Functional validation of key cytochrome P450 monooxygenase and UDP-glycosyltransferase genes conferring cyantraniliprole resistance in Aphis gossypii Glover

Uridine diphosphate (UDP)-glycosyltransferases (UGTs) are associated with insecticide resistance in the major malaria vectors Anopheles gambiae s.l. and Anopheles funestus

Malaria remains one of the highest causes of morbidity and mortality, with 249 million cases and over 608,000 deaths in 2022. Insecticides, which target the Anopheles mosquito vector, are the primary method to control malaria. The widespread nature of resistance to the most important insecticide class, the pyrethroids, threatens the control of this disease. To reverse the stall in malaria control there is urgent need for new vector control tools, which necessitates understanding the molecular basis of pyrethroid resistance. In this study we utilised multi-omics data to identify uridine-diphosphate (UDP)-glycosyltransferases (UGTs) potentially involved in resistance across multiple Anopheles species. Phylogenetic analysis identifies sequence similarities between Anopheline UGTs and those involved in agricultural pesticide resistance to pyrethroids, pyrroles and spinosyns. Expression of five UGTs was characterised in An. gambiae and An. coluzzii to determine constitutive over-expression, induction, and tissue specificity. Furthermore, a UGT inhibitor, sulfinpyrazone, restored susceptibility to pyrethroids and DDT in An. gambiae, An. coluzzii, An. arabiensis and An. funestus, the major African malaria vectors. Taken together, this study provides clear association of UGTs with pyrethroid resistance as well as highlighting the potential use of sulfinpyrazone as a novel synergist for vector control.

Risk assessment, fitness cost and transcriptome analysis of cyantraniliprole resistance in Spodoptera frugiperda

Spodoptera frugiperda is a notorious invasive pest causing substantial yield losses of crops and has developed resistance to various types of insecticides. In this study, a cyantraniliprole-resistant strain, SfCYAN-R, was obtained from a susceptible strain, SfCYAN-S, after 13 generations of selection with cyantraniliprole. The fitness cost in SfCYAN-R strain was evaluated, and the putative resistance-related genes were explored by RNA-seq analysis. The results showed that SfCYAN-R strain developed 23.97-fold resistance to cyantraniliprole with the realistic heritability of 0.127. The development time of eggs, larvae, prepupae and pupae in SfCYAN-R strain was significantly prolonged than that in SfCYAN-S strain, but no difference in pupation rate, emergence rate and female fecundity was observed between SfCYAN-R and SfCYAN-S strains. Comparative gene expression analysis between SfCYAN-R and SfCYAN-S strains identified 776 significant differentially expressed genes (DEGs), among which several DEGs associated with xenobiotic metabolism were upregulated in SfCYAN-R strain. These results provide insights into the resistance mechanisms of cyantraniliprole and would be helpful for resistance management of S. frugiperda.

Expression and Functional Analysis of Two Cytochrome P450 Monooxygenase Genes and a UDP-Glycosyltransferase Gene Linked with Thiamethoxam Resistance in the Colorado Potato Beetle

Cytochrome P450 monooxygenases (P450s) and UDP-glycosyltransferases (UGTs) are involved in the evolution of insecticide resistance. Leptinotarsa decemlineata (Say), the Colorado potato beetle (CPB), is a notorious insect that has developed resistance to various insecticides including neonicotinoids. This study investigated whether the differentially expressed P450 genes CYP9Z140 and CYP9AY1 and UGT gene UGT321AP1, found in our transcriptome results, conferred resistance to thiamethoxam in L. decemlineata. Resistance monitoring showed that the sampled field populations of L. decemlineata adults collected from Urumqi City and Qapqal, Jimsar, and Mulei Counties of Xinjiang in 2021-2023 developed low levels of resistance to thiamethoxam with resistance ratios ranging from 6.66- to 9.52-fold. Expression analyses indicated that CYP9Z140, CYP9AY1, and UGT321AP1 were significantly upregulated in thiamethoxam-resistant populations compared with susceptible populations. The expression of all three genes also increased significantly after thiamethoxam treatment compared with the control. Spatiotemporal expression patterns showed that the highest expression of CYP9Z140 and CYP9AY1 occurred in pupae and the midgut, whereas UGT321AP1 was highly expressed in adults and Malpighian tubules. Knocking down all three genes individually or simultaneously using RNA interference increased the sensitivity of adult L. decemlineata to thiamethoxam. These results suggest that overexpression of CYP9Z140, CYP9AY1, and UGT321AP1 contributes to the development of thiamethoxam resistance in L. decemlineata and provides a scientific basis for improving new resistance management of CPB.

UDP-Glycosyltransferases UGT350C3 and UGT344L7 Confer Tolerance to Neonicotinoids in Field Populations of Aphis gossypii

The cotton aphid, Aphis gossypii, is a polyphagous pest that stunts host plant growth via direct feeding or transmitting plant virus. Due to the long-term application of insecticides, A. gossypii has developed different levels of resistance to numerous insecticides. We found that five field populations had evolved multiple resistances to neonicotinoids. To explore the resistance mechanism mediated by uridine diphosphate glycosyltransferases (UGTs), two upregulated UGT genes in these five strains, UGT350C3 and UGT344L7, were selected for functional analysis of their roles in neonicotinoid detoxification. Transgenic Drosophila bioassay results indicated that compared with the control lines, the UGT350C3 and UGT344L7 overexpression lines were more tolerant to thiamethoxam, imidacloprid, and dinotefuran. Knockdown of UGT350C3 and UGT344L7 significantly increased A. gossypii sensitivity to thiamethoxam, imidacloprid, and dinotefuran. Molecular docking analysis demonstrated that these neonicotinoids could bind to the active pockets of UGT350C3 and UGT344L7. This study provides functional evidence of neonicotinoid detoxification mediated by UGTs and will facilitate further work to identify strategies for preventing the development of neonicotinoid resistance in insects.

Lethal and Sublethal Effects of Cyantraniliprole on the Biology and Metabolic Enzyme Activities of Two Lepidopteran Pests, Spodoptera littoralis and Agrotis ipsilon, and A Generalist Predator, Chrysoperla carnea (Neuroptera: Chrysopidae)

Cyantraniliprole is a novel anthranilic diamide insecticide registered for controlling chewing and sucking insect pests. Here, the lethal and sublethal effects of this insecticide on two destructive lepidopteran pests, Spodoptera littoralis Boisduval and Agrotis ipsilon Hufnagel, were evaluated. Because the effects of novel insecticides on beneficial and non-target arthropods must be considered, the impact of cyantraniliprole on a generalist biological control agent, Chrysoperla carnea [Stephens 1836], were also examined. Overall, our study revealed that cyantraniliprole was more toxic to A. ipsilon than to S. littoralis. Moreover, the LC15 and LC50 of the insecticide significantly prolonged the duration of the larval and pupal stages and induced enzymatic detoxification activity in both species. Treatment of the second-instar larvae of C. carnea with the recommended concentration of cyantraniliprole (0.75 mg/L) doubled the mortality rates and resulted in a slight negative effect on the biology and detoxification enzymes of C. carnea. Our results indicate that both sublethal and lethal concentrations of cyantraniliprole can successfully suppress S. littoralis and A. ipsilon populations. They also suggest that C. carnea, as a generalist predator, is compatible with cyantraniliprole under the modelled realistic field conditions. In future investigations, insights into the effects of cyantraniliprole on S. littoralis, A. ipsilon, and C. carnea under field conditions will be required to appropriately validate our results.

Two cuticle-enriched chemosensory proteins confer multi-insecticide resistance in Spodoptera frugiperda

Recent studies revealed that insect chemosensory proteins (CSPs) both play essential roles in insect olfaction and insect resistance. However, functional evidence supporting the crosslink between CSP and insecticide resistance remains unexplored. In the present study, 22 SfruCSP transcripts were identified from the fall armyworm (FAW) and SfruCSP1 and SfruCSP2 are enriched in the larval cuticle and could be induced by multiple insecticides. Both SfruCSP1 and SfruCSP2 are highly expressed in the larval inner endocuticle and outer epicuticle, and these two proteins exhibited high binding affinities with three insecticides (chlorfenapyr, chlorpyrifos and indoxacarb). The knockdown of SfruCSP1 and SfruCSP2 increased the susceptibility of FAW larvae to the above three insecticides, and significantly increased the penetration ratios of these insecticides. Our in vitro and in vivo evidence suggests that SfruCSP1 and SfruCSP2 are insecticide binding proteins and confer FAW larval resistance to chlorfenapyr, chlorpyrifos and indoxacarb by an insecticide sequestration mechanism. The study should aid in the exploration of larval cuticle-enriched CSPs for insect resistance management.

Characterization and functional analysis of UDP-glycosyltransferases reveal their contribution to phytochemical flavone tolerance in Spodoptera litura

Efficient detoxification is the key factor for phytophagous insect to adapt to phytochemicals. However, the role of uridine diphosphate (UDP)-glycosyltransferases (UGTs) in insect anti-defense to phytochemical flavone is largely unknown. In this study, 52 UGT genes were identified in Spodoptera litura and they presented evident gene duplication. UGT played a crucial part in larval tolerance to flavone because the enzyme activity and transcriptional level of 77 % UGT members were remarkably upregulated by flavone administration and suppression of UGT enzyme activity and gene expressions significantly increased larval susceptibility to flavone. Bacteria coexpressing UGTs had high survival rates under flavone treatment and flavone was dramatically metabolized by UGT recombinant cells, which indicated the involvement of UGTs in flavone detoxification. What's more, ecdysone pathway was activated by flavone. Topical application of 20-hydroxyecdysone highly upregulated UGT enzyme activity and more than half of UGT expressions. The effects were opposite when ecdysone receptor (EcR) and ultraspiracle (USP)-mediated ecdysone signaling pathway was inhibited. Furtherly, promoter reporter assays of 5 UGT genes showed that their transcription activities were notably increased by cotransfection with EcR and USP. In consequence, this study suggested that UGTs were involved in flavone detoxification and their transcriptional expressions were regulated by ecdysone pathway.

Functional Characterization of CYP6QE1 and CYP6FV21 in Resistance to λ-Cyhalothrin and Imidacloprid in Bradysia odoriphaga

Cytochrome P450 monooxygenases (P450s) belong to a family of metabolic enzymes that are involved in the detoxification of insecticides. In this study, our bioassay results showed that a field-collected population of Bradysia odoriphaga displayed a moderate resistance to λ-cyhalothrin and imidacloprid. Compared to susceptible population, CYP6QE1 and CYP6FV21 were significantly overexpressed in the field population. The expression of CYP6QE1 and CYP6FV21 was more abundant in the third and fourth larval stages, and CYP6QE1 and CYP6FV21 were most highly expressed in the midgut and Malpighian tubules. Exposure to λ-cyhalothrin and imidacloprid significantly increased the expression levels of CYP6QE1 and CYP6FV21. Furthermore, the silencing of CYP6QE1 and CYP6FV21 significantly increased the susceptibility of B. odoriphaga larvae to λ-cyhalothrin and imidacloprid. The overexpression of CYP6QE1 and CYP6FV21 significantly enhanced the tolerance of transgenic Drosophila melanogaster lines to λ-cyhalothrin and imidacloprid. In addition, molecular docking revealed that these two P450 proteins have strong binding affinity toward λ-cyhalothrin and imidacloprid insecticides. Taken together, these results indicate that the overexpression of CYP6QE1 and CYP6FV21 is responsible for resistance to λ-cyhalothrin and imidacloprid in B. odoriphaga.

A masked gene concealed hand in glove in the forkhead protein crocodile regulates the predominant detoxification CYP6DA1 in Aphis gossypii Glover

Cytochrome P450-mediated metabolism is an important mechanism of insecticide resistance, most studies show upregulated transcript levels of P450s in resistant insect strains. Our previous studies illustrated that some upregulated P450s were associated with cyantraniliprole resistance, and it is more comprehensive to use the tissue specificity of transcriptomes to compare resistant (CyR) and susceptible (SS) strains. In this study, the expression profiles of P450s in a CyR strain compared with a SS strain in remaining carcass or midgut were investigated by RNA sequencing, and candidate genes were selected for functional study. Drosophila melanogaster bioassays suggested that ectopic overexpression of CYP4CK1, CYP6CY5, CYP6CY9, CYP6CY19, CYP6CZ1 and CYP6DA1 in flies was sufficient to confer cyantraniliprole resistance, among which CYP6DA1 was the predominant contributor to resistance (12.24-fold). RNAi suppression of CYP4CK1, CYP6CY5, CYP6CY9 and CYP6DA1 significantly increased CyR aphid sensitivity to cyantraniliprole. The CYP6DA1 promoter had two predicted binding sites for crocodile (CROC), an intron-free ORF with bidirectional transcription yielding CROC (+) and CROC (-). Y1H, RNAi and EMSA found that CROC (-) was a transcription factor directly regulating CYP6DA1 expression. In conclusion, P450 genes contribute to cyantraniliprole resistance, and the transcription factor CROC (-) regulates the expression of CYP6DA1 in A. gossypii.

Risk of resistance and the metabolic resistance mechanism of Laodelphax striatellus (Fallén) to cyantraniliprole

Cyantraniliprole is a highly effective diamide insecticide used to control of Laodelphax striatellus (Fallén). This study aimed to assess the insecticide resistance risk of L. striatellus and its metabolic resistance mechanisms. After 25 continuous generations of selection, the resistance of L. striatellus to cyantraniliprole increased by 17.14-fold. The realistic heritability of resistance was 0.0751. After successive rearing for five generations without exposure to insecticides, the resistance ratio for the resistant strain of L. striatellus decreased by 3.47-fold, and the average resistance decline rate per generation was 0.0266. Cyantraniliprole-resistant strains did not exhibit cross-resistance to triflumezopyrim, pymetrozine, flonicamid, sulfoxaflor, dinotefuran, clothianidin, thiamethoxam, nitenpyram, or imidacloprid. Compared to those of the sensitive strain, the 2nd, 3rd, and 4th instars, nymphal stage durations, total preoviposition period, and average generation time of the resistant strain were markedly reduced. Furthermore, the activity of cytochrome P450 monooxygenase (P450) and carboxylesterase (CarE) were markedly increased. The upregulation of CYP419A1v2 expression was most evident among the P450 genes, with a 6.10-fold increase relative to that in the sensitive strain. The CarE gene LsCarE5 was significantly upregulated by 1.94-fold compared with that in the sensitive strain. With the continuous use of cyantraniliprole, L. striatellus may develop resistance to this insecticide. This resistance may be related to the increase in metabolic enzyme activities regulated by the overexpression of P450 and CarE genes.

Functional analysis of UDP-glycosyltransferase genes conferring indoxacarb resistance in Spodoptera litura

UDP-glycosyltransferase (UGT) is the major detoxification enzymes of phase II involved in xenobiotics metabolism, which potentially mediates the formation of insect resistance. Previous transcriptome sequencing studies have found that several UGT genes were upregulated in indoxacarb resistant strains of Spodoptera litura, but whether these UGT genes were involved in indoxacarb resistance and their functions in resistance were unclear. In this study, the UGTs inhibitor, 5-nitrouracil, enhanced the toxicity of indoxacarb against S. litura, preliminarily suggesting that UGTs were participated in indoxacarb resistance. Two UGT genes, UGT33J17 and UGT41D10 were upregulated in the resistant strains and could be induced by indoxacarb. Alignment of UGT protein sequences revealed two conserved donor-binding regions with several key residues that interact with catalytic sites and sugar donors. Further molecular modeling and docking analysis indicated that two UGT proteins were able to stably bind indoxacarb and N-decarbomethoxylated metabolite (DCJW). Furthermore, knockdown of UGT33J17 and UGT41D10 decreased viability of Spli-221 cells and enhanced susceptibility of larvae to indoxacarb. Transgenic overexpression of these genes reduced the toxicity of indoxacarb in Drosophila melanogaster. This work revealed that upregulation of UGT genes significantly contributes to indoxacarb resistance in S. litura, and is of great significance for the development of integrated and sustainable management strategies for resistant pests in the field.

Over-expression of UDP-glycosyltransferase UGT353G2 confers resistance to neonicotinoids in whitefly (Bemisia tabaci)

The whitefly, Bemisia tabaci, comes up high metabolic resistance to most neonicotinoids in long-term evolution, which is the key problem of pest control. UGT glycosyltransferase, as a secondary detoxification enzyme, plays an indispensable role in detoxification metabolism. In this study, UGT inhibitors, 5-nitrouracil and sulfinpyrazone, dramatically augmented the toxic damage of neonicotinoids to B. tabaci. A UGT named UGT353G2 was identified in whitefly, which was notably up-regulated in resistant strain (3.92 folds), and could be induced by most neonicotinoids. Additionally, the using of RNA interference (RNAi) suppresses UGT353G2 substantially increased sensitivity to neonicotinoids in resistant strain. Our results support that UGT353G2 may be involved in the neonicotinoids resistance of whitefly. These findings will help further verify the functional role of UGTs in neonicotinoid resistance.

Inducible Cytochrome P450s in the Fat Body and Malpighian Tubules of the Polyphagous Pests of Spodoptera litura Confer Xenobiotic Tolerance

Cytochrome P450 plays vital roles in detoxifying xenobiotics. In this study, SlCYP340A and SlCYP340L expression in the Spodoptera litura fat body and SlCYP332A1, SlCYP6AB12, SlCYP6AB58, SlCYP6AB59, and SlCYP6AN4 expression in the Malpighian tubules were significantly upregulated after cyantraniliprole exposure, and SlCYP6AB58 and SlCYP6AB59 expression levels were simultaneously increased in the Malpighian tubules after gossypol treatment. Drosophila ectopically expressing candidate P450 genes showed that SlCYP332A1, SlCYP6AB12, SlCYP6AB59, SlCYP6AN4, and SlCYP340A conferred cyantraniliprole tolerance. The overexpression of SlCYP6AB58 and SlCYP6AB59 in Drosophila increased the number of eggs laid under the gossypol treatment. Moreover, the knockdown of SlCYP332A1, SlCYP6AB12, SlCYP6AB59, SlCYP6AN4, and SlCYP340A increased S. litura mortality under the cyantraniliprole treatment. Homology modeling and molecular docking results suggested that candidate P450 has the potential to bind with cyantraniliprole. These results indicate that the CYP3 and CYP4 genes participate in cyantraniliprole detoxification and that SlCYP6AB59 may be simultaneously involved in the gossypol tolerance of S. litura.

Overexpression of the UDP-glycosyltransferase UGT34A23 confers resistance to the diamide insecticide chlorantraniliprole in the tomato leafminer, Tuta absoluta

The tomato leafminer, Tuta absoluta, is an invasive crop pest that has evolved resistance to many of the insecticides used for its control. To facilitate the investigation of the underpinning mechanisms of resistance in this species we generated a contiguous genome assembly using long-read sequencing data. We leveraged this genomic resource to investigate the genetic basis of resistance to the diamide insecticide chlorantraniliprole in Spanish strains of T. absoluta that exhibit high levels of resistance to this insecticide. Transcriptomic analyses revealed that, in these strains, resistance is not associated with previously reported target-site mutations in the diamide target-site, the ryanodine receptor, but rather is associated with the marked overexpression (20- to >100-fold) of a gene encoding a UDP-glycosyltransferase (UGT). Functional expression of this UGT, UGT34A23, via ectopic expression in Drosophila melanogaster demonstrated that it confers strong and significant resistance in vivo. The genomic resources generated in this study provide a powerful resource for further research on T. absoluta. Our findings on the mechanisms underpinning resistance to chlorantraniliprole will inform the development of sustainable management strategies for this important pest.

Expression profile of the entire detoxification gene inventory of the western honeybee, Apis mellifera across life stages

The western honeybee, Apis mellifera, is a managed pollinator of many crops and potentially exposed to a wide range of foreign compounds, including pesticides throughout its life cycle. Honeybees as well as other insects recruit molecular defense mechanisms to facilitate the detoxification of xenobiotic compounds. The inventory of detoxification genes (DETOXome) is comprised of five protein superfamilies: cytochrome P450 monooxygenases (P450), carboxylesterases, glutathione S-transferases (GST), UDP-glycosyl transferases (UGT) and ATP-binding cassette (ABC) transporters. Here we characterized the gene expression profile of the entire honeybee DETOXome by analyzing 47 transcriptomes across the honeybee life cycle, including different larval instars, pupae, and adults. All life stages were well separated by principal component analysis, and K-means clustering revealed distinct temporal patterns of gene expression. Indeed, >50% of the honeybee detoxification gene inventory is found in one cluster and follows strikingly similar expression profiles, i.e., increased expression during larval development, followed by a sharp decline after pupation and a steep increase again in adults. This cluster includes 29 P450 genes dominated by CYP3 and CYP4 clan members, 15 ABC transporter genes mostly belonging to the ABCC subfamily and 13 carboxylesterase genes including almost all members involved in dietary/detox and hormone/semiochemical processing. RT-qPCR analysis of selected detoxification genes from all families revealed high expression levels in various tissues, especially Malpighian tubules, fatbody and midgut, supporting the view that these tissues are essential for metabolic clearance of environmental toxins and pollutants in honeybees. Our study is meant to spark further research on the molecular basis of detoxification in this critical pollinator to better understand and evaluate negative impacts from potentially toxic substances. Additionally, the entire gene set of 47 transcriptomes collected and analyzed provides a valuable resource for future honeybee research across different disciplines.

The molecular mechanisms of insecticide resistance in aphid crop pests

Aphids are a group of hemipteran insects that include some of the world's most economically important agricultural pests. The control of pest aphids has relied heavily on the use of chemical insecticides, however, the evolution of resistance poses a serious threat to their sustainable control. Over 1000 cases of resistance have now been documented for aphids involving a remarkable diversity of mechanisms that, individually or in combination, allow the toxic effect of insecticides to be avoided or overcome. In addition to its applied importance as a growing threat to human food security, insecticide resistance in aphids also offers an exceptional opportunity to study evolution under strong selection and gain insight into the genetic variation fuelling rapid adaptation. In this review we summarise the biochemical and molecular mechanisms underlying resistance in the most economically important aphid pests worldwide and the insights study of this topic has provided on the genomic architecture of adaptive traits.

Efficacy of Oil and Photosensitizer against Frankliniella occidentalis in Greenhouse Sweet Pepper

Many common insect pests have developed resistance against the pesticides currently available, to the point where pest and disease management has become extremely difficult and expensive, increasing pressure on agriculture and food production. There is an urgent need to explore and utilize alternatives. Due to their unique mode of action, photosensitizers may be able to control insect pests effectively, especially in combination with oil-based products, without the risk of resistance build-up. In this study, the efficacy of a mineral oil-based horticultural spray oil, PureSpray™ Green (PSG), and a sodium magnesium chlorophyllin photosensitizer formulation, SUN-D-06 PS, were evaluated and compared to a registered cyantraniliprole insecticide (as positive control) and a negative control against western flower thrips (WFT), Frankliniella occidentalis. In detached leaf ingestion assays, PSG at high concentration was more effective than low concentration, causing >70% WFT mortality, whilst SUN-D-06 PS + PSG caused higher mortality than cyantraniliprole after five days of feeding. The same combination was as effective as cyantraniliprole in the contact assay. In greenhouse pepper, the photosensitizer decreased the WFT more than mineral oil applied alone, whilst a combination treatment of SUN-D-06 PS + PSG was most effective, decreasing the WFT population to fewer than four WFT per plant. SUN-D-06 PS + PSG shows promise as a sustainable, economical way of controlling WFT, with the potential to be incorporated into existing integrated pest (and disease) management (IPM) programs with ease.

A novel V263I mutation in the glutamate-gated chloride channel of Plutella xylostella (L.) confers a high level of resistance to abamectin

The frequent and extensive use of insecticides leads to the evolution of insecticide resistance, which has become one of the constraints on global agricultural production. Avermectins are microbial-derived insecticides that target a wide number of insect pests, including the diamondback moth Plutella xylostella, an important global pest of brassicaceous vegetables. However, field populations of P. xylostella have evolved serious resistance to avermectins, including abamectin, thereby threatening the efficiency of these insecticides. In this study, a novel valine to isoleucine mutation (V263I) was identified in the glutamate-gated chloride channel (GluCl) of field P. xylostella populations, which showed different levels of resistance to abamectin. Electrophysiological analysis revealed that the V263I mutation significantly reduced the sensitivity of PxGluCl to abamectin by 6.9-fold. Genome-modified Drosophila melanogaster carrying the V263I mutation exhibited 27.1-fold resistance to abamectin. Then, a knockin strain (V263I-KI) of P. xylostella expressing the homozygous V263I mutation was successfully constructed using the CRISPR/Cas9. The V263I-KI had high resistance to abamectin (106.3-fold), but significantly reduced fecundity. In this study, the function of V263I mutation in PxGluCl was verified for the first time. These findings provide a more comprehensive understanding of abamectin resistance mechanisms and lay the foundation for providing a new molecular detection method for abamectin resistance monitoring.

Identification and characterization of UDP-glycosyltransferase genes and the potential role in response to insecticides exposure in Bactrocera dorsalis

BACKGROUND

The oriental fruit fly, Bactrocera dorsalis (Hendel) is a worldwide pest damaging a wide range of hosts. Due to the long-term indiscriminate use of insecticides, B. dorsalis has developed serious resistance to several insecticides. UDP-glycosyltransferases (UGTs) are secondary metabolic enzymes involved in biotransformation and play an important role in the metabolism of plant secondary metabolites and synthetic insecticides in insects. Thus, we suspect that UGTs in B. dorsalis play an important role in insecticide tolerance.

RESULTS

In this study, 31 UGT genes were identified in the genome of B. dorsalis, belonging to 13 subfamilies. Real-time quantitative polymerase chain reaction (RT-qPCR) results revealed that 12 UGT genes were highly expressed in the antennae, midgut, Malpighian tubule and fat body. The mRNA expressions of 17 UGT genes were up-regulated upon exposure to λ-cyhalothrin, imidacloprid, abamectin and chlorpyrifos. Knockdown of the selected five UGT genes (BdUGT301D2, BdUGT35F2, BdUGT36K2, BdUGT49D2, BdUGT50B5) by RNA interference increased the mortality of B. dorsalis from 9.29% to 27.22% upon exposure to four insecticides.

CONCLUSION

The abundance of UGTs in B. dorsalis is similar to other insect species, and 12 out of 31 UGTs were specifically expressed in metabolic tissues, suggesting a key role in detoxification. Down-regulation of five selected UGT genes increased the susceptibility of B. dorsalis to various insecticides, indicating that UGTs may play an important role in tolerance of B. dorsalis to multiple insecticides. © 2022 Society of Chemical Industry.

Dynamic changes in species richness and community diversity of symbiotic bacteria in five reproductive morphs of cotton aphid Aphis gossypii Glover (Hemiptera: Aphididae)

Introduction

Reproductive polymorphism and symbiotic bacteria are commonly observed in aphids, but their interaction remains largely unclear. In polymorphic aphid species (Aphis gossypii), offspring of parthenogenetic females (PFs) develops into sexuparae which produces gynoparae and males successively. Gynoparae further produces sexual females (SFs), and these sexual females mate with males to produce offspring.

Methods

In this study, we investigated the dynamic changes of symbiotic bacteria during the above-mentioned five reproductive morph switch in A. gossypii via 16S rRNA sequencing technology.

Results

The results showed that species richness and community diversity of symbiotic bacteria in males were the highest. Proteobacteria was absolutely dominant bacterial phylum (with relative abundance of more than 90%) in the five reproductive morphs of A. gossypii, and Buchnera was absolutely dominant genus (with relative abundance of >90%), followed by Rhodococcus, Pseudomonas, and Pantoea. Male-killing symbiont Arsenophonus presented the highest relative abundance in gynoparae, a specific morph whose offsprings were exclusively sexual females. Both principal component analysis (PCA) and clustering analysis showed trans-generation similarity in microbial community structure between sexuparae and sexual females, between PFs and gynoparae. PICRUSt 2 analysis showed that symbiotic bacteria in the five reproductive morphs were mainly enriched in metabolic pathways.

Discussion

Reproductive morph switch induced by environmental changes might be associated with bacterial community variation and sexual polymorphism of aphids. This study provides a new perspective for further deciphering the interactions between microbes and reproductive polymorphism in host aphids.

Functional Validation of the Roles of Cytochrome P450s in Tolerance to Thiamethoxam and Imidacloprid in a Field Population of Aphis gossypii

Field populations of Aphis gossypii (SDR) have evolved high resistance to neonicotinoids, including thiamethoxam and imidacloprid. Synergism bioassays and transcriptomic comparison of the SDR and susceptible (SS) strains revealed that the cytochrome P450s may contribute to the neonicotinoid resistance evolution. The transcripts of some P450s were constitutively overexpressed in the SDR strain, and many genes showed expression plasticity under insecticide exposure. Drosophila that ectopically expressed CYPC6Y9, CYP4CK1, CYP6DB1, and CYP6CZ1 showed greater resistance (>8.0-fold) to thiamethoxam, and Drosophila that expressed CYPC6Y9, CYP6CY22, CYP6CY18, and CYP6D subfamily genes showed greater resistance (>5-fold) to imidacloprid. Five P450 genes that caused thiamethoxam resistance also conferred resistance to α-cypermethrin. Furthermore, the knockdown of CYP4CK1, CYP6CY9, CYP6CY18, CYPC6Y22, CYP6CZ1, and CYP6DB1 dramatically increased the sensitivity of the SDR strain to thiamethoxam or imidacloprid. These results indicate the involvement of multiple P450 genes, rather than one key gene, in neonicotinoid resistance in field populations.

Functional characterization of ABC transporters mediates multiple neonicotinoid resistance in a field population of Aphis gossypii Glover

The ATP-binding cassette (ABC) transporters C and G subfamilies have been reported to be involved in insecticide detoxification, with most studies showing increased gene transcript levels in response to insecticide exposure. Our previous studies have suggested that ABCC and G transporters participate in cyantraniliprole and thiamethoxam resistance of Aphis gossypii. In this study, we focused on the potential roles of the ABCC and G transporters of an A. gossypii field population (SDR) in neonicotinoid detoxification. The results of leaf dip bioassays showed 629.17- and 346.82-fold greater resistance to thiamethoxam and imidacloprid in the SDR strain, respectively, than in the susceptible strain (SS). Verapamil, an ABC inhibitor, was used for synergism bioassays, and the results showed synergistic effects with thiamethoxam, with synergistic ratios (SRs) of 2.07 and 6.68 in the SS and SDR strains, respectively. In addition to thiamethoxam, verapamil increased imidacloprid toxicity by 1.68- and 1.62-fold in the SS and SDR strains respectively. Then, the expression levels of several ABCC and G transporters were analyzed in different treatments. We found that the transcript levels of AgABCG4, AgABCG17, AgABCG26, AgMRP8 and AgMRP12 were higher in the SDR strain than in the SS strain. The mRNA expression of AgABCG4, AgABCG7, AgABCG13, AgABCG17, AgABCG26, AgMRP8 and AgMRP12 in the SDR strain was increased after thiamethoxam and imidacloprid exposure. The results of transgenic Drosophila melanogaster bioassays suggested that overexpression of AgABCG4, AgABCG7, AgABCG13, AgABCG17, AgABCG26, AgMRP8 and AgMRP12 in transgenic flies was sufficient to confer thiamethoxam and imidacloprid resistance, and AgABCG4, AgABCG7, AgABCG13, AgABCG26 and AgMRP12 may be related to α-cypermethrin cross-resistance with weak effects. In addition, the knockdown of AgABCG4, AgABCG13, AgABCG26, AgMRP8 and AgMRP12, and the knockdown of AgABCG7 and AgABCG26 increased thiamethoxam and imidacloprid mortality in the SDR strain, respectively. Our results suggest that changes in the expression levels of ABCC and G transporters may contribute to neonicotinoid detoxification in the SDR strain, and provide a foundation for clarify the potential roles of ABCC and G transporters in insecticide resistance.

Cytochrome P450 Gene, CYP6CX3, Is Involved in the Resistance to Cyantraniliprole in Bemisia tabaci

Bemisia tabaci is an important agricultural sucking pest, and it develops serious resistance to various insecticides. Although cytochrome P450 was involved in the resistance to cyantraniliprole, limited studies have been conducted on B. tabaci. In the present study, piperonyl butoxide significantly increased the toxicity of cyantraniliprole. P450 activities in two resistant populations were 1.97- and 2.17-fold higher than that in the susceptible population. Among 79 P450 genes, CYP6CX3 expressions in two resistant populations were 3.08- and 3.67-fold higher than that in the susceptible population. When CYP6CX3 was knocked down, the toxicity of cyantraniliprole increased significantly. The LC₅₀ value of cyantraniliprole to the Drosophila melanogaster line overexpressing B. tabaci CYP6CX3 increased 7.34-fold. The content of cyantraniliprole was decreased by 25.74 ± 4.27% after mixing with CYP6CX3 and CPR for 2 h. These results suggested that the overexpression of CYP6CX3 was likely involved in the resistance to cyantraniliprole in B. tabaci.

Overexpression of Multiple Cytochrome P450 Genes Conferring Clothianidin Resistance in Bradysia odoriphaga

Cytochrome P450 monooxygenases (P450s) play important roles in the detoxification metabolism of xenobiotics and are involved in the resistance of insects to many insecticides. In this study, piperonyl butoxide (PBO), an inhibitor of P450 enzyme activity, significantly increased the toxicity of clothianidin in the clothianidin-resistant (CL-R) population of Bradysia odoriphaga. The enzyme activity of P450 in the CL-R population was significantly higher than that in the SS population. Furthermore, four P450 genes were found to be significantly overexpressed in the CL-R population. Tissue-specific expression analysis indicates that CYP9J57, CYP3828A1, CYP6SX1, and CYP6QE1 were most highly expressed in the midgut and/or Malpighian tubules. After exposure to LC₃₀ of clothianidin, the expression levels of the four P450 genes were significantly upregulated. The RNAi-mediated knockdown of CYP9J57, CYP3828A1, and CYP6QE1 significantly increased the susceptibility of B. odoriphaga to clothianidin. These results suggest that P450 genes are involved in clothianidin resistance in B. odoriphaga. This provides a better understanding of P450-mediated clothianidin resistance in B. odoriphaga and will contribute to the management of insect resistance to insecticides.

Chemosensory proteins confer adaptation to the ryanoid anthranilic diamide insecticide cyantraniliprole in Aphis gossypii glover

Chemosensory proteins (CSPs) are a class of small transporter proteins expressed only in arthropods with various functions beyond chemoreception. Previous studies have been reported that CSPs are involved in the insecticide resistance. In this study, we found that AgoCSP1, AgoCSP4, and AgoCSP5 were constitutively overexpressed in an insecticide-resistant strain of Aphis gossypii and showed higher expression in broad body tissue (including fat bodies) than in the midgut but without tissue specificity. However, the function of these three upregulated AgoCSPs remains unknown. Here, we investigated the function of AgoCSPs in resistance to the diamide insecticide cyantraniliprole. Suppression of AgoCSP1, AgoCSP4 and AgoCSP5 transcription by RNAi significantly increased the sensitivity of resistant aphids to cyantraniliprole. Molecular docking and competitive binding assays indicated that these AgoCSPs bind moderate with cyantraniliprole. Transgenic Drosophila melanogaster expressing these AgoCSPs in the broad body or midgut showed higher tolerance to cyantraniliprole than control flies with the same genetic background; AgoCSP4 was more effective in broad body tissue, and AgoCSP1 and AgoCSP5 were more effective in the midgut, indicating that broad body and midgut tissues may be involved in the insecticide resistance mediated by the AgoCSPs examined. The present results strongly indicate that AgoCSPs participate in xenobiotic detoxification by sequestering and masking toxic insecticide molecules, providing insights into new factors involved in resistance development in A. gossypii.

Functional analysis of cyantraniliprole tolerance ability mediated by ATP-binding cassette transporters in Aphis gossypii glover

Cyantraniliprole, a second-generation anthranilic diamide insecticide, is widely used to control chewing and sucking pests. ATP-binding cassette transporters (ABCs) are a ubiquitous family of membrane proteins that play important roles in insect detoxification mechanisms. However, the potential effects of ABCs on cyantraniliprole-resistance remain unclear. In the present study, synergism bioassays revealed that verapamil, an ABC inhibitor, increased the toxicity of cyantraniliprole by 2.00- and 12.25-fold in the susceptible and cyantraniliprole-resistant strains of Aphis gossypii. Based on transcriptome data, the expression levels of ABCB4, ABCB5, ABCD1, ABCG4, ABCG7, ABCG13, ABCG16, ABCG17, ABCG26 and MRP12 were upregulated 1.56-, 1.32-, 1.51-, 2.03-, 1.65-, 1.50-, 4.18-, 6.07-, 4.68- and 4.69-fold, respectively, in the cyantraniliprole-resistant strain (CyR) compared to the susceptible strain (SS), as determined using RT-qPCR. Drosophila melanogaster ectopically overexpressing ABCB5, ABCG4, ABCG7, ABCG16, ABCG17, ABCG26 and MRP12 exhibited significantly increased tolerance to cyantraniliprole by 11.71-, 2.39-, 4.85-, 2.06-, 3.75-, 4.20- and 3.50-fold, respectively, with ABCB5 and ABCG family members being the most effective. Furthermore, the suppression of ABCB5, ABCG4, ABCG7, ABCG16, ABCG17, ABCG26 and MRP12 significantly increased the sensitivity of the CyR strain to cyantraniliprole. These results indicate that ABCs may play crucial roles in cyantraniliprole resistance and may provide information for shaping resistance management strategies.

Functional investigation of lncRNAs and target cytochrome P450 genes related to spirotetramat resistance in Aphis gossypii Glover

BACKGROUND

Spirotetramat is a tetramic acid derivative insecticide with novel modes of action for controlling Aphis gossypii Glover in the field. Previous studies have shown that long noncoding RNAs (lncRNAs) and cytochrome P450 monooxygenases (P450s) are involved in the detoxification process. However, the functions of lncRNAs in regulating P450 gene expression in spirotetramat resistance in A. gossypii are unknown.

RESULTS

In this study, we found CYP4CJ1, CYP6CY7 and CYP6CY21 expression levels to be significantly upregulated in a spirotetramat-resistant (SR) strain compared with a susceptible (SS) strain. Furthermore, knockdown of CYP4CJ1, CYP6CY7 and CYP6CY21 increased nymph and adult mortality in the SR strain following exposure to spirotetramat. Drosophila ectopically expressing CYP380C6, CYP4CJ1, CYP6DA2, CYP6CY7 and CYP6CY21 showed significantly decreased mortality after spirotetramat exposure, and CYP380C6, CYP4CJ1 and CYP6CY21 are putative targets of six lncRNAs. Silencing of lncRNAs MSTRG.36649.2/5 and MSTRG.71880.1 changed CYP6CY21 and CYP380C6 expression, altering the sensitivity of the SR strain to spirotetramat. Moreover, MSTRG.36649.2/5 did not compete for microRNA (miRNA) binding to regulate CYP6CY21 expression.

CONCLUSION

Our results confirm that CYP380C6, CYP4CJ1, CYP6DA2, CYP6CY7 and CYP6CY21 are potentially involved in the development of spirotetramat resistance in A. gossypii, and MSTRG.36649.2/5 and MSTRG.71880.1 probably regulate CYP6CY21 and CYP380C6 expression other than through the "sponge effect" of competing for miRNA binding. Our results provide a favorable molecular basis for studying cotton aphid P450 genes and lncRNA functions in spirotetramat resistance development.

Overexpression of UDP-glucuronosyltransferase and cytochrome P450 enzymes confers resistance to sulfoxaflor in field populations of the aphid, Myzus persicae

The green peach aphid, Myzus persicae, is a highly damaging, globally distributed crop pest that has evolved multiple resistance to numerous insecticides. It is thus imperative that insecticides that are not strongly compromised by pre-existing resistance are carefully managed to maximise their effective life span. Sulfoxaflor is a sulfoximine insecticide that retains efficacy against M. persicae clones that exhibit resistance to older insecticides. In the current study we monitored the efficacy of sulfoxaflor against M. persicae populations collected in Western Australia, following reports of control failures in this region. We identified clones with low (4-23-fold across multiple independent bioassay experiments), but significant, levels of resistance to sulfoxaflor compared with a reference susceptible clone. Furthermore, we demonstrate that sulfoxaflor resistance can persist after many months of culturing in the laboratory in the absence of insecticide exposure. Resistance was not conferred by known mechanisms of resistance to neonicotinoid insecticides, that act on the same target-site as sulfoxaflor, i.e. the R81T mutation or overexpresssion of the P450 gene CYP6CY3. Rather, transcriptome profiling of multiple resistant and susceptible clones identified the P450 CYP380C40 and the UDP-glucuronosyltransferase UGT344P2 as highly overexpressed (21-76-fold and 6-33-fold respectively) in the resistant clones. Transgenic expression of these genes demonstrated that they confer, low, but significant, levels of resistance to sulfoxaflor in vivo. Taken together, our data reveal the presence of low-level resistance to sulfoxaflor in M. persicae populations in Australia and uncover two novel mechanisms conferring resistance to this compound. The findings and tools generated in this study provide a platform for the development of strategies that aim to slow, prevent or overcome the evolution of more potent resistance to sulfoxaflor.

Chemosensory Proteins Are Associated with Thiamethoxam and Spirotetramat Tolerance in Aphis gossypii Glover

Chemosensory proteins (CSPs) are a class of transporters in arthropods. Deeper research on CSPs showed that CSPs may be involved in some physiological processes beyond chemoreception, such as insect resistance to pesticides. We identified two upregulated CSPs in two resistant strains of Aphis gossypii Glover. To understand their role in the resistance of aphids to pesticides, we performed the functional verification of CSP1 and CSP4 in vivo and in vitro. Results showed that the sensitivity of the thiamethoxam-resistant strain to thiamethoxam increased significantly with the silencing of CSP1 and CSP4 by RNAi (RNA interference), and the sensitivity of the spirotetramat-resistant strain to spirotetramat increased significantly with the silencing of CSP4. Transgenic Drosophila melanogaster expressing CSPs exhibited stronger resistance to thiamethoxam, spirotetramat, and alpha-cypermethrin than the control did. In the bioassay of transgenic Drosophila, CSPs showed different tolerance mechanisms for different pesticides, and the overexpressed CSPs may play a role in processes other than resistance to pesticides. In brief, the present results prove that CSPs are related to the resistance of cotton aphids to insecticides.