. J., Li, X., Zhou, J. J., Liang, P., Gao, X. W., & Gu, S. H. (2022). Plant volatile compound methyl benzoate is highly effective against Spodoptera frugiperda and safe to non-target organisms as an eco-friendly botanical-insecticide. Ecotoxicology and environmental safety, 245, 114101.
  More info

  Recent studies have indicated that the plant volatile methyl benzoate (MB) exhibits significant insecticidal bioactivity against several common insects. However, the potential environmental hazards of MB and its safety to non-target organisms is poorly understood. In the present study, these characteristics were investigated through laboratory experiments and field investigations. The results revealed that MB was highly toxic to the agricultural pest, fall armyworm Spodoptera frugiperda. Compared with the commercial pesticide lambda-cyhalothrin, the toxicities of MB against S. frugiperda larvae and adults were comparable and 3.41 times higher, respectively. Behavioral bioassays showed that the percentage repellency of MB to S. frugiperda larvae was 56.72 %, and MB induced 69.40 % oviposition deterrence rate in S. frugiperda female adults. Furthermore, in terms of median lethal concentration (LC) and median lethal doses (LD), MB exhibited non-toxic effects on non-target animals with 3-d LC of > 1 % to natural predators (Coccinella septempunctata and Harmonia axyridis), 3-d LD of 467.86 µg/bee to the bumblebee Bombus terrestris, 14-d LC of 971.09 mg/kg to the earthworm Eisenia fetida, and 4-d LC of 47.30 mg/L to the zebrafish Brachydanio rerio. The accumulation of MB in the soil and earthworms was found to be extremely limited. Our comparative study clearly demonstrated that MB is effective as a selective botanical pesticide against S. frugiperda and it is safe to use in the tested environment, with no toxic effects on non-target animals and natural predators.
• Deng, Z., Zhang, Y., Li, L., Xie, X., Huang, J., Zhang, M., Ni, X., & Li, X. (2021). A dual-luciferase reporter system for characterization of small RNA target genes in both mammalian and insect cells. Insect science.
  More info

  MicroRNAs (miRNAs) are regulatory RNA molecules that bind to target messenger RNAs (mRNAs) and affect the stability or translational efficiency of the bound mRNAs. Single or dual-luciferase reporter systems have been successfully used to identify miRNA target genes in mammalian cells. These reporter systems, however, are not sensitive enough to verify miRNA-target gene relationships in insect cell lines because the promoters of the target luciferase (usually Renilla) used in these reporter systems are too weak to drive sufficient expression of the target luciferase in insect cells. In this study, we replaced the SV40 promoter in the psiCHECK-2 reporter vector, which is widely used with mammalian cell lines, with the HSV-TK or AC5.1 promoter to yield two new dual-luciferase reporter vectors, designated psiCHECK-2-TK and psiCHECK-2-AC5.1, respectively. Only psiCHECK-2 and psiCHECK-2-AC5.1 had suitable target (Renilla)/reference (firefly) luciferase activity ratios in mammalian (HeLa and HEK293) and insect (Sf9, S2, Helicoverpa zea fat body and ovary) cell lines, while psiCHECK-2-TK had suitable Renilla/firefly luciferase activity ratios regardless of the cell line. Moreover, psiCHECK-2-TK successfully detected the interaction between Helicoverpa armigera miRNA9a and its target, the 3'-untranslated region of heat shock protein 90, in both mammalian and H. zea cell lines, but psiCHECK-2 failed to do so in H. zea cell lines. Furthermore, psiCHECK-2-TK with the target sequence, HzMasc (H. zea Masculinizer), accurately differentiated between H. zea cell lines with or without the negative regulation factor (miRNA or piRNA) of HzMasc. These data demonstrate that psiCHECK-2-TK can be used to functionally characterize small RNA target genes in both mammalian and insect cells.
• Deng, Z., Zhang, Y., Li, Y., Huang, K., Chen, X., Zhang, M., Huang, J., Ni, X., & Li, X. (2021). Identification and Characterization of the Masculinizing Function of the Gene. International journal of molecular sciences, 22(16).
  More info

  The () gene has been known to control sex development and dosage compensation in lepidopterans. However, it remains unclear whether its ortholog exists and plays the same roles in distantly related lepidopterans such as . To address this question, we cloned from (), which contains all essential functional domains of BmMasc, albeit with less than 30% amino acid sequence identity with BmMasc. Genomic PCR and qPCR analyses showed that is a Z chromosome-linked gene since its genomic content in males (ZZ) was two times greater than that in females (ZW). RT-PCR and RT-qPCR analyses revealed that expression was sex- and stage-biased, with significantly more transcripts in males and eggs than in females and other stages. Transfection of a mixture of three siRNAs of into a male embryonic cell line of led to the appearance of female-specific mRNA splicing isoforms of (), a downstream target gene of in the sex determination pathway. The knockdown of starting from the third instar larvae resulted in a shift of splicing from male to female isoforms, smaller male pupa and testes, fewer but larger/longer spermatocytes and sperm bundles, delayed pupation and internal fusion of the testes and follicles. These data demonstrate that functions as a masculinizing gene in the sex-determination cascade.
• Fabrick, J. A., LeRoy, D. M., Mathew, L. G., Wu, Y., Unnithan, G. C., Yelich, A. J., Carrière, Y., Li, X., & Tabashnik, B. E. (2021). CRISPR-mediated mutations in the ABC transporter gene ABCA2 confer pink bollworm resistance to Bt toxin Cry2Ab. Scientific reports, 11(1), 10377.
  More info

  Crops genetically engineered to produce insecticidal proteins from Bacillus thuringiensis (Bt) have many benefits and are important globally for managing insect pests. However, the evolution of pest resistance to Bt crops reduces their benefits. Understanding the genetic basis of such resistance is needed to better monitor, manage, and counter pest resistance to Bt crops. Previous work shows that resistance to Bt toxin Cry2Ab is associated with mutations in the gene encoding the ATP-binding cassette protein ABCA2 in lab- and field-selected populations of the pink bollworm (Pectinophora gossypiella), one of the world's most destructive pests of cotton. Here we used CRISPR/Cas9 gene editing to test the hypothesis that mutations in the pink bollworm gene encoding ABCA2 (PgABCA2) can cause resistance to Cry2Ab. Consistent with this hypothesis, introduction of disruptive mutations in PgABCA2 in a susceptible strain of pink bollworm increased the frequency of resistance to Cry2Ab and facilitated creation of a Cry2Ab-resistant strain. All Cry2Ab-resistant individuals tested in this study had disruptive mutations in PgABCA2. Overall, we found 17 different disruptive mutations in PgABCA2 gDNA and 26 in PgABCA2 cDNA, including novel mutations corresponding precisely to single-guide (sgRNA) sites used for CRISPR/Cas9. Together with previous results, these findings provide the first case of practical resistance to Cry2Ab where evidence identifies a specific gene in which disruptive mutations can cause resistance and are associated with resistance in field-selected populations.
• Li, L., Wang, S., Huang, K., Zhang, Y., Li, Y., Zhang, M., Huang, J., Deng, Z., Ni, X., & Li, X. (2021). Identification and Characterization of MicroRNAs in Gonads of (Lepidoptera: Noctuidae). Insects, 12(8).
  More info

  The high fecundity of the most destructive pest and its great resistance risk to insecticides and Bt crops make the reproductive-destruction-based control of this pest extremely appealing. To find suitable targets for disruption of its reproduction, we observed the testis and ovary development of and conducted deep sequencing of the ovary and testis small RNAs of and quantitative RT-PCR (RT-qPCR) validation to identify reproduction-related micro RNAs (miRNAs). A total of 7,592,150 and 8,815,237 clean reads were obtained from the testis and ovary tissue, respectively. After further analysis, we obtained 173 novel and 74 known miRNAs from the two libraries. Among the 74 known miRNAs, 60 miRNAs existed in the ovary and 72 existed in the testis. Further RT-qPCR validation of 5 miRNAs from the ovary and 6 miRNAs from the testis confirmed 8 of them were indeed ovary- (miR-989a, miR-263-5p, miR-34) or testis-biased (miR-2763, miR-998, miR-2c, miR-2765, miR-252a-5p). The 8 ovary- or testis-biased miRNAs had a total of 30,172 putative non-redundant target transcripts, as predicted by miRanda and RNAhybrid. Many of these target transcripts are assigned to reproduction-related GO terms (e.g., oocyte maturation, vitellogenesis, spermatogenesis) and are members of multiple reproduction-related KEGG pathways, such as the JAK-STAT signaling pathway, oocyte meiosis, the insulin signaling pathway, and insect hormone biosynthesis. These results suggest that the 8 gonad-biased miRNAs play important roles in reproduction and may be used as the targets for the development of reproductive-destruction-based control of and, possibly, other lepidopteran pests.
• Li, S., Chen, S., Xie, X., Dong, S., & Li, X. (2021). Identification of Wild-Type CYP321A2 and Comparison of Allelochemical-Induced Expression Profiles of CYP321A2 with Its Paralog CYP321A1 in Helicoverpa zea. Insects, 12(1).
  More info

  One possible way to overcome the diversity of toxic plant allelochemicals idiosyncratically distributed among potential host plants is to have more counterdefense genes via gene duplication or fewer gene losses. Cytochrome P450 is the most important gene family responsible for detoxification of the diversity of plant allelochemicals. We have recently reported the identification and cloning of the transposon ()-disrupted non-functional , a duplicated paralog of the xenobiotic-metabolizing P450 from a laboratory colony of . Here we report the identification of the wild-type intact allele of from another colony. This allele encodes a deduced protein of 498 amino acids and has the P450 signature motifs. Quantitative RT-PCR experiments showed that this allele was highly expressed in midgut and fat body and achieved the highest expression level in the developmental stage of 5th and 3rd instar larvae. and were constitutively expressed in low levels but can be differentially and significantly induced by a range of the plant allelochemicals and plant signal molecules, among which xanthotoxin, flavone, and coumarin were the most prominent inducers of both in midgut and fat body, whereas flavone, coumarin, and indole-3-carbinol were the prominent inducers of in midgut and fat body. Moreover, xanthotoxin- and flavone-responsive regulatory elements of were also detected in the promoter region of . Our results enrich the P450 inventory by identifying an allelochemical broadly induced , a paralog of in . Our data also suggest that the / paralogs are a pair of duplicated genes of multigene families and could potentially be involved in the detoxification of plant allelochemicals and adaptation of to its chemical environment.
• Li, S., Dong, S., Zhang, M., Deng, Z., Ni, X., Huang, J., & Li, X. (2021). Spontaneous transposition of HzSINE1 into CYP321A2 is undetectable in the field populations of Helicoverpa zea. Journal of Asia-Pacific Entomology, 24(3), 882-888. doi:https://doi.org/10.1016/j.ibmb.2021.103528.
  More info

  Abstract: The enrichment of transposable elements (TEs) within allelochemical- and insecticide-metabolizing P450 alleles in Helicoverpa zea enables these P450s to gain TE-introduced adaptive variations otherwise not readily available to cope with the ever-changing and diverse xenobiotic stress factors in varying cropping systems. The critical role of each TE-inserted P450 allele depends on whether the inserted P450 allele is more adaptive than its TE-free counterpart or not. Previous study has reported a HzSINE1-inserted CYP321A2 allele in a laboratory strain of H. zea reared with xenobiotic-free artificial diets. Here we show that the HzSINE1-inserted CYP321A2 allele transcribes into two HzSINE1 sequence-containing mutant mRNA isoforms of different length that encode an identical C terminus-truncated and heme-binding region deleted non-functional P450. Nonetheless, HzSINE1 insertion does not disrupt the regulatory functional aspect of CYP321A2 since this allele is constitutively expressed and highly inducible by the allelochemicals xanthotoxin, quercetin and chlorogenic acid. Furthermore, while the HzSINE1-inserted CYP321A2 allele is fixed in the laboratory strain, the insertion is purged in the bifenthrin-resistant strain and the Georgia field population of H. zea. To sum up, the HzSINE1-inserted CYP321A2 allele represents an allelochemical-inducible non-functional P450 allele that is selected against in the field populations frequently encountering toxic plant allelochemicals and synthetic insecticides. However, such an insertion can reach fixation under the xenobiotic-free laboratory rearing conditions most likely due to random genetic drift across multiple generations.
• Pang, R., Xing, K., Yuan, L., Liang, Z., Chen, M., Yue, X., Dong, Y., Ling, Y., He, X., Li, X., & Zhang, W. (2021). Peroxiredoxin alleviates the fitness costs of imidacloprid resistance in an insect pest of rice. PLoS biology, 19(4), e3001190.
  More info

  Chemical insecticides have been heavily employed as the most effective measure for control of agricultural and medical pests, but evolution of resistance by pests threatens the sustainability of this approach. Resistance-conferring mutations sometimes impose fitness costs, which may drive subsequent evolution of compensatory modifier mutations alleviating the costs of resistance. However, how modifier mutations evolve and function to overcome the fitness cost of resistance still remains unknown. Here we show that overexpression of P450s not only confers imidacloprid resistance in the brown planthopper, Nilaparvata lugens, the most voracious pest of rice, but also leads to elevated production of reactive oxygen species (ROS) through metabolism of imidacloprid and host plant compounds. The inevitable production of ROS incurs a fitness cost to the pest, which drives the increase or fixation of the compensatory modifier allele T65549 within the promoter region of N. lugens peroxiredoxin (NlPrx) in the pest populations. T65549 allele in turn upregulates the expression of NlPrx and thus increases resistant individuals' ability to clear the cost-incurring ROS of any source. The frequent involvement of P450s in insecticide resistance and their capacity to produce ROS while metabolizing their substrates suggest that peroxiredoxin or other ROS-scavenging genes may be among the common modifier genes for alleviating the fitness cost of insecticide resistance.
• Tabashnik, B. E., Liesner, L. R., Ellsworth, P. C., Unnithan, G. C., Fabrick, J. A., Naranjo, S. E., Li, X., Dennehy, T. J., Antilla, L., Staten, R. T., & Carrière, Y. (2021). Transgenic cotton and sterile insect releases synergize eradication of pink bollworm a century after it invaded the United States. Proceedings of the National Academy of Sciences of the United States of America, 118(1).
  More info

  Invasive organisms pose a global threat and are exceptionally difficult to eradicate after they become abundant in their new habitats. We report a successful multitactic strategy for combating the pink bollworm (), one of the world's most invasive pests. A coordinated program in the southwestern United States and northern Mexico included releases of billions of sterile pink bollworm moths from airplanes and planting of cotton engineered to produce insecticidal proteins from the bacterium (Bt). An analysis of computer simulations and 21 y of field data from Arizona demonstrate that the transgenic Bt cotton and sterile insect releases interacted synergistically to reduce the pest's population size. In Arizona, the program started in 2006 and decreased the pest's estimated statewide population size from over 2 billion in 2005 to zero in 2013. Complementary regional efforts eradicated this pest throughout the cotton-growing areas of the continental United States and northern Mexico a century after it had invaded both countries. The removal of this pest saved farmers in the United States $192 million from 2014 to 2019. It also eliminated the environmental and safety hazards associated with insecticide sprays that had previously targeted the pink bollworm and facilitated an 82% reduction in insecticides used against all cotton pests in Arizona. The economic and social benefits achieved demonstrate the advantages of using agricultural biotechnology in concert with classical pest control tactics.
• Wang, Q., Liu, J. T., Zhang, Y. J., Chen, J. L., Li, X. C., Liang, P., Gao, X. W., Zhou, J. J., & Gu, S. H. (2021). Coordinative mediation of the response to alarm pheromones by three odorant binding proteins in the green peach aphid Myzus persicae. Insect biochemistry and molecular biology, 130, 103528.
  More info

  Odorant binding proteins (OBPs) play an essential role for insect chemosensation in insect peripheral nervous systems of antennae. Each antennal sensilla contains more than one OBP at high concentrations but the interactions and cooperation between co-localized OBPs are rarely reported. In present study, we cloned, expressed and purified eight OBPs of the green peach aphid Myzus persicae. The effects of knocking down the expression of these OBP genes by RNAi on the electrophysiological and behavioural responses of M. persicae to the aphid alarm pheromone, (E)-β-farnesene (EβF) were investigated. The results showed that the aphids could still be repelled by EβF when the expression of each of three OBP genes was individually knocked down. However, the simultaneous knockdown of MperOBP3/7/9 expression significantly reduced the electrophysiological response and the repellent behaviours of M. persicae to EβF than the single OBP gene knockdown (P 
• Chen, Y. J., Li, Y. J., Wu, S., Yang, W. C., Miao, J., Gu, S. H., Li, J. H., Miao, X. Q., & Li, X. (2020). Transcriptional identification of differentially expressed genes associated with division of labor in Apis cerana cerana. Insect science.
  More info

  Workers of Apis cerana cerana undergo an in-hive nursing to outdoor foraging transition, but the genes underlying this age-related transition remain largely unknown. Here, we sequenced the head transcriptomes of its 7-day-old normal nurses, 18- and 22-day-old normal foragers, 7-day-old precocious foragers and 22-day-old over-aged nurses to unravel the genes associated with this transition. Mapping of the sequence reads to Apis mellifera genome showed that the three types of foragers had a greater percentage of reads from annotated exons and intergenic regions, whereas the two types of nurses had a greater percentage of reads from introns. Pair- and group-wise comparisons of the five transcriptomes revealed 59 uniquely expressed genes (18 in nurses and 41 in foragers) and 14 nurse- and 15 forager-upregulated genes. The uniquely expressed genes are usually low-abundance long noncoding RNAs, transcription factors, transcription coactivators, RNA-binding proteins, kinases or phosphatases that are involved in signaling and/or regulation, whereas the nurse- or forager-upregulated genes are often high-abundance downstream genes that directly perform the tasks of nurses or foragers. Taken together, these results suggest that the nurse-forager transition is coordinated by a social signal-triggered epigenetic shift from introns to exons/intergenic regions and the resulting transcriptional shift between the nurse- and forager-associated genes.
• Deng, Z., Zhang, Y., Zhang, M., Huang, J., Li, C., Ni, X., & Li, X. (2020). Characterization of the First W-Specific Protein-Coding Gene for Sex Identification in. Frontiers in genetics, 11, 649.
  More info

  is a globally-important crop pest with a WZ (female)/ZZ (male) sex chromosome system. The absence of discernible sexual dimorphism in its egg and larval stages makes it impossible to address any sex-related theoretical and applied questions before pupation unless a W-specific sequence marker is available for sex diagnosis. To this end, we used one pair of morphologically pre-sexed pupae to PCR-screen 17 non-transposon transcripts selected from 4855 W-linked candidate reads identified by mapping a publicly available egg transcriptome of both sexes to the male genome of this species and detected the read SRR1015458.67499 only in the female pupa. Subsequent PCR screenings of this read and the previously reported female-specific RAPD (random amplified polymorphic DNA) marker with ten more pairs of pre-sexed pupae and different annealing positions and/or temperatures as well as its co-occurrence with the female-specific transcript splicing isoforms of gene of and amplification and sequencing of their 5' unknown flanking sequences in three additional pairs of pre-sexed pupae verified that SRR1015458.67499 is a single copy protein-coding gene unique to W chromosome (named ) while is a multicopy MITE transposon located on various chromosomes. Test application of as a marker to sex 30 neonates of yielded a female/male ratio of 1.14: 1.00. Both and splicing isoforms assays revealed that the embryo cell line QB-Ha-E-1 is a male cell line. Taken together, is not only a reliable DNA marker for sexing all stages of and its cell lines, but also represents the first W-specific protein-coding gene in lepidopterans.
• Fabrick, J. A., LeRoy, D. M., Unnithan, G. C., Yelich, A. J., Carrière, Y., Li, X., & Tabashnik, B. E. (2020). Shared and Independent Genetic Basis of Resistance to Bt Toxin Cry2Ab in Two Strains of Pink Bollworm. Scientific reports, 10(1), 7988.
  More info

  Evolution of pest resistance threatens the benefits of crops genetically engineered to produce insecticidal proteins from Bacillus thuringiensis (Bt). Field populations of the pink bollworm (Pectinophora gossypiella), a global pest of cotton, have evolved practical resistance to transgenic cotton producing Bt toxin Cry2Ab in India, but not in the United States. Previous results show that recessive mutations disrupting an autosomal ATP-binding cassette gene (PgABCA2) are associated with pink bollworm resistance to Cry2Ab in field-selected populations from India and in one lab-selected strain from the United States (Bt4-R2). Here we discovered that an independently derived, lab-selected Cry2Ab-resistant pink bollworm strain from the United States (BX-R) also harbors mutations that disrupt PgABCA2. Premature stop codons introduced by mis-splicing of PgABCA2 pre-mRNA were prevalent in field-selected larvae from India and in both lab-selected strains. The most common mutation in field-selected larvae from India was also detected in both lab-selected strains. Results from interstrain crosses indicate BX-R has at least one additional mechanism of resistance to Cry2Ab that does not involve PgABCA2 and is not completely recessive or autosomal. We conclude that recessive mutations disrupting PgABCA2 are the primary, but not the only, mechanism of resistance to Cry2Ab in pink bollworm.
• Fabrick, J. A., Mathew, L. G., LeRoy, D. M., Hull, J. J., Unnithan, G. C., Yelich, A. J., Carrière, Y., Li, X., & Tabashnik, B. E. (2020). Reduced cadherin expression associated with resistance to Bt toxin Cry1Ac in pink bollworm. Pest management science, 76(1), 67-74.
  More info

  Better understanding of the molecular basis of resistance is needed to improve management of pest resistance to transgenic crops that produce insecticidal proteins from Bacillus thuringiensis (Bt). Here we analyzed resistance of the pink bollworm (Pectinophora gossypiella) to Bt toxin Cry1Ac, which is used widely in transgenic Bt cotton. Field-evolved practical resistance of pink bollworm to Cry1Ac is widespread in India, but not in China or the United States. Previous work with laboratory- and field-selected pink bollworm indicated that resistance to Cry1Ac is caused by changes in the amino acid sequence of a midgut cadherin protein (PgCad1) that binds Cry1Ac in susceptible larvae.
• Jia, D., Ji, Z., Yuan, X., Zhang, B., Liu, Y., Hu, J., Wang, Y., Li, X., & Ma, R. (2020). Molecular Cloning and Expression Profiles of Thermosensitive TRP Genes in. Insects, 11(8).
  More info

  Global warming has gradually reduced the control efficacy of against the invasive weed . To better understand the summer collapse of populations, we cloned the cDNA sequences of the high temperature-sensing , , and from , and analyzed their temporal expressions and the impacts of high temperatures on their expression in eggs, the most vulnerable stage of to hot temperatures. All the three genes obtained had the signature domains of TRPA channels and were constitutively expressed in eggs, larvae (L1, L2, L3), pupae, and adults, but had the highest expression, followed by , and . The lowest and highest expression stages were adult and pupae for , egg and L3 for , and pupae/adult and L2 for . The expressions of , , and remained low at the preferred temperature range of 25-28 °C, elevated to their peak levels at 37.5, 30, and 30 °C, respectively, then fell to their 25-28 °C levels (, ) or a lower level () at one or more temperatures >30 or 37.5 °C. These results suggest that their temperature-sensing roles and importance may be different, stage-specific, and their expression may be decoupled from their activation.
• Li, X., Deng, Z., & Chen, X. (2020). Regulation of insect P450s in response to phytochemicals. Current opinion in insect science, 43, 108-116.
  More info

  Insect herbivores use phytochemicals as signals to induce expression of their phytochemical-detoxifying cytochrome P450 monooxygenases (P450s). The regulatory cascades that transduce phytochemical signals to enhanced expression of P450s are the focus of this review. At least seven signaling pathways, including RTK/MAPK, GPCR/CREB, GPCR/NFκB, ROS/CncC/Keap1, AhR/ARNT, cytosol NR, and nucleus-located NR, may be involved in phytochemical induction of P450s. Constitutive overexpression, overphosphorylation, and/or activation of one or more effectors in the corresponding pathway are common causes of P450 overexpression that lead to phytochemical or insecticide resistance. Future research should pay more attentions to the starting point of each pathway, the number of pathways and their cross talk for a given phytochemical, and the pathways for downregulation of P450s.
• Wang, J., Xu, D., Wang, L., Cong, S., Wan, P., Lei, C., Fabrick, J. A., Li, X., Tabashnik, B. E., & Wu, K. (2020). Bt resistance alleles in field populations of pink bollworm from China: Similarities with the United States and decreased frequency from 2012 to 2015. Pest management science, 76(2), 527-533.
  More info

  Although most monitoring of pest resistance to widely cultivated transgenic crops producing insecticidal proteins from Bacillus thuringiensis (Bt) relies on bioassays, DNA screening for alleles associated with resistance has some advantages, particularly for rare, recessively inherited resistance. In China's Yangtze River Valley, where farmers first planted transgenic cotton producing Bt toxin Cry1Ac in 2000, bioassays have been used to monitor the recessive resistance of pink bollworm (Pectinophora gossypiella). Previous bioassay results show a small but significant increase in resistance to Cry1Ac during 2008-2010, followed by a significant decrease in resistance during 2011-2015 associated with extensive planting of second-generation hybrid cotton seeds that boosted the percentage of non-Bt cotton. Here we screened DNA from 19 748 pink bollworm collected during 2012-2015 from the Yangtze River Valley for seven alleles associated with resistance to Cry1Ac. These alleles were previously identified from lab-selected strains; three from the U.S. and four from China.
• Wang, L., Ma, Y., Wei, W., Wan, P., Liu, K., Xu, M., Cong, S., Wang, J., Xu, D., Xiao, Y., Li, X., Tabashnik, B. E., & Wu, K. (2020). Cadherin repeat 5 mutation associated with Bt resistance in a field-derived strain of pink bollworm. Scientific reports, 10(1), 16840.
  More info

  Evolution of resistance by pests reduces the benefits of transgenic crops that produce insecticidal proteins from Bacillus thuringiensis (Bt). Here we analyzed resistance to Bt toxin Cry1Ac in a field-derived strain of pink bollworm (Pectinophora gossypiella), a global pest of cotton. We discovered that the r14 allele of the pink bollworm cadherin gene (PgCad1) has a 234-bp insertion in exon 12 encoding a mutant PgCad1 protein that lacks 36 amino acids in cadherin repeat 5 (CR5). A strain homozygous for this allele had 237-fold resistance to Cry1Ac, 1.8-fold cross-resistance to Cry2Ab, and developed from neonate to adult on Bt cotton producing Cry1Ac. Inheritance of resistance to Cry1Ac was recessive and tightly linked with r14. PgCad1 transcript abundance in midgut tissues did not differ between resistant and susceptible larvae. Toxicity of Cry1Ac to transformed insect cells was lower for cells expressing r14 than for cells expressing wild-type PgCad1. Wild-type PgCad1 was transported to the cell membrane, whereas PgCad1 produced by r14 was not. In larval midgut tissue, PgCad1 protein occurred primarily on the brush border membrane only in susceptible larvae. The results imply r14 mediates pink bollworm resistance to Cry1Ac by reduced translation, increased degradation, and/or mislocalization of cadherin.
• Wang, S., Zhang, M., Huang, J., Li, L., Huang, K., Zhang, Y., Li, Y., Deng, Z., Ni, X., & Li, X. (2020). Inductive and synergistic interactions between plant allelochemical flavone and Bt toxin Cry1Ac in Helicoverpa armigera. Insect science.
  More info

  Genetically engineered crops simultaneously produce defensive allelochemicals and Bacillus thuringiensis (Bt) toxin proteins to kill some of the world's most devastating insect pests. How the two types of toxins, when ingested sequentially or simultaneously, interact at both lethal and sublethal doses in these pests remains underexplored. Here, we examined the toxicological interactions between the Bt toxin Cry1Ac and the flavonoid allelochemical flavone in Helicoverpa armigera. Simultaneous exposure of H. armigera neonates to lethal doses (LC ) of Cry1Ac and flavone caused a mortality significantly higher than that of either toxin alone and their expected additive mortality. Preexposure for 24 h to a sublethal dose (LC ) of Cry1Ac followed by 6-d simultaneous exposure to the same dose of Cry1Ac plus a lethal dose (1.6 mg/g diets, LC ) of flavone resulted in a mortality significantly higher than that of the LC dose of flavone alone and the expected additive mortality of the LC dose of flavone plus the LC dose of Cry1Ac. One-day preexposure to the sublethal dose (LC ) of flavone followed by 6-d simultaneous exposure to the LC dose (6 ng/cm ) of Cry1Ac plus the LC dose of flavone yielded a mortality significantly higher than that of the LC dose of Cry1Ac but similar to the expected additive mortality of the LC dose of Cry1Ac plus the LC dose of flavone. The results suggest that Cry1Ac induces and synergizes the toxicity of flavone against H. armigera larvae.
• Carrière, Y., Degain, B., Unnithan, G. C., Harpold, V. S., Li, X., & Tabashnik, B. E. (2019). Seasonal Declines in Cry1Ac and Cry2Ab Concentration in Maturing Cotton Favor Faster Evolution of Resistance to Pyramided Bt Cotton in Helicoverpa zea (Lepidoptera: Noctuidae). Journal of economic entomology, 112(6), 2907-2914.
  More info

  Under ideal conditions, widely adopted transgenic crop pyramids producing two or more distinct insecticidal proteins from Bacillus thuringiensis (Bt) that kill the same pest can substantially delay evolution of resistance by pests. However, deviations from ideal conditions diminish the advantages of such pyramids. Here, we tested the hypothesis that changes in maturing cotton producing Cry1Ac and Cry2Ab affect evolution of resistance in Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae), a pest with low inherent susceptibility to both toxins. In terminal leaves of field-grown Bt cotton, the concentration of both toxins was significantly higher for young, squaring plants than for old, fruiting plants. We used laboratory bioassays with plant material from field-grown cotton to test H. zea larvae from a strain selected for resistance to Cry1Ac in the laboratory, its more susceptible parent strain, and their F1 progeny. On young Bt cotton, no individuals survived to pupation. On old Bt cotton, survival to pupation was significantly higher for the lab-selected strain and the F1 progeny relative to the unselected parent strain, indicating dominant inheritance of resistance. Redundant killing, the extent to which insects resistant to one toxin are killed by another toxin in a pyramid, was complete on young Bt cotton, but not on old Bt cotton. No significant fitness costs associated with resistance were detected on young or old non-Bt cotton. Incorporation of empirical data into simulations indicates the observed increased selection for resistance on old Bt cotton could accelerate evolution of resistance to cotton producing Cry1Ac and Cry2Ab in H. zea.
• Du, Y., Xu, K., Ma, W., Su, W., Tai, M., Zhao, H., Jiang, Y., & Li, X. (2019). Contact Chemosensory Genes Identified in Leg Transcriptome of Apis cerana cerana (Hymenoptera: Apidae). Journal of economic entomology, 112(5), 2015-2029.
  More info

  Correct gustatory recognition and selection of foods both within and outside the hive by honey bee workers are fundamental to the maintenance of colonies. The tarsal chemosensilla located on the legs of workers are sensitive to nonvolatile compounds and proposed to be involved in gustatory detection. However, little is known about the molecular mechanisms underlying the gustatory recognition of foods in honey bees. In the present study, RNA-seq was performed with RNA samples extracted from the legs of 1-, 10-, and 20-d-old workers of Apis cerana cerana Fabricius, a dominant indigenous crop pollinator with a keen perception ability for phytochemicals. A total of 124 candidate chemosensory proteins (CSPs), including 15 odorant-binding proteins (OBPs), 5 CSPs, 7 gustatory receptors (GRs), 2 sensory neuron membrane proteins (SNMPs), and 95 odorant receptors (ORs), were identified from the assembled leg transcriptome. In silico analysis of expression showed that 36 of them were differentially expressed among the three different ages of A. c. cerana workers. Overall, the genes encoding OBPs and CSPs had great but extremely variable FPKM values and thus were highly expressed in the legs of workers, whereas the genes encoding ORs, GRs, and SNMPs (except SNMP2) were expressed at low levels. Tissue-specific expression patterns indicated that two upregulated genes, AcerOBP15 and AcerCSP3, were predominately expressed in the legs of 20-d-old foragers, suggesting they may play an essential role in gustatory recognition and selection of plant nectars and pollens. This study lays a foundation for further research on the feeding preferences of honey bees.
• Fabrick, J. A., Mathew, L. G., LeRoy, D. M., Hull, J. J., Unnithan, G. C., Yelich, A. J., Carrière, Y., Li, X., & Tabashnik, B. E. (2019). Reduced cadherin expression associated with resistance to Bt toxin Cry1Ac in pink bollworm.. Pest Manag Sci..
  More info

  BACKGROUND:Better understanding of the molecular basis of resistance is needed to improve management of pest resistance to transgenic crops that produce insecticidal proteins from Bacillus thuringiensis (Bt). Here we analyzed resistance of the pink bollworm (Pectinophora gossypiella) to Bt toxin Cry1Ac, which is used widely in transgenic Bt cotton. Field-evolved practical resistance of pink bollworm to Cry1Ac is widespread in India, but not in China or the United States. Previous work with laboratory- and field-selected pink bollworm indicated that resistance to Cry1Ac is caused by changes in the amino acid sequence of a midgut cadherin protein (PgCad1) that binds Cry1Ac in susceptible larvae.RESULTS:Relative to a susceptible strain, the laboratory-selected APHIS-R strain had 530-fold resistance to Cry1Ac with autosomal recessive inheritance. Unlike previous results, resistance in this strain was not consistently associated with insertions or deletions in the expected amino acid sequence of PgCad1. However, this resistance was associated with 79- to 190-fold reduced transcription of the PgCad1 gene and markedly lower abundance of PgCad1 protein.CONCLUSION:The ability of pink bollworm and other major pests to evolve resistance to Bt toxins via both qualitative and quantitative changes in receptor proteins demonstrates their remarkable adaptability and presents challenges for monitoring and managing resistance to Bt crops.
• Hussain, F., ul, A. Z., Arif, M. J., Jamil, A., & Li, X. (2019). Isolation and Characterization of Immune Suppressive Genes through Bioinformatic Analysis of Venom Glands Transcriptome of Bracon hebetor (Hymenoptera: Braconidae). INTERNATIONAL JOURNAL OF AGRICULTURE AND BIOLOGY, 21(6), 1189-1196.
• Li, S., Hussain, F., Unnithan, G. C., Dong, S., UlAbdin, Z., Gu, S., Mathew, L. G., Fabrick, J. A., Ni, X., Carrière, Y., Tabashnik, B. E., & Li, X. (2019). A long non-coding RNA regulates cadherin transcription and susceptibility to Bt toxin Cry1Ac in pink bollworm, Pectinophora gossypiella. Pesticide biochemistry and physiology, 158, 54-60.
  More info

  Extensive planting of transgenic crops producing insecticidal proteins from the bacterium Bacillus thuringiensis (Bt) has spurred increasingly rapid evolution of resistance in pests. In the pink bollworm, Pectinophora gossypiella, a devastating global pest, resistance to Bt toxin Cry1Ac produced by transgenic cotton is linked with mutations in a gene (PgCad1) encoding a cadherin protein that binds Cry1Ac in the larval midgut. We previously reported a long non-coding RNA (lncRNA) in intron 20 of cadherin alleles associated with both resistance and susceptibility to Cry1Ac. Here we tested the hypothesis that reducing expression of this lncRNA decreases transcription of PgCad1 and susceptibility to Cry1Ac. Quantitative RT-PCR showed that feeding susceptible neonates small interfering RNAs (siRNAs) targeting this lncRNA but not PgCad1 decreased the abundance of transcripts of both the lncRNA and PgCad1. Moreover, neonates fed the siRNAs had lower susceptibility to Cry1Ac. The results imply that the lncRNA increases transcription of PgCad1 and susceptibility of pink bollworm to Cry1Ac. The results suggest that disruption of lncRNA expression could be a novel mechanism of pest resistance to Bt toxins.
• Ni, X., Cottrell, T. E., Buntin, G. D., Li, X., Wang, W., & Zhuang, H. (2019). Monitoring of brown stink bug (Hemiptera: Pentatomidae) population dynamics in corn to predict its abundance using weather data. INSECT SCIENCE, 26(3), 536-544.
• Wang, J., Xu, D., Cong, S., Wan, P., Lei, C., Fabrick, J. A., Li, X., Tabashnik, B. E., & Wu, K. (2019). Bt resistance alleles in field populations of pink bollworm from China: Similarities with the United States and decreased frequency from 2012 to 2015.. Pest Manag Sci..
  More info

  BACKGROUND:Although most monitoring of pest resistance to widely cultivated transgenic crops producing insecticidal proteins from Bacillus thuringiensis (Bt) relies on bioassays, DNA screening for alleles associated with resistance has some advantages, particularly for rare, recessively inherited resistance. In China's Yangtze River Valley, where farmers first planted transgenic cotton producing Bt toxin Cry1Ac in 2000, bioassays have been used to monitor the recessive resistance of pink bollworm (Pectinophora gossypiella). Previous bioassay results show a small but significant increase in resistance to Cry1Ac during 2008-2010, followed by a significant decrease in resistance during 2011-2015 associated with extensive planting of second-generation hybrid cotton seeds that boosted the percentage of non-Bt cotton. Here we screened DNA from 19 748 pink bollworm collected during 2012-2015 from the Yangtze River Valley for seven alleles associated with resistance to Cry1Ac. These alleles were previously identified from lab-selected strains; three from the U.S. and four from China.RESULTS:The most common resistance allele was first identified from the U.S. and accounted for over 71% of all resistance alleles detected. Resistance was rare, with the total frequency of the seven resistance alleles showing a significant, 2.3-fold decrease from 0.0105 (95% CI: 0.0084-0.0132) in 2012 to 0.0046 (0.0031-0.0067) in 2015.CONCLUSIONS:The DNA screening data confirm results from bioassays showing pink bollworm resistance to Cry1Ac remained rare in the Yangtze River Valley from 2012-2015. The prevalence in China of the resistance allele identified from the U.S. implies a shared genetic basis of resistance that could facilitate molecular monitoring of resistance.
• Wang, L., Ma, Y., Guo, X., Wan, P., Liu, K., Cong, S., Wang, J., Xu, D., Xiao, Y., Li, X., Tabashnik, B. E., & Wu, K. (2019). Pink Bollworm Resistance to Bt Toxin Cry1Ac Associated with an Insertion in Cadherin Exon 20. Toxins, 11(4).
  More info

  Insecticidal proteins from (Bt) are widely used to control insect pests, but their efficacy is reduced when pests evolve resistance. We report on a novel allele () of the cadherin gene () in pink bollworm () associated with resistance to Bt toxin Cry1Ac, which is produced by transgenic cotton. The allele isolated from a field population in China has 1545 base pairs of a degenerate transposon inserted in exon 20 of , which generates a mis-spliced transcript containing a premature stop codon. A strain homozygous for had 300-fold resistance to Cry1Ac, 2.6-fold cross-resistance to Cry2Ab, and completed its life cycle on transgenic Bt cotton producing Cry1Ac. Inheritance of Cry1Ac resistance was recessive and tightly linked with . Compared with transfected insect cells expressing wild-type , cells expressing were less susceptible to Cry1Ac. Recombinant cadherin protein was transported to the cell membrane in cells transfected with the wild-type allele, but not in cells transfected with . Cadherin occurred on brush border membrane vesicles (BBMVs) in the midgut of susceptible larvae, but not resistant larvae. These results imply that the allele mediates Cry1Ac resistance in pink bollworm by interfering with the localization of cadherin.
• Wang, L., Wang, J., Ma, Y., Wan, P., Liu, K., Cong, S., Xiao, Y., Xu, D., Wu, K., Fabrick, J. A., Li, X., & Tabashnik, B. E. (2019). Transposon insertion causes cadherin mis-splicing and confers resistance to Bt cotton in pink bollworm from China. Scientific reports, 9(1), 7479.
  More info

  Transgenic crops producing insecticidal proteins from Bacillus thuringiensis (Bt) are cultivated extensively, but rapid evolution of resistance by pests reduces their efficacy. We report a 3,370-bp insertion in a cadherin gene associated with resistance to Bt toxin Cry1Ac in the pink bollworm (Pectinophora gossypiella), a devastating global cotton pest. We found the allele (r15) harboring this insertion in a field population from China. The insertion is a miniature inverted repeat transposable element (MITE) that contains two additional transposons and produces two mis-spliced transcript variants (r15A and r15B). A strain homozygous for r15 had 290-fold resistance to Cry1Ac, little or no cross-resistance to Cry2Ab, and completed its life cycle on Bt cotton producing Cry1Ac. Inheritance of resistance was recessive and tightly linked with r15. For transformed insect cells, susceptibility to Cry1Ac was greater for cells producing the wild-type cadherin than for cells producing the r15 mutant proteins. Recombinant cadherin protein occurred on the cell surface in cells transformed with the wild-type or r15A sequences, but not in cells transformed with the r15B sequence. The similar resistance of pink bollworm to Cry1Ac in laboratory- and field-selected insects from China, India and the U.S. provides a basis for developing international resistance management practices.
• Zhang, M., Wei, J., Ni, X., Zhang, J., Jurat-Fuentes, J. L., Fabrick, J. A., Carriere, Y., Tabashnik, B. E., & Li, X. (2019). Decreased Cry1Ac activation by midgut proteases associated with Cry1Ac resistance in Helicoverpa zea. PEST MANAGEMENT SCIENCE, 75(4), 1099-1106.
• Zhang, S., Gu, S., Ni, X., & Li, X. (2019). Genome Size Reversely Correlates With Host Plant Range in Species. Frontiers in physiology, 10, 29.
  More info

  In organisms with very low percentages of transposable elements (TEs), genome size may positively or negatively correlate with host range, depending on whether host adaptation or host modification is the main route to host generalism. To test if this holds true for insect herbivores with greater percentages of TEs, we conducted flow cytometry to measure the endopolyploidy levels and C-values of the host modification (salivary gland and mandibular gland in head), host adaptation (midgut), and host use-independent tissues (male gonad, hemolymph, and Malpighian tubules) of the generalist and the head of its older specialist sister . Larval salivary gland displayed a consecutive chain of endopolyploidy particles from 8Cx to higher than 32Cx and larval head and midgut had endopolyploidy nuclei clusters of 16Cx and 32Cx, whereas larval male gonad, hemolymph, and Malpighian tubules possessed no endopolyploidy nuclei of higher than 8Cx. The estimated genome size of the Solanaceae plant specialist is 430 Mb, significantly larger than that of its older generalist sister (408 Mb) and those of its two generalist descendants (394 Mb) and (363 Mb). These data not only reveal a negative correlation between host plant range and genome size in this terminal lineage, but also imply that species appear to depend more on host modification than on host adaptation to achieve polyphagy.
• Zhang, Y., Deng, Z., Gu, S., & Li, X. (2019). Identification and functional analysis of the dosage compensation related gene Hamsl1 in Helicoverpa armigera (Lepidoptera: Noctuidae). Acta Entomologica Sinica., 62(7), 799-813. doi:doi:10.16380/j.kcxb.2019.07.003
  More info

  【Aim】 The dosage compensation mechanism of Helicoverpa armigera is still unclear. This study aims to clone male-specific lethal 1 gene Hamsl1 from H. armigera and to investigate whether it regulates dosage compensation of H. armigera by RNA interference technology. 【Methods】 The full-length cDNA of Hamsl1 sequence of H. armigera was cloned by RT-PCR based on homologous sequence alignment. The gene expression profiles of Hamsl1 in different developmental stages of H. armigera were detected by qPCR. After RNAi of Hamsl1 via microinjection of Hamsl1 siRNA into the 3rd instar larvae of H. armigera, the expression levels of 15 Z-linked genes were detected by qPCR to verify whether Hamsl1 regulates the dose of genes on Z chromosome. 【Results】 The full-length cDNA of Hamsl1 was successfully cloned from H. armigera, and its mRNA was identified to have two alternative splicing transcripts, which were designated as Hamsl1a (GenBank accession no.: MK564008) and Hamsl1b (GenBank accession no.: MK564009), respectively. Functional domain analysis showed that HaMSL1 contains a typical PEHE domain and a coiled-coil domain, which are the characteristics of MSL1 protein. The qPCR analysis demonstrated that Hamsl1 gene was located on the Z chromosome of H. armigera. The expression of both Hamsl1a and Hamsl1b showed the developmental stage specificity, peaking at the adult stage, and the sex specificity with significantly different expression level between female and male after pupation. Fifteen Z-linked genes were identified by homologous alignment and qPCR at the DNA level. Microinjecting Hamsl1 siRNA into the 3rd instar larvae of H. armigera for 72 h resulted in a RNA interference efficiency of 36.01%-64.27%, but no male specific lethal phenomenon was found in the tested insects. The 15 Z-linked genes in the Hamsl1 RNAi group showed significantly up-regulated expression in males as compared to those in the control group, but no significant expression change in females. 【Conclusion】 This study preliminarily proves that Hamsl1 gene is located on the Z chromosome of H. armigera and may regulate the dosage compensation by inhibiting the expression of Z-linked genes in male H. armigera. This study provides a theoretical foundation for further study of the molecular mechanism of dosage compensation and environmentally-friendly control of H. armigera.
• Carriere, Y., Degain, B. A., Unnithan, G. C., Harpold, V. S., Heuberger, S., Li, X., & Tabashnik, B. E. (2018). Effects of seasonal changes in cotton plants on the evolution of resistance to pyramided cotton producing the Bt toxins Cry1Ac and Cry1F in Helicoverpa zea. PEST MANAGEMENT SCIENCE, 74(3), 627-637.
• Carrière, Y., Degain, B. A., Unnithan, G. C., Harpold, V. S., Heuberger, S., Li, X., & Tabashnik, B. E. (2018). Effects of seasonal changes in cotton plants on the evolution of resistance to pyramided cotton producing the Bt toxins Cry1Ac and Cry1F in Helicoverpa zea. Pest Management Science, 74(3), 627-637.
• Chen, L., Gu, S., Wang, X., & Li, X. (2018). Comparative analysis of microbiota between insecticide resistant and susceptible strains of Bemisia tabaci. Plant Protection, 59-66.
• Deng, Z., Zhang, S., Gu, S., Ni, X., Zeng, W., & Li, X. (2018). Useful Bicistronic Reporter System for Studying Poly(A) Site-Defining cis Elements and Regulation of Alternative Polyadenylation. INTERNATIONAL JOURNAL OF MOLECULAR SCIENCES, 19(1).
• Deng, Z., Zhang, S., Gu, S., Ni, X., Zeng, W., & Li, X. (2018). Useful Bicistronic Reporter System for Studying Poly(A) Site-Defining cis Elements and Regulation of Alternative Polyadenylation. International journal of molecular sciences, 19(1).
  More info

  The link between polyadenylation (pA) and various biological, behavioral, and pathological events of eukaryotes underlines the need to develop in vivo polyadenylation assay methods for characterization of the cis-acting elements, trans-acting factors and environmental stimuli that affect polyadenylation efficiency and/or relative usage of two alternative polyadenylation (APA) sites. The current protein-based CAT or luciferase reporter systems can measure the polyadenylation efficiency of a single pA site or candidate cis element but not the choice of two APA sites. To address this issue, we developed a set of four new bicistronic reporter vectors that harbor either two luciferase or fluorescence protein open reading frames connected with one Internal Ribosome Entry Site (IRES). Transfection of single or dual insertion constructs of these vectors into mammalian cells demonstrated that they could be utilized not only to quantify the strength of a single candidate pA site or cis element, but also to accurately measure the relative usage of two APA sites at both the mRNA (qRT-PCR) and protein levels. This represents the first reporter system that can study polyadenylation efficiency of a single pA site or element and regulation of two APA sites at both the mRNA and protein levels.
• Huang, G. Z., Liu, J. T., Zhou, J. J., Wang, Q., Dong, J. Z., Zhang, Y. J., Li, X. C., Li, J., & Gu, S. H. (2018). Expressional and functional comparisons of two general odorant binding proteins in Agrotis ipsilon. Insect biochemistry and molecular biology, 98, 34-47.
  More info

  Insect general odorant binding proteins (GOBPs) have been long thought to bind and transport host plant volatiles to the olfactory receptors on the dendrite membrane of the olfactory neurons. Recent studies indicate that they can also bind female sex pheromones. In present study, two GOBP genes, AipsGOBP1 and AipsGOBP2 were cloned from the adult antennae of Agrotis ipsilon. Tissue expression profiles indicated that both of them are antennae-specific and more abundant in the female antennae than in the male antennae. Temporal expression profiles showed that both AipsGOBP1 and AipsGOBP2 began to express in antennae 3 days prior to adult emergence from pupae, and reached their highest expression level 3 and 4 days after adult emergence, respectively. Mating increased their expression in the female antennae but reduced their expression in the male antennae. In situ hybridization and immunolocalization demonstrated that both AipsGOBP1 and AipsGOBP2 are expressed and co-localized in sensilla basiconica and sensilla trichodea of both sexes. AipsGOBP2 exhibited a high binding affinity in vitro with the two major sex pheromone components Z7-12:Ac and Z9-14:Ac and the four plant volatiles cis-3-hexen-1-ol, oleic acid, dibutyl phthalate and β-caryophyllene with Ki values less than 5 μM. AipsGOBP1, on the other hand, showed medium binding affinities with the five A. ipsilon sex pheromones and six plant volatiles. AipsGOBP2 also showed a broader ligand-binding spectrum and a greater ligand-binding affinity than AipsGOBP1 with the tested aldehyde and alcohol sex pheromones of Lepidoptera species. Taken together, our results indicate that AipsGOBP2 may play greater roles than AipsGOBP1 does in binding sex pheromones and host plant volatiles.
• Huang, G., Liu, J., Zhou, J., Wang, Q., Dong, J., Zhang, Y., Li, X., Li, J., & Gu, S. (2018). Expressional and functional comparisons of two general odorant binding proteins in Agrotis ipsilon. INSECT BIOCHEMISTRY AND MOLECULAR BIOLOGY, 98, 34-47.
• Mathew, L. G., Ponnuraj, J., Mallappa, B., Chowdary, L. R., Zhang, J., Tay, W. T., Walsh, T. K., Gordon, K. H., Heckel, D. G., Downes, S., Carrière, Y., Li, X., Tabashnik, B. E., & Fabrick, J. A. (2018). ABC transporter mis-splicing associated with resistance to Bt toxin Cry2Ab in laboratory- and field-selected pink bollworm. Scientific reports, 8(1), 13531.
  More info

  Evolution of pest resistance threatens the benefits of genetically engineered crops that produce Bacillus thuringiensis (Bt) insecticidal proteins. Strategies intended to delay pest resistance are most effective when implemented proactively. Accordingly, researchers have selected for and analyzed resistance to Bt toxins in many laboratory strains of pests before resistance evolves in the field, but the utility of this approach depends on the largely untested assumption that laboratory- and field-selected resistance to Bt toxins are similar. Here we compared the genetic basis of resistance to Bt toxin Cry2Ab, which is widely deployed in transgenic crops, between laboratory- and field-selected populations of the pink bollworm (Pectinophora gossypiella), a global pest of cotton. We discovered that resistance to Cry2Ab is associated with mutations disrupting the same ATP-binding cassette transporter gene (PgABCA2) in a laboratory-selected strain from Arizona, USA, and in field-selected populations from India. The most common mutation, loss of exon 6 caused by alternative splicing, occurred in resistant larvae from both locations. Together with previous data, the results imply that mutations in the same gene confer Bt resistance in laboratory- and field-selected strains and suggest that focusing on ABCA2 genes may help to accelerate progress in monitoring and managing resistance to Cry2Ab.
• Mathew, L. G., Ponnuraj, J., Mallappa, B., Chowdary, L. R., Zhang, J., Tay, W. T., Walsh, T. K., Gordon, K., Heckel, D. G., Downes, S., Carriere, Y., Li, X., Tabashnik, B. E., & Fabrick, J. A. (2018). ABC transporter mis-splicing associated with resistance to Bt toxin Cry2Ab in laboratory- and field-selected pink bollworm. SCIENTIFIC REPORTS, 8.
• Wang, L., Ma, Y., Wan, P., Liu, K., Xiao, Y., Wang, J., Cong, S., Xu, D., Wu, K., Fabrick, J. A., Li, X., & Tabashnik, B. E. (2018). Resistance to Bacillus thuringiensis linked with a cadherin transmembrane mutation affecting cellular trafficking in pink bollworm from China. INSECT BIOCHEMISTRY AND MOLECULAR BIOLOGY, 94, 28-35.
• Wang, L., Ma, Y., Wan, P., Liu, K., Xiao, Y., Wang, J., Cong, S., Xu, D., Wu, K., Fabrick, J. A., Li, X., & Tabashnik, B. E. (2018). Resistance to Bacillus thuringiensis linked with a cadherin transmembrane mutation affecting cellular trafficking in pink bollworm from China. Insect biochemistry and molecular biology, 94, 28-35.
  More info

  Evolution of pest resistance reduces the efficacy of insecticidal proteins from the gram-positive bacterium Bacillus thuringiensis (Bt) used widely in sprays and transgenic crops. In some previously studied strains of three major lepidopteran pests, resistance to Bt toxin Cry1Ac is associated with mutations disrupting the extracellular or cytoplasmic domains of cadherin proteins that bind Cry1Ac in the midgut of susceptible larvae. Here we report the first case of a cadherin transmembrane mutation associated with insect resistance to Bt. We discovered this mutation in a strain of the devastating global cotton pest, the pink bollworm (Pectinophora gossypiella), derived from a field population in the Yangtze River Valley of China. The mutant allele analyzed here has a 207 base pair deletion and encodes a cadherin protein lacking its transmembrane domain. Relative to a susceptible strain, a strain homozygous for this allele had 220-fold resistance to Cry1Ac and 2.1-fold cross-resistance to Cry2Ab. On transgenic cotton plants producing Cry1Ac, no susceptible larvae survived, but the resistant strain completed its life cycle. Inheritance of resistance to Cry1Ac was autosomal, recessive and tightly linked with the cadherin gene. Transportation of cadherin protein to the cell membrane and susceptibility to Cry1Ac occurred in transfected insect cells expressing the wild type cadherin allele, but not in transfected insect cells expressing the mutant cadherin allele. The results imply that the mutant allele analyzed here confers resistance to Cry1Ac by disrupting cellular trafficking of cadherin.
• Wang, Q., Zhang, J., Liu, J., Huang, G., Xu, W., Zhang, Q., Chen, J., Zhang, Y., Li, X., & Gu, S. (2019). Integrative transcriptomic and genomic analysis of odorant binding proteins and chemosensory proteins in aphids. Insect Molecular Biology, 28(1), 1-22. doi:doi: 10.1111/imb.12513. Epub 2018 Oct 5.
• Wei, J., Liang, G., Wu, K., Gu, S., Guo, Y., Ni, X., & Li, X. (2018). Cytotoxicity and binding profiles of activated Cry1Ac and Cry2Ab to three insect cell lines. INSECT SCIENCE, 25(4), 655-666.
• Wei, J., Zhang, M., Liang, G., & Li, X. (2018). ALP2 is a functional receptor of Cry1Ac but not Cry2Ab in Helicoverpa zea. Insect Molecular Biology. doi:https://doi.org/10.1111/imb.12556.
• Zhang, M., Wei, J., Ni, X., Zhang, J., Jurat-Fuentes, J. L., Fabrick, J. A., Carrière, Y., Tabashnik, B. E., & Li, X. (2018). Decreased Cry1Ac activation by midgut proteases associated with Cry1Ac resistance in Helicoverpa zea. Pest management science.
  More info

  Field-evolved resistance of Helicoverpa zea to Bacillus thuringiensis (Bt) toxin Cry1Ac was first reported more than a decade ago, yet the underlying mechanisms remain elusive. Towards understanding the mechanisms of resistance to Cry1Ac, we analyzed a susceptible (LAB-S) and two resistant (GA and GA-R) strains of H. zea. The GA strain was derived from Georgia and exposed to Bt toxins only in the field. The GA-R strain was derived from the GA strain and selected for increased resistance to Cry1Ac in the laboratory.
• Carrière, Y., Degain, B. A., Unnithan, G. C., Harpold, V. S., Heuberger, S., Li, X., & Tabashnik, B. E. (2017). Effects of seasonal changes in cotton plants on the evolution of resistance to pyramided cotton producing the Bt toxins Cry1Ac and Cry1F in Helicoverpa zea. Pest management science.
  More info

  In pests with inherently low susceptibility to Bacillus thuringiensis (Bt) toxins, seasonal declines in the concentration of Bt toxins in transgenic crops could accelerate evolution of resistance by increasing the dominance of resistance. Here, we evaluated Helicoverpa zea survival on young and old cotton plants that produced the Bt toxins Cry1Ac and Cry1F or did not produce Bt toxins.
• Cheng, Q., Gu, S., Liu, Z., Wang, C. Z., & Li, X. (2017). Expressional divergence of the fatty acid-amino acid conjugate-hydrolyzing aminoacylase 1 (L-ACY-1) in Helicoverpa armigera and Helicoverpa assulta. Scientific reports, 7(1), 8721.
  More info

  How FACs-producing generalist and specialist herbivores regulate their FACs-hydrolyzing enzyme L-ACY-1 to balance FACs' beneficial vs. detrimental effects remains unknown. To address this question, we compared L-ACY-1 expression in Helicoverpa armigera and Helicoverpa assulta, a pair of closely related sibling species differing mainly in their host range, by the same sets of hostplants, protein to digestible carbohydrate (P:C) ratios, or allelochemical. L-ACY-1 expression remained low/unchanged in H. armigera, but was induced by hot pepper fruits and repressed by cotton bolls in H. assulta. The representative allelochemicals of the tested hostplants significantly (capsaicin) or insignificantly (gossypol and nicotine) induced L-ACY-1 expression in H. armigera, but insignificantly inhibited (capsaicin and gossypol) or induced (nicotine) it in H. assulta. L-ACY-1 expression remained low/unaltered on balanced (P50:C50 and P53:C47) or protein-biased diets and induced on carbohydrate-biased diets in H. armigera, but was at the highest level on balanced diets and reduced on either protein- or carbohydrate-biased diets in H. assulta. Furthermore, L-ACY-1 expression was significantly higher in H. assulta than in H. armigera for most of feeding treatments. Such expressional divergences suggest that FACs are utilized mainly for removal of excessive nitrogen in generalists but for nitrogen assimilation in specialists.
• Cheng, Q., Gu, S., Liu, Z., Wang, C., & Li, X. (2017). Expressional divergence of the fatty acid-amino acid conjugate-hydrolyzing aminoacylase 1 (LACY-1) in Helicoverpa armigera and Helicoverpa assulta. SCIENTIFIC REPORTS, 7.
• Li, R. T., Ning, C., Huang, L. Q., Dong, J. F., Li, X., & Wang, C. Z. (2017). Expressional divergences of two desaturase genes determine the opposite ratios of two sex pheromone components in Helicoverpa armigera and Helicoverpa assulta. Insect biochemistry and molecular biology, 90, 90-100.
  More info

  The sympatric closely related species Helicoverpa armigera and Helicoverpa assulta use 97:3 and 7:93 of (Z)-11-hexadecenal and (Z)-9-hexadecenal, respectively, as their sex pheromone to find/locate correct sex mates. Moreover, (Z)-11-hexadecenyl alcohol and (Z)-9-hexadecenyl alcohol are more abundant in the pheromone gland of H. assulta than in that of H. armigera. To clarify the molecular basis of these differences, we sequenced the pheromone gland transcriptomes of the two species and compared the expression patterns of the candidate enzyme genes involved in the pheromone biosynthetic pathways by FPKM values and quantitative RT-PCR analysis. We found that the desaturase gene LPAQ expressed about 70 times higher in H. armigera than in H. assulta, whereas another desaturase gene NPVE expressed about 60 times higher in H. assulta than in H. armigera. We also observed significantly higher expression of the fatty acyl reductase (FAR) gene FAR1 and the aldehyde reductase (AR) gene AR3 in H. assulta than in H. armigera. Examination of the pheromone glands of the backcross offspring of their hybrids to H. assulta showed a positive linear correlation between the expression level of LPAQ and the amount of Z11-16:Ald and between the expression level of NPVE and the amount of Z9-16:Ald in the pheromone glands. Taken together, these data demonstrate that the expressional divergences of LPAQ and NPVE determine the opposite sex pheromone component ratios in the two species and the divergent expression of FAR1 and AR3 may account for the greater accumulation of alcohols in the pheromone gland of H. assulta.
• Li, R., Ning, C., Huang, L., Dong, J., Li, X., & Wang, C. (2017). Expressional divergences of two desaturase genes determine the opposite ratios of two sex pheromone components in Helicoverpa armigera and Helicoverpa assulta. INSECT BIOCHEMISTRY AND MOLECULAR BIOLOGY, 90, 90-100.
• Ni, X., Cottrell, T. E., Buntin, G. D., Li, X., Wang, W., & Zhuang, H. (2017). Monitoring of brown stink bug (Hemiptera: Pentatomidae) population dynamics in corn to predict its abundance using weather data. Insect science.
  More info

  The brown stink bug (BSB), Euschistus servus (Say) (Hemiptera: Pentatomidae), is a serious economic pest of corn production in the southeastern United States. The BSB population dynamics was monitored for 17 weeks from tasseling to preharvest of corn plants (i.e., late May to mid-September) using pheromone traps in three corn fields from 2005 to 2009. The trap data showed two peaks in early June and mid-August, respectively. The relationship between trap catch and pregrowing season weather data was examined using correlation and stepwise multiple factor regression analyses. Weather indices used for the analyses were accumulated growing degree day (AGDD), number of days with minimum temperature below 0 °C (Subz), accumulated daily maximum (AMaxT) and minimum temperatures (AMinT) and rainfall (ARain). The weather indices were calculated with lower (10 °C) and upper (35 °C) as biological thresholds. The parameters used in regression analysis were seasonal abundance (or overall mean of BSB adult catch) (BSBm), number of BSB adults caught at a peak (PeakBSB), and peak week (Peakwk). The BSBm was negatively related to high temperature (AmaxT or AGDD) consistently, whereas 1stPeakBSB was positively correlated to both ARain and Subz, irrespective of weather data durations (the first 4, 4.5, and 5 months). In contrast, the 7-month weather data (AGDD7) were negatively correlated to the BSBm only, but not correlated to the second PeakBSB. The 5-year monitoring study demonstrated that weather data can be used to predict the BSB abundance at its first peak in tasseling corn fields in the southeastern U.S. states.
• Wan, P., Xu, D., Cong, S., Jiang, Y., Huang, Y., Wang, J., Wu, H., Wang, L., Wu, K., Carriere, Y., Mathias, A., Li, X., & Tabashnik, B. E. (2017). Hybridizing transgenic Bt cotton with non-Bt cotton counters resistance in pink bollworm. PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA, 114(21), 5413-5418.
• Wan, P., Xu, D., Cong, S., Jiang, Y., Huang, Y., Wang, J., Wu, H., Wang, L., Wu, K., Carrière, Y., Mathias, A., Li, X., & Tabashnik, B. E. (2017). Hybridizing transgenic Bt cotton with non-Bt cotton counters resistance in pink bollworm. Proceedings of the National Academy of Sciences of the United States of America, 114(21), 5413-5418.
  More info

  Extensive cultivation of crops genetically engineered to produce insecticidal proteins from the bacterium Bacillus thuringiensis (Bt) has suppressed some major pests, reduced insecticide sprays, enhanced pest control by natural enemies, and increased grower profits. However, these benefits are being eroded by evolution of resistance in pests. We report a strategy for combating resistance by crossing transgenic Bt plants with conventional non-Bt plants and then crossing the resulting first-generation (F1) hybrid progeny and sowing the second-generation (F2) seeds. This strategy yields a random mixture within fields of three-quarters of plants that produce Bt toxin and one-quarter that does not. We hypothesized that the non-Bt plants in this mixture promote survival of susceptible insects, thereby delaying evolution of resistance. To test this hypothesis, we compared predictions from computer modeling with data monitoring pink bollworm (Pectinophora gossypiella) resistance to Bt toxin Cry1Ac produced by transgenic cotton in an 11-y study at 17 field sites in six provinces of China. The frequency of resistant individuals in the field increased before this strategy was widely deployed and then declined after its widespread adoption boosted the percentage of non-Bt cotton plants in the region. The correspondence between the predicted and observed outcomes implies that this strategy countered evolution of resistance. Despite the increased percentage of non-Bt cotton, suppression of pink bollworm was sustained. Unlike other resistance management tactics that require regulatory intervention, growers adopted this strategy voluntarily, apparently because of advantages that may include better performance as well as lower costs for seeds and insecticides.
• Wang, X. Y., Bai, S. F., Li, X., An, S. H., Yin, X. M., & Li, X. C. (2017). Differential responses of Helicoverpa armigera C-type immunlectin genes to the endoparasitoid Campoletis chlorideae. Archives of insect biochemistry and physiology, 94(3).
  More info

  The C-type lectins mediate nonself recognition in insects. The previous studies focused on host immunlectin response to bacterial infection; however, the molecular basis of immunlectin reactions to endoparasitoids has not been elucidated. The present study investigated the effect of parasitization by Campoletis chlorideae on hemagglutination activity (HA; defined as the ability of lectin to agglutinate erythrocytes or other cells), and transcriptional expression of C-type immunlectin genes in the larval host, Helicoverpa armigera. Parasitization induced four- to eightfold higher HA in the parasitized larvae, compared to nonparasitized larvae at days 2 and 6 postparasitization (PP), however inhibited HA at other days PP. Eight C-type lectins were differentially expressed in different host developmental stages, from feeding to wandering stage. The mRNA levels of HaCTL1, HaCTL3, HaCTL4, and HaCTL5 were upregulated and HaCTL2 and HaCTL7 were downregulated. Tissue analysis showed that HaCTLs were mainly expressed in fat body or hemocytes, while HaCTL5 was highly expressed in testes. The effects of parasitization on the lectin expression patterns differed. Lectins except HaCTL6 or HaCTL5 were significantly down- or upregulated in parasitized larvae at day 4 or 6 PP compared with that of nonparasitized larvae. We infer from our results that C-type immunlectins are involved in host-parasitoid interactions, and parasitization alter host immunlectin levels both in inhibiting and promoting host immune defenses to endoparasitoids. These immunlectin genes indicated an altered physiological status of the host insect, depending on developmental stage, tissue, and parasitization.
• Wei, J., Liang, G., Wu, K., Gu, S., Guo, Y., Ni, X., & Li, X. (2017). Cytotoxicity and binding profiles of activated Cry1Ac and Cry2Ab to three insect cell lines. Insect science.
  More info

  While Cry1Ac has been known to bind with larval midgut proteins cadherin, APN (amino peptidase N), ALP (alkaline phosphatase) and ABCC2 (adenosine triphosphate-binding cassette transporter subfamily C2), little is known about the receptors of Cry2Ab. To provide a clue to the receptors of Cry2Ab, we tested the baseline cytotoxicity of activated Cry1Ac and Cry2Ab against the midgut and fat body cell lines of Helicoverpa zea and the ovary cell line of Spodoptera frugiperda (SF9). As expected, the descending order of cytotoxicity of Cry1Ac against the three cell lines in terms of 50% lethal concetration (LC50 ) was midgut (31.0 μg/mL) > fat body (59.0 μg/mL) and SF9 cell (99.6 μg/mL). By contrast, the fat body cell line (LC50 = 7.55 μg/mL) was about twice more susceptible to Cry2Ab than the midgut cell line (16.0 μg/mL), the susceptibility of which was not significantly greater than that of SF9 cells (27.0 μg/mL). Further, ligand blot showed the binding differences between Cry1Ac and Cry2Ab in the three cell lines. These results indicated that the receptors of Cry2Ab were enriched in fat body cells and thus largely different from the receptors of Cry1Ac, which were enriched in midgut cells.
• Xie, W., Chen, C., Yang, Z., Guo, L., Yang, X., Wang, D., Chen, M., Huang, J., Wen, Y., Zeng, Y., Liu, Y., Xia, J., Tian, L., Cui, H., Wu, Q., Wang, S., Xu, B., Li, X., Tan, X., , Ghanim, M., et al. (2017). Genome sequencing of the sweetpotato whitefly Bemisia tabaci MED/Q. GIGASCIENCE, 6(5).
• Xie, W., Chen, C., Yang, Z., Guo, L., Yang, X., Wang, D., Chen, M., Huang, J., Wen, Y., Zeng, Y., Liu, Y., Xia, J., Tian, L., Cui, H., Wu, Q., Wang, S., Xu, B., Li, X., Tan, X., , Ghanim, M., et al. (2017). Genome sequencing of the sweetpotato whitefly Bemisia tabaci MED/Q. GigaScience, 6(5), 1-7.
  More info

  The sweetpotato whitefly Bemisia tabaci is a highly destructive agricultural and ornamental crop pest. It damages host plants through both phloem feeding and vectoring plant pathogens. Introductions of B. tabaci are difficult to quarantine and eradicate because of its high reproductive rates, broad host plant range, and insecticide resistance. A total of 791 Gb of raw DNA sequence from whole genome shotgun sequencing, and 13 BAC pooling libraries were generated by Illumina sequencing using different combinations of mate-pair and pair-end libraries. Assembly gave a final genome with a scaffold N50 of 437 kb, and a total length of 658 Mb. Annotation of repetitive elements and coding regions resulted in 265.0 Mb TEs (40.3%) and 20 786 protein-coding genes with putative gene family expansions, respectively. Phylogenetic analysis based on orthologs across 14 arthropod taxa suggested that MED/Q is clustered into a hemipteran clade containing A. pisum and is a sister lineage to a clade containing both R. prolixus and N. lugens. Genome completeness, as estimated using the CEGMA and Benchmarking Universal Single-Copy Orthologs pipelines, reached 96% and 79%. These MED/Q genomic resources lay a foundation for future 'pan-genomic' comparisons of invasive vs. noninvasive, invasive vs. invasive, and native vs. exotic Bemisia, which, in return, will open up new avenues of investigation into whitefly biology, evolution, and management.
• Yang, L., Wang, X., Bai, S., Li, X., Gu, S., Wang, C. Z., & Li, X. (2017). Expressional divergence of insect GOX genes: From specialist to generalist glucose oxidase. Journal of insect physiology, 100, 21-27.
  More info

  Insect herbivores often secrete glucose oxidase (GOX) onto plants to counteract plant defenses and potential pathogens. Whether generalist herbivores always have significantly higher GOX activities than their specialist counterparts at any comparable stage or conditions and how this is realized remain unknown. To address these two general questions, we subjected larvae of a pair of sister species differed mainly in host range, the generalist Helicoverpa armigera and its specialist counterpart Helicoverpa assulta, to the same sets of stage, protein to digestible carbohydrate (P:C) ratio, allelochemical or host plant treatments for simultaneous analyses of GOX transcripts and activities in their labial glands. GOX activity and transcripts are upregulated concurrently with food ingestion and body growth, downregulated with stopping ingestion and wandering for pupation in both species. The three tested host plants upregulated GOX transcripts, and to a lesser extent, GOX activity in both species. There were significant differences in both GOX transcripts and activity elicited by allelochemicals, but only in GOX transcripts by P:C ratios in both species. GOX activities were higher in H. armigera than H. assulta in all the comparable treatments, but GOX transcripts were significantly higher either in generalists or in specialists, depending on the developmental stages, host plants, P:C ratio and allelochemicals they encounter. These data indicate that the greater GOX activity in generalist herbivores is not achieved by greater transcription rate, but by greater transcript stability, greater translation rate, better enzyme stability and/or their combination.
• Yang, L., Wang, X., Bai, S., Li, X., Gu, S., Wang, C., & Li, X. (2017). Expressional divergence of insect GOX genes: From specialist to generalist glucose oxidase. JOURNAL OF INSECT PHYSIOLOGY, 100, 21-27.
• Lu, S., Jiang, M., Huo, T., Li, X., & Zhang, Y. (2016). 3-hydroxy-3-methyl glutaryl coenzyme A reductase: an essential actor in the biosynthesis of cantharidin in the blister beetle Epicauta chinensis Laporte. INSECT MOLECULAR BIOLOGY, 25(1), 58-71.
• Shu, C., Zhou, J., Crickmore, N., Li, X., Song, F., Liang, G., He, K., Huang, D., & Zhang, J. (2016). In vitro template-change PCR to create single crossover libraries: a case study with B. thuringiensis Cry2A toxins. SCIENTIFIC REPORTS, 6.
• Shu, C., Zhou, J., Crickmore, N., Li, X., Song, F., Liang, G., He, K., Huang, D., & Zhang, J. (2016). In vitro template-change PCR to create single crossover libraries: a case study with B. thuringiensis Cry2A toxins. Scientific reports, 6, 23536.
  More info

  During evolution the creation of single crossover chimeras between duplicated paralogous genes is a known process for increasing diversity. Comparing the properties of homologously recombined chimeras with one or two crossovers is also an efficient strategy for analyzing relationships between sequence variation and function. However, no well-developed in vitro method has been established to create single-crossover libraries. Here we present an in vitro template-change polymerase change reaction that has been developed to enable the production of such libraries. We applied the method to two closely related toxin genes from B. thuringiensis and created chimeras with differing properties that can help us understand how these toxins are able to differentiate between insect species.
• Wang, L., Wan, P., Cong, S., Wang, J., Huang, M., Tabashnik, B. E., Li, X., & Wu, K. (2016). Adult Exposure to Bt Toxin Cry1Ac Reduces Life Span and Reproduction of Resistant and Susceptible Pink Bollworm (Lepidoptera: Gelechiidae). JOURNAL OF ECONOMIC ENTOMOLOGY, 109(3), 1357-1363.
• Wang, L., Wan, P., Cong, S., Wang, J., Huang, M., Tabashnik, B. E., Li, X., & Wu, K. (2016). Adult Exposure to Bt Toxin Cry1Ac Reduces Life Span and Reproduction of Resistant and Susceptible Pink Bollworm (Lepidoptera: Gelechiidae). Journal of economic entomology.
  More info

  Insecticidal proteins from Bacillus thuringiensis (Bt) are used widely in sprays and transgenic plants to control insect pests. Although much research has elucidated the effects of Bt toxins on larvae, relatively little is known about their effects on adults. Here, we evaluated the effects of exposing adults to Bt toxin Cry1Ac on the life span and reproduction of two strains of pink bollworm (Pectinophora gossypiella (Saunders)). In larval diet bioassays, the concentration of Cry1Ac killing 50% of larvae (LC50) was 640 times higher for the laboratory-selected resistant strain (AZP-R) than the susceptible strain (APHIS-S). In experiments with adults, the highest concentrations of Cry1Ac tested (160 and 640 µg Cry1Ac per ml of 5% honey water) reduced life span for both strains. Treatments with 10, 40, and 160 µg Cry1Ac per ml reduced the duration of the oviposition period as well as the number of eggs laid by both strains, but did not affect the percentage of pairs producing eggs, the duration of the preoviposition period, or the percentage of eggs hatching for either strain. Adult life span did not differ between strains at low to moderate concentrations of Cry1Ac, but it was significantly greater for the resistant strain than the susceptible strain at the two highest concentrations of Cry1Ac tested. The reduced susceptibility to high concentrations of Cry1Ac in adults of the AZP-R strain relative to the APHIS-S strain provides the first evidence of expression of resistance to a Bt toxin in adult Lepidoptera.
• Wei, J., Zhang, M., Liang, G., Wu, K., Guo, Y., Ni, X., & Li, X. (2016). APN1 is a functional receptor of Cry1Ac but not Cry2Ab in Helicoverpa zea. SCIENTIFIC REPORTS, 6.
• Wei, J., Zhang, M., Liang, G., Wu, K., Guo, Y., Ni, X., & Li, X. (2016). APN1 is a functional receptor of Cry1Ac but not Cry2Ab in Helicoverpa zea. Scientific reports, 6, 19179.
  More info

  Lepidopteran midgut aminopeptidases N (APNs) are phylogenetically divided into eight clusters, designated as APN1-8. Although APN1 has been implicated as one of the receptors for Cry1Ac in several species, its potential role in the mode of action of Cry2Ab has not been functionally determined so far. To test whether APN1 also acts as one of the receptors for Cry1Ac in Helicoverpa zea and even for Cry2Ab in this species, we conducted a gain of function analysis by heterologously expressing H. zea APN1 (HzAPN1) in the midgut and fat body cell lines of H. zea and the ovarian cell line of Spodoptera frugiperda (Sf9) and a loss of function analysis by RNAi (RNA interference) silencing of the endogenous APN1 in the three cell lines using the HzAPN1 double strand RNA (dsRNA). Heterologous expression of HzAPN1 significantly increased the susceptibility of the three cell lines to Cry1Ac, but had no effects on their susceptibility to Cry2Ab. Knocking down of the endogenous APN1 made the three cell lines resistant to Cry1Ac, but didn't change cell lines susceptibility to Cry2Ab. The findings from this study demonstrate that HzAPN1 is a functional receptor of Cry1Ac, but not Cry2Ab.
• Wu, M., Gao, S., Yang, Y., Gu, S., Wang, M., & Li, X. (2016). Differences in neonates’ host plant preference between Helicoverpa armigera and Helicoverpa assulta. Plant Protection, 42(3), 63-69.
• Yin, S., Zhang, C., Zhang, Y., & Li, X. (2016). Resistance status of the diamondback moth Plutella xylostella (L.) to nine insecticides in Shaanxi province.. Journal of Northwest A&F University (Natural Science Edition), 44(1), 102-110.
• Zhang, S., Gu, S., & Li, X. (2016). Entomology Moves into the Genomics Era. SCIENTIA SINICA Vitae, 46(10), 1162-1173.
• Chen, W., Liu, C., Xiao, Y., Zhang, D., Zhang, Y., Li, X., Tabashnik, B. E., & Wu, K. (2015). A Toxin-Binding Alkaline Phosphatase Fragment Synergizes Bt Toxin Cry1Ac against Susceptible and Resistant Helicoverpa armigera. PLOS ONE, 10(4).
• Chen, W., Liu, C., Xiao, Y., Zhang, D., Zhang, Y., Li, X., Tabashnik, B. E., & Wu, K. (2015). A toxin-binding alkaline phosphatase fragment synergizes Bt toxin Cry1Ac against susceptible and resistant Helicoverpa armigera. PloS one, 10(4), e0126288.
  More info

  Evolution of resistance by insects threatens the continued success of pest control using insecticidal crystal (Cry) proteins from the bacterium Bacillus thuringiensis (Bt) in sprays and transgenic plants. In this study, laboratory selection with Cry1Ac yielded five strains of cotton bollworm, Helicoverpa armigera, with resistance ratios at the median lethal concentration (LC50) of activated Cry1Ac ranging from 22 to 1700. Reduced activity and reduced transcription of an alkaline phosphatase protein that binds Cry1Ac was associated with resistance to Cry1Ac in the four most resistant strains. A Cry1Ac-binding fragment of alkaline phosphatase from H. armigera (HaALP1f) was not toxic by itself, but it increased mortality caused by Cry1Ac in a susceptible strain and in all five resistant strains. Although synergism of Bt toxins against susceptible insects by toxin-binding fragments of cadherin and aminopeptidase N has been reported previously, the results here provide the first evidence of synergism of a Bt toxin by a toxin-binding fragment of alkaline phosphatase. The results here also provide the first evidence of synergism of a Bt toxin by any toxin-binding peptide against resistant insects.
• Gu, S., Zhou, J., Gao, S., Wang, D., Li, X., Guo, Y., & Zhang, Y. (2015). Identification and comparative expression analysis of odorant binding protein genes in the tobacco cutworm Spodoptera litura. Scientific reports, 5, 13800.
  More info

  Insect odorant binding proteins (OBPs) are thought to involve in insects' olfaction perception. In the present study, we identified 38 OBP genes from the antennal transcriptomes of Spodoptera litura. Tissue expression profiles analysis revealed that 17 of the 38 SlitOBP transcripts were uniquely or primarily expressed in the antennae of both sexes, suggesting their putative role in chemoreception. The RPKM value analysis revealed that seven OBPs (SlitPBP1-3, SlitGOBP1-2, SlitOBP3 and SlitOBP5) are highly abundant in male and female antennae. Most S. litura antennal unigenes had high homology with Lepidoptera insects, especially genes of the genus Spodoptera. Phylogenetic analysis of the Lepidoptera OBPs demonstrated that the OBP genes from the genus Spodoptera (S. litura, Spodoptera littoralis and Spodoptera exigua) had a relatively close evolutionary relationship. Some regular patterns and key conserved motifs of OBPs in genus Spodoptera are identified by MEME, and their putative roles in detecting odorants are discussed here. The motif-patterns between Lepidoptera OBPs and CSPs are also compared. The SlitOBPs identified here provide a starting point to facilitate functional studies of insect OBPs at the molecular level both in vivo and in vitro.
• Li, J., He, F., Yang, Y., Xiao, Y., Peng, R., Yao, H., Li, X., Peng, J., Hong, H., & Liu, K. (2015). Establishment and characterization of a novel cell line from midgut tissue of Helicoverpa armigera (Lepidoptera: Noctuidae). IN VITRO CELLULAR & DEVELOPMENTAL BIOLOGY-ANIMAL, 51(6), 562-571.
• Li, J., He, F., Yang, Y., Xiao, Y., Peng, R., Yao, H., Li, X., Peng, J., Hong, H., & Liu, K. (2015). Establishment and characterization of a novel cell line from midgut tissue of Helicoverpa armigera (Lepidoptera: Noctuidae). In vitro cellular & developmental biology. Animal, 51(6), 562-71.
  More info

  The midgut of lepidopteran larvae serves as a target for many pathogens such as Bacillus thuringiensis (Bt). Cell lines originating from midgut tissues will be very helpful tools in many research fields. However, to date, no Bt-susceptible midgut-derived cell lines are available. Here, we reported that a novel cell line, designated as HNU-Ha-MG1, was established from midgut tissue of the fourth instar larvae of Helicoverpa armigera. This cell line grew well in Grace's insect cell culture medium supplemented with 10-15% fetal bovine serum. The shape of the most cells was round or polygonal, and some tended to aggregate to form multiple cell masses. The size of the cells was 13.8 ± 1.8 μm in diameter, and the maximum density reached (2.40 ± 0.15) × 10(6) cells/ml. The population doubling time during logarithmic growth phase was 58.6 ± 7.0 h at 28°C. The number of chromosomes was about 90-130, which exhibited typical chromosome characteristics of lepidopteran cell lines. The patterns of random amplified polymorphic DNA of the cell line were different from those of Sl-HP and Hi5 cell lines which were frequently used in our laboratory. 20-Hydroxyecdysterone induced apoptosis in a very small part of cells at 2 μg/ml but did not affect expression of autophagy-related protein 8 (Atg8) and its lipidation at 36 h post-treatment. The cell line was permissive to Autographa californica nuclear polyhedrosis virus (AcMNPV) and H. armigera nuclear polyhedrosis virus (HaSNPV). This cell line was found to be susceptible to activated Cry1C at the final concentration of 0.5-1.0 μg/ml but not to the activated Cry1Ac.
• Liu, S., Wang, M. o., & Li, X. (2015). Overexpression of Tyrosine hydroxylase and Dopa decarboxylase associated with pupal melanization in Spodoptera exigua. SCIENTIFIC REPORTS, 5.
• Liu, S., Wang, M. o., & Li, X. (2015). Pupal melanization is associated with higher fitness in Spodoptera exigua. SCIENTIFIC REPORTS, 5.
• Liu, S., Wang, M., & Li, X. (2015). Overexpression of Tyrosine hydroxylase and Dopa decarboxylase associated with pupal melanization in Spodoptera exigua. Scientific reports, 5, 11273.
  More info

  Melanism has been found in a wide range of species, but the molecular mechanisms involved remain largely elusive. In this study, we studied the molecular mechanisms of the pupal melanism in Spodoptera exigua. The full length cDNA sequences of tyrosine hydroxylase (TH) and dopa decarboxylase (DDC), two key enzymes in the biosynthesis pathway of melanin, were cloned, and their temporal expression patterns in the integument were compared during the larval-pupal metamorphosis process of the S. exigua wild type (SEW) and melanic mutant (SEM) strains. No amino acid change in the protein sequence of TH and DDC was found between the two strains. Both DDC and TH were significantly over-expressed in the integument of the SEM strain at late-prepupa and 0 h pupa, respectively, compared with those of the SEW strain. Feeding 5(th) instar larvae of SEM with diets incorporated with 1 mg/g of the DDC inhibitor L-α-Methyl-DOPA and 0.75 mg/g of the TH inhibitor 3-iodo-tyrosine (3-IT) resulted in 20% pupae with partially-rescued phenotype and 68.2% of pupae with partially- or fully-rescued phenotype, respectively. These results indicate that overexpressions of TH and DDC are involved in the pupal melanization of S. exigua.
• Liu, S., Wang, M., & Li, X. (2015). Pupal melanization is associated with higher fitness in Spodoptera exigua. Scientific reports, 5, 10875.
  More info

  Melanism has long been thought to be a habitat adaptation with a fitness cost. Here we reported a homozygous melanic strain (SEM) of Spodoptera exigua (Hübner) (Insecta: Lepidoptera: Noctuidae) established with black pupae spontaneously occurring within a typical laboratory population (SEW). The melanization is expressed globally, and only in the pupal stage. After pupation, the melanic SEM pupae gradually accumulate melanin to become completely black within 6 hours, whereas the wild-type SEW pupae gradually turn yellow-brown. The melanic SEM strain exhibits faster development in all life stages, heavier pupa weight, more mating time, higher fecundity, and accordingly, higher net reproductive rate and population trend index. While no reproductive isolation was observed between the SEM and SEW strains, the mating times per female of the reciprocal crosses and the SEM intracrosses were significantly higher than those of the SEW intracrosses. This represents a rare case of melanization that has fitness gains, rather than costs. Analysis of the life-history traits of this case and 14 previously reported cases of insect melanism indicate that none of melanization origin, stage, space and variation type determining whether melanism will cause fitness gain or cost.
• Ma, L., Dai, W., Li, X., Zhang, Y., & Zhang, C. (2015). Molecular cloning and expression analysis of soluble and membrane-bound trehalase genes in the cotton bollworm, Helicaverpa armigera. JOURNAL OF ASIA-PACIFIC ENTOMOLOGY, 18(2), 187-195.
• Tabashnik, B. E., Zhang, M., Fabrick, J. A., Wu, Y., Gao, M., Huang, F., Wei, J., Zhang, J., Yelich, A., Unnithan, G. C., Bravo, A., Soberon, M., Carriere, Y., & Li, X. (2015). Dual mode of action of Bt proteins: protoxin efficacy against resistant insects. SCIENTIFIC REPORTS, 5.
• Tabashnik, B. E., Zhang, M., Fabrick, J. A., Wu, Y., Gao, M., Huang, F., Wei, J., Zhang, J., Yelich, A., Unnithan, G. C., Bravo, A., Soberón, M., Carrière, Y., & Li, X. (2015). Dual mode of action of Bt proteins: protoxin efficacy against resistant insects. Scientific reports, 5, 15107.
  More info

  Transgenic crops that produce Bacillus thuringiensis (Bt) proteins for pest control are grown extensively, but insect adaptation can reduce their effectiveness. Established mode of action models assert that Bt proteins Cry1Ab and Cry1Ac are produced as inactive protoxins that require conversion to a smaller activated form to exert toxicity. However, contrary to this widely accepted paradigm, we report evidence from seven resistant strains of three major crop pests showing that Cry1Ab and Cry1Ac protoxins were generally more potent than the corresponding activated toxins. Moreover, resistance was higher to activated toxins than protoxins in eight of nine cases evaluated in this study. These data and previously reported results support a new model in which protoxins and activated toxins kill insects via different pathways. Recognizing that protoxins can be more potent than activated toxins against resistant insects may help to enhance and sustain the efficacy of transgenic Bt crops.
• Wang, X., Bai, S., Li, X., Yin, X., & Li, X. (2015). THE ENDOPARASITOID Campoletis chlorideae INDUCES A HEMOLYTIC FACTOR IN THE HERBIVOROUS INSECT Helicoverpa armigera. Archives of insect biochemistry and physiology, 90(1), 14-27.
  More info

  Although lysis of invading organisms is a major innate form of immunity used by invertebrates, it remains unclear whether herbivorous insects have hemolysin or not. To address this general question, we tested the hemolytic (HL) activity of the hemolymph and tissue extracts from various stages of the polyphagous insect Helicoverpa armigera (Hübner) against the erythrocytes from chicken, duck, and rabbit. An HL activity was identified in the hemolymph of H. armigera larvae. Further studies demonstrated that the HL activity is proteinaceous as it was precipitable by deproteinizing agents. Hemolysins were found in Helicoverpa egg, larva, pupa, and adult, but the activity was higher in feeding larvae than in molting or newly molted larvae. Hemolysins were distributed among a variety of larval tissues including salivary gland, fat body, epidermis, midgut, or testes, but the highest activity was found in salivary gland and fat body. Relative to nonparasitized larvae, parasitization of H. armigera larvae by the endoparasitoid Campoletis chlorideae Uchida induced a 3.4-fold increase in the HL activity in the plasma of parasitized host at day two postparasitization. The present study shows the presence of a parasitoid inducible HL factor in the parasitized insect. The HL activity increased significantly in H. armigera larvae at 12 and 24 h postinjection with Escherichia coli. We infer the HL factor(s) is inducible or due to de novo synthesis, which means that the HL factor(s) is associated with insect immune response by inhibiting or clearance of invading organisms.
• Wei, J., Guo, Y., Liang, G., Wu, K., Zhang, J., Tabashnik, B. E., & Li, X. (2015). Cross-resistance and interactions between Bt toxins Cry1Ac and Cry2Ab against the cotton bollworm. SCIENTIFIC REPORTS, 5.
• Wei, J., Guo, Y., Liang, G., Wu, K., Zhang, J., Tabashnik, B. E., & Li, X. (2015). Cross-resistance and interactions between Bt toxins Cry1Ac and Cry2Ab against the cotton bollworm. Scientific reports, 5, 7714.
  More info

  To delay evolution of pest resistance to transgenic crops producing insecticidal proteins from Bacillus thuringiensis (Bt), the "pyramid" strategy uses plants that produce two or more toxins that kill the same pest. We conducted laboratory diet experiments with the cotton bollworm, Helicoverpa armigera, to evaluate cross-resistance and interactions between two toxins in pyramided Bt cotton (Cry1Ac and Cry2Ab). Selection with Cry1Ac for 125 generations produced 1000-fold resistance to Cry1Ac and 6.8-fold cross-resistance to Cry2Ab. Selection with Cry2Ab for 29 generations caused 5.6-fold resistance to Cry2Ab and 61-fold cross-resistance to Cry1Ac. Without exposure to Bt toxins, resistance to both toxins decreased. For each of the four resistant strains examined, 67 to 100% of the combinations of Cry1Ac and Cry2Ab tested yielded higher than expected mortality, reflecting synergism between these two toxins. Results showing minor cross-resistance to Cry2Ab caused by selection with Cry1Ac and synergism between these two toxins against resistant insects suggest that plants producing both toxins could prolong the efficacy of Bt cotton against this pest in China. Including toxins against which no cross-resistance occurs and integrating Bt cotton with other control tactics could also increase the sustainability of management strategies.
• Welch, K. L., Unnithan, G. C., Degain, B. A., Wei, J., Zhang, J., Li, X., Tabashnik, B. E., & Carriere, Y. (2015). Cross-resistance to toxins used in pyramided Bt crops and resistance to Bt sprays in Helicoverpa zea. JOURNAL OF INVERTEBRATE PATHOLOGY, 132, 149-156.
• Welch, K. L., Unnithan, G. C., Degain, B. A., Wei, J., Zhang, J., Li, X., Tabashnik, B. E., & Carrière, Y. (2015). Cross-resistance to toxins used in pyramided Bt crops and resistance to Bt sprays in Helicoverpa zea. Journal of invertebrate pathology, 132, 149-56.
  More info

  To delay evolution of resistance by insect pests, farmers are rapidly increasing their use of transgenic crops producing two or more Bacillus thuringiensis (Bt) toxins that kill the same pest. A key condition favoring durability of these "pyramided" crops is the absence of cross-resistance between toxins. Here we evaluated cross-resistance in the major lepidopteran pest Helicoverpa zea (Boddie) to Bt toxins used in pyramids. In the laboratory, we selected a strain of this pest with Bt toxin Cry1Ac followed by selection with MVP II, a formulation containing a hybrid protoxin that is identical to Cry1Ac in the active portion of the toxin and 98.5% identical overall. We calculated the resistance ratio as the EC50 (concentration causing mortality or failure to develop beyond the first instar of 50% of larvae) for the laboratory-selected strain divided by the EC50 for its field-derived parent strain that was not selected in the laboratory. The resistance ratio was 20.0-33.9 (mean=27.0) for MVP II, 57.0 for Cry1Ac, 51.3 for Cry1A.105, 22.4 for Cry1Ab, 3.3 for Cry2Ab, 1.8 for Cry1Fa, and 1.6 for Vip3Aa. Resistance ratios were 2.9 for DiPel ES and 2.0 for Agree VG, which are commercial Bt spray formulations containing Cry1Ac, other Bt toxins, and Bt spores. By the conservative criterion of non-overlap of 95% fiducial limits, the EC50 was significantly higher for the selected strain than its parent strain for MVP II, Cry1Ac, Cry1A.105, Cry1Ab, Cry2Ab and DiPel ES. For Cry1Fa, Vip3Aa, and Agree VG, significantly lower susceptibility to a high concentration indicated low cross-resistance. The resistance ratio for toxins other than Cry1Ac was associated with their amino acid sequence similarity to Cry1Ac in domain II. Resistance to Cry1Ac and the observed cross-resistance to other Bt toxins could accelerate evolution of H. zea resistance to currently registered Bt sprays and pyramided Bt crops.
• Cao, G., Feng, H., Guo, F., Wu, K., Li, X., Liang, G., & Desneux, N. (2014). Quantitative Analysis of Fitness Costs Associated with the Development of Resistance to the Bt Toxin Cry1Ac in Helicoverpa armigera. SCIENTIFIC REPORTS, 4.
• Cao, G., Feng, H., Guo, F., Wu, K., Li, X., Liang, G., & Desneux, N. (2014). Quantitative analysis of fitness costs associated with the development of resistance to the Bt toxin Cry1Ac in Helicoverpa armigera. Scientific reports, 4, 5629.
  More info

  Transgenic Bacillus thuringiensis (Bt) crops play an increasing role in pest control, and resistance management is a major issue in large-scale cultivation of Bt crops. The fitness cost of resistance in targeted pests is considered to be one of the main factors delaying resistance when using the refuge strategy. By comparing 10 resistant Helicoverpa armigera (Hubner) strains, showing various resistance levels to Bt toxin (Cry1Ac), to a susceptible strain, we showed an increasing fitness cost corresponding with increasing levels of resistance. The relationship between overall fitness cost C and the resistance ratio Rr could be described by C = 24.47/(1 + exp([1.57 - Log10Rr]/0.2)). This model predicted that the maximum overall fitness cost would be ~24% (± 5.22) in the strains with the highest resistance level. The overall fitness cost was closely linked to egg hatching rate, fecundity, emergence rate, larval survival rate, and developmental duration of adults. Among fitness components measured, fecundity was the most sensitive trait linked to the resistance selection. To integrate the results into simulation models would be valuable in evaluating how variation in fitness cost may influence the development of resistance in pest populations, thus helping to develop enhanced refuge strategies.
• Chiel, E., Kelly, S. E., Harris, A. M., Gebiola, M., Li, X. -., Zchori-Fein, E., & Hunter, M. S. (2014). Characteristics, phenotype and transmission of Wolbachia in the sweet potato whitefly, Bemisia tabaci (Hemiptera: Aleyrodidae), and its parasitoid Eretmocerus sp. nr. emiratus (Hymenoptera: Aphelinidae). Environmental Entomology.
• Chiel, E., Kelly, S. E., Harris, A. M., Gebiola, M., Li, X., Zchori-Fein, E., & Hunter, M. S. (2014). Characteristics, Phenotype, and Transmission of Wolbachia in the Sweet Potato Whitefly, Bemisia tabaci (Hemiptera: Aleyrodidae), and Its Parasitoid Eretmocerus sp nr. emiratus (Hymenoptera: Aphelinidae). ENVIRONMENTAL ENTOMOLOGY, 43(2), 353-362.
• Chiel, E., Kelly, S. E., Harris, A. M., Gebiola, M., Li, X., Zchori-Fein, E., & Hunter, M. S. (2014). Characteristics, phenotype, and transmission of Wolbachia in the sweet potato whitefly, Bemisia tabaci (Hemiptera: Aleyrodidae), and its parasitoid Eretmocerus sp. nr. emiratus (Hymenoptera: Aphelinidae). Environmental entomology, 43(2), 353-62.
  More info

  Wolbachia is a common intracellular bacterial endosymbiont of insects, causing a variety of effects including reproductive manipulations such as cytoplasmic incompatibility (CI). In this study, we characterized Wolbachia in the whitefly Bemisia tabaci and in the whitefly parasitoid Eretmocerus sp. nr. emiratus. We also tested for horizontal transmission of Wolbachia between and within trophic levels, and we determined the phenotype of Wolbachia in E. sp. nr. emiratus. Using multilocus sequence typing and phylogenetic analyses, we found that B. tabaci and E. sp. nr. emiratus each harbor a different and unique strain of Wolbachia. Both strains belong to the phylogenetic supergroup B. No evidence for horizontal transmission of Wolbachia between and within trophic levels was found in our study system. Finally, crossing results were consistent with a CI phenotype; when Wolbachia-infected E. sp. nr. emiratus males mate with uninfected females, wasp progeny survival dropped significantly, and the number of females was halved. This is the first description of CI caused by Wolbachia in the economically important genus Eretmocerus. Our study underscores the expectation that horizontal transmission events occur rarely in the dynamics of secondary symbionts such as Wolbachia, and highlights the importance of understanding the effects of symbionts on the biology of natural enemies.
• Fabrick, J. A., Ponnuraj, J., Singh, A., Tanwar, R. K., Unnithan, G. C., Yelich, A. J., Li, X., Carriere, Y., & Tabashnik, B. E. (2014). Alternative Splicing and Highly Variable Cadherin Transcripts Associated with Field-Evolved Resistance of Pink Bollworm to Bt Cotton in India. PLOS ONE, 9(5).
• Fabrick, J. A., Ponnuraj, J., Singh, A., Tanwar, R. K., Unnithan, G. C., Yelich, A. J., Li, X., Carrière, Y., & Tabashnik, B. E. (2014). Alternative splicing and highly variable cadherin transcripts associated with field-evolved resistance of pink bollworm to bt cotton in India. PloS one, 9(5), e97900.
  More info

  Evolution of resistance by insect pests can reduce the benefits of insecticidal proteins from Bacillus thuringiensis (Bt) that are used extensively in sprays and transgenic crops. Despite considerable knowledge of the genes conferring insect resistance to Bt toxins in laboratory-selected strains and in field populations exposed to Bt sprays, understanding of the genetic basis of field-evolved resistance to Bt crops remains limited. In particular, previous work has not identified the genes conferring resistance in any cases where field-evolved resistance has reduced the efficacy of a Bt crop. Here we report that mutations in a gene encoding a cadherin protein that binds Bt toxin Cry1Ac are associated with field-evolved resistance of pink bollworm (Pectinophora gossypiella) in India to Cry1Ac produced by transgenic cotton. We conducted laboratory bioassays that confirmed previously reported resistance to Cry1Ac in pink bollworm from the state of Gujarat, where Bt cotton producing Cry1Ac has been grown extensively. Analysis of DNA from 436 pink bollworm from seven populations in India detected none of the four cadherin resistance alleles previously reported to be linked with resistance to Cry1Ac in laboratory-selected strains of pink bollworm from Arizona. However, DNA sequencing of pink bollworm derived from resistant and susceptible field populations in India revealed eight novel, severely disrupted cadherin alleles associated with resistance to Cry1Ac. For these eight alleles, analysis of complementary DNA (cDNA) revealed a total of 19 transcript isoforms, each containing a premature stop codon, a deletion of at least 99 base pairs, or both. Seven of the eight disrupted alleles each produced two or more different transcript isoforms, which implicates alternative splicing of messenger RNA (mRNA). This represents the first example of alternative splicing associated with field-evolved resistance that reduced the efficacy of a Bt crop.
• Gu, S. H., Sun, L., Yang, R. N., Wu, K. M., Guo, Y. Y., Li, X. C., Zhou, J. J., & Zhang, Y. J. (2014). Molecular characterization and differential expression of olfactory genes in the antennae of the black cutworm moth Agrotis ipsilon. PloS one, 9(8), e103420.
  More info

  Insects use their sensitive and selective olfactory system to detect outside chemical odorants, such as female sex pheromones and host plant volatiles. Several groups of olfactory proteins participate in the odorant detection process, including odorant binding proteins (OBPs), chemosensory proteins (CSPs), odorant receptors (ORs), ionotropic receptors (IRs) and sensory neuron membrane proteins (SNMPs). The identification and functional characterization of these olfactory proteins will enhance our knowledge of the molecular basis of insect chemoreception. In this study, we report the identification and differential expression profiles of these olfactory genes in the black cutworm moth Agrotis ipsilon. In total, 33 OBPs, 12 CSPs, 42 ORs, 24 IRs, 2 SNMPs and 1 gustatory receptor (GR) were annotated from the A. ipsilon antennal transcriptomes, and further RT-PCR and RT-qPCR revealed that 22 OBPs, 3 CSPs, 35 ORs, 14 IRs and the 2 SNMPs are uniquely or primarily expressed in the male and female antennae. Furthermore, one OBP (AipsOBP6) and one CSP (AipsCSP2) were exclusively expressed in the female sex pheromone gland. These antennae-enriched OBPs, CSPs, ORs, IRs and SNMPs were suggested to be responsible for pheromone and general odorant detection and thus could be meaningful target genes for us to study their biological functions in vivo and in vitro.
• Lei, Y., Zhu, X., Xie, W., Wu, Q., Wang, S., Guo, Z., Xu, B., Li, X., Zhou, X., & Zhang, Y. (2014). Midgut transcriptome response to a Cry toxin in the diamondback moth, Plutella xylostella (Lepidoptera: Plutellidae). GENE, 533(1), 180-187.
• Lei, Y., Zhu, X., Xie, W., Wu, Q., Wang, S., Guo, Z., Xu, B., Li, X., Zhou, X., & Zhang, Y. (2014). Midgut transcriptome response to a Cry toxin in the diamondback moth, Plutella xylostella (Lepidoptera: Plutellidae). Gene, 533(1), 180-7.
  More info

  To investigate the response of Plutella xylostella transcriptome in defending against a Bt toxin, high-throughput RNA-sequencing was carried out to examine Cry1Ac-susceptible and -resistant strains. The comparative analysis indentified over 2900 differentially expressed unigenes (DEUs) between these two strains. Gene Ontology analysis placed these unigenes primarily into cell, cell part, organelle, binding, catalytic, cellular process, metabolic process, and response to stimulus categories. Based on pathway analyses, DEUs were enriched in oxidoreductase activity and membrane lipid metabolic processes, and they were also significantly enriched in pathways related to the metabolic and biosynthesis of secondary metabolites. Most of the unigenes involved in the metabolic pathway were up-regulated in resistant strains. Within the ABC transporter pathway, majority of the down-regulated unigenes belong to ABCC2 and ABCC10, respectively, while up-regulated unigenes were mainly categorized as ABCG2. Furthermore, two aminopeptidases, and four cadherins encoding genes were significantly elevated as well. This study provides a transcriptome foundation for the identification and functional characterization of genes involved in the Bt resistance in an agriculturally important insect pest, P. xylostella.
• Li, X. (2014). Molecular Characterization and Differential Expression of Olfactory Genes in the Antennae of the Black Cutworm Moth Agrotis ipsilon.. PLoS ONE, 9(8), e103420.
• Liu, C., Xiao, Y., Li, X., Oppert, B., Tabashnik, B. E., & Wu, K. (2014). Cis-mediated down-regulation of a trypsin gene associated with Bt resistance in cotton bollworm. SCIENTIFIC REPORTS, 4.
• Liu, C., Xiao, Y., Li, X., Oppert, B., Tabashnik, B. E., & Wu, K. (2014). Cis-mediated down-regulation of a trypsin gene associated with Bt resistance in cotton bollworm. Scientific reports, 4, 7219.
  More info

  Transgenic plants producing insecticidal proteins from the bacterium Bacillus thuringiensis (Bt) are useful for pest control, but their efficacy is reduced when pests evolve resistance. Here we examined the mechanism of resistance to Bt toxin Cry1Ac in the laboratory-selected LF5 strain of the cotton bollworm, Helicoverpa armigera. This strain had 110-fold resistance to Cry1Ac protoxin and 39-fold resistance to Cry1Ac activated toxin. Evaluation of five trypsin genes revealed 99% reduced transcription of one trypsin gene (HaTryR) was associated with resistance. Silencing of this gene with RNA interference in susceptible larvae increased their survival on diets containing Cry1Ac. Bioassays of progeny from crosses revealed that resistance to Cry1Ac was genetically linked with HaTryR. We identified mutations in the promoter region of HaTryR in the resistant strain. In transfected insect cell lines, transcription was lower when driven by the resistant promoter compared with the susceptible promoter, implicating cis-mediated down-regulation of HaTryR transcription as a mechanism of resistance. The results suggest that H. armigera can adapt to Bt toxin Cry1Ac by decreased expression of trypsin. Because trypsin activation of protoxin is a critical step in toxicity, transgenic plants with activated toxins rather than protoxins might increase the durability of Bt crops.
• Ni, X., Lei, Z., He, K., Li, X., Li, X., & Xu, W. (2014). Integrated pest management is the lucrative bridge connecting the ever emerging knowledge islands of genetics and ecology PREFACE. INSECT SCIENCE, 21(5), 537-540.
• Ni, X., Lei, Z., He, K., Li, X., Li, X., & Xu, W. (2014). Integrated pest management is the lucrative bridge connecting the ever emerging knowledge islands of genetics and ecology. Insect science, 21(5), 537-40.
• Ni, X., Wilson, J. P., Toews, M. D., Buntin, G. D., Lee, R. D., Li, X., Lei, Z., He, K., Xu, W., Li, X., Huffaker, A., & Schmelz, E. A. (2014). Evaluation of spatial and temporal patterns of insect damage and aflatoxin level in the pre-harvest corn fields to improve management tactics. INSECT SCIENCE, 21(5), 572-583.
• Ni, X., Wilson, J. P., Toews, M. D., Buntin, G. D., Lee, R. D., Li, X., Lei, Z., He, K., Xu, W., Li, X., Huffaker, A., & Schmelz, E. A. (2014). Evaluation of spatial and temporal patterns of insect damage and aflatoxin level in the pre-harvest corn fields to improve management tactics. Insect science, 21(5), 572-83.
  More info

  Spatial and temporal patterns of insect damage in relation to aflatoxin contamination in a corn field with plants of uniform genetic background are not well understood. After previous examination of spatial patterns of insect damage and aflatoxin in pre-harvest corn fields, we further examined both spatial and temporal patterns of cob- and kernel-feeding insect damage, and aflatoxin level with two samplings at pre-harvest in 2008 and 2009. The feeding damage by each of the ear/kernel-feeding insects (i.e., corn earworm/fall armyworm damage on the silk/cob, and discoloration of corn kernels by stink bugs) and maize weevil population were assessed at each grid point with five ears. Sampling data showed a field edge effect in both insect damage and aflatoxin contamination in both years. Maize weevils tended toward an aggregated distribution more frequently than either corn earworm or stink bug damage in both years. The frequency of detecting aggregated distribution for aflatoxin level was less than any of the insect damage assessments. Stink bug damage and maize weevil number were more closely associated with aflatoxin level than was corn earworm damage. In addition, the indices of spatial-temporal association (χ) demonstrated that the number of maize weevils was associated between the first (4 weeks pre-harvest) and second (1 week pre-harvest) samplings in both years on all fields. In contrast, corn earworm damage between the first and second samplings from the field on the Belflower Farm, and aflatoxin level and corn earworm damage from the field on the Lang Farm were dissociated in 2009.
• Wan, H., Liu, Y., Li, M., Zhu, S., Li, X., Pittendrigh, B. R., & Qiu, X. (2014). Nrf2/Maf-binding-site-containing functional Cyp6a2 allele is associated with DDT resistance in Drosophila melanogaster. PEST MANAGEMENT SCIENCE, 70(7), 1048-1058.
• Wan, H., Liu, Y., Li, M., Zhu, S., Li, X., Pittendrigh, B. R., & Qiu, X. (2014). Nrf2/Maf-binding-site-containing functional Cyp6a2 allele is associated with DDT resistance in Drosophila melanogaster. Pest management science, 70(7), 1048-58.
  More info

  Increased insecticide detoxification mediated by cytochrome P450s is a common mechanism of insecticide resistance. Although Cyp6a2 has been observed to be overexpressed in many 4,4'-dichlorodiphenyltrichloroethane (DDT)-resistant strains of Drosophila melanogaster, how Cyp6a2 is regulated and whether its overproduction confers DDT resistance remain elusive.
• Xiao, Y., Zhang, T., Liu, C., Heckel, D. G., Li, X., Tabashnik, B. E., & Wu, K. (2014). Mis-splicing of the ABCC2 gene linked with Bt toxin resistance in Helicoverpa armigera. SCIENTIFIC REPORTS, 4.
• Xiao, Y., Zhang, T., Liu, C., Heckel, D. G., Li, X., Tabashnik, B. E., & Wu, K. (2014). Mis-splicing of the ABCC2 gene linked with Bt toxin resistance in Helicoverpa armigera. Scientific reports, 4, 6184.
  More info

  Toxins from the bacterium Bacillus thuringiensis (Bt) are used widely for insect control in sprays and transgenic plants, but their efficacy is reduced when pests evolve resistance. Previous work showed that mutations in a gene encoding the transporter protein ABCC2 are linked with resistance to Bt toxins Cry1Ab, Cry1Ac or both in four species of Lepidoptera. Here we compared the ABCC2 gene of Helicoverpa armigera (HaABCC2) between susceptible strains and a laboratory-selected strain with >1,000-fold resistance to Cry1Ac relative its susceptible parent strain. We discovered a 73-base pair (bp) insertion in the cDNA of the resistant strain that generates a premature stop codon expected to yield a truncated ABCC2 protein. Sequencing of genomic DNA revealed that this insertion is an intron that is not spliced out because of a 6-bp deletion at its splicing site. Analysis of progeny from crosses revealed tight genetic linkage between HaABCC2 and resistance to Cry1Ac. These results provide the first evidence that mis-splicing of a gene encoding an ABCC2 protein confers resistance to a Bt toxin.
• Yang, X. Q., Liu, J. Y., Li, X. C., Chen, M. H., & Zhang, Y. L. (2014). Key amino acid associated with acephate detoxification by Cydia pomonella carboxylesterase based on molecular dynamics with alanine scanning and site-directed mutagenesis. Journal of chemical information and modeling, 54(5), 1356-70.
  More info

  Insecticide-detoxifying carboxylesterase (CE) gene CpCE-1 was cloned from Cydia pomonella. Molecular dynamics (MD) simulation and computational alanine scanning (CAS) indicate that Asn 232 in CpCE-1 constitutes an approximate binding hot-spot with a binding free energy difference (ΔΔGbind) value of 3.66 kcal/mol. The catalytic efficiency (kcat/km) of N232A declined dramatically, and the half inhibitory concentrations (IC50) value increased by more than 230-fold. Metabolism assay in vitro reveals that the acephate could be metabolized by wild CpCE-1, whereas N232A mutation is unable to metabolize the acephate, which suggests that the hot-spot Asn 232 is a crucial residue for acephate metabolism. Mutation detection suggests that low frequency of Asn 232 replacement occurred in Europe field strains. Our MD, CAS, site-directed mutagenesis, and metabolism studies introduce a new amino acid residue Asn 232 involved in the metabolism of the acephate with CpCE-1, and this method is reliable in insecticide resistance mechanism research and prediction of key amino acids in a protein which is associated with specific physiological and biochemical functions.
• Zhang, C., Wong, A., Zhang, Y., Ni, X., & Li, X. (2014). Common and unique cis-acting elements mediate xanthotoxin and flavone induction of the generalist P450 CYP321A1. SCIENTIFIC REPORTS, 4.
• Zhang, C., Wong, A., Zhang, Y., Ni, X., & Li, X. (2014). Common and unique cis-acting elements mediate xanthotoxin and flavone induction of the generalist P450 CYP321A1. Scientific reports, 4, 6490.
  More info

  How polyphagous herbivores up-regulate their counterdefense genes in response to a broad range of structurally different allelochemicals remains largely unknown. To test whether this is accomplished by having more allelochemical-response elements or the similar number of functionally more diverse elements, we mapped out the cis-acting elements mediating the induction of the allelochemical-metabolizing CYP321A1 from the generalist Helicoverpa zea by xanthotoxin and flavone, two structurally distinct allelochemicals with very different encounter rate by this species. Seven xanthotoxin-responsive elements were localized by analyzing promoter activities of varying length of CYP321A1 promoter in H. zea fatbody cells. Compared with the 5 flavone-responsive elements mapped out previously, there are four common elements (1 essential element, 2 enhancers, and 1 negative element) mediating induction of CYP321A1 by both of the two allelochemicals. The remaining four elements (3 enhancers and 1 negative element), however, only regulate induction of CYP321A1 by either of the two allelochemicals. Co-administration of the two allelochemicals resulted in an induction fold that is significantly lower than the expected additive value of the two allelochemicals. These results indicate that xanthotoxin- and flavone-induced expressions of CYP321A1 are mediated mainly by the functionally more diverse common elements although the allelochemical-unique elements also play a role.
• Brévault, T., Heuberger, S., Zhang, M., Ellers-Kirk, C., Ni, X., Masson, L., Li, X. -., Tabashnik, B. E., & Carrière, Y. (2013). Potential shortfall of pyramided Bt cotton for resistance management. Proc. Natl. Acad. Sci. USA., 110, 5806-5811.
• Brévault, T., Heuberger, S., Zhang, M., Ellers-Kirk, C., Xinzhi, N. i., Masson, L., Xianchiun, L. i., Tabashnik, B. E., & Carrière, Y. (2013). Potential shortfall of pyramided transgenic cotton for insect resistance management. Proceedings of the National Academy of Sciences of the United States of America, 110(15), 5806-5811.
  More info

  PMID: 23530245;PMCID: PMC3625267;Abstract: To delay evolution of pest resistance to transgenic crops producing insecticidal proteins from Bacillus thuringiensis (Bt), the "pyramid" strategy uses plants that produce two or more toxins that kill the same pest. In the United States, this strategy has been adopted widely, with two-toxin Bt cotton replacing one-toxin Bt cotton. Although two-toxin plants are likely to be more durable than one-toxin plants, the extent of this advantage depends on several conditions. One key assumption favoring success of two-toxin plants is that they kill insects selected for resistance to one toxin, which is called "redundant killing." Here we tested this assumption for a major pest, Helicoverpa zea, on transgenic cotton producing Bt toxins Cry1Ac and Cry2Ab. Selection with Cry1Ac increased survival on two-toxin cotton, which contradicts the assumption. The concentration of Cry1Ac and Cry2Ab declined during the growing season, which would tend toexacerbate this problem. Furthermore, analysis of results from 21 selection experiments with eight species of lepi-dopteran pests indicates that some cross-resistance typically occurs between Cry1A and Cry2A toxins. Incorporation of empirical data into simulation models shows that the observed deviations from ideal conditions could greatly reduce the benefits of the pyramid strategy for pests like H. zea, which have inherently low susceptibility to Bt toxins and have been exposed extensively to one of the toxins in the pyramid before two-toxin plants are adopted. For such pests, the pyramid strategy could be improved by incorporating empirical data on deviations from ideal assumptions about redundant killing and cross-resistance.
• Cao, G., Zhang, L., Liang, G., Li, X. -., & Wu, K. (2013). Involvements of Non-binding Site Proteins Enzymes in the Development of Resistance of Helicoverpa armigera to Cry1Ac. J. Econ. Entomol. Journal of Economic Entomology, 106(6), 2514-2521.
• Cao, G., Zhang, L., Liang, G., Li, X., & Wu, K. (2013). Involvement of Nonbinding Site Proteinases in the Development of Resistance of Helicoverpa armigera (Lepidoptera: Noctuidae) to Cry1Ac. JOURNAL OF ECONOMIC ENTOMOLOGY, 106(6), 2514-2521.
• Cao, G., Zhang, L., Liang, G., Xianchun, L. i., & Kongming, W. u. (2013). Involvement of nonbinding site proteinases in the development of resistance of Helicoverpa armigera (Lepidoptera: Noctuidae) to Cry1Ac. Journal of Economic Entomology, 106(6), 2514-2521.
  More info

  Abstract: Development of resistance to transgenic crops expressing the Cry toxin from Bacterium thuringiensis (Bt) has been the major concern for the long-term success of Bt crops. Alterations in nonbinding site proteinases and Bt toxin receptors are the two types of mechanisms responsible for Bt resistance in resistant insects. However, little is known about the relative contributions of the two types of mechanisms in the early and late phases of the development of Bt resistance. To address the relative contributions of four nonbinding site proteinases including esterase, total protease, chymotrypsin, and glutathione S-transferase in the early and late phases of the development of Cry1Ac resistance, we analyzed the relationships between nonbinding site proteinases and resistance of three groups of Helicoverpa armigera H*ubner (Lepidoptera: Noctuidae) strains with different resistance levels because of different geographic origins and selection pressures. Positive correlation (esterase, glutathione-S-tranferases [GST], and chymotrypsin) and negative correlation (total midgut protease) were observed within the low to moderate group II resistant strains. Such correlations were less obvious within the low to moderate group III resistant strains because of only threefold differences in LC50 values. Relative to the unselected susceptible 96S strain, the two highly resistant group I resistant strains BtI and BtR have the same amounts of esterase, GST, and chymotrypsin and disproportionally decreased the amount of total midgut protease. Overall, the low to moderate resistant strains had the lowest amount of the nonbinding site proteinases. The results obtained suggest that alternations in the nonbinding site proteinases probably can only confer low to moderate levels of resistance and thus are enriched in the early phase of the development of Cry1Ac resistance. © 2013 Entomological Society of America.
• Chu, D., Pan, H. P., Li, X. C., Guo, D., Tao, Y. L., Liu, B. M., & Zhang, Y. J. (2013). Spatial genetic heterogeneity in populations of a newly invasive whitefly in china revealed by a nation-wide field survey. PloS one, 8(11), e79997.
  More info

  Even though introductions of exotic species provide ready-made experiments of rapid evolution, few studies have examined the genetic structure of an exotic species shortly after its initial introduction and subsequent spread. To determine the genetic structure of its populations during the initial introduction, we investigated the invasive sweet potato whitefly (Bemisia tabaci Q, commonly known as B. tabaci biotype Q) in China, which was introduced in approximately 2003. A total of 619 B. tabaci Q individuals in 20 provinces throughout China were collected and analyzed using five microsatellite loci.
• Chu, D., Pan, H., Li, X. -., Guo, D., Tao, Y., Liu, B., & Zhang, Y. (2013). Spatial genetic heterogeneity in populations of a newly invasive whitefly in China revealed by a nation-wide field survey. PLoS ONE.
• Chu, D., Pan, H., Li, X., Guo, D., Tao, Y., Liu, B., & Zhang, Y. (2013). Spatial genetic heterogeneity in populations of a newly invasive whitefly in China revealed by a nation-wide field survey. PLoS ONE, 8(11).
  More info

  Abstract: Background: Even though introductions of exotic species provide ready-made experiments of rapid evolution, few studies have examined the genetic structure of an exotic species shortly after its initial introduction and subsequent spread. To determine the genetic structure of its populations during the initial introduction, we investigated the invasive sweet potato whitefly (Bemisia tabaci Q, commonly known as B. tabaci biotype Q) in China, which was introduced in approximately 2003. A total of 619 B. tabaci Q individuals in 20 provinces throughout China were collected and analyzed using five microsatellite loci. Results: The introduced populations of B. tabaci Q in China represent eight genetic clusters with different geographic distributions. The populations in Yunnan Province, where B. tabaci Q was first detected, are genetically different from the other populations in China. Conclusion: The introduced populations of B. tabaci Q in China have high spatial genetic heterogeneity. Additional research is required to determine whether the heterogeneity results from multiple introductions, rapid evolution following one or few introductions, or some combination of multiple introductions and rapid evolution. The heterogeneity, however, is inconsistent with a single introduction at Yunnan Province, where B. tabaci Q was first detected, followed by spread. © 2013 Chu et al.
• Pan, H., Chu, D., Liu, B., Shi, X., Guo, L., Xie, W., Carrière, Y., Li, X. -., & Zhang, Y. (2013). Differential effects of an exotic plant virus on its two closely related vectors. Nature SCIENTIFIC REPORTS.
• Wan, H., Liu, Y., Mei, L. i., Zhu, S., Xianchun, L. i., Pittendrigh, B. R., & Qiu, X. (2013). Nrf2/Maf-binding-site-containing functional Cyp6a2 allele is associated with DDT resistance in Drosophilamelanogaster. Pest Management Science.
  More info

  Abstract: BACKGROUND: Increased insecticide detoxification mediated by cytochrome P450s is a common mechanism of insecticide resistance. Although Cyp6a2 has been observed to be overexpressed in many 4,4'-dichlorodiphenyltrichloroethane (DDT)-resistant strains of Drosophilamelanogaster, how Cyp6a2 is regulated and whether its overproduction confers DDT resistance remain elusive. RESULTS: Molecular analysis identified five Cyp6a2 alleles (Cyp6a2Canton-S-1, Cyp6a2Canton-S-2, Cyp6a291-C, Cyp6a291-R and Cyp6a2Wisconsin-WD) from four D.melanogaster strains, notably differing in the presence or absence of an intact Nrf2/Maf (a transcription factor) binding site in the 5'-promoter core region, a 'G1410' frameshift deletion mutation in the heme-binding region and a long terminal repeat (LTR) of transposable element 17.6 in the 3'-untranslated region (UTR). Linkage analysis confirmed that DDT resistance was genetically linked to a Nrf2/Maf-binding-site-containing, LTR-lacking functional allele of Cyp6a2 (Cyp6a291-R). The qRT-PCR results showed that overexpression of functional Cyp6a2 was consistently associated with DDT resistance. Luciferase reporter gene assays revealed that an intact Nrf2/Maf binding site in the 5'-promoter core region enhanced the constitutive transcription of Cyp6a2. CONCLUSION: The results suggest that the Nrf2/Maf binding-site-containing functional Cyp6a2allele is associated with DDT resistance in the D.melanogaster strains under study. © 2013 Society of Chemical Industry.
• Wan, H., Zhang, H., Liu, Y., Li, M., Zhu, S., Li, X. -., Pittendrigh, B. R., & Qiu, X. (2013). Nrf2/Maf binding site-containing functional Cyp6a2 allele is associated with DDT resistance in Drosophila melanogaster. Pest Management Science.
  More info

  doi: 10.1002/ps.3645. [Epub ahead of print]
• Xia, L. i., Xu, X. X., Han, L. Z., Wang, M., & Hou, M. L. (2013). Effects of different rice varieties on larval development, survival, adult reproduction, and flight capacity of Cnaphalocrocis medinalis (Guenée). Shengtai Xuebao/ Acta Ecologica Sinica, 33(14), 4370-4376.
  More info

  Abstract: The rice leafroller, Cnaphalocrocis medinalis (Cuenée), is an important rice pest in the main rice-growing areas of China. In recent years, it has caused substantial damage and seriously threatened rice production. C. medinalis is a seasonal and long-distance migratory species; its flight behavior is probably affected by many environmental factors, such as food quality during the larval stage, population density, photoperiod, and weather. Deterioration or shortage of food during the larval stage not only influences the development of C. medinalis but can also cause reproductive diapause to induce its migration. To determine how larval host quality affected development, survival, reproduction, and flight ability, we investigated larval survival, adult ovarian development, fecundity, and flight capacity of C. medinalis feeding on six different varieties of rice. The varieties were Wuyujing 3 (japonica rice), Ningjing 1 (hybrid japonica), TNI (indica), Shanyou 63 (hybrid indica), Liangyoupei 9 (super hybrid indica), and Yongyou 9 (super hybrid indica X japonica). These six varieties were the major ones cultivated in different rice-growing areas of China. Development, survival, and fecundity of C. medinalis on the different rice varieties were observed by determining semi-natural population life tables on each variety. Ovary development and the flight abilities of adults feeding on different rice hosts were investigated by dissecting the female ovaries and by tethered flight tests, respectively. The results showed that C. medinalis exhibited significantly lower survival in the immature stage and significantly lower adult fecundity when larvae fed on Wuyujing 3 and Ningjing 1 than when they ate Yongyou 9 or Liangyoupei 9. Similarly, the larval and pupal developmental stages of C. medinalis larvae that used Wuyujing 3 and Ningjing 1 as hosts were significantly longer compared to those that developed on Yongyou 9 and Liangyoupei 9. Furthermore, the average ovary developmental grades of C. medinalis from Wuyujing 3 and Ningjing 1 were significantly lower than those from Yongyou 9 and Liangyoupei 9 in both mated and virgin moths. Conversely, both mated and unmated 3 and 4 day old adults had significantly higher flight abilities when they had fed on Ningjing 1 as larvae than those than had fed on other rice varieties. The results indicated that the different rice varieties significantly influenced the survival, development, reproduction, and flight abilities of C. medinalis. The rice varieties could be ranked in order of their negative influence on C. medinalis as follows: Ningjing 1 > Wuyujing 3 > TNI > Shanyou 63 > Yongyou 9 > Liangyoupei 9. This paper discusses probable explanations for the observed differences in development, survival, fecundity, and flight abilities of C. medinalis. Leaf morphological characters, high cellular contents of silicon, and the thickness of the wax layer may be the major reason for the decline in fitness of C. medinalis feeding on japonica rice varieties. In addition, a shortage of some amino acids and low levels of juvenile hormone resulting from low-nutrient or deteriorated hosts may inhibit ovary development and contribute to the migration of C. medinalis. These results could provide the foundation for C. medinalis population forecasting and the development of sustainable management tactics.
• Yang, X., Li, X. -., & Yalin, Y. (2013). Molecular Cloning and Expression of CYP9A61:A Chlorpyrifos-Ethyl and Lambda-Cyhalothrin-Inducible Cytochrome P450 cDNA from Cydia pomonella. International Journal of Molecular Science, 14(12), 24211-29.
• Yang, X., Li, X., & Zhang, Y. (2013). Molecular Cloning and Expression of CYP9A61: A Chlorpyrifos-Ethyl and Lambda-Cyhalothrin-Inducible Cytochrome P450 cDNA from Cydia pomonella. INTERNATIONAL JOURNAL OF MOLECULAR SCIENCES, 14(12), 24211-24229.
• Yang, X., Xianchun, L. i., & Zhang, Y. (2013). Molecular cloning and expression of CYP9A61: A chlorpyrifos-ethyl and lambda-cyhalothrin-inducible cytochrome P450 cDNA from Cydia pomonella. International Journal of Molecular Sciences, 14(12), 24211-24229.
  More info

  Abstract: Cytochrome P450 monooxygenases (CYPs or P450s) play paramount roles in detoxification of insecticides in a number of insect pests. However, little is known about the roles of P450s and their responses to insecticide exposure in the codling moth Cydia pomonella (L.), an economically important fruit pest. Here we report the characterization and expression analysis of the first P450 gene, designated as CYP9A61, from this pest. The full-length cDNA sequence of CYP9A61 is 2071 bp long and its open reading frame (ORF) encodes 538 amino acids. Sequence analysis shows that CYP9A61 shares 51%-60% identity with other known CYP9s and contains the highly conserved substrate recognition site SRS1, SRS4 and SRS5. Quantitative real-time PCR showed that CYP9A61 were 67-fold higher in the fifth instar larvae than in the first instar, and more abundant in the silk gland and fat body than other tissues. Exposure of the 3rd instar larvae to 12.5 mg L-1 of chlorpyrifos-ethyl for 60 h and 0.19 mg L-1 of lambda-cyhalothrin for 36 h resulted in 2.20- and 3.47-fold induction of CYP9A61, respectively. Exposure of the 3rd instar larvae to these two insecticides also significantly enhanced the total P450 activity. The results suggested that CYP9A61 is an insecticide-detoxifying P450. © 2013 by the authors; licensee MDPI, Basel, Switzerland.
• You, M., Yue, Z., He, W., Yang, X., Yang, G., Xie, M., Zhan, D., Baxter, S. W., Vasseur, L., Gurr, G. M., Douglas, C. J., Bai, J., Wang, P., Cui, K., Huang, S., & Li, X. -. (2013). A heterozygous moth genome provides insights into herbivory and detoxification. Nature Genetics, 45, 220–225.
• You, M., Yue, Z., Weiyi, H. e., Yang, X., Yang, G., Xie, M., Zhan, D., Baxter, S. W., Vasseur, L., Gurr, G. M., Douglas, C. J., Bai, J., Wang, P., Cui, K., Huang, S., Xianchun, L. i., Zhou, Q., Zhangyan, W. u., Chen, Q., , Liu, C., et al. (2013). A heterozygous moth genome provides insights into herbivory and detoxification. Nature Genetics, 45(2), 220-225.
  More info

  PMID: 23313953;Abstract: How an insect evolves to become a successful herbivore is of profound biological and practical importance. Herbivores are often adapted to feed on a specific group of evolutionarily and biochemically related host plants, but the genetic and molecular bases for adaptation to plant defense compounds remain poorly understood. We report the first whole-genome sequence of a basal lepidopteran species, Plutella xylostella, which contains 18,071 protein-coding and 1,412 unique genes with an expansion of gene families associated with perception and the detoxification of plant defense compounds. A recent expansion of retrotransposons near detoxification-related genes and a wider system used in the metabolism of plant defense compounds are shown to also be involved in the development of insecticide resistance. This work shows the genetic and molecular bases for the evolutionary success of this worldwide herbivore and offers wider insights into insect adaptation to plant feeding, as well as opening avenues for more sustainable pest management. © 2013 Nature America, Inc. All rights reserved.
• Carriere, Y., Ellers-Kirk, C., Hartfield, K., Larocque, G., Degain, B., Dutilleul, P., Dennehy, T. J., Marsh, S. E., Crowder, D. W., Li, X., Ellsworth, P. C., Naranjo, S. E., Palumbo, J. C., Fournier, A. l., Antilla, L., & Tabashnik, B. E. (2012). Large-scale, spatially-explicit test of the refuge strategy for delaying insecticide resistance. PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA, 109(3), 775-780.
• Carrière, Y., Ellers-Kirk, C., Hartfield, K., Larocque, G., Degain, B., Dutilleul, P., Dennehy, T. J., Marsh, S. E., Crowder, D. W., Xianchun, L. i., Ellsworth, P. C., Naranjo, S. E., Palumbo, J. C., Fournier, A., Antilla, L., & Tabashnik, B. E. (2012). Large-scale, spatially-explicit test of the refuge strategy for delaying insecticide resistance. Proceedings of the National Academy of Sciences of the United States of America, 109(3), 775-780.
  More info

  PMID: 22215605;PMCID: PMC3271916;Abstract: The refuge strategy is used worldwide to delay the evolution of pest resistance to insecticides that are either sprayed or produced by transgenic Bacillus thuringiensis (Bt) crops. This strategy is based on the idea that refuges of host plants where pests are not exposed to an insecticide promote survival of susceptible pests. Despite widespread adoption of this approach, large-scale tests of the refuge strategy have been problematic. Here we tested the refuge strategy with 8 y of data on refuges and resistance to the insecticide pyriproxyfen in 84 populations of the sweetpotato whitefly (Bemisia tabaci) from cotton fields in central Arizona. We found that spatial variation in resistance to pyriproxyfen within each year was not affected by refuges of melons or alfalfa near cotton fields. However, resistance was negatively associated with the area of cotton refuges and positively associated with the area of cotton treated with pyriproxyfen. A statistical model based on the first 4 y of data, incorporating the spatial distribution of cotton treated and not treated with pyriproxyfen, adequately predicted the spatial variation in resistance observed in the last 4 y of the study, confirming that cotton refuges delayed resistance and treated cotton fields accelerated resistance. By providing a systematic assessment of the effectiveness of refuges and the scale of their effects, the spatially explicit approach applied here could be useful for testing and improving the refuge strategy in other crop-pest systems.
• Chu, D., Hu, X., Gao, C., Zhao, H., Nichols, R. L., & Li, X. (2012). Use of Mitochondrial Cytochrome Oxidase I Polymerase Chain Reaction-Restriction Fragment Length Polymorphism for Identifying Subclades of Bemisia tabaci Mediterranean Group. JOURNAL OF ECONOMIC ENTOMOLOGY, 105(1), 242-251.
• Chu, D., Xiangshun, H. u., Gao, C., Zhao, H., Nichols, R. L., & Xianchun, L. i. (2012). Use of mitochondrial cytochrome oxidase i polymerase chain reaction-restriction fragment length polymorphism for identifying subclades of bemisia tabaci mediterranean group. Journal of Economic Entomology, 105(1), 242-251.
  More info

  PMID: 22420277;Abstract: The Mediterranean group (commonly known as Q biotype; hereafter MED) of the sweetpotato whitefly, Bemisia tabaci (Gennadius), originated in the Mediterranean region, but it now has been found in at least 10 countries outside the Mediterranean. Collections of B. tabaci from some of these countries exhibit different pest behaviors and pesticide resistance characteristics, yet all may be classified as MED. A phylogenetic analysis of 120 mitochondrial cytochrome oxidase I (mtCOI) sequences (JN966761-JN966880) of MED whiteflies collected in Arizona and of 417 retrieved from the GenBank database resolves the MED into five subclades, designated as Q1-Q5. Only subclades Q1 and Q2 have been detected in the United States. Q1 and the other four subclades (Q2-Q5) differ in the number or position of the AluI recognition sites. Based on the differences in the AluI recognition sites reported here and the previously reported differences in VspI recognition sites, we developed a simple diagnostic technique to identify subclades Q1-Q5 by using mtCOI polymerase chain reaction (PCR)-restriction fragment-length polymorphism (RFLP). A test of a worldwide collection of whiteflies demonstrates that this combination mtCOI PCR-RFLP technique can reliably distinguish not only the MED from the Middle East-Asia Minor 1 group but also the Q1 from any of the other four MED subclades. © 2012 Entomological Society of America.
• Li, X., Bai, S., & Cass, B. N. (2012). Accord insertion in the 5 ' flanking region of CYP6G1 confers nicotine resistance in Drosophila melanogaster. GENE, 502(1), 1-8.
• Li, X., Degain, B. A., Harpold, V. S., Marcon, P. G., Nichols, R. L., Fournier, A. J., Naranjo, S. E., Palumbo, J. C., & Ellsworth, P. C. (2012). Baseline susceptibilities of B- and Q-biotype Bemisia tabaci to anthranilic diamides in Arizona. PEST MANAGEMENT SCIENCE, 68(1), 83-91.
• Pan, H., Li, X., Ge, D., Wang, S., Wu, Q., Xie, W., Jiao, X., Chu, D., Liu, B., Xu, B., & Zhang, Y. (2012). Factors Affecting Population Dynamics of Maternally Transmitted Endosymbionts in Bemisia tabaci. PLOS ONE, 7(2).
• Pan, H., Xianchun, L. i., & Zhang, Y. (2012). Sex affects the infection frequencies of symbionts in Bemisia tabaci. Communicative and Integrative Biology, 5(4), 337-339.
  More info

  PMID: 23060956;PMCID: PMC3460837;Abstract: While biotype, host plant and geographical location are known to affect the infection dynamics of the six secondary symbionts (S-symbionts) including Hamiltonella, Arsenophonus, Cardinium, Wolbachia, Rickettsia and Fritschea in Bemisia tabaci, it remains unclear whether sex of B. tabaci has an impact on the infection frequencies of the six S-symbionts. To address this issue, gene-specific PCR were conducted to screen for the presence of the six S-symbionts in five host plant-adapted laboratory sub-populations with the same genetic background. Significant variations were exhibited in the infection rates of Rickettsia, Cardinium, Rickettsia + Hamiltonella (RH), Rickettsia + Cardinium (RC), Hamiltonella + Cardinium (HC) and Rickettsia + Hamiltonella + Cardinium (RHC) among the five host plant-adapted subpopulations. Moreover, Rickettsia, Hamiltonella, Cardinium, RH, RC, HC and RHC were present at a significantly higher frequency in the females than in the males of the five host plant-adapted sub-populations. This indicates that sex is another important factor affecting the population dynamics of S-symbionts in B. tabaci.
• Pan, H., Xianchun, L. i., Daqing, G. e., Wang, S., Qingjun, W. u., Xie, W., Jiao, X., Chu, D., Liu, B., Baoyun, X. u., & Zhang, Y. (2012). Factors affecting population dynamics of maternally transmitted endosymbionts in bemisia tabaci. PLoS ONE, 7(2).
  More info

  PMID: 22383972;PMCID: PMC3285672;Abstract: While every individual of Bemisia tabaci (Hemiptera: Aleyrodidae) harbors the primary symbiont (P-symbiont) Portiera, the infection frequencies of the six secondary symbionts (S-symbionts) including Hamiltonella, Arsenophonus, Cardinium, Wolbachia, Rickettsia and Fritschea vary greatly among different populations. To characterize the factors influencing the infection dynamics of the six S-symbionts in B. tabaci, gene-specific PCR were conducted to screen for the presence of the P-symbiont Portiera and the six S-symbionts in 61 (17 B and 44 Q biotypes) field populations collected from different plant species and locations in China. All individuals of the 61 populations hosted the P-symbiont Portiera, but none of them harbored Arsenophonus and Fritschea. The presence and infection rates of Hamiltonella, Cardinium, Rickettsia, Wolbachia and their co-infections Rickettsia + Hamiltonella (RH), Rickettsia + Cardinium (RC), Hamiltonella + Cardinium (HC) and Rickettsia + Hamiltonella + Cardinium (RHC) varied significantly among the 61 field populations; and the observed variations can be explained by biotypes, sexes, host plants and geographical locations of these field populations. Taken together, at least three factors including biotype, host plant and geographical location affect the infection dynamics of S-symbionts in B. tabaci. © 2012 Pan et al.
• Wang, J., Li, Y., Han, Z., Zhu, Y., Xie, Z., Wang, J., Liu, Y., & Li, X. (2012). Molecular Characterization of a Ryanodine Receptor Gene in the Rice Leaffolder, Cnaphalocrocis medinalis (Guenee). PLOS ONE, 7(5).
• Wang, J., Wang, A., Han, Z., Zhang, Z., Fei, L. i., & Xianchun, L. i. (2012). Characterization of three novel sine families with unusual features in Helicoverpa armigera. PLoS ONE, 7(2).
  More info

  PMID: 22319625;PMCID: PMC3272025;Abstract: Although more than 120 families of short interspersed nuclear elements (SINEs) have been isolated from the eukaryotic genomes, little is known about SINEs in insects. Here, we characterize three novel SINEs from the cotton bollworm, Helicoverpa armigera. Two of them, HaSE1 and HaSE2, share similar 5′ -structure including a tRNA-related region immediately followed by conserved central domain. The 3′ -tail of HaSE1 is significantly similar to that of one LINE retrotransposon element, HaRTE1.1, in H. armigera genome. The 3′ -region of HaSE2 showed high identity with one mariner-like element in H. armigera. The third family, termed HaSE3, is a 5S rRNA-derived SINE and shares both body part and 3′-tail with HaSE1, thus may represent the first example of a chimera generated by recombination between 5S rRNA and tRNA-derived SINE in insect species. Further database searches revealed the presence of these SINEs in several other related insect species, but not in the silkworm, Bombyx mori, indicating a relatively narrow distribution of these SINEs in Lepidopterans. Apart from above, we found a copy of HaSE2 in the GenBank EST entry for the cotton aphid, Aphis gossypii, suggesting the occurrence of horizontal transfer. © 2012 Wang et al.
• Wang, J., Wang, A., Han, Z., Zhang, Z., Li, F., & Li, X. (2012). Characterization of Three Novel SINE Families with Unusual Features in Helicoverpa armigera. PLOS ONE, 7(2).
• Wang, J., Yanqing, L. i., Han, Z., Zhu, Y., Xie, Z., Wang, J., Liu, Y., & Xianchun, L. i. (2012). Molecular characterization of a ryanodine receptor gene in the rice leaffolder, cnaphalocrocis medinalis (Guenée). PLoS ONE, 7(5).
  More info

  PMID: 22567170;PMCID: PMC3342285;Abstract: Ryanodine receptors (RyRs) are the targets of two novel classes of synthetic insecticidal chemicals, phthalic acid diamides and anthranilic diamides. Isolation of full-length RyR cDNAs is a critical step towards the structural and functional characterization of insect RyRs and an understanding of the molecular mechanisms underlying the species selective toxicity of diamide insecticides. However, there has been little research on the insect RyR genes due to the high molecular weight of the RyR proteins. In this study, we isolated a full-length RyR cDNA (named as CmRyR) from Cnaphalocrocis medinalis, an important rice pest throughout Southeast Asia. The composite CmRyR gene contains an ORF of 15264 bp encoding a protein of 5087 amino acid residues, which shares 79% overall identity with its Drosophila melanogaster homologue. All hallmarks of the RyR proteins are conserved in the CmRyR protein, suggesting that CmRyR is a structural and functional analogue of known RyRs. A multiple sequence alignment illustrates that the insect RyRs share high levels of amino acid sequence identity at the the COOH-terminal region. However, the amino acid residues analogous to the CmRyR residues N4922, N4924, N4935, L4950, L4981, N5013 and T5064 are unique to lepidopteran RyRs compared with non-lepidopteran insect RyRs. This finding suggests that these residues may be involved in the differences in channel properties between lepidopteran and non-lepidopteran insect RyRs and in the species selective toxicity of diamide insecticides. Furthermore, two alternative splicing sites were identified in the CmRyR gene, one of which was located in the central part of the predicted second SPRY domain. Diagnostic PCR showed that the inclusion frequencies of two mutually exclusive exons (a/b) and one optional exon (c) differed between developmental stages or adult anatomical regions. Our results imply that alternative splicing may be a major means of generating functional diversity in C. medinalis RyR channel. © 2012 Wang et al.
• Xianchun, L. i., Bai, S., & Cass, B. N. (2012). Accord insertion in the 5' flanking region of CYP6G1 confers nicotine resistance in Drosophila melanogaster. Gene, 502(1), 1-8.
  More info

  PMID: 22543020;Abstract: What has driven the sweep of the Accord retrotransposon insertion allele of CYP6G1 in the natural populations of Drosophila melanogaster is unknown. Previous studies on the DDT selection hypothesis produced conflicting data. To reexamine the DDT selection hypothesis and search for alternative explanations, we conducted a series of correlation and genetic linkage experiments with eight D. melanogaster natural populations collected from California (CM1, CM2, CM3, and CM7) and Africa (AM2, AM3, AM4, AM7). Diagnostic PCR showed that CM1, CM2, CM7, and AM3 have the Accord insertion in the CYP6G1 locus, whereas the other four strains do not. RT-PCR analysis exhibits a 100% correlation between Accord insertion and CYP6G1 overexpression. However, among the four strains with Accord-mediated CYP6G1 overexpression only CM1 and CM7 are resistant to DDT, and the other two strains (CM2 and AM3), like the four Accord-free strains, are susceptible to DDT. By contrast, all the four strains with Accord-mediated CYP6G1 overexpression are resistant to nicotine, a plant allelochemical. Genetic crosses between DDT resistant and susceptible Accord-insertion strains, as well as crosses between Accord-insertion and Accord-free strains demonstrated that Accord insertion and CYP6G1 overexpression are genetically linked to nicotine resistance rather than DDT resistance. These results suggest that naturally-occurring allelochemicals such as nicotine are the initial driving force for the worldwide prevalence of the Accord insertion allele of CYP6G1 in D. melanogaster natural populations. © 2012 Elsevier B.V.
• Xianchun, L. i., Degain, B. A., Harpold, V. S., Marçon, P. G., Nichols, R. L., Fournier, A. J., Naranjo, S. E., Palumbo, J. C., & Ellsworth, P. C. (2012). Baseline susceptibilities of B- and Q-biotype Bemisia tabaci to anthranilic diamides in Arizona. Pest Management Science, 68(1), 83-91.
  More info

  PMID: 21714059;Abstract: Background: Development of pyriproxyfen and neonicotinoid resistance in the B-biotype whitefly and recent introduction of the Q biotype have the potential to threaten current whitefly management programs in Arizona. The possibility of integrating the novel anthranilic diamides chlorantraniliprole and cyantraniliprole into the current program to tackle these threats largely depends on whether these compounds have cross-resistance with pyriproxyfen and neonicotinoids in whiteflies. To address this question, the authors bioassayed a susceptible B-biotype strain, a pyriproxyfen-resistant B-biotype strain, four multiply resistant Q-biotype strains and 16 B-biotype field populations from Arizona with a systemic uptake bioassay developed in the present study. Results: The magnitude of variations in LC 50 and LC 99 among the B-biotype populations or the Q-biotype strains was less than fivefold and tenfold, respectively, for both chlorantraniliprole and cyantraniliprole. The Q-biotype strains were relatively more tolerant than the B-biotype populations. No correlations were observed between the LC 50 (or LC 99) values of the two diamides against the B- and Q-biotype populations tested and their survival rates at a discriminating dose of pyriproxyfen or imidacloprid. Conclusion: These results indicate the absence of cross-resistance between the two anthranilic diamides and the currently used neonicotinoids and pyriproxyfen. Future variation in susceptibility of field populations to chlorantraniliprole and cyantraniliprole could be documented according to the baseline susceptibility range of the populations tested in this study. © 2011 Society of Chemical Industry.
• Xinzhi, N. i., Wilson, J. P., Toews, M. D., Buntin, G. D., Lee, R. D., Xin, L. i., Lei, Z., Kanglai, H. e., Wenwei, X. u., Xianchun, L. i., Huffaker, A., & Schmelz, E. A. (2012). Evaluation of spatial and temporal patterns of insect damage and aflatoxin level in the pre-harvest corn fields to improve management tactics. Insect Science.
  More info

  Abstract: Spatial and temporal patterns of insect damage in relation to aflatoxin contamination in a corn field with plants of uniform genetic background are not well understood. After previous examination of spatial patterns of insect damage and aflatoxin in pre-harvest corn fields, we further examined both spatial and temporal patterns of cob- and kernel-feeding insect damage, and aflatoxin level with two samplings at pre-harvest in 2008 and 2009. The feeding damage by each of the ear/kernel-feeding insects (i.e., corn earworm/fall armyworm damage on the silk/cob, and discoloration of corn kernels by stink bugs) and maize weevil population were assessed at each grid point with five ears. Sampling data showed a field edge effect in both insect damage and aflatoxin contamination in both years. Maize weevils tended toward an aggregated distribution more frequently than either corn earworm or stink bug damage in both years. The frequency of detecting aggregated distribution for aflatoxin level was less than any of the insect damage assessments. Stink bug damage and maize weevil number were more closely associated with aflatoxin level than was corn earworm damage. In addition, the indices of spatial-temporal association (χ) demonstrated that the number of maize weevils was associated between the first (4 weeks pre-harvest) and second (1 week pre-harvest) samplings in both years on all fields. In contrast, corn earworm damage between the first and second samplings from the field on the Belflower Farm, and aflatoxin level and corn earworm damage from the field on the Lang Farm were dissociated in 2009. Published 2012. This article is a U.S. Government work and is in the public domain in the USA.
• Du, E., Ni, X., Zhao, H., & Xianchun, L. i. (2011). Natural history and intragenomic dynamics of the Transib transposon Hztransib in the cotton bollworm Helicoverpa zea. Insect Molecular Biology, 20(3), 291-301.
  More info

  PMID: 21166910;PMCID: PMC3086985;Abstract: Hztransib, recently identified from Helicoverpa zea, represents the first intact and transcriptionally active Transib element. Its open reading frame was detected in Helicoverpa armigera, from which H. zea evolved, and in Helicoverpa assulta, the common ancestor of H. zea and H. armigera, but its remaining parts were found only in H. armigera. Thirty-nine Hztransib insertion sites, all of which are polymorphic, were detected from eight populations of H. zea. Out of the 39 insertion sites, 35 were not frequently occupied, with 1-33 occurrences in a total of 128 individuals from the eight populations (16 larvae per population). Its copy number ranged from 5.8 to 14.2 per individual, with putative intact copies always more abundant than internally deleted ones. Taking this evidence together, Hztransib probably transferred to H. zea from H. armigera and most likely still retains its capacity to maintain structural integrity, increase copy number and remobilize in H. zea. © 2010 The Authors Insect Molecular Biology © 2010 The Royal Entomological Society.
• Fabrick, J. A., Mathew, L. G., Tabashnik, B. E., & Li, X. (2011). Insertion of an intact CR1 retrotransposon in a cadherin gene linked with Bt resistance in the pink bollworm, Pectinophora gossypiella. Insect Molecular Biology, 20(5), 651-665.
  More info

  PMID: 21815956;Abstract: Three mutations in the Pectinophora gossypiella cadherin gene PgCad1 are linked with resistance to Bacillus thuringiensis (Bt) toxin Cry1Ac. Here we show that the r3 mutation entails recent insertion into PgCad1 of an active chicken repeat (CR1) retrotransposon, designated CR1-1-Pg. Unlike most other CR1 elements, CR1-1-Pg is intact, transcribed by a flanking promoter, contains target site duplications and has a relatively low number of copies. Examination of transcripts from the PgCad1 locus revealed that CR1-1-Pg disrupts both the cadherin protein and a long noncoding RNA of unknown function. Together with previously reported data, these findings show that transposable elements disrupt eight of 12 cadherin alleles linked with resistance to Cry1Ac in three lepidopteran species, indicating that the cadherin locus is a common target for disruption by transposable elements. © Published 2011. This article is a U.S. Government work and is in the public domain in the U.S.A.
• Hu, X., Dennehy, T. J., Ni, X., Zhao, H., Nichols, R. L., & Li, X. (2011). Potential adaptation of a Q biotype whitefly population from poinsettia to field crops. INSECT SCIENCE, 18(6), 719-728.
• Ni, X., Chen, Y., Hibbard, B. E., Wilson, J. P., Williams, W. P., Buntin, G. D., Ruberson, J. R., & Li, X. (2011). FOLIAR RESISTANCE TO FALL ARMYWORM IN CORN GERMPLASM LINES THAT CONFER RESISTANCE TO ROOT- AND EAR-FEEDING INSECTS. FLORIDA ENTOMOLOGIST, 94(4), 971-981.
• Ni, X., Sparks Jr., A. N., Riley, D. G., & Li, X. (2011). Impact of Applying Edible Oils to Silk Channels on Ear Pests of Sweet Corn. JOURNAL OF ECONOMIC ENTOMOLOGY, 104(3), 956-964.
• Xiangshun, H. u., Dennehy, T. J., Xinzhi, N. i., Zhao, H., Nichols, R. L., & Xianchun, L. i. (2011). Potential adaptation of a Q biotype whitefly population from poinsettia to field crops. Insect Science, 18(6), 719-728.
  More info

  Abstract: The invasive Q biotype whitefly was first detected in the US on poinsettia in 2004 and is still not a pest outside of greenhouse environments in the US. To assess the potential for the establishment of the Q biotype on field crops, population cage experiments were conducted to compare the performance of a poinsettia-derived Q population named P'06 on poinsettia and six field crops (alfalfa, tomato, melon, cotton, cowpea and cabbage). P'06 adults reared on poinsettia as nymphs laid eggs on all six field crops. Significantly more eggs were laid on alfalfa, tomato, melon and cotton than on cabbage, cowpea and poinsettia. These eggs hatched and the nymphs developed to adults on the six field crops. Relative to poinsettia, whitefly survival was similar on cowpea, alfalfa, tomato and cabbage, but significantly higher on cotton and melon. Moreover, P'06 had significantly shorter development times from egg to adult on cotton, melon, cowpea, tomato and alfalfa than they did on poinsettia. However, the F1 adults raised on the six field crops had significantly shorter lifespans and laid 11- to 18-fold fewer eggs than did the F1 adults raised on poinsettia. Taken together, while P'06 may have some potential to establish on field crops, the shorter lifespans and extremely low fecundities of the F1 adults raised on the six field crops suggests that P'06 is incapable of rapidly adapting to them. Poor adaptation to field crops may explain, at least partially, why the Q biotype has not established in the US field system. © 2011 The Authors Journal compilation © Institute of Zoology, Chinese Academy of Sciences.
• Xinzhi, N. i., Chen, Y., Hibbard, B. E., Wilson, J. P., Williams, W. P., Buntin, G. D., Ruberson, J. R., & Xianchun, L. i. (2011). Foliar resistance to fall armyworm in corn germplasm lines that confer resistance to root- and ear-feeding insects. Florida Entomologist, 94(4), 971-981.
  More info

  Abstract: A holistic approach to developing new corn germplasm that confers multiple insect resistance in various plant tissues at different growth stages was examined. Eight corn germplasm lines were examined for their foliar resistance to fall armyworm [Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae)] and natural enemy attraction at V6V8 (or 68 leaf) stages in 2008 and 2009. Four corn germplasm lines with known levels of resistance to root- and ear-feeding insects ['CRW3(S1)C6', 'B37*H84', 'SIM6' and 'EPM6'], and four germplasm entries with different levels of S. frugiperda resistance ('Mp708', 'Ab24E', 'FAW7061' and 'FAW7111') were evaluated in the study. All plants were manually infested with 1520 neonate S. frugiperda larvae per plant, and injury was rated 7 and 14 d after infestation. Based on cluster analysis of S. frugiperda injury rating and predator survey data, 'Mp708' and 'FAW7061' were the most resistant, whereas 'Ab24E' and 'EPM6' were the most susceptible to fall armyworm feeding. The western corn rootworm-resistant 'CRW3(S1)C6' showed resistance to S. frugiperda feeding. Surveys for the diversity and abundance of predators of S. frugiperda in each experimental plot were also conducted 7 d after infestation. 'CRW3(S1)C6' and 'Ab24E' had the highest and lowest predator abundance, respectively. However, there was no direct correlation between S. frugiperda injury ratings and predator abundance. The current study demonstrated the feasibility of developing foliage-, root-, and ear-feeding insect-resistant germplasm covering multiple corn growth stages. In addition, the possibility of utilizing plant volatiles to attract predators, and reduce pest populations and crop damage is discussed.
• Xinzhi, N. i., Sparks Jr., A. N., Riley, D. G., & Xianchun, L. i. (2011). Impact of applying edible oils to silk channels on ear pests of sweet corn. Journal of Economic Entomology, 104(3), 956-964.
  More info

  PMID: 21735916;Abstract: The impact of applying edible oils to corn silks on ear-feeding insects in sweet corn, Zea mays L., production was evaluated in 2006 and 2007. Six edible oils used in this experiment were canola, corn, olive, peanut, sesame, and soybean. Water and two commercial insecticidal oils (Neemix neem oil and nC21 Sunspray Ultrafine, a horticultural mineral oil) were used as the controls for the experiment. Six parameters evaluated in this experiment were corn earworm [Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae)] damage rating, the number of sap beetle [Carpophilus spp. (Coleoptera: Nitidulidae) ] adults and larvae, the number of corn silk fly (or picture-winged fly) (Diptera: Ulidiidae) larvae, common smut [Ustilago maydis (D.C.) Corda] infection rate, and corn husk coverage. Among the two control treatments, neem oil reduced corn earworm damage at both preand postpollination applications in 2006, but not in 2007, whereas the mineral oil applied at postpollination treatments reduced corn earworm damage in both years. The mineral oil also reduced the number of sap beetle adults, whereas the neem oil applied at postpollination attracted the most sap beetle adults in 2007. Among the six edible oil treatments, the corn and sesame oils applied at postpollination reduced corn earworm damage only in 2007. The application of the peanut oil at postpollination attracted more sap beetle adults in 2006, and more sap beetle larvae in 2007. Olive and neem oils significantly reduced husk coverage compared with the water control in both years. The mineral oil application consistently increased smut infection rate in both 2006 and 2007. Ramifications of using oil treatments in ear pest management also are discussed. © 2011 Entomological Society of America.
• Dennehy, T. J., Degain, B. A., Harpold, V. S., Zaborac, M., Morin, S., Fabrick, J. A., Nichols, R. L., Brown, J. K., Byrne, F. J., & Li, X. (2010). Extraordinary Resistance to Insecticides Reveals Exotic Q Biotype of Bemisia tabaci in the New World. JOURNAL OF ECONOMIC ENTOMOLOGY, 103(6), 2174-2186.
• Dennehy, T. J., Degain, B. A., Harpold, V. S., Zaborac, M., Morin, S., Fabrick, J. A., Nichols, R. L., Brown, J. K., Byrne, F. J., & Xianchun, L. i. (2010). Extraordinary resistance to insecticides reveals exotic Q biotype of Bemisia tabaci in the New World. Journal of Economic Entomology, 103(6), 2174-2186.
  More info

  PMID: 21309242;Abstract: A strain of the whitefly Bemisia tabaci (Gennadius) possessing unusually high levels of resistance to a wide range of insecticides was discovered in 2004 in the course of routine resistance monitoring in Arizona. The multiply resistant insects, collected from poinsettia (Euphorbia pulcherrima Willd. ex Klotzsch) plants purchased at a retail store in Tucson, were subjected to biotype analysis in three laboratories. Polyacrylamide gel electrophoresis of naphthyl esterases and sequencing of the mitochondrial cytochrome oxidase I gene (780 bp) confirmed the first detection of the Q biotype of B. tabaci in the New World. This U.S. Q biotype strain, referred to as Poinsettia'04, was highly resistant to two selective insect growth regulators, pyriproxyfen and buprofezin, and to mixtures of fenpropathrin and acephate. It was also unusually low in susceptibility to the neonicotinoid insecticides imidacloprid, acetamiprid, and thiamethoxam, relative to B biotype whiteflies. In 100 collections of whiteflies made in Arizona cotton (Gossypium spp.), vegetable, and melon (Cucumis melo L.) fields from 2001 to 2005, no Q biotypes were detected. Regions of the United States that were severely impacted by the introduction of the B biotype of B. tabaci in the 1980s would be well advised to promote measures that limit movement of the Q biotype from controlled environments into field systems and to formulate alternatives for managing this multiply-resistant biotype, in the event that it becomes more widely distributed.
• Ma, W., Li, X., Dennehy, T. J., Lei, C., Wang, M., Degain, B. A., & Nichols, R. L. (2010). Pyriproxyfen resistance of Bemisia tabaci (Homoptera: Aleyrodidae) biotype b: Metabolic mechanism. Journal of Economic Entomology, 103(1), 158-165.
  More info

  PMID: 20214381;Abstract: Juvenile hormone (JH) analog insecticides are relatively nontoxic to vertebrates and provide efficient control of key arthropod pests. One JH analog, pyriproxyfen, has provided over a decade of exceptional management of whiteflies in cotton of the southwestern United States. Thwarting resistance to pyriproxyfen in Bemisia tabaci (Gannadius) (a.k.a. Bemisia argentifolii Bellows and Perring) has been the focus of an integrated resistance management program because this insecticide was first registered for use in Arizona cotton in 1996. Resistance levels have increased slowly in field populations in recent years but have not demonstrably affected field performance of pyriproxyfen. Resistant strains have been isolated and studied in the laboratory to determine the mechanism of resistance and identify optimal strategies for controlling resistant whiteflies. Synergism bioassays showed that resistance in a laboratory-selected strain QC02-R, was partially suppressible with piperonyl butoxid (PBO) and diethyl maleate (DEM) but not with S, S, S-tributyl phosphorotrithioate (DEF). Consistent with the synergism bioassay results, enzymatic assays revealed that the enzyme activities of cytochrome P450 monooxygenases (P450) and glutathione S-transferases (GST) but not esterases were significantly higher in the pyriproxyfen-resistant QC02-R strain than in the susceptible strain. These results indicate that both P450 and GST are involved in whitefly resistance to pyriproxyfen. © 2010 Entomological Society of America.
• Orsini, F., D'Urzo, M. P., Inan, G., Serra, S., Oh, D., Mickelbart, M. V., Consiglio, F., Xia, L. i., Jeong, J. C., Yun, D., Bohnert, H. J., Bressan, R. A., & Maggio, A. (2010). A comparative study of salt tolerance parameters in 11 wild relatives of Arabidopsis thaliana. Journal of Experimental Botany, 61(13), 3787-3798.
  More info

  PMID: 20595237;PMCID: PMC2921208;Abstract: Salinity is an abiotic stress that limits both yield and the expansion of agricultural crops to new areas. In the last 20 years our basic understanding of the mechanisms underlying plant tolerance and adaptation to saline environments has greatly improved owing to active development of advanced tools in molecular, genomics, and bioinformatics analyses. However, the full potential of investigative power has not been fully exploited, because the use of halophytes as model systems in plant salt tolerance research is largely neglected. The recent introduction of halophytic Arabidopsis-Relative Model Species (ARMS) has begun to compare and relate several unique genetic resources to the well-developed Arabidopsis model. In a search for candidates to begin to understand, through genetic analyses, the biological bases of salt tolerance, 11 wild relatives of Arabidopsis thaliana were compared: Barbarea verna, Capsella bursa-pastoris, Hirschfeldia incana, Lepidium densiflorum, Malcolmia triloba, Lepidium virginicum, Descurainia pinnata, Sisymbrium officinale, Thellungiella parvula, Thellungiella salsuginea (previously T. halophila), and Thlaspi arvense. Among these species, highly salt-tolerant (L. densiflorum and L. virginicum) and moderately salt-tolerant (M. triloba and H. incana) species were identified. Only T. parvula revealed a true halophytic habitus, comparable to the better studied Thellungiella salsuginea. Major differences in growth, water transport properties, and ion accumulation are observed and discussed to describe the distinctive traits and physiological responses that can now be studied genetically in salt stress research. © 2010 The Author.
• Tabashnik, B. E., Sisterson, M. S., Ellsworth, P. C., Dennehy, T. J., Antilla, L., Liesner, L., Whitlow, M., Staten, R. T., Fabrick, J. A., Unnithan, G. C., Yelich, A. J., Ellers-Kirk, C., Harpold, V. S., Li, X., & Carriere, Y. (2010). Suppressing resistance to Bt cotton with sterile insect releases. NATURE BIOTECHNOLOGY, 28(12), 1304-U119.
• Tabashnik, B. E., Sisterson, M. S., Ellsworth, P. C., Dennehy, T. J., Antilla, L., Liesner, L., Whitlow, M., Staten, R. T., Fabrick, J. A., Unnithan, G. C., Yelich, A. J., Ellers-Kirk, C., Harpold, V. S., Xianchun, L. i., & Carrière, Y. (2010). Suppressing resistance to Bt cotton with sterile insect releases. Nature Biotechnology, 28(12), 1304-1307.
  More info

  PMID: 21057498;Abstract: Genetically engineered crops that produce insecticidal toxins from Bacillus thuringiensis (Bt) are grown widely for pest control. However, insect adaptation can reduce the toxins' efficacy. The predominant strategy for delaying pest resistance to Bt crops requires refuges of non-Bt host plants to provide susceptible insects to mate with resistant insects. Variable farmer compliance is one of the limitations of this approach. Here we report the benefits of an alternative strategy where sterile insects are released to mate with resistant insects and refuges are scarce or absent. Computer simulations show that this approach works in principle against pests with recessive or dominant inheritance of resistance. During a large-scale, four-year field deployment of this strategy in Arizona, resistance of pink bollworm (Pectinophora gossypiella) to Bt cotton did not increase. A multitactic eradication program that included the release of sterile moths reduced pink bollworm abundance by >99%, while eliminating insecticide sprays against this key invasive pest. © 2010 Nature America, Inc. All rights reserved.
• Zhang, C., Luo, X., Ni, X., Zhang, Y., & Li, X. (2010). Functional characterization of cis-acting elements mediating flavone-inducible expression of CYP321A1. INSECT BIOCHEMISTRY AND MOLECULAR BIOLOGY, 40(12), 898-908.
• Zhang, C., Luo, X., Xinzhi, N. i., Zhang, Y., & Xianchun, L. i. (2010). Functional characterization of cis-acting elements mediating flavone-inducible expression of CYP321A1. Insect Biochemistry and Molecular Biology, 40(12), 898-908.
  More info

  PMID: 20854909;Abstract: How plant allelochemicals elicit herbivore counterdefense genes remains largely unknown. To define the cis-acting elements for flavone inducibility of the allelochemical-metabolizing CYP321A1 from Helicoverpa zea, functions of varying length of CYP321A1 promoter are examined in H. zea fatbody cells. Progressive 3' deletions reveal presence of positive elements in the 5' untranslated region (UTR). Progressive 5' deletions map out regions of one essential element, four enhancers, and two silencers. Further progressive 5'deletions localize the essential element to a 36-bp region from -109 to -74. This essential element, designated as xenobiotic response element to flavone (XRE-Fla), contains a 5' AT-only TAAT inverted repeat, a GCT mirror repeat and a 3' antioxidant response element-like element. Internal deletions and substitution mutations show that the TAAT repeat is only necessary for the maximal flavone inducibility, whereas the other two components are necessary for the basal and flavone-induced expression of CYP321A1. Electrophoresis mobility shift assays demonstrate that XRE-Fla specifically binds to H. zea fatbody cell nuclear extracts and flavone treatment increases the nuclear concentrations of the yet-to-be characterized transcription factors binding to XRE-Fla. Taken together, CYP321A1 expression is regulated primarily by XRE-Fla and secondarily by other cis elements scattered in its promoter and 5' UTR. © 2010.
• Ma, W., Li, X., Dennehy, T. J., Lei, C., Wang, M., Degain, B. A., & Nichols, R. L. (2009). Utility of MtCOI polymerase chain reaction-restriction fragment length polymorphism in differentiating between Q and B whitefly Bemisia tabaci biotypes. Insect Science, 16(2), 107-114.
  More info

  Abstract: The invasive, insecticide-resistant, Q whitefly biotype, has gradually spread to other countries including the US via human-mediated movement of plant materials. We assessed the utility of the VspI-based mtCOI (mitochondrion cytochrome oxidase I) polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) technique as a rapid, cost-effective, and reliable alternative for differentiating the Q from the dominant B biotype in Arizona. Using the standard mtCOI gene sequencing and mtCOI PCR-RFLP techniques, we biotyped eight whitefly strains of five individuals each collected from poinsettia and cotton at different locations in Arizona. Complete concordance was observed between the two methods, with three strains being identified as the Q biotype and five samples as the B biotype. We also scanned the mtCOI gene sequences for VspI polymorphisms in the B and Q biotype whiteflies currently available in the GenBank database. This global screening revealed the existence of three and four VspI polymorphic types for the Q and B biotypes, respectively. Nevertheless, all three VspI polymorphic Q biotype whiteflies shared a common and unique VspI site that can be used to differentiate Q biotype from the four VspI polymorphic B biotype whiteflies identified. These results demonstrate that the VspI-based mtCOI gene PCR-RFLP provides a reliable diagnostic tool for differentiating the Q and B biotype whiteflies in the US and elsewhere. © 2009 Institute of Zoology, Chinese Academy of Sciences.
• Tabashnik, B. E., Unnithan, G. C., Masson, L., Crowder, D. W., Li, X., & Carriere, Y. (2009). Asymmetrical cross-resistance between Bacillus thuringiensis toxins Cry1Ac and Cry2Ab in pink bollworm. PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA, 106(29), 11889-11894.
• Tabashnik, B. E., Unnithan, G. C., Masson, L., Crowder, D. W., Xianchun, L. i., & Carrière, Y. (2009). Asymmetrical cross-resistance between Bacillus thuringiensis toxins Cry1Ac and Cry2Ab in pink bollworm. Proceedings of the National Academy of Sciences of the United States of America, 106(29), 11889-11894.
  More info

  PMID: 19581574;PMCID: PMC2706268;Abstract: Transgenic crops producing Bacillus thuringiensis (Bt) toxins kill some key insect pests and can reduce reliance on insecticide sprays. Sustainable use of such crops requires methods for delaying evolution of resistance by pests. To thwart pest resistance, some transgenic crops produce 2 different Bt toxins targeting the same pest. This "pyramid" strategy is expected to work best when selection for resistance to 1 toxin does not cause cross-resistance to the other toxin. The most widely used pyramid is transgenic cotton producing Bt toxins Cry1Ac and Cry2Ab. Cross-resistance between these toxins was presumed unlikely because they bind to different larval midgut target sites. Previous results showed that laboratory selection with Cry1Ac caused little or no cross-resistance to Cry2A toxins in pink bollworm (Pectinophora gossypiella), a major cotton pest. We show here, however, that laboratory selection of pink bollworm with Cry2Ab caused up to 420-fold cross-resistance to Cry1Ac as well as 240-fold resistance to Cry2Ab. Inheritance of resistance to high concentrations of Cry2Ab was recessive. Larvae from a laboratory strain resistant to Cry1Ac and Cry2Ab in diet bioassays survived on cotton bolls producing only Cry1Ac, but not on cotton bolls producing both toxins. Thus, the asymmetrical cross-resistance seen here does not threaten the efficacy of pyramided Bt cotton against pink bollworm. Nonetheless, the results here and previous evidence indicate that cross-resistance occurs between Cry1Ac and Cry2Ab in some key cotton pests. Incorporating the potential effects of such cross-resistance in resistance management plans may help to sustain the efficacy of pyramided Bt crops.
• Chen, S., & Li, X. (2008). Molecular characterization of the first intact Transib transposon from Helicoverpa zea. GENE, 408(1-2), 51-63.
• Chen, S., & Xianchun, L. i. (2008). Molecular characterization of the first intact Transib transposon from Helicoverpa zea. Gene, 408(1-2), 51-63.
  More info

  PMID: 18031956;Abstract: Transib is a superfamily of DNA transposons recently reconstructed in silico from degenerate elements in the genomes of Drosophila melanogaster and Anopheles gambiae. Here we report characterization of the first intact Transib transposon designated Hztransib from Helicoverpa zea. At least two Hztransib copies (one full-length, one internally-deleted) exist in the genomes of a midgut cell line and a laboratory strain of H. zea. The full-length Hztransib has 3518 bp including a 5′ terminal inverted repeat (TIR) of 552 bp, a promoter sequence of 381 bp, an intact open reading frame encoding 507 amino acids, and a 3′ TIR of 502 bp, and is flanked by 5-bp (CGTCG) target site duplications. The full-length Hztransib is transcriptionally active, producing an 3′-truncated mRNA lacking a termination codon (known as nonstop mRNA) due to alternative polyadenylation in two somatic tissues (midgut and fat body) and one germline tissue (ovary). A BLAST search with the deduced Hztransib transposase identified 51 novel Transib elements from 11 insect genomes. While the full-length Hztransib inserts into the 5′-flanking region of a xenobiotic-metabolizing P450 gene CYP6B8 in the midgut cell line, it does not insert into the 5′-flanking region of CYP6B8 in the laboratory strain. Such an insertion dimorphism, together with its complete structural features and mRNA transcripts, demonstrates that the full-length Hztransib not only represents the first known intact Transib element in any organism, but has been recently transposed in H. zea. The fact that the intact Hztransib is transcribed into a 3′-truncated nonstop mRNA which may encode a non-functional transposase or be blocked from further translation via nonstop mRNA decay suggests that it is silenced at the translational or transpositional level. © 2007 Elsevier B.V. All rights reserved.
• Ma, W., Chen, L., Wang, M. o., & Li, X. (2008). Trade-offs between melanisation and life-history traits in Helicoverpa armigera. ECOLOGICAL ENTOMOLOGY, 33(1), 37-44.
• Weihua, M. a., Chen, L., Wang, M., & Xianchun, L. i. (2008). Trade-offs between melanisation and life-history traits in Helicoverpa armigera. Ecological Entomology, 33(1), 37-44.
  More info

  Abstract: 1. Previously we established a homozygous melanic strain (JBM) with 16 black pupae spontaneously occurring within a laboratory population (JBW) of Helicoverpa armigera and demonstrated that the melanisation is controlled by a single recessive autosomal gene. 2. Data obtained indicate that the melanisation is globally expressed in the pupal and adult stages (except for the body hairs of adults) but not in the egg and larval stages. No differences in body colour can be found between the melanic JBM and the wild-type JBW strains before the metamorphic pupation moult. After pupation, the JBM pupae gradually blacken, whereas the wild-type JBW pupae gradually turn brown, indicating that the biosynthetic steps leading to brown pigments are shut off in the JBM strain. In the adult stage, wings are darker and hairs on the abdomen and tergum are lighter in the melanic moths than in the wild-type individuals. 3. Life-table experiments reveal that the melanism is associated with slower development in all life stages, smaller body weight, lower mating rate and fecundity, less mating time, and accordingly, lower net reproduction rate and population trend index. 4. Single pair inbreeding and reciprocal crosses show that the mating rate is much lower in the inter-strain crosses than in the intra-strain crosses, indicating the presence of mating preference for its own colour morph and the presence to some degree of reproductive isolation between the two colour morphs. © 2007 The Royal Entomological Society.
• Chen, S., & Li, X. (2007). Transposable elements are enriched within or in close proximity to xenobiotic-metabolizing cytochrome P450 genes. BMC EVOLUTIONARY BIOLOGY, 7.
• Chen, S., & Xianchun, L. i. (2007). Transposable elements are enriched within or in close proximity to xenobiotic-metabolizing cytochrome P450 genes. BMC Evolutionary Biology, 7.
  More info

  PMID: 17381843;PMCID: PMC1852546;Abstract: Background. Transposons, i.e. transposable elements (TEs), are the major internal spontaneous mutation agents for the variability of eukaryotic genomes. To address the general issue of whether transposons mediate genomic changes in environment-adaptation genes, we scanned two alleles per each of the six xenobiotic-metabolizing Helicoverpa zea cytochrome P450 loci, including CYP6B8, CYP6B27, CYP321A1, CYP321A2, CYP9A12v3 and CYP9A14, for the presence of transposon insertions by genome walking and sequence analysis. We also scanned thirteen Drosophila melanogaster P450s genes for TE insertions by in silico mapping and literature search. Results. Twelve novel transposons, including LINEs (long interspersed nuclear elements), SINEs (short interspersed nuclear elements), MITEs (miniature inverted-repeat transposable elements), one full-length transib-like transposon, and one full-length Tcl-like DNA transpson, are identified from the alleles of the six H. zea P450 genes. The twelve transposons are inserted into the 5'flanking region, 3'flanking region, exon, or intron of the six environment-adaptation P450 genes. In D. melanogaster, seven out of the eight Drosophila P450s (CYP4E2, CYP6A2, CYP6A8, CYP6A9, CYP6G1, CYP6W1, CYP12A4, CYP12D1) implicated in insecticide resistance are associated with a variety of transposons. By contrast, all the five Drosophila P450s (CYP302A1, CYP306A1, CYP307A1, CYP314A1 and CYP315A1) involved in ecdysone biosynthesis and developmental regulation are free of TE insertions. Conclusion. These results indicate that TEs are selectively retained within or in close proximity to xenobiotic-metabolizing P450 genes. © 2007 Chen and Li; licensee BioMed Central Ltd.
• Li, X., Schuler, M. A., & Berenbaum, M. R. (2007). Molecular mechanisms of metabolic resistance to synthetic and natural xenobiotics. ANNUAL REVIEW OF ENTOMOLOGY, 52, 231-253.
• Xian, L. i., Wen, Z., Bohnert, H. J., Schuler, M. A., & Kushad, M. M. (2007). Myrosinase in horseradish (Armoracia rusticana) root: Isolation of a full-length cDNA and its heterologous expression in Spodoptera frugiperda insect cells. Plant Science, 172(6), 1095-1102.
  More info

  Abstract: Myrosinase (β-thioglucoside glucohydrolase, EC. 3.2.3.1), is the only known S-glucosidase in plants, catalyzing the hydrolysis of glucosinolates into compounds that have diverse biological activities. In the present study, a full-length cDNA encoding myrosinase (ArMY1) was cloned from horseradish (Armoracia rusticana) root. ArMY1 has an open reading frame of 1614 nucleotides with a deduced protein of 538 amino acids and molecular mass of 61.6 kD. ArMY1 shows highest overall amino acid identity (72%) with Arabidopsis thaliana myrosinase TGG2. Heterologous expression of ArMY1 in baculovirus-infected Sf9 cells resulted in an immunologically active recombinant ArMY1 protein, when probed with myrosinase-specific monoclonal antibody 3D7, with apparent mass 65 kD. ArMY1 mRNA signal of about 1.95 kb was detected in the leaves and roots of horseradish, but not in the florets of broccoli. Phylogenetic analysis showed that ArMY1 does not cluster with any of the currently known myrosinase subfamilies, MA, MB, MC, and may represent a novel myrosinase subfamily. This is the first report of cloning of myrosinase cDNA from horseradish root. It provides important sequence information that will enable further studies of myrosinase expression patterns and their interaction with myrosinase-binding proteins and other myrosinase-associated proteins. © 2007 Elsevier Ireland Ltd. All rights reserved.
• Xianchun, L. i., Schuler, M. A., & Berenbaum, M. R. (2007). Molecular mechanisms of metabolic resistance to synthetic and natural xenobiotics. Annual Review of Entomology, 52, 231-253.
  More info

  PMID: 16925478;Abstract: Xenobiotic resistance in insects has evolved predominantly by increasing the metabolic capability of detoxificative systems and/or reducing xenobiotic target site sensitivity. In contrast to the limited range of nucleotide changes that lead to target site insensitivity, many molecular mechanisms lead to enhancements in xenobiotic metabolism. The genomic changes that lead to amplification, overexpression, and coding sequence variation in the three major groups of genes encoding metabolic enzymes, i.e., cytochrome P450 monooxygenases (P450s), esterases, and glutathione-S-transferases (GSTs), are the focus of this review. A substantial number of the adaptive genomic changes associated with insecticide resistance that have been characterized to date are transposon mediated. Several lines of evidence suggest that P450 genes involved in insecticide resistance, and perhaps insecticide detoxification genes in general, may share an evolutionary association with genes involved in allelochemical metabolism. Differences in the selective regime imposed by allelochemicals and insecticides may account for the relative importance of regulatory or structural mutations in conferring resistance. Copyright © 2007 by Annual Reviews. All rights reserved.
• Xian, L. i., & Kushad, M. M. (2005). Purification and characterization of myrosinase from horseradish (Armoracia rusticana) roots. Plant Physiology and Biochemistry, 43(6), 503-511.
  More info

  PMID: 15922609;Abstract: Myrosinase (β-thioglucoside glucohydrolase; EC 3.2.3.147) from horseradish (Armoracia rusticana) roots was purified to homogeneity by ammonium sulfate fractionation, Q-sepharose, and concanavalin A sepharose affinity chromatography. The purified protein migrated as a single band with a mass of about 65 kDa on SDS-polyacrylamide gel electrophoresis. Using LC-MS/MS, this band was identified as myrosinase. Western blot analysis, using the anti-myrosinase monoclonal antibody 3D7, showed a single band of about 65 kDa for horseradish crude extract and for the purified myrosinase. The native molecular mass of the purified myrosinase was estimated, using gel filtration, to be about 130 kDa. Based on these data, it appeared that myrosinase from horseradish root consists of two subunits of similar molecular mass of about 65 kDa. The enzyme exhibited high activity at broad pH (pH 5.0-8.0) and temperature (37 and 45°C). The purified enzyme remained stable at 4°C for more than 1 year. Using sinigrin as a substrate, the Km and Vmax values for the purified enzyme were estimated to be 0.128 mM and 0.624 μmol min-1, respectively. The enzyme was strongly activated by 0.5 mM ascorbic acid and was able to breakdown intact glucosinolates in a crude extract of broccoli. © 2005 Elsevier SAS. All rights reserved.
• Xianchun, L. i., Baudry, J., Berenbaum, M. R., & Schuler, M. A. (2004). Structural and functional divergence of insect CYP6B proteins: From specialist to generalist cytochrome P450. Proceedings of the National Academy of Sciences of the United States of America, 101(9), 2939-2944.
  More info

  PMID: 14981232;PMCID: PMC365724;Abstract: How polyphagous herbivores cope with the diversity and unpredictability of plant defenses remains largely unknown at both the genetic and molecular levels. To examine whether generalist counterdefense enzymes are structurally more flexible and functionally more diverse, two counterdefensive allelochemical-metabolizing cytochrome P450 proteins, CYP6B1 from the specialist Papilio polyxenes, feeding on furanocoumarin-containing plants, and CYP6B8 from the generalist Helicoverpa zea, feeding on hundreds of host plant species, are compared structurally and functionally. Molecular modeling indicates that CYP6B8 has more flexible overall folding, a more elastic catalytic pocket, and one more substrate access channel than CYP6B1. Baculovirus-mediated expression of the CYP6B8 and CYP6B1 proteins demonstrates that CYP6B8 metabolizes six biosynthetically diverse plant allelochemicals (xanthotoxin, quercetin, flavone, chlorogenic acid, indole-3-carbinol, and rutin) and three insecticides (diazinon, cypermethrin, and aldrin), whereas CYP6B1 metabolizes only two allelochemicals (xanthotoxin and flavone) and one insecticide (diazinon) of those tested. These results indicate that generalist counterdefense proteins are capable of accepting a more structurally diverse array of compounds compared with specialist counterdefense proteins.
• Xianchun, L. i., Berenbaum, M. R., & Schuler, M. A. (2002). Cytochrome P450 and actin genes expressed in Helicoverpa zea and Helicoverpa armigera: Paralogy/orthology identification, gene conversion and evolution. Insect Biochemistry and Molecular Biology, 32(3), 311-320.
  More info

  PMID: 11804803;Abstract: Molecular phylogenetic analysis was conducted using conserved cytoplasmic actin and diversified cytochrome P450 (P450) sequences isolated from Helicoverpa zea and Helicoverpa armigera, two species thought to be closely related based on allozyme analyses. These sequences were compared in turn with published sequences from other insects to gain insight into how different gene families evolve. In Bombyx mori and these Helicoverpa species, cytoplasmic actin genes are present as a pair of tandemly duplicated paralogs with coding sequence identities as high as 95.5% (B. mori), 98.9% (H. zea) and 98.5% (H. armigera) due to recent 5′-polar gene conversions. Phylogeny and interspecies comparisons assign the six actin genes into two orthologous groups: HaA3a/HzA3a/BmA3 and HaA3b/HzA3b/BmA4, which exhibit more similarities between H. zea and H. armigera than between Helicoverpa species and B. mori. Like the actin genes in H. zea, four CYP6B genes exist as two pairs of duplicated paralogs with recent 5′-polar gene conversions. Interspecific comparisons and phylogeny analysis identified three groups of orthologous CYP6B genes: H. zea CYP6B8 or CYP6B28/H. armigera CYP6B7, H. zea CYP6B27/H. armigera CYP6B6, and H. zea CYP6B9/H. armigera CYP6B2/Heliothis virescens CYP6B10. The low degree of divergence in the first two of these groups is comparable to allelic variation within a single species. These orthologous relationships and the high degrees of similarity in both actin and P450 genes strongly indicate that these Helicoverpa species are extremely closely related. © 2002 Elsevier Science Ltd. All rights reserved.
• Xianchun, L. i., Berenbaum, M. R., & Schuler, M. A. (2002). Plant allelochemicals differentially regulate Helicoverpa zea cytochrome P450 genes. Insect Molecular Biology, 11(4), 343-351.
  More info

  PMID: 12144700;Abstract: Four cytochrome P450 genes, CYP6B8, CYP6B9, CYP6B27 and CYP6B28, exist in the Helicoverpa zea genome as two pairs of paralogs that evolved from gene duplication and 5′-polar gene conversion events. RT-PCR gel blot analyses have shown that all of these genes are expressed constitutively in midguts of all larval instars, suggesting that they have primary roles in the detoxification of plant allelochemicals. Among these, CYP6B9 is expressed only in midgut tissue whereas its paralog, CYP6B27, is expressed primarily in midgut and secondarily in fat body and ovary. CYP6B28 is expressed in midgut, fat body and, to lesser extents in ovary and integument whereas its paralog, CYP6B8, is expressed in midgut and to some extent in fat body. Comparison of the expression levels induced by eight plant allelochemicals, one drug (phenobarbital), and an insecticide (α-cypermethrin) indicates that, for the most part, the four P450s respond individually to these inducers, with all four induced strongly by chlorogenic acid, a shikimate pathway intermediate and a lignin biosynthesis intermediate present in a wide variety of plants, and indole-3-carbinol, a glucobrassicin breakdown product present in the Brassicaceae. The multiple levels at which these P450 genes are apparently diverging (e.g. transcriptional responses, protein sequences) support the suggestion that gene conversion events facilitate gene evolution by allowing duplicated copies greater time to acquire selectable differences in both coding and promoter sequences.
• Xianchun, L. i., Schuler, M. A., & Berenbaum, M. R. (2002). Jasmonate and salicylate induce expression of herbivore cytochrome P450 genes. Nature, 419(6908), 712-715.
  More info

  PMID: 12384696;Abstract: Jasmonate and salicylate are plant-produced signals that activate plant defence genes after herbivory or pathogen attack. Amplification of these signals, evoked by either enemy attack or experimental manipulation, leads to an increase in the synthesis of toxic compounds (allelochemicals) and defence proteins in the plants. Although the jasmonate and salicylate signal cascades activate different sets of plant defence genes or even act antagonistically, there is substantial communication between the pathways. Jasmonate and salicylate also contribute to protecting plants against herbivores by causing plants that experience insect damage to increase their production of volatile molecules that attract natural enemies of herbivorous insects. In response to plant defences, herbivores increase their production of enzymes that detoxify allelochemicals, including cytochrome P450s (refs 15, 16). But herbivores are potentially vulnerable to toxic allelochemicals in the duration between ingesting toxins and induction of detoxification systems. Here we show that the corn earworm Helicoverpa zea uses jasmonate and salicylate to activate four of its cytochrome P450 genes that are associated with detoxification either before or concomitantly with the biosynthesis of allelochemicals. This ability to 'eavesdrop' on plant defence signals protects H. zea against toxins produced by host plants.
• Li, Y., Dennehy, T. J., Li, X., & Wigert, M. E. (2000). Susceptibility of Arizona whiteflies to chloronicotinyl insecticides and IGRS: New developments in the 1999 season. 2000 Proceedings Cotton Conferences Volume 2, 1325-1330.
  More info

  Abstract: Whiteflies are serious pests of cotton, melons, and winter vegetables in Arizona's low deserts. Successful management of whiteflies requires an integrated approach, a critical element of which is routine pest monitoring. In this paper we report findings of our 1999 investigations of resistance of Arizona whiteflies to insect growth regulators (IGRs) and chloronicotinyl insecticides. Whiteflies collected from cotton fields, melon fields and greenhouses were tested for susceptibility to imidacloprid (Admire®/Provado®), and two other chloronicotinyl insecticides, acetamiprid and thiamethoxam, and to two insect growth regulators (IGRs), buprofezin (Applaud®) and pyriproxyfen (Knack®). Contrasts of 1998 and 1999 results indicated increased susceptibilities, on average, to both imidacloprid and buprofezin of whiteflies collected from cotton. A cropping system study showed that whiteflies collected from spring melons had significantly lower susceptibility to imidacloprid than those collected from cotton or fall melons. The opposite was found for pyriproxyfen, to which whiteflies from cotton and fall melons had lower susceptibility than those from spring melons. As in 1998, whiteflies with reduced susceptibility to imidacloprid continue to be found in certain locations, particularly in spring melon fields and greenhouses. Results of our laboratory bioassays on susceptibility of Arizona whiteflies to chloronicotinyl insecticides provided evidence of a low order cross-resistance between imidacloprid, acetamiprid and thiamethoxam. Monitoring in 1999 provided the first evidence of reduced susceptibility of Arizona whiteflies to pyriproxyfen.
• Xianchun, L. I., Zangerl, A. R., Schuler, M. A., & Berenbaum, M. R. (2000). Cross-resistance to α-cypermethrin after xanthotoxin ingestion in Helicoverpa zea (lepidoptera: noctuidae). Journal of Economic Entomology, 93(1), 18-25.
  More info

  PMID: 14658506;Abstract: Cytochrome P450 monooxygenases (P450) are membrane-bound hemoproteins that play important roles in conferring protection against both naturally occurring phytochemicals and synthetic organic insecticides. Despite the potential for common modes of detoxification, crossresistance between phytochemicals and synthetic organic insecticides has rarely been documented. In this study, we examined the responses of a susceptible strain of corn earworm, Helicocerpa zea (Boddie), a polyphagous noctuid, to exposure by an allelochemical infrequently encountered in its host plants and by an insecticide widely used for control purposes. Within a single generation, survivors of xanthotoxin exposure displayed higher levels of tolerance to α-cypermethrin than did unexposed control larvae. The F1 offspring of xanthotoxin-exposed survivors also displayed higher α-cypermethrin tolerance than did offspring of unexposed control larvae, suggesting that increased α-cypermethrin tolerance after xantholoxin exposure represents, at least in part, heritable resistance. Administration of piperonyl butoxide, a P450 Synergist, demonstrated that resistance to both xantholoxin and α-cypermethrin is P450-mediated. α-Cypermethrin-exposed survivors, however, failed to show superior growth on xanthotoxin diets. Assays with control larvae, larvae induced by both xanthotoxin and α-cypermethrin, and survivors of LD50 doses of both compounds indicated that H. zea midgut P450s are capable of metabolizing both xanthotoxin and α-cypermethrin. Metabolism of each compound is significantly inhibited by the presence of the other compound, suggesting that at least one form of P450 in H. zea midguts degrades both compounds and may constitute the biochemical basis for possible cross-resistance. Compared with control larvae, xanthotoxin- and α-cypermethrin-induced larvae displayed 2- to 4-fold higher P450-mediated metabolism of both compounds. However, xanthotoxin- and α-cyperniethrin-exposed survivors exhibited much higher (2.5- to 11-fold) metabolism of both compounds than did the induced larvae. The metabolism results, like the bioassay results, are consistent with the interpretation that increased α-cypermethrin tolerance after xanthotoxin exposure is attributable mainly to heritable resistance. © 2000 Entomological Society of America.
• Xianchun, L. i., Berenbaum, M. R., & Schuler, M. A. (2000). Molecular cloning and expression of CYP6B8: A xanthotoxin-inducible cytochrome P450 cDNA from Helicoverpa zea. Insect Biochemistry and Molecular Biology, 30(1), 75-84.
  More info

  PMID: 10646973;Abstract: Xanthotoxin, a plant allelochemical, induces α-cypermethrin insecticide tolerance in Helicoverpa zea (corn earworm); inhibition of tolerance by piperonyl butoxide implicates cytochrome P450 monooxygenases (P4950s) in the detoxification of this insecticide. To characterize the xanthotoxin-inducible P450 that might mediate α-cypemethrin tolerance in this species, a cDNA library prepared from xanthotoxin-induced H. zea fifth instar larvae was screened with cDNAs encoding furanocoumarin-metabolizing P450s from Papilio polyxenes (CYP6B1v2) and P. glaucus (CYP6B4v2) as well as a sequence-related P450 from Helicoverpa armigera (CYP6B2). One full-length cDNA isolated in this screening shares 51-99% amino acid identity with the CYP6B subfamily of P450S isolated from Papilio and Helicoverpa species and, thus, has been designated CYP6B8. All of these CYP6B subfamily members share a number of highly conserved domains, including substrate recognition site 1 (SRS 1) that is critical for xanthotoxin metabolism by CYP6B 1 v2 from Papilio polyxenes and coumarin metabolism by CYP2a5 from Mus musculus. Northern and RT-PCR analyses indicate that CYP6B8 expression is strongly induced by xanthotoxin and phenobarbital and negligibly induced by α-cypermethrin.
• Han, Z., Wang, Y., Zhang, Q., Li, X., & Li, G. (1999). Dynamics of pyrethroid resistance in a field population of Helicoverpa armigera (Hubher) in China. Pesticide Science, 55(4), 462-466.
  More info

  Abstract: Dynamics of pyrethroid resistance in a field population of cotton bollworm (Helicoverpa armigera) was demonstrated by continuous monitoring with twin discriminating dosages, and the influencing factors were also experimentally analysed. Resistance in a field population in China increased rapidly in the 3rd and 4th generations when population density became higher and insecticides were applied repeatedly, then decreased suddenly during over-wintering and slowly in the 1st and 2nd generations when insecticide spraying was suspended. Resistance increase could be countered by dilution as a result of immigration of susceptible moths from corn fields, which were found to be a natural refuge for this pest in China. The reduction of resistance during over-wintering and the 1st and 2nd generations was affected by the lower fitness of resistant cotton bollworms to low temperature and disadvantages in reproduction. The possibilities of managing the resistance in field populations on the basis of these observations are discussed.
• Xianchun, L., Yinchang, W., Qiansong, Z., Ganjun, Y., Dunyang, Z., Yantao, Y., Zhi, Z., Jianping, Z., Shoushan, L., Caixia, C., & Shiyin, D. (1997). Insecticide resistance in field strains of Pectinophora gossypiella (Saunders) in China and effect of synergists on deltamethrin and parathion-methyl activity. Pesticide Science, 50(3), 183-186.
  More info

  Abstract: Filter-paper residual toxicities of some insecticides used extensively in China were determined during 1994 using newly hatched (within 30 min) larvae of four Pectinophora gossypiella (Saunders) strains. The strains were field collections collected in the Yangtze River cotton-belt areas. Compared with the susceptible laboratory strain from Qunli (Lishui County, Jiangsu province), the four field strains from Anqing (Anhui province), Jiangling (Hubei province), Cixi(Zhejiang province) and Tongzhou(Jiangsu province) had developed 185-, 6.7-, 698- and 249-fold resistance, respectively, to deltamethrin. Cixi and Tongzhou field strains had also developed 103- and 94-fold resistance to fenvalerate, and 10- and 3.6- fold resistance to parathion-methyl. Percentage of survivors at diagnostic dosage for deltamethrin showed that the strains from Anqing, Jiangling, Cixi and Tongzhou had 87.2, 18.3, 90.1 and 74.6% resistant individuals respectively. Cixi and Tongzhou field strains had 88.9 and 65.3% resistant individuals after application of parathion-methyl, which was consistent with the corresponding resistance ratios. Studies of the effect of synergists piperonyl butoxide (PBO), triphenyl phosphate (TPP) with deltamethrin and parathion-methyl in Cixi, Anqing and Tongzhou field strains suggested that metabolic resistance mechanisms such as carboxylesterases (CarE) and mixed function oxygenases (MFO) were involved in parathion-methyl resistance, but not in deltamethrin resistance.

Presentations

• Deng, Z., Liu, S., Zhang, Y., Ni, X., & Li, X. (2022, April 10-13). A transposon-introduced G-quadruplex motif is selectively retained and constrained to downregulate an insect P450 (invited talk). . The 2022 Pacific Branch meeting of Entomological Society of America (ESA), Santa Rosa, CA. Santa Rosa, CA: Entomological Society of America (ESA).
• Li, X. (2022, Dec. 5). Allelochemical regulation of Insect P450s (Invited seminar online). . Invited seminar by College of Plant Protection, Shanxi Agricultural University. Online: College of Plant Protection, Shanxi Agricultural University.
  More info

  Invited seminar
• Deng, Z., Zhang, Y., & Li, X. (2019, Nov. 19). Molecular and functional characterization of masculinizer gene in Helicoverpa armigera.. The 2019 ESA annual meeting. St Louis, MO: ESA.
  More info

  Submitted talk and presented by Zhongyuan Deng
• Li, X. (2019, May 25, 2019). Mechanistic understanding of resistance to Bt cotton in pink bollowrm. Invited seminar. Taigu, Shanxi, China: Shanxi Agricultural University.
  More info

  Invited research seminar
• Li, X. (2019, October 23, 2019). How do generalist and specialist herbivores regulate their effector and elicitors-hydrolyzing genes?. The 2019 Yangling International Agri-Science Forum. Yangling, China: Northwest A&F University.
• Li, X., Yang, L. Y., Cheng, Q., & Wang, X. (2019, Nov. 19). Expressional divergence of GOXx and L-ACY-1 in specialist and generalist Helicoverpa species. The 2019 ESA annual meeting. St Louis, MO: ESA.
  More info

  Submitted oral presentation
• Fabrick, J. A., Mathew, L. G., Li, X., Carrière, Y., & Tabashnik, B. E. (2018, November 4-10). Shared GENES INVOLVED IN resistance to Bt cotton IN pink bollworm Selected in ThE LAb and field. XLI National Congress of Biological Control. Mexican Society for Biological Control. Puerto Vallarta, Jalisco, Mexico.
  More info

  Submitted talk. Presented by Jeff Fabrick.
• Li, X. (2018, June). How to achieve polyphagy?. Invited seminar. Taigu, China: Shanxi Agricultural University.
• Li, X. (2018, May). How to achieve host generalism?. Invited seminar. Zhengzhou, China: Zhengzhou University.
• Li, X. (2018, October 30). Genome shrinks with Host expansion in Helicoverpa speceis. Invited seminar. Guangzhou, China: Zhongshan University.
• Li, X. (2018, October 31). Mechanistic understanding of resistance to Bt cotton in pink bollworm. Invited seminar. Guangzhou, China: Guangdong Academy of Agricultural Science.
• Li, X. (2017, 2017-04-04). Expressional divergence of GOX and L-ACY-1 genes in Helicoverpa species. The Annual Meeting of the Pacific Branch of the Entomological Society of America. Portland, Oregon: The Pacific Branch of the Entomological Society of America.
  More info

  Invited oral prevention at the annual meeting of the Pacific Branch of the Entomological Society of America.
• Li, X. (2017, 2017-04-10). How does corn earworm transduce allelochemicals to escalate its counter defenses?. Michangan State University, Department of Entomology seminar. East Lansing, MI 48824, USA: Michangan State University.
  More info

  Invited seminar
• Li, X. (2017, 2017-06-05). What triggers alternative use of two radically different poly (A) sites?. Henan Agricultural University, College of Plant Protection seminar. Zhengzhou, China: Henan Agricultural University.
• Li, X. (2017, 2017-06-13). Involvement of a piRNA in poly(A) site recognition and alternative polyadenylation.. Shanxi Agricultural University seminar. Taigu, China: Shanxi Agricultural University.
  More info

  Invited seminar
• Li, X. (2017, 2017-07-05). Stress-dependent reactivation and jumping of Hztransib in Helicoverpa zea and H. armigera.. Sicuan Academy of Agricultural Science, Institute of Plant Protection seminar. Chengdu, China: Sicuan Academy of Agricultural Science, Institute of Plant Protection.
  More info

  Invited seminar
• Li, X. (2017, 2017-07-28). Expressional divergence of GOX and L-ACY-1 genes in Helicoverpa species. The Fourth National Inspection and Quarantine Academic Forum of China. Beijing, China: The National Inspection and Quarantine society of China.
  More info

  Invited talk at The Fourth National Inspection and Quarantine Academic Forum.
• Li, X. (2016, 09-16-2016). What triggers alternative use of two radically different poly (A) sites?. 2016 Entomology/Entomology & Insect Science, Fall Seminar Series, University of Arizona.
• Li, X. (2016, 09-30-2016). How do insect herbivores “spy” on their host plants?. 2016 International Congress of Entomology (ICE2016), Orlando, Florida. Orlando, Florida: Entomological Society of America (ESA).
• Mathew, L. G., Carriere, Y., Li, X., Tabashnik, B. E., & Fabrick, J. A. (2016, September/2016). Genetic basis of resistance to Bt toxin Cry2Ab in pink bollworm. 2016 International Congress of Entomology (ICE2016), Orlando, Florida. Orlando, Florida: Entomological Society of America (ESA).
• Li, X. (2015, 05-21-2015). Pupal melanism in Spodoptera exigua: fitness gain and mechanism. Seminar. Zhengzhou, P. R. China: Henan Agricultural University.
• Li, X. (2015, 07-07-2015). Diversity of sex determination in insects. Seminar. Beijing, P. R. China: Institute of Plant Protection, Chinese Academy of Agricultural Science.
• Li, X. (2015, 08-04-2015). Resistance mechanisms of cotton bollworm to Cry1Ac. Seminar. Taigu, Shanxi province, P. R. China: Shanxi Agricultural University.
• Li, X. (2014, August 7). Potential contributions of proteases to Cry1Ac resistance in Helicoverpa zea.. Invited talk at The 1st International Symposium on Insecticide Toxicology. Guangzhou, China.: The Entomological Society of China and National Natural Science Foundation of China.
• Li, X. (2014, July 10). Insights into herbivory and detoxification through the Plutella xylostella genome. Invited talk at The 30th Conferenece of the International Society of Chemical Ecology. Urbana-Champaign, IL, USA: International Society of Chemical Ecology.
• Li, X. (2014, June 10). Insect genomes and the –omics. Invited talk at The 1st Summer course in Insect Systems Biology. wuhan, China: huazhong Agricultural University.
• Li, X. (2014, June 11). Embryogenesis: segmentation and segment identity. Invited talk at The 1st Summer course in Insect Systems Biology. Wuhan, China: Huazhong Agricultural University.
• Li, X. (2014, June 12). Circadian rhythms. Invited talk at The 1st Summer course in Insect Systems Biology.
• Li, X. (2014, June 12). Plant-insect arms race: How does cotton bollworm eavesdrops on plant-derived signals?. Invited seminar. Wuhan, P.R. China: Huazhong Normal University, Wuhan, P.R. China.
• Li, X. (2014, June 13). Transposable elements. Invited talk at The 1st Summer course in Insect Systems Biology. Wuhan, China: Huazhong Agricultural University.
• Li, X. (2014, June 9). Insect systems biology: from molecule to cell, organism. Invited talk at The 1st Summer course in Insect Systems Biology. Wuhan, China: Huazhong Agricultural University.
• Li, X. (2014, November 16). Alternative splicing and highly variable cadherin transcripts are associated with field-evolved resistance of pink bollworm to Bt cotton in India. The 2014 ESA Annual Meeting. Oregon Convention Center Portland, OR: ESA.
  More info

  Ten min talk given by my collaborator Jeffrey A. Fabrick of USDA - ARS.
• Li, X. (2014, November 17). Picky caterpillars: Feeding choices and adaptation to Bt crops by cotton bollworm (Helicoverpa zea). The 2014 ESA Annual Meeting. Oregon Convention Center Portland, OR: ESA.
  More info

  Graduate student 10 min presentation given by Yves's graduate student Robert Orpet.
• Li, X. (2014, November 18). Baseline susceptibility of three cell lines to activated Cry1Ac and Cry2Ab. The 2014 ESA Annual Meeting. Oregon Convention Center Portland, OR: ESA.
  More info

  Ten min oral presentation given by Mmy PhD student Jizhen Wei.
• Ellsworth, P. C., Li, X. -., Carriere, Y. -., Brown, L., & Nichols, R. L. (2013, March). Cotton Pest Management Research Update: Resistance & Resistance Management. Southwest Ag Summit. Arizona Western College, Yuma, AZ: 2013 Southwest Ag Summit.
  More info

  30 participants. 0.5 AZ CEU, 0.5 CA CEU, 0.5 CCA CEU
• Ellsworth, P. C., Li, X. -., Dennehy, T. J., Palumbo, J. C., Castle, S., Prabhaker, N., & Nichols, R. L. (2013, May). Is Monitoring Susceptibility of Bemisia tabaci to Insecticides Useful to Management?. First International Whitefly Symposium. Kolymbari, Crete, Greece.
  More info

  200 participants
• Li, X. -. (2013, August). How does Helicoverpsa zea spy and transduce plant-derived signals?. invited seminar. Huazhong Agricultural University, Wuhan, P. R. China: Huazhong Agricultural University.
• Li, X. -. (2013, August). How does cotton bollworm spy and transduce plant-derived signals?. Invited seminar. Fujian Agricultural University, Fuzhou, P.R. China: Fujian Agricultural University.
• Li, X. -. (2013, July). How is sex determined in humans and insects?. Invited seminar. Northwest A. & F. University, Yangling, Shaanxi province, P. R. China: Northwest A. & F. University.
• Li, X. -. (2013, July). How is sex determined in humans and insects?. The 4th Summer Symposia (Summer School) in Entomology. Beijing, China: Institute of zoology, Chinese Academy of Sciences.
• Li, X. -. (2013, June). Plant-Insect Arms Race: How does cotton bollworm spy and transduce plant-derived signals?. The 4th international insect biochemistry and molecular symposium.. Nanjing, P. R. China: Entomological Society of China.
• Li, X. -., Zhang, M., Jeffrey, J. A., Carrière, Y., & Tabashnik, B. E. (2013, November). Potential contributions of proteases to Cry1Ac resistance in Helicoverpa zea. 2013 ESA annua Conference. Austin, Texas: ESA.

Poster Presentations

• Fabrick, J. A., Heu, C. C., LeRoy, D. M., DeGain, B. A., Unnithan, G. C., Yelich, A. J., Li, X., Carriere, Y., & Tabashnik, B. E. (2022, June 26-July 1). CRISPR/Cas9 gene editing confirms the function of a Bacillus thuringiensis Cry2Ab receptor in two lepidopteran pests (submitted poster presentation). The Gordon Research Conference on Genetic Biocontrol. Ventura, CA: The Gordon Research Conference.
  More info

  Dr. Fabrick presented.