Transcriptome profiling and functional analysis suggest that the constitutive overexpression of four cytochrome P450s confers resistance to abamectin in Tetranychus urticae from China

Expression reduction and a variant of a P450 gene mediate chlorpyrifos resistance in Tetranychus urticae Koch

INTRODUCTION

Understanding how insects and mites develop resistance to chlorpyrifos is crucial for effective field management. Although extensive research has demonstrated that T. urticae exhibits high resistance to chlorpyrifos, the specific resistance mechanism remains elusive. Investigating this mechanism could provide valuable insights for pest control strategies.

OBJECTIVES

This study aimed to reveal the mechanism of chlorpyrifos resistance in T. urticae.

METHODS

The expression level of the CYP392D8 gene in T. urticae strains were analyzed using real- time quantitative PCR and western blot techniques. Functional validation of CYP392D8 was conducted through RNAi and heterogeneous expression. The production of chlorpyrifos-oxon in both resistant and susceptible strains were quantified using LC-MS/MS. Furthermore, the metabolic capabilities of CYP392D8 variants were verified using HPLC-MS and molecular docking.

RESULTS

The results showed the expression of CYP392D8 was reduced in some Chinese resistant populations and mites with knocked down CYP392D8 showed decreased susceptibility to chlorpyrifos. Chlorpyrifos-oxon, the active metabolite of chlorpyrifos, was generated when chlorpyrifos was incubated with recombinant CYP392D8 protein in vitro. And a higher efficiency of chlorpyrifos-oxon formation was observed with the CYP392D8-S variant from susceptible mites compared to the CYP392D8-R variant from resistant mites. After treatment with low doses of chlorpyrifos, susceptible mite extracts produced substantial amounts of chlorpyrifos-oxon, while resistant mites only showed trace amounts. In addition, molecular docking studies showed that CYP392D8-S had a higher binding capacity to chlorpyrifos than the CYP392D8-R variant.

CONCLUSION

This study reveals a mechanism of insecticide resistance due to the bioactivation reduction in combination with the sequence variation in a pest mite. These findings provide an important theoretical bias for management strategies of mites in the field and comprehensive control.

The cytochrome P450 subfamilies CYP392A and CYP392D are key players in acaricide metabolism in Tetranychusurticae

The spider mite Tetranychus urticae is a major agricultural pest with a global distribution, extremely diverse host range and a remarkable ability to develop resistance to a wide variety of acaricides. P450 mono-oxygenases have been frequently associated with resistance development in this species. In particular enzymes of the CYP392A-subfamily were shown to metabolize a number of key acaricides, including abamectin, amitraz, fenpyroximate and the active metabolite of pyflubumide. However, transcriptomic studies comparing highly resistant and susceptible populations have often revealed high expression of members of the CYP392D-subfamily, but these have been only poorly studied. Here, we conducted a meta-analysis of gene expression data of 20 populations and identified two key enzymes of this family, CYP392D2 and CYP392D8, whose expression is associated with resistance. We subsequently functionally expressed these enzymes, together with CYP392A11 and CYP392A16 as known metabolizers, and compared their potential to accept a wide diversity of acaricides as substrate. This study overall confirms previous discovered substrates for CYP392A11 and CYP392A16, but also reveals unreported metabolic activity towards new acaricides. These include carbaryl, chlorpyrifos and etoxazole for CYP392A16 and carbaryl, chlorpyrifos and NNI-0711-NH pyflubumide for CYP392A11. For the newly studied CYP392D-family, we show that CYP392D2 metabolizes pyridaben, fenpyroximate, etoxazole and chlorpyrifos, while CYP392D8 metabolizes carbaryl, fenazaquin and tebufenpyrad. Last, we observed that both CYP392A- and CYP392D-subfamily enzymes activate chlorpyrifos to its corresponding oxon. Our study indicates that there is both overlap and specificity in the activity of A- and D-subfamily enzymes against acaricides and model substrates. With the recent advent of highly efficient CRISPR/Cas9 gene editing protocols in T. urticae, the way is now paved to conduct further genetic experiments revealing and quantifying the role of these enzymes in the resistance phenotype in field populations.

Cross-resistance, inheritance and biochemical mechanism of abamectin resistance in a field-derived strain of the citrus red mite, Panonychus citri (Acari: Tetranychidae)

BACKGROUND

The citrus red mite, Panonychus citri (McGregor), a global pest of citrus, has developed different levels of resistance to various acaricides in the field. Abamectin is one of the most important insecticides/acaricides worldwide, targetting a wide number of insect and mite pests. The evolution of abamectin resistance in P. citri is threatening the sustainable use of abamectin for mite control.

RESULTS

The abamectin resistant strain (NN-Aba), derived from a field strain NN by consistent selection with abamectin, showed 4279-fold resistance to abamectin compared to a relatively susceptible strain (SS) of P. citri. Cross-resistance of NN-Aba was observed between abamectin and emamectin benzoate, pyridaben, fenpropathrin and cyflumetofen. Inheritance analyses indicated that abamectin resistance in the NN-Aba strain was autosomal, incompletely recessive and polygenic. The synergy experiment showed that abamectin toxicity was synergized by piperonyl butoxide (PBO), diethyl maleate (DEM) and tributyl phosphorotrithiotate (TPP) in the NN-Aba strain, and synergy ratios were 2.72-, 2.48- and 2.13-fold, respectively. The glutathione-S-transferases activity in the NN-Aba strain were significantly increased by 2.08-fold compared with the SS strain.

CONCLUSION

The abamectin resistance was autosomal, incompletely recessive and polygenic in P. citri. The NN-Aba strain showed cross-resistance to various acaricides with different modes of action. Metabolic detoxification mechanism participated in abamectin resistance in NN-Aba strain. These findings provide useful information for resistance management of P. citri in the field. © 2023 Society of Chemical Industry.

Contrasting roles of cytochrome P450s in amitraz and chlorfenapyr resistance in the crop pest Tetranychus urticae

The molecular mechanisms of amitraz and chlorfenapyr resistance remain only poorly understood for major agricultural pests and vectors of human diseases. This study focusses on a multi-resistant field strain of the crop pest Tetranychus urticae, which could be readily selected in the laboratory to high levels of amitraz and chlorfenapyr resistance. Toxicity experiments using tralopyril, the active toxophore of chlorfenapyr, suggested decreased activation as a likely mechanism underlying resistance. Starting from the same parental strain, transcriptome profiling revealed that a cluster of detoxifying genes was upregulated after amitraz selection, but unexpectedly downregulated after chlorfenapyr selection. Further functional validation associated the upregulation of CYP392A16 with amitraz metabolism and the downregulation of CYP392D8 with reduced activation of chlorfenapyr to tralopyril. Genetic mapping (QTL analysis by BSA) was conducted in an attempt to unravel the genetic mechanisms of expression variation and resistance. This revealed that chlorfenapyr resistance was associated with a single QTL, while 3 QTLs were uncovered for amitraz resistance. Together with the observed contrasting gene expression patterns, we argue that transcriptional regulators most likely underly the distinct expression profiles associated with resistance, but these await further functional validation.

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.

GARP: A family of glycine and alanine-rich proteins that helps spider mites feed on plants

Spider mites (Tetranychidae) are destructive agricultural pests which have evolved strategies to overcome plant defenses, such as the ability to puncture the leaves of their hosts to feed. The expression of many genes with unknown functions is altered during feeding, but little is known about the role of these genes in plant-mite interactions. Here, we identified 3 novel gene families through analysis of genomic and transcriptomic data from 3 spider mite species. These GARP family genes encode glycine and alanine-rich proteins; they are present in mites (Acariformes) but absent in ticks (Parasitiformes) in the subclass Acari, indicating that these genes have undergone a significant expansion in spider mites and thus play important adaptive roles. Transcriptomic analysis revealed that the expression of GARP genes is strongly correlated with feeding and the transfer to new hosts. We used RNA interference to silence GARP1d in the two-spotted spider mite Tetranychus urticae, which inhibited feeding and egg laying and significantly increased mortality when the mites were transferred to soybean shoots; a similar effect was observed after TuVATPase was silenced. However, no changes in mite mortality were observed after TuGARP1d-silenced mites were placed on an artificial diet, which was different from the effect of TuVATPase silencing. Our results indicate that GARP family members play important roles in mite-plant interactions. Additional studies are needed to clarify the mechanisms underlying these interactions.

Assessment of the role of an ABCC transporter TuMRP1 in the toxicity of abamectin to Tetranychus urticae

The rapid evolution of pest resistance threatens the sustainable utilization of bioinsecticides such as abamectin, and so deciphering the molecular mechanisms affecting toxicity and resistance is essential for their long-term application. Historical studies of abamectin resistance in arthropods have mainly focused on mechanisms involving the glutamate-gated chloride channel (GluCl) targets, with the role of metabolic processes less clear. The two-spotted spider mite, Tetranychus urticae, is a generalist herbivore notorious for rapidly developing resistance to pesticides worldwide, and abamectin has been widely used for its control in the field. After reanalyzing previous transcriptome and RNA-seq data, we here identified an ABC transporter subfamily C gene in T. urticae named multidrug resistance-associated protein 1 (TuMRP1), whose expression differed between susceptible and resistant populations. Synergism bioassays with the inhibitor MK-571, the existence of a genetic association between TuMRP1 expression and susceptibility to abamectin, and the effect of RNA interference mediated silencing of TuMRP1 were all consistent with a direct role of this transporter protein in the toxicity of abamectin. Although ABC transporters are often involved in removing insecticidal compounds from cells, our data suggest either an alternative role for these proteins in the mechanism of action of abamectin or highlight an indirect association between their expression and abamectin toxicity.

A review of the molecular mechanisms of acaricide resistance in mites and ticks

The Arachnida subclass of Acari comprises many harmful pests that threaten agriculture as well as animal health, including herbivorous spider mites, the bee parasite Varroa, the poultry mite Dermanyssus and several species of ticks. Especially in agriculture, acaricides are often used intensively to minimize the damage they inflict, promoting the development of resistance. Beneficial predatory mites used in biological control are also subjected to acaricide selection in the field. The development and use of new genetic and genomic tools such as genome and transcriptome sequencing, bulked segregant analysis (QTL mapping), and reverse genetics via RNAi or CRISPR/Cas9, have greatly increased our understanding of the molecular genetic mechanisms of resistance in Acari, especially in the spider mite Tetranychus urticae which emerged as a model species. These new techniques allowed to uncover and validate new resistance mutations in a larger range of species. In addition, they provided an impetus to start elucidating more challenging questions on mechanisms of gene regulation of detoxification associated with resistance.

Pharmacokinetic and pharmacodynamic considerations for treating sarcoptic mange with cross-relevance to Australian wildlife

Sarcoptes scabiei is the microscopic burrowing mite responsible for sarcoptic mange, which is reported in approximately 150 mammalian species. In Australia, sarcoptic mange affects a number of native and introduced wildlife species, is particularly severe in bare-nosed wombats (Vombatus ursinus) and an emerging issue in koala and quenda. There are a variety of acaricides available for the treatment of sarcoptic mange which are generally effective in eliminating mites from humans and animals in captivity. In wild populations, effective treatment is challenging, and concerns exist regarding safety, efficacy and the potential emergence of acaricide resistance. There are risks where acaricides are used intensively or inadequately, which could adversely affect treatment success rates as well as animal welfare. While reviews on epidemiology, treatment strategies, and pathogenesis of sarcoptic mange in wildlife are available, there is currently no review evaluating the use of specific acaricides in the context of their pharmacokinetic and pharmacodynamic properties, and subsequent likelihood of emerging drug resistance, particularly for Australian wildlife. This review critically evaluates acaricides that have been utilised to treat sarcoptic mange in wildlife, including dosage forms and routes, pharmacokinetics, mode of action and efficacy. We also highlight the reports of resistance of S. scabiei to acaricides, including clinical and in vitro observations.

Molecular Mechanisms Underlying Metabolic Resistance to Cyflumetofen and Bifenthrin in Tetranychus urticae Koch on Cowpea

Tetranychus urticae Koch (T. urticae) is one of the most tremendous herbivores due to its polyphagous characteristics, and is resistant to most acaricides. In this study, enzyme-linked immunosorbent assay (ELISA), transcriptome sequencing (RNA-seq) and quantitative real-time PCR (qRT-PCR) were carried out to analyze the mechanisms of T. urticae metabolic resistance to cyflumetofen and bifenthrin on cowpea. The enzyme activity of UDP-glucuronosyltransferases (UGTs) and carboxylesterases (CarEs) in the cyflumetofen-resistant (R_cfm) strain significantly decreased, while that of cytochrome P450 monooxygenases (P450s) significantly increased. Meanwhile, the activities of glutathione-S-transferases (GSTs), CarEs and P450s in the bifenthrin-resistant (R_bft) strain were significantly higher than those in the susceptible strain (Lab_SS). According to the Kyoto Encyclopedia of Genes and Genomes (KEGG) and Gene Ontology (GO) analyses, in the R_cfm mite strain, two carboxyl/cholinesterase (CCE) genes and two P450 genes were upregulated and one gene was downregulated, namely CYP392E7; in the R_bft mite strain, eleven CCE, nine UGT, two P450, four GST and three ABC genes were upregulated, while four CCE and three P450 genes were downregulated. Additionally, 94 differentially expressed genes (DEGs) were common to the two resistant groups. Specifically, TuCCE46 and TuCCE70 were upregulated in both resistant groups. Furthermore, the qRT-PCR validation data were consistent with those from the transcriptome sequencing analysis. Specifically, TuCCE46 (3.37-fold) was significantly upregulated in the R_cfm strain, while in the R_bft strain, TeturUGT22 (5.29-fold), teturUGT58p (1.74-fold), CYP392A11 (2.89-fold) and TuGSTd15 (5.12-fold) were significantly upregulated and TuCCE01 (0.13-fold) and CYP392A2p (0.07-fold) were significantly downregulated. Our study indicates that TuCCE46 might play the most important role in resistance to cyflumetofen, and TuCCE01, teturUGT58p, teturUGT22, CYP392A11, TuGSTd15, TuGSTm09 and TuABCG-13 were prominent in the resistance to bifenthrin. These findings provide further insight into the critical genes involved in the metabolic resistance of T. urticae to cyflumetofen and bifenthrin.

Biochemical and Molecular Analysis of Field Resistance to Spirodiclofen in Panonychus citri (McGregor)

Spirodiclofen is one of the most widely used acaricides in China. The citrus red mite, Panonychus citri (McGregor) (Acari: Tetranychidae), is one of the most destructive citrus pests worldwide and has developed a high resistance to spirodiclofen. However, the molecular mechanism of spirodiclofen resistance in P. citri is still unknown. In this study, we identified a field spirodiclofen-resistant strain (DL-SC) that showed 712-fold resistance to spirodiclofen by egg bioassay compared to the susceptible strain. Target-site resistance was not detected as non-synonymous mutations were not found by amplification and sequencing of the ACCase gene of resistant and susceptible strains; in addition, the mRNA expression levels of ACCase were similar in both resistant and susceptible strains. The activity of detoxifying enzymes P450s and CCEs in the resistant strain was significantly higher than in the susceptible strain. The transcriptome expression data showed 19 xenobiotic metabolisms genes that were upregulated. Stage-specific expression profiling revealed that the most prominent upregulated gene, CYP385C10, in transcriptome data was significantly higher in resistant strains in all stages. Furthermore, functional analysis by RNAi indicated that the mortality caused by spirodiclofen was significantly increased by silencing the P450 gene CYP385C10. The current results suggest that overexpression of the P450 gene, CYP385C10, may be involved in spirodiclofen resistance in P. citri.

The insecticidal effect of the botanical insecticide chlorogenic acid on Mythimna separata (Walker) is related to changes in MsCYP450 gene expression

The oriental armyworm Mythimna separata (Walker) (Lepidoptera: Noctuidae) can feed on the leaves of many crops, resulting in vast areas of damage and severe losses. Therefore, this insect has become a significant agricultural pest in north Asia. In this study, we fed 3^rd instar larvae with artificial diets containing different concentrations of chlorogenic acid and found a significant lethal effect and the mortality increased with increasing chlorogenic acid concentration. Next, we measured the sublethal effect of chlorogenic acid at LC₂₀ on the growth and development of M. separata larvae. The durations of the 4^th and 5^th instar were longer than those of the control group (prolonged by 0.8 and 0.6 days, respectively), and the 6^th instar was shorter (by 1.1 days). The total survival rate, pupation rate, eclosion rate, sex ratio, and oviposition amount in the LC₂₀ chlorogenic acid-treated group were significantly lower than those in the control group. Furthermore, transcriptome analysis of 3^rd instar larvae fed various concentrations of chlorogenic acid revealed that several MsCYP450 genes were significantly up-regulated, and this finding was further validated by qRT-PCR. In addition, various concentrations of chlorogenic acid and different treatment times significantly affected the enzyme activity of CYP450 in 3^rd instar larvae. Importantly, dietary ingestion of dsMsCYP450 significantly reduced the mRNA level of MsCYP450 genes and increased mortality in the presence of chlorogenic acid. Our results revealed that MsCYP6B6, MsCYP321A7, and MsCYP6B7-like play an essential role in the detoxification of chlorogenic acid by M. separata. This study provides evidence of control effect by botanical insecticide chlorogenic acid on M. separata, and potential detoxification mechanism mediated by P450 of botanical insecticide in arthropods.

Localized efficacy of environmental RNAi in Tetranychus urticae

Environmental RNAi has been developed as a tool for reverse genetics studies and is an emerging pest control strategy. The ability of environmental RNAi to efficiently down-regulate the expression of endogenous gene targets assumes efficient uptake of dsRNA and its processing. In addition, its efficiency can be augmented by the systemic spread of RNAi signals. Environmental RNAi is now a well-established tool for the manipulation of gene expression in the chelicerate acari, including the two-spotted spider mite, Tetranychus urticae. Here, we focused on eight single and ubiquitously-expressed genes encoding proteins with essential cellular functions. Application of dsRNAs that specifically target these genes led to whole mite body phenotypes—dark or spotless. These phenotypes were associated with a significant reduction of target gene expression, ranging from 20 to 50%, when assessed at the whole mite level. Histological analysis of mites treated with orally-delivered dsRNAs was used to investigate the spatial range of the effectiveness of environmental RNAi. Although macroscopic changes led to two groups of body phenotypes, silencing of target genes was associated with the distinct cellular phenotypes. We show that regardless of the target gene tested, cells that displayed histological changes were those that are in direct contact with the dsRNA-containing gut lumen, suggesting that the greatest efficiency of the orally-delivered dsRNAs is localized to gut tissues in T. urticae.

Frequencies and mechanisms of pesticide resistance in Tetranychus urticae field populations in China

The two-spotted spider mite Tetranychus urticate is an important agricultural pest worldwide. It is extremely polyphagous and has developed resistance to many pesticides. Here, we assessed the pesticide resistance of seven field populations of T. urticae in China, their target site mutations and the activities of their detoxification enzymes. The results showed that abamectin and the traditional pesticides pyridaben, profenofos and bifenthrin had higher resistance or lower toxicity than more recently developed pesticides including chlorfenapyr, spinetoram, cyflumetofen, cyenopyrafen, bifenazate and B-azolemiteacrylic. The frequency of point mutations related to abamectin resistance, G314D in the glutamate-gated chloride channel 1 (GluCl1) and G326E in GluCl3, ranged 47%-70% and 0%-97%, respectively. The frequency of point mutations in A1215D and F1538I of the voltage-gated sodium channel gene (VGSC), which may increase resistance to pyrethroids, ranged 88%-100% and 10%-100%, respectively. For target sites related to organophosphate resistance, mutation frequencies ranged 25%-92% for G119S and 0%-23% for A201S in the acetycholinesterase gene (Ace). Mutation G126S in the bifenazate resistance-related cytochrome b gene (Cytb) was observed in three of the seven T. urticae populations. Higher activities of detoxification enzymes (P450, GST, CarEs and UGTs) were observed in two T. urticae populations, with significant difference in the XY-SX population. These results provide useful information on the status of pesticide resistance of T. urticae in China and suggest that T. urticae field populations may have multiple resistance mechanisms.

Comparative analysis on transcriptomics of ivermectin resistant and susceptible strains of Haemonchus contortus

Background

Ivermectin (IVM) is one of the most important and widely used anthelmintics in veterinary medicine. However, its efficacy is increasingly compromised by widespread resistance, and the exact mechanism of IVM resistance remains unclear for most parasitic nematodes, including Haemonchus contortus, a blood-sucking parasitic nematode of small ruminants.

Methods

In this study, an H. contortus IVM-resistant strain from Zhaosu, Xinjiang, China, was isolated and assessed by the control test, faecal egg count reduction test (FECRT) and the larval development assay (LDA). Subsequently, comparative analyses on the transcriptomics of IVM-susceptible and IVM-resistant adult worms of this parasite were carried out using RNA sequencing (RNA-seq) and bioinformatics.

Results

In total, 543 (416 known, 127 novel) and 359 (309 known, 50 novel) differentially expressed genes (DEGs) were identified in male and female adult worms of the resistant strain compared with those of the susceptible strain, respectively. In addition to several previously known candidate genes which were supposed to be associated with IVM resistance and whose functions were involved in receptor activity, transport, and detoxification, we found some new potential target genes, including those related to lipid metabolism, structural constituent of cuticle, and important pathways such as antigen processing and presentation, lysosome, autophagy, apoptosis, and NOD1-like receptor signalling pathways. Finally, the results of quantitative real-time polymerase chain reaction confirmed that the transcriptional profiles of selected DEGs (male: 8 genes, female: 10 genes) were consistent with those obtained by the RNA-seq.

Conclusions

Our results indicate that IVM has multiple effects, including both neuromuscular and non-neuromuscular targets, and provide valuable information for further studies on the IVM resistance mechanism in H. contortus.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-022-05274-y.

Contribution of multiple overexpressed carboxylesterase genes to indoxacarb resistance in Spodoptera litura

BACKGROUND

As an important family of detoxification enzymes, carboxylesterases (CarEs) have important roles in the development of insecticide resistance in almost all agricultural pests. Previous studies have suggested that enhancement of CarE activity is an important mechanism mediating indoxacarb resistance in Spodoptera litura, and several CarE genes have been found to be overexpressed in indoxacarb-resistant strains. However, the functions of these CarE genes in indoxacarb resistance needs to be further investigated.

RESULTS

The synergist triphenyl phosphate effectively reduced the resistance of S. litura to indoxacarb, suggesting an involvement of CarEs in indoxacarb resistance. Among seven identified S. litura CarE genes (hereafter SlituCOE), six were overexpressed in two indoxacarb-resistant strains, but there were no significant differences in gene copy number. Knockdown of SlituCOE009 and SlituCOE050 enhanced indoxacarb sensitivity in both susceptible and resistant strains, whereas knockdown of SlituCOE090, SlituCOE093 and SlituCOE074 enhanced indoxacarb sensitivity in only the resistant strain. Knockdown of the sixth gene, SlituCOE073, did not have any effect. Furthermore, simultaneous knockdown of the five SlituCOE genes had a greater effect on increasing indoxacarb sensitivity than silencing them individually. By contrast, overexpression of the five SlituCOE genes individually in Drosophila melanogaster significantly decreased the toxicity of indoxacarb to transgenic fruit flies. Furthermore, modeling and docking analysis indicated that the catalytic pockets of SlituCOE009 and SlituCOE074 were ideally shaped for indoxacarb and N-decarbomethoxylated metabolite (DCJW), but the binding affinity for DCJW was stronger than for indoxacarb.

CONCLUSION

This study reveals that multiple overexpressed CarE genes are involved in indoxacarb resistance in S. litura.

Functionally characterized arthropod pest and pollinator cytochrome P450s associated with xenobiotic metabolism

The cytochrome P450 family (P450s) of arthropods includes diverse enzymes involved in endogenous essential physiological functions and in the oxidative metabolism of xenobiotics, insecticides and plant allelochemicals. P450s can also establish insecticide selectivity in bees and pollinators. Several arthropod P450s, distributed in different phylogenetic groups, have been associated with xenobiotic metabolism, and some of them have been functionally characterized, using different in vitro and in vivo systems. The purpose of this review is to summarize scientific publications on arthropod P450s from major insect and mite agricultural pests, pollinators and Papilio sp, which have been functionally characterized and shown to metabolize xenobiotics and/or their role (direct or indirect) in pesticide toxicity or resistance has been functionally validated. The phylogenetic relationships among these P450s, the functional systems employed for their characterization and their xenobiotic catalytic properties are presented, in a systematic approach, including critical aspects and limitations. The potential of the primary P450-based metabolic pathway of target and non-target organisms for the development of highly selective insecticides and resistance-breaking formulations may help to improve the efficiency and sustainability of pest control.

Co-Expression of a Homologous Cytochrome P450 Reductase Is Required for In Vivo Validation of the Tetranychus urticae CYP392A16-Based Abamectin Resistance in Drosophila

Simple Summary

The two-spotted spider mite, Tetranychus urticae, is one of the most damaging agricultural pests worldwide, feeding on over 1100 plant species and causing extensive damage to several crops. Chemical acaricides remain the most widely used strategy to control this pest. However, T. urticae has developed significant resistance to numerous acaricide compounds, due to certain features of mite biology and extensive acaricide applications that lead to the selection of resistant pests and subsequently the emergence of resistant populations. Several molecular/genetic mechanisms may contribute to these highly resistant phenotypes. Such mechanisms frequently involve expression of P450 detoxification enzymes, which act together with a partner protein named cytochrome P450 reductase (CPR). In this study, we investigated the potential of a mite P450 enzyme, CYP392A16, to confer resistance to the acaricide abamectin in vivo, when expressed in tissues of the model fruit fly Drosophila melanogaster. We confirmed that expression of this enzyme contributes to abamectin resistance in the fruit fly model, but only when a homologous mite CPR is co-expressed. Our findings indicate that the Drosophila model system can be engineered to facilitate validation of the candidate mite P450s, in order to elucidate resistance mechanisms and their underlying interactions.

Abstract

Overexpression of the cytochrome P450 monooxygenase CYP392A16 has been previously associated with abamectin resistance using transcriptional analysis in the two-spotted spider mite Tetranychus urticae, an important pest species worldwide; however, this association has not been functionally validated in vivo despite the demonstrated ability of CYP392A16 to metabolize abamectin in vitro. We expressed CYP392A16 in vivo via a Gal4 transcription activator protein/Upstream Activating Sequence (GAL4/UAS) system in Drosophila melanogaster flies, driving expression with detoxification tissue-specific drivers. We demonstrated that CYP392A16 expression confers statistically significant abamectin resistance in toxicity bioassays in Drosophila only when its homologous redox partner, cytochrome P450 reductase (TuCPR), is co-expressed in transgenic flies. Our study shows that the Drosophila model can be further improved, to facilitate the functional analysis of insecticide resistance mechanisms acting alone or in combination.