Identification of two ABCC transporters involved in malathion detoxification in the red flour beetle, Tribolium castaneum

ABC transporters have been suggested to be involved in insecticide detoxification in different insect species mainly based on the indirect observation of transcriptional upregulation of ABC gene expression in response to insecticide exposure. Previous studies performed by us and others in the red flour beetle, Tribolium castaneum, have analyzed the function of TcABCA-C and TcABCG-H genes using RNA interference (RNAi) and demonstrated that specific TcABCA and TcABCC genes are involved in the elimination of the pyrethroid tefluthrin and the benzoylurea diflubenzuron, because gene silencing increased the beetle's susceptibility to the insecticides. In this study, we focused on the potential functions of TcABCA-C genes in detoxification of the pyrethroid cyfluthrin (CF), the organophosphate malathion (MAL) and the diacylhdyazine tebufenozide (TBF). Analysis of transcript levels of selected TcABCA-C genes in response to treatment with these three chemically unrelated insecticides revealed that some genes were particularly upregulated after insecticide treatment. In addition, the ABC inhibitor verapamil synergized significantly the toxicity of MAL but only negligibly CF and TBF toxicities. Finally, silencing of two TcABCC genes by RNAi revealed a significant increase in susceptibility to MAL. In contrast, we did not observe a significant increase in insecticide-induced mortalities when knocking down TcABC genes in larvae treated with CF or TBF, although they were upregulated in response to insecticide treatment. Our results suggest that two pleiotropic ABCC transporters expressed in metabolic and excretory tissues contribute to the elimination of MAL.

Effect of salivary CYP4EM1 and CYP4EM2 gene silencing on the life span of Chagas disease vector Rhodnius prolixus (Hemiptera, Reduviidae) exposed to sublethal dose of deltamethrin

Control of Chagas disease in endemic countries is primarily accomplished through insecticide spraying for triatomine vectors. In this context, pyrethroids are the first-choice insecticide, and the evolution of insect resistance to these insecticides may represent an important barrier to triatomine control. In insects, cytochrome P450s are enzymes involved in the metabolism of xenobiotics and endogenous chemicals that are encoded by genes divided into different families. In this work, we evaluated the role of three Rhodnius prolixus CYP4EM subfamily genes during blood meal and after deltamethrin exposure. CYP4 gene members were expressed in different insect organs (integument, salivary glands (SGs), midgut, fat body and malpighian tubules) at distinct transcriptional levels. CYP4EM1 gene was highly expressed in the SG and was clearly modulated after insect blood meal. Injection of CYP4EM1dsRNA promoted significant reduction in mRNA levels of both CYP4EM1 and CYP4EM2 genes and induced deleterious effects in R. prolixus nymphs subsequently exposed to sublethal doses of deltamethrin (3.4 or 3.8 ng/nymph treated). The higher dose reduced the survival over time and increased susceptibility of R. prolixus nymphs to deltamethrin. A better understanding of this mechanism can help in developing of more efficient strategies to reduce Trypanosoma cruzi vector transmission in Americas.

Functional analysis of ABCG and ABCH transporters from the red flour beetle, Tribolium castaneum

BACKGROUND

ATP-binding cassette transporter (ABC transporter) subfamilies ABCA-C and ABCG-H have been implicated in insecticide detoxification, mostly based on findings of elevated gene expression in response to insecticide treatment. We previously characterized TcABCA-C genes from the model beetle and pest Tribolium castaneum and demonstrated that TcABCA and TcABCC genes are involved in the elimination of diflubenzuron, because RNA interference (RNAi)-mediated gene silencing increased susceptibility. In this study, we focused on the potential functions of TcABCG and TcABCH genes in insecticide detoxification.

RESULTS

When we silenced the expression of TcABCG-H genes using RNAi, we noticed a previously unreported developmental RNAi phenotype for TcABCG-4F, which is characterized by 50% mortality and ecdysial arrest during adult moult. When we knocked down the Drosophila brown orthologue TcABCG-XC, we did not obtain apparent eye colour phenotypes but did observe a loss of riboflavin uptake by Malpighian tubules. Next, we determined the expression profiles of all TcABCG-H genes in different tissues and developmental stages and analysed transcript levels in response to treatment with four chemically unrelated insecticides. We found that some genes were specifically upregulated after insecticide treatment. However, when we determined insecticide-induced mortalities in larvae that were treated by double-stranded RNA injection to silence those TcABCG-H genes that were upregulated, we did not observe a significant increase in susceptibility to insecticides.

CONCLUSION

Our findings suggest that the observed insecticide-dependent induction of TcABCG-H gene expression reflects an unspecific stress response, and hence underlines the significance of functional studies on insecticide detoxification. © 2021 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Symbiont-Mediated Insecticide Detoxification as an Emerging Problem in Insect Pests

Pesticide use is prevalent with applications from the backyard gardener to large-scale agriculture and combatting pests in homes and industrial settings. Alongside the need to control unwanted pests comes the selective pressure generated by sustained pesticide use has become a concern leading to environmental contamination, pest resistance, and, thus, reduced pesticide efficacy. Despite efforts to improve the environmental impact and reduce off-target effects, chemical pesticides are relied on and control failures are costly. Though pesticide resistance mechanisms vary, one pattern that has recently emerged is symbiont-mediated detoxification within insect pests. The localization within the insect host, the identity of the symbiotic partner, and the stability of the associations across different systems vary. The diversity of insects and ecological settings linked to this phenomenon are broad. In this mini-review, we summarize the recent trend of insecticide detoxification modulated by symbiotic associations between bacteria and insects, as well as highlight the implications for pesticide development, pest management strategies, and pesticide bioremediation.

Silencing of Cytochrome P450 in Spodoptera frugiperda (Lepidoptera: Noctuidae) by RNA Interference Enhances Susceptibility to Chlorantraniliprole

Fall armyworm, Spodoptera frugiperda (Smith), has caused significant losses for crop production in China. The fall armyworm is mainly controlled by the chemical insecticides, whereas the frequent application of insecticides would result in the resistance development. Insect cytochrome P450 monooxygenases play an essential part in the detoxification of insecticides. In this study, five P450 genes were selected to determine the role in response to insecticides by RNA interference (RNAi). Developmental expression pattern analysis revealed that S. frugiperda CYP321A8, CYP321A9, and CYP321B1 were highest in second-instar larvae among developmental stages, with 2.04-, 3.39-, and 8.58-fold compared with eggs, whereas CYP337B5 and CYP6AE44 were highest in adult stage, with 16.3- and 10.6-fold in comparison of eggs, respectively. Tissue-specific expression pattern analysis exhibited that CYP321A8, CYP321B1, and CYP6AE44 were highest in the midguts, with 3.56-, 3.33-, and 3.04-fold compared with heads, whereas CYP321A9 and CYP337B5 were highest in wings, with 3.07- and 3.36-fold compared with heads, respectively. RNAi was also conducted to explore detoxification effects of the five P450 genes on chlorantraniliprole. The second-instar larvae became more sensitive to chlorantraniliprole with a higher mortality rate than the control, after silencing CYP321A8, CYP321A9, and CYP321B1, respectively. These findings strongly supported our viewpoint that CYP321A8, CYP321A9, and CYP321B1 may play a critical role in insecticide detoxification. It will provide a basis for further study on regulation of P450 genes and the management of S. frugiperda.

Identification and Functional Analysis of a Delta Class Glutathione S-Transferase Gene Associated with Insecticide Detoxification in Bradysia odoriphaga

A delta class glutathione S-transferase gene (BoGSTd2) is identified from Bradysia odoriphaga for the first time. Developmental expression analysis showed that expression of BoGSTd2 is significantly higher in the fourth instar larval stage and the adult stage. Tissue-specific expression analysis found that BoGSTd2 was expressed predominantly in the midgut and Malpighian tubules in the fourth instar larvae and the abdomen of adults. Expression of BoGSTd2 was significantly upregulated following exposure to chlorpyrifos and clothianidin. In vitro inhibition and metabolic assays indicated that recombinant BoGSTd2 could not directly metabolize chlorpyrifos and clothianidin. Nevertheless, disk diffusion assays indicated that BoGSTd2 plays an important role in protection against oxidative stress. RNAi assays showed that BoGSTd2 participates in the elimination of reactive oxygen species induced by chlorpyrifos and clothianidin. These results strongly suggest that BoGSTd2 plays an important role in chlorpyrifos and clothianidin detoxification in B. odoriphaga by protecting tissues from oxidative stress induced by these insecticides.

Exposure to herbicides reduces larval sensitivity to insecticides in Spodoptera litura (Lepidoptera: Noctuidae)

Herbicides and insecticides are widely used in modern agriculture. It has been reported in various studies that application of insecticides can increase tolerance of herbivorous insects to insecticides. However, limited information exists on susceptibility to insecticides when insects are exposed to herbicides. This study was conducted to investigate the potential impact of the herbicides trifluralin and 2-methyl-4-chlorophenoxyacetic acid sodium salt (MCPA-Na) on the susceptibility of the nocturnal moth Spodoptera litura to the insecticides λ-cyhalothrin, phoxim and bifenthrin. We found that larvae exposed to trifluralin or MCPA-Na became significantly less susceptible to both insecticides than non-exposed control larvae. Herbicide-treated larvae did not show altered growth under the used test conditions. However, heads of herbicide-treated larvae showed increased expression of the acetylcholinesterase genes SlAce1 and SlAce2. Moreover, the fat body and midgut of herbicide-treated larvae displayed elevated expression of detoxification genes (the carboxylesterase gene SlCarE; the glutathione S-transferase genes SlGSTe2 and SlGSTe3; the cytochrome P450 monooxygenase genes CYP6B48, CYP9A40 and CYP321B1). The CYP6B48 gene exhibited highest inducibility. In conclusion, the data of this study suggest that exposure of S. litura larvae to herbicides may stimulate detoxification mechanisms that compromise the efficacy of insecticides.

Changes in the expression of four ABC transporter genes in response to imidacloprid in Bemisia tabaci Q (Hemiptera: Aleyrodidae)

Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae), a globally invasive species complex that causes serious damage to field crops, has developed resistance to imidacloprid and many other pesticides. Insect detoxify to pesticides may partially depend on ABC transporters, which contribute to the detoxification of xenobiotics. To determine whether genes in the ABCG subfamily are involved in imidacloprid detoxification in B. tabaci Q, we cloned four ABCG subfamily genes based on the published MED/Q genome and on our previous study of the transcriptional response of ABC transporters in B. tabaci Q adults to imidacloprid. As indicated by the quantification of mRNA levels after a 6-h exposure, the expression level of ABCG3 was 3.3-fold higher in B. tabaci Q adults exposed to 100 μg/mL imidacloprid rather than to the buffer control. The expression level of ABCG3 was higher in females than in males but did not significantly differ among eggs or nymphal stages and did not significantly differ among head, thorax, and abdomen tissues of adults. Knockdown of ABCG3 via RNA interference significantly increased the mortality of imidacloprid-treated laboratory and field-collected adults of B. tabaci Q. These results indicate that the ABCG3 gene may be involved in imidacloprid detoxification by B. tabaci Q.

Identification, Expression, and Regulation of an Omega Class Glutathione S-transferase in Rhopalosiphum padi (L.) (Hemiptera: Aphididae) Under Insecticide Stress

Glutathione S-transferases (GSTs) play an essential role in the detoxification of xenobiotic toxins in insects, including insecticides. However, few data are available for the bird cherry-oat aphid, Rhopalosiphum padi (L.). In this study, we cloned and sequenced the full-length cDNA of an omega GST gene (RpGSTO1) from R. padi, which contains 720 bp in length and encodes 239 amino acids. A phylogenetic analysis revealed that RpGSTO1 belongs to the omega class of insect GSTs. RpGSTO1 gene was highly expressed in transformed Escherichia coli and the protein was purified by affinity chromatography. The recombinant RpGSTO1 displayed reduced glutathione (GSH)-dependent conjugating activity toward the substrate 1-chloro-2, 4-dinitrobenzene (CDNB) substrate. The recombinant RpGSTO1 protein exhibited optimal activity at pH 7.0 and 30°C. In addition, a disk diffusion assay showed that E. coli overexpressing RpGSTO1 increased resistance to cumene hydroperoxide-induced oxidative stress. Real-time quantitative PCR analysis showed that the relative expression level of RpGSTO1 was different in response to different insecticides, suggesting that the enzyme could contribute to insecticide metabolism in R. padi. These findings indicate that RpGSTO1 may play a crucial role in counteracting oxidative stress and detoxifying the insecticides. The results of our study contribute to a better understanding the mechanisms of insecticide detoxification and resistance in R. padi.

Molecular characterisation of two α-esterase genes involving chlorpyrifos detoxification in the diamondback moth, Plutella xylostella

BACKGROUND

Carboxylesterases (CarEs) are involved in metabolic detoxification of dietary and environmental xenobiotics in insects. However, owing to the complexity of the protein family, the involvement of CarEs in insecticide metabolism in Plutella xylostella has not been fully elucidated. This study aimed to characterise two CarE genes and assess their potential roles in response to chlorpyrifos in P. xylostella.

RESULTS

Synergistic tests showed that triphenyl phosphate decreased the resistance of the third-instar larvae to chlorpyrifos. The treatment of the third-instar larvae with chlorpyrifos at the LC₃₀ dose led to a significant increase in CarE activity. Two CarE cDNAs (Pxae18 and Pxae28) were subsequently sequenced and characterised. Both genes were expressed predominantly in the larval midgut. Most importantly, two CarE genes showed significantly higher expression in the chlorpyrifos-resistant strain than in the susceptible strain. RNAi knockdown of Pxae18 and Pxae28 significantly increased the mortality to chlorpyrifos from 40% in the control to 73.8 and 63.3% respectively.

CONCLUSION

RNAi knockdown of Pxae18 and Pxae28 significantly inhibited detoxification ability and increased the mortality in P. xylostella. The results indicate that these two CarE genes play important roles in the detoxification of chlorpyrifos in P. xylostella. © 2016 Society of Chemical Industry.

Identification of Four ATP-Binding Cassette Transporter Genes in Cnaphalocrocis medinalis and Their Expression in Response to Insecticide Treatment

The ATP-binding cassette (ABC) transporters belong to a superfamily of genes involved in the transport of specific molecules across lipid membranes, as well as insecticide resistance, present in all living organisms. In this study, we combined the Cnaphalocrocis medinals transcriptome database with a bioinformatics approach to identify four C. medinals ABCs (CmABCs), including CmABCG1, CmABCG4, CmABCC2 and CmABCC3. Tissue expression analysis showed that these genes had a tissue-specific expression pattern. CmABCG1 had significantly higher expression in the haemolymph and head compared to the other tissues. The expression of CmABCG4, CmABCC2 and CmABCC3 was highest in the midgut, followed by expression in the fat body. The developmental stage expression analysis showed that CmABCG1, CmABCG4, CmABCC2 and CmABCC3 were mainly expressed in adults. The transcription of CmABCG1, CmABCG4 and CmABCC2 was significantly induced by chlorpyrifos. Taken together, the results of our study provided useful information for understanding of the detoxification system of C. medinalis.

RNA interference of cytochrome P450 CYP6F subfamily genes affects susceptibility to different insecticides in Locusta migratoria

BACKGROUND

Many insect cytochrome P450s (CYPs) play critical roles in detoxification of insecticides. The CYP6 family is unique to the class Insecta, and its biochemical function has essentially been associated with the metabolism of xenobiotics. In this study, we sequenced and characterised the full-length cDNAs of five CYP genes from Locusta migratoria, a highly destructive agricultural pest worldwide.

RESULTS

The five genes were predominantly expressed in brain, guts, fat bodies or Malpighian tubules. CYP6FE1, CYP6FF1 and CYP6FG1 were expressed at higher levels in fourth-instar nymphs than in other developmental stages. CYPFD2 is specifically expressed in adults, whereas CYP6FD1, CYP6FD2 and CYP6FE1 showed significantly lower expression in eggs than in other developmental stages. Deltamethrin suppressed CYP6FD1 expression in third-instar nymphs and upregulated the expression level of CYP6FD2, CYP6FF1 and CYP6FG1 at the dose of LD₁₀ . Efficient RNA interference-mediated gene silencing was established for four of the five CYP genes. Silencing of CYP6FF1 increased the nymphal mortality from 23 to 50% in response to deltamethrin. Silencing of CYP6FD2 and CYP6FE1 increased the nymphal mortality from 32 to 72 and 66%, respectively, to carbaryl.

CONCLUSION

Three of the four CYP6F subfamily genes in L. migratoria were associated with the detoxification of deltamethrin or carbaryl. The role of CYPs in insecticide detoxification appears to be both gene and insecticide specific. © 2016 Society of Chemical Industry.

Identification and Characterization of CYP9A40 from the Tobacco Cutworm Moth (Spodoptera litura), a Cytochrome P450 Gene Induced by Plant Allelochemicals and Insecticides

Cytochrome P450 monooxygenases (P450s) of insects play crucial roles in the metabolism of endogenous and dietary compounds. Tobacco cutworm moth (Spodoptera litura), an important agricultural pest, causes severe yield losses in many crops. In this study, we identified CYP9A40, a novel P450 gene of S. litura, and investigated its expression profile and potential role in detoxification of plant allelochemicals and insecticides. The cDNA contains an open reading frame encoding 529 amino acid residues. CYP9A40 transcripts were found to be accumulated during various development stages of S. litura and were highest in fifth and sixth instar larvae. CYP9A40 was mainly expressed in the midgut and fat body. Larval consumption of xenobiotics, namely plant allelochemicals (quercetin and cinnamic acid) and insecticides (deltamethrin and methoxyfenozide) induced accumulation of CYP9A40 transcripts in the midgut and fat body. Injection of dsCYP9A40 (silencing of CYP9A40 by RNA interference) significantly increased the susceptibility of S. litura larvae to the tested plant allelochemicals and insecticides. These results indicate that CYP9A40 expression in S. litura is related to consumption of xenobiotics and suggest that CYP9A40 is involved in detoxification of these compounds.

Identification of Genes Putatively Involved in Chitin Metabolism and Insecticide Detoxification in the Rice Leaf Folder (Cnaphalocrocis medinalis) Larvae through Transcriptomic Analysis

The rice leaf roller (Cnaphalocrocis medinalis) is one of the most destructive agricultural pests. Due to its migratory behavior, it is difficult to control worldwide. To date, little is known about major genes of C. medinalis involved in chitin metabolism and insecticide detoxification. In order to obtain a comprehensive genome dataset of C. medinalis, we conducted de novo transcriptome sequencing which focused on the major feeding stage of fourth-instar larvae, and our work revealed useful information on chitin metabolism and insecticide detoxification and target genes of C. medinalis. We acquired 29,367,797 Illumina reads and assembled these reads into 63,174 unigenes with an average length of 753 bp. Among these unigenes, 31,810 were annotated against the National Center for Biotechnology Information non-redundant (NCBI nr) protein database, resulting in 24,246, 8669 and 18,176 assigned to Swiss-Prot, clusters of orthologous group (COG), and gene ontology (GO), respectively. We were able to map 10,043 unigenes into 285 pathways using the Kyoto Encyclopedia of Genes and Genomes Pathway database (KEGG). Specifically, 16 genes, including five chitin deacetylases, two chitin synthases, five chitinases and four other related enzymes, were identified to be putatively involved in chitin biosynthesis and degradation, whereas 360 genes, including cytochrome P450s, glutathione S-transferases, esterases, and acetylcholinesterases, were found to be potentially involved in insecticide detoxification or as insecticide targets. The reliability of the transcriptome data was determined by reverse transcription quantitative PCR (RT-qPCR) for the selected genes. Our data serves as a new and valuable sequence resource for genomic studies on C. medinalis. The findings should improve our understanding of C. medinalis genetics and contribute to management of this important agricultural pest.

GLUTATHIONE S-TRANSFERASE Genes IN THE RICE LEAFFOLDER, Cnaphalocrocis medinalis (LEPIDOPTERA: PYRALIDAE): IDENTIFICATION AND EXPRESSION PROFILES

In insects, glutathione S-transferases (GSTs) play critical roles in the detoxification of various insecticides, resulting in insecticide resistance. The rice leaffolder, Cnaphalocrocis medinalis, is an economically important pest of rice in Asia. GST genes have not been largely identified in this insect species. In the present study, by searching the transcriptome dataset, 25 candidate GST genes were identified in C. medinalis for the first time. Of these, 23 predicted GST proteins fell into five cytosolic classes (delta, epsilon, omega, sigma, and zeta), and two were assigned to the "unclassified" subgroup. Real-time quantitative PCR analysis showed that these GST genes were differentially expressed in various tissues, including the midgut, Malpighian tubules, and fat body of larvae, and the antenna, abdomen, and leg of adults, indicating diversified functions for these genes. Transcription levels of CmGSTd2, CmGSTe6, and CmGSTe7 increased significantly in larvae following exposure to chlorpyrifos, suggesting that these GST genes could be involved in the detoxification of this insecticide. The results of our study pave the way to a better understanding of the detoxification system of C. medinalis.