Identification and interaction of multiple genes resulting in DDT resistance in the 91-R strain of Drosophila melanogaster by RNAi approaches

The cytochrome P450 gene CYP4g1 driven by high temperature confers abamectin tolerance on Liriomyza trifolii through promoting cuticular hydrocarbons biosynthesis

Liriomyza trifolii, an invasive pest, poses a substantial threat to horticultural and vegetable plants. It spreads rapidly, especially in hot weather, leading to large-scale outbreaks with strong thermotolerance and insecticide resistance. In this study, mortality and LtCYP4g1 expression in L. trifolii were evaluated after thermal and insecticides exposure. Furthermore, functional verification of LtCYP4g1 was conducted through RNA interference and bacterial survival assays in Escherichia coli containing recombinant LtCYP4g1 protein. Results indicated that a short time exposure to high temperature incresed insecticide tolerance of L. trifolii, attributed to decreased mortality and induced LtCYP4g1 expression; LtCYP4g1 was involved in stimulating synthesis of cuticular hydrocarbons (CHCs) and elevating epicuticle lipid content and thickness, and E. coli cells overexpressing LtCYP4g1 exhibited significant tolerance to thermal and insecticide stress. In general, P450-mediated tolerance of L. trifolii was enhanced by high temperature, with LtCYP4g1 playing a role in promoting biosynthesis of CHCs for thickening epidermal lipid barrier and reducing cuticular penetration. This study provides a framework for delving into the function of CYP450s in insecticide detoxification and illustrates the role of global warming in driving the evolution of L. trifolii.

Insights into the role of non-coding RNAs in the development of insecticide resistance in insects

Pest control heavily relies on chemical pesticides has been going on for decades. However, the indiscriminate use of chemical pesticides often results in the development of resistance in pests. Almost all pests have developed some degree of resistance to pesticides. Research showed that the mechanisms of insecticide resistance in insects encompass metabolic resistance, behavioral resistance, penetration resistance and target-site resistance. Research on the these mechanisms has been mainly focused on the cis-regulatory or trans-regulatory for the insecticide resistance-related genes, with less attention paid to non-coding RNAs (ncRNAs), such as microRNA (miRNA), long non-coding RNA (lncRNA), and circular RNA (circRNA). There has been increased studies focus on understanding how these ncRNAs are involved in post-transcriptional regulation of insecticide resistance-related genes. Besides, the formatted endogenous RNA (ceRNA) regulatory networks (lncRNA/circRNA-miRNA-mRNA) has been identified as a key player in governing insect resistance formation. This review delves into the functions and underlying mechanisms of miRNA, lncRNA, and circRNA in regulating insect resistance. ncRNAs orchestrate insect resistance by modulating the expression of detoxification enzyme genes, insecticide target genes, as well as receptor genes, effectively regulating both target-site, metabolic and penetration resistance in insects. It also explores the regulatory mechanisms of ceRNA networks in the development of resistance. By enhancing our understanding of the mechanisms of ncRNAs in insecticide resistance, it will not only provide valuable insights into the new mechanisms of insecticide resistance but also help to enrich new directions in ncRNAs gene regulation research.

The development of abamectin resistance in Liriomyza trifolii and its contribution to thermotolerance

BACKGROUND

Liriomyza trifolii is an economically significant, invasive pest of horticultural and vegetable crops. The larvae form tunnels in foliage and hasten senescence and death. Outbreaks of L. trifolii often erupt in hot weather and are driven by thermotolerance; furthermore, the poor effectiveness of pesticides has made outbreaks more severe. But it is still unclear whether the development of insecticide tolerance will contribute to thermotolerance in L. trifolii.

RESULTS

To explore potential synergistic relationships between insecticide exposure and thermotolerance in L. trifolii, we first generated an abamectin-resistant (AB-R) strain. Knockdown behavior, eclosion and survival rates, and expression levels of genes encoding heat shock proteins (Hsps) in L. trifolii were then examined in AB-R and abamectin-susceptible (AB-S) strains. Our results demonstrated that long-term selection pressure for abamectin resistance made L. trifolii more prone to develop cross-resistance to other insecticides containing similar ingredients. Furthermore, the AB-R strain exhibited enhanced thermotolerance and possessed an elevated critical thermal maximum temperature, and upregulated expression levels of Hsps during heat stress.

CONCLUSION

Collectively, our results indicate that thermal adaptation in L. trifolii was accompanied by emerging abamectin resistance. This study provides a theoretical basis for investigating the synergistic or cross-adaptive mechanisms that insects use to cope with adversity and demonstrates the complexity of insect adaptation to environmental and chemical stress. © 2023 Society of Chemical Industry.

Enthralling genetic regulatory mechanisms meddling insecticide resistance development in insects: role of transcriptional and post-transcriptional events

Insecticide resistance in insects severely threatens both human health and agriculture, making insecticides less compelling and valuable, leading to frequent pest management failures, rising input costs, lowering crop yields, and disastrous public health. Insecticide resistance results from multiple factors, mainly indiscriminate insecticide usage and mounted selection pressure on insect populations. Insects respond to insecticide stress at the cellular level by modest yet significant genetic propagations. Transcriptional, co-transcriptional, and post-transcriptional regulatory signals of cells in organisms regulate the intricate processes in gene expressions churning the genetic information in transcriptional units into proteins and non-coding transcripts. Upregulation of detoxification enzymes, notably cytochrome P450s (CYPs), glutathione S-transferases (GSTs), esterases [carboxyl choline esterase (CCE), carboxyl esterase (CarE)] and ATP Binding Cassettes (ABC) at the transcriptional level, modification of target sites, decreased penetration, or higher excretion of insecticides are the noted insect physiological responses. The transcriptional regulatory pathways such as AhR/ARNT, Nuclear receptors, CncC/Keap1, MAPK/CREB, and GPCR/cAMP/PKA were found to regulate the detoxification genes at the transcriptional level. Post-transcriptional changes of non-coding RNAs (ncRNAs) such as microRNAs (miRNA), long non-coding RNAs (lncRNA), and epitranscriptomics, including RNA methylation, are reported in resistant insects. Additionally, genetic modifications such as mutations in the target sites and copy number variations (CNV) are also influencing insecticide resistance. Therefore, these cellular intricacies may decrease insecticide sensitivity, altering the concentrations or activities of proteins involved in insecticide interactions or detoxification. The cellular episodes at the transcriptional and post-transcriptional levels pertinent to insecticide resistance responses in insects are extensively covered in this review. An overview of molecular mechanisms underlying these biological rhythms allows for developing alternative pest control methods to focus on insect vulnerabilities, employing reverse genetics approaches like RNA interference (RNAi) technology to silence particular resistance-related genes for sustained insect management.

Delivery of Methoprene-Tolerant dsRNA to Improve RNAi Efficiency by Modified Liposomes for Pest Control

The application of RNA interference (RNAi) technology for pest control is environmentally friendly and accurate. However, the efficiency of RNAi is often inconsistent and unreliable, and finding a suitable carrier element is considered critical to success in overcoming biotic and abiotic barriers to reach the target site. The fall armyworm, Spodoptera frugiperda (FAW), which is one of most important global agricultural pests, has recently spread rapidly to other parts of the world. In this study, a method to improve the stability and RNAi efficiency of the dsRNA carrier complex was reported. Methoprene-tolerant gene (Met) was selected as a target, a gene which is critical to the growth and development of FAW. Biomaterials nanoliposomes (LNPs) were modified with polyethylenimine (PEI) to deliver the dsRNA of Met. The synthesized Met3@PEI@LNPs reached a size of 385 nm and were found to load dsRNA effectively. Through stability and protection assays, it was found that LNPs provided reliable protection. In addition, the release curve also demonstrated that LNPs were able to prevent premature release under alkaline condition of the insect midgut but accelerate the release after entering the acidic environment of the target cells. The cell transfection efficiency of the prepared LNPs reached 96.4%. Toxicity tests showed that the use of LNPs could significantly improve the interference efficiency, with 91.7% interference efficiency achieved when the concentration of dsRNA in LNPs was only 25% of that of the control. Successful interference of Met demonstrated it could significantly shorten the larval period and make the larvae pupate earlier, thus achieving the purpose of control. In this study, we have demonstrated the use of nanotechnology to provide a novel RNAi delivery method for pest control.

Synthetic Nanoscale RNAi Constructs as Pesticides for the Control of Locust Migratoria

The low efficiency of RNA interference (RNAi) in insects via the oral administration of double-stranded RNA (dsRNA) is a considerable obstacle preventing its application in insect pest control. The instability of dsRNA and insufficient dsRNA uptake are known to limit the RNAi efficiency. To overcome these limitations, the block copolymer poly(ethylene glycol)-polylysine(thiol) [PEG-PLys(SH)] was designed in this study to form well-defined, core-shell nanoparticles to protect dsRNA from premature degradation and to facilitate its movement through various physiological barriers. The developed material had excellent structural stability and dsRNA-protecting capacity, thereby enabling the prolonged survival of dsRNA in the digestive tract for endocytosis into the midgut cells of the migratory locust, Locusta migratoria. After encapsulation of a dsLmCHS2 payload (a midgut gene), a 60% down-regulation of LmCHS2, accompanied with observations of amorphous and discontinuous linings of the peritrophic matrix and abnormal phenotypes, was observed. In addition, the elaborated nanoscale dsRNA condensates appeared to readily extravasate through the narrow fenestrations in the linings of midgut epithelial cells into the hemolymph and be distributed throughout the body. After encapsulation of a dsLmCHS1 payload (a cuticle gene), a distinctive lethal phenotype with molting failure was observed as a result of a 50% down-regulation in LmCHS1. The persistent leaf adherence of these dsRNA constructs was also capable of resisting continuous rinsing. Therefore, these dsRNA constructs represent a robust type of RNAi pesticide, which has potential as a versatile pesticide against a variety of molecular targets for the control of destructive insects and insects resistant to conventional pesticides.

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.

A versatile contribution of both aminopeptidases N and ABC transporters to Bt Cry1Ac toxicity in the diamondback moth

BACKGROUND

Biopesticides and transgenic crops based on Bacillus thuringiensis (Bt) toxins are extensively used to control insect pests, but the rapid evolution of insect resistance seriously threatens their effectiveness. Bt resistance is often polygenic and complex. Mutations that confer resistance occur in midgut proteins that act as cell surface receptors for the toxin, and it is thought they facilitate its assembly as a membrane-damaging pore. However, the mechanistic details of the action of Bt toxins remain controversial.

RESULTS

We have examined the contribution of two paralogous ABC transporters and two aminopeptidases N to Bt Cry1Ac toxicity in the diamondback moth, Plutella xylostella, using CRISPR/Cas9 to generate a series of homozygous polygenic knockout strains. A double-gene knockout strain, in which the two paralogous ABC transporters ABCC2 and ABCC3 were deleted, exhibited 4482-fold resistance to Cry1A toxin, significantly greater than that previously reported for single-gene knockouts and confirming the mutual functional redundancy of these ABC transporters in acting as toxin receptors in P. xylostella. A double-gene knockout strain in which APN1 and APN3a were deleted exhibited 1425-fold resistance to Cry1Ac toxin, providing the most direct evidence to date for these APN proteins acting as Cry1Ac toxin receptors, while also indicating their functional redundancy. Genetic crosses of the two double-gene knockouts yielded a hybrid strain in which all four receptor genes were deleted and this resulted in a > 34,000-fold resistance, indicating that while both types of receptor need to be present for the toxin to be fully effective, there is a level of functional redundancy between them. The highly resistant quadruple knockout strain was less fit than wild-type moths, but no fitness cost was detected in the double knockout strains.

CONCLUSION

Our results provide direct evidence that APN1 and APN3a are important for Cry1Ac toxicity. They support our overarching hypothesis of a versatile mode of action of Bt toxins, which can compensate for the absence of individual receptors, and are consistent with an interplay among diverse midgut receptors in the toxins' mechanism of action in a super pest.

NCs-Delivered Pesticides: A Promising Candidate in Smart Agriculture

Pesticides have been used extensively in the field of plant protection to maximize crop yields. However, the long-term, unmanaged application of pesticides has posed severe challenges such as pesticide resistance, environmental contamination, risk in human health, soil degradation, and other important global issues. Recently, the combination of nanotechnology with plant protection strategies has offered new perspectives to mitigate these global issues, which has promoted a rapid development of NCs-based pesticides. Unlike certain conventional pesticides that have been applied inefficiently and lacked targeted control, pesticides delivered by nanocarriers (NCs) have optimized formulations, controlled release rate, and minimized or site-specific application. They are receiving increasing attention and are considered as an important part in sustainable and smart agriculture. This review discussed the limitation of traditional pesticides or conventional application mode, focused on the sustainable features of NCs-based pesticides such as improved formulation, enhanced stability under harsh condition, and controlled release/degradation. The perspectives of NCs-based pesticides and their risk assessment were also suggested in this view for a better use of NCs-based pesticides to facilitate sustainable, smart agriculture in the future.

Transcriptomic identification and characterization of genes commonly responding to sublethal concentrations of six different insecticides in the common fruit fly, Drosophila melanogaster

Pretreatment with sublethal concentrations (LC₁₀) of six insecticides (chlorantraniliprole, cypermethrin, dinotefuran, indoxacarb, ivermectin, and spinosad) significantly elevated tolerance of the common fruit fly Drosophila melanogaster to lethal concentration of the respective insecticide. Commonly responding genes to sublethal treatments of the six insecticides were identified by transcriptome analysis based on a fold change >1.5 or < -1.5, and p < 0.05 as selection criteria. Following treatment with all the six insecticides, 26 transcripts were commonly over-transcribed, whereas 30 transcripts were commonly under-transcribed. Reliability of the transcriptome data was confirmed by quantitative PCR. A majority of the over-transcribed genes included those related to olfactory behavior, such as odorant-binding proteins, as well as immune-related genes, including attacin, diptericin, and immune-induced molecule 18. In contrast, genes belonging to the mitochondrial respiratory chain, such as mitochondrial NADH-ubiquinone oxidoreductase chain 1/3/4/5 and mitochondrial cytochrome b/c, were commonly under-transcribed. Furthermore, genes related to eggshell formation and motion were also under-transcribed, which may indicate a possible energy trade-off for xenobiotic stress. In summary, most of the differentially expressed genes were not directly related to well-known detoxification genes, suggesting that the roles of commonly expressed tolerance-related genes are not likely related to direct metabolic detoxification, but rather are associated with restoration of homeostasis.

A second generation of 1,2,4-oxadiazole derivatives with enhanced solubility for inhibition of 3-hydroxykynurenine transaminase (HKT) from Aedes aegypti

The most widely used method for the control of the Aedes aegypti mosquito population is the chemical control method. It represents a time- and cost-effective way to curb several diseases (e.g. dengue, Zika, chikungunya, yellow fever) through vector control. For this reason, the discovery of new compounds with a distinct mode of action from the available ones is essential in order to minimize the rise of insecticide resistance. Detoxification enzymes are an attractive target for the discovery of new insecticides. The kynurenine pathway is an important metabolic pathway, and it leads to the chemically stable xanthurenic acid, biosynthesized from 3-hydroxykynurenine, a precursor of reactive oxygen and nitrogen species, by the enzyme 3-hydroxykynurenine transaminase (HKT). Previously, we have reported the effectiveness of 1,2,4-oxadiazole derivatives acting as larvicides for A. aegypti and AeHKT inhibitors from in vitro and in silico studies. Here, we report the synthesis of new sodium 4-[3-(aryl)-1,2,4-oxadiazol-5-yl] propanoates and the cognate HKT-inhibitory activity. These new derivatives act as competitive inhibitors with IC50 values in the range of 42 to 339 μM. We further performed molecular docking simulations and QSAR analysis for the previously synthesized sodium 4-[3-(aryl)-1,2,4-oxadiazol-5-yl] butanoates reported earlier by our group and the data produced herein. Most of the 1,2,4-oxadiazole derivatives, including the canonical compounds for both series, showed a similar binding mode with HKT. The binding occurs similarly to the co-crystallized inhibitor via anchoring to Arg356 and positioning of the aromatic ring and its substituents outwards at the entry of the active site. QSAR analysis was performed in search of more than 770 molecular descriptors to establish a relationship between the lowest energy conformations and the IC50 values. The five best descriptors were selected to create and validate the model, which exhibited parameters that attested to its robustness and predictability. In summary, we observed that compounds with a para substitution and heavier groups (i.e. CF3 and NO2 substituents) had an enhanced HKT-inhibition profile. These compounds comprise a series described as AeHKT inhibitors via enzymatic inhibition experiments, opening the way to further the development of new substances with higher potency against HKT from Aedes aegypti.

Nanoparticle-mediated double-stranded RNA delivery system: A promising approach for sustainable pest management

RNA interference (RNAi) targeting lethal genes in insects has great potential for sustainable crop protection. Compared with traditional double-stranded (ds)RNA delivery systems, nanoparticles such as chitosan, liposomes, and cationic dendrimers offer advantages in delivering dsRNA/small interfering (si)RNA to improve RNAi efficiency, thus promoting the development and practice of RNAi-based pest management strategies. Here, we illustrate the limitations of traditional dsRNA delivery systems, reveal the mechanism of nanoparticle-mediated RNAi, summarize the recent progress and successful applications of nanoparticle-mediated RNAi in pest management, and finally address the prospects of nanoparticle-based RNA pesticides.

The insulin signaling pathway in Drosophila melanogaster: A nexus revealing an "Achilles' heel" in DDT resistance

Insecticide resistance is an ongoing challenge in agriculture and disease vector control. Here, we demonstrate a novel strategy to attenuate resistance. We used genomics tools to target fundamental energy-associated pathways and identified a potential "Achilles' heel" for resistance, a resistance-associated protein that, upon inhibition, results in a substantial loss in the resistance phenotype. Specifically, we compared the gene expression profiles and structural variations of the insulin/insulin-like growth factor signaling (IIS) pathway genes in DDT-susceptible (91-C) and -resistant (91-R) Drosophila melanogaster (Drosophila) strains. A total of eight and seven IIS transcripts were up- and down-regulated, respectively, in 91-R compared to 91-C. A total of 114 nonsynonymous mutations were observed between 91-C and 91-R, of which 51.8% were fixed. Among the differentially expressed transcripts, phosphoenolpyruvate carboxykinase (PEPCK), down-regulated in 91-R, encoded the greatest number of amino acid changes, prompting us to perform PEPCK inhibitor-pesticide exposure bioassays. The inhibitor of PEPCK, hydrazine sulfate, resulted in a 161- to 218-fold decrease in the DDT resistance phenotype (91-R) and more than a 4- to 5-fold increase in susceptibility in 91-C. A second target protein, Glycogen synthase kinase 3β (GSK3β-PO), had one amino acid difference between 91-C and 91-R, and the corresponding transcript was also down-regulated in 91-R. A GSK3β-PO inhibitor, lithium chloride, likewise reduced the resistance but to a lesser extent than did hydrazine sulfate for PEPCK. We demonstrate the potential role of IIS genes in DDT resistance and the potential discovery of an "Achilles' heel" against pesticide resistance in this pathway.

Association between overexpression of cytochrome P450 genes and deltamethrin resistance in Rhipicephalus microplus

Cytochrome P450 monooxygenases mediated metabolic detoxification has been recognized as one of the mechanisms involved in resistance to pyrethroids, which is a class of pesticides that includes acaricides such as deltamethrin. Several cytochrome P450 (CYP) genes were identified in arthropod pests which are upregulated in response to exposure to pesticides used as acaricides. However, to date, limited information is available with respect to CYP genes and their response to acaricide exposure in ticks. We cloned and sequenced four CYP genes, the CYP41, CYP3006G8, CYP319A1 and CYP4W1 from reference susceptible IVRI-I strain of Rhipicephalus microplus. The expression pattern of the genes was investigated using qPCR in reference susceptible IVRI-I, pyrethroid-resistant IVRI-IV and multi-acaricide resistant IVRI-V strains. The effect of a single exposure of deltamethrin, at a concentration of 2600 μg/mL and 299.7 μg/mL on IVRI-IV and IVRI-V strains, respectively, on the expression of the four CYP genes was evaluated. In IVRI-IV strain, the CYP41 gene was highly overexpressed (FC 8.72) while CYP3006G8 was underexpressed with FC of 0.06. All the four genes were overexpressed in IVRI-V strain. After exposure to deltamethrin, the CYP3006G8 transcript levels were significantly upregulated at all time intervals in both resistant strains with the highest FC of 11.62 at 12 h in IVRI-IV and 13.38 at 3 h in IVRI-V. Our results suggest that the constitutive overexpression of CYP41 and deltamethrin induced upregulation of CYP3006G8 contribute to the development of pyrethroid resistance, specifically deltamethrin, in these two reference strains.

Post-transcriptional modulation of cytochrome P450s, Cyp6g1 and Cyp6g2, by miR-310s cluster is associated with DDT-resistant Drosophila melanogaster strain 91-R

The role of miRNAs in mediating insecticide resistance remains largely unknown, even for the model species Drosophila melanogaster. Building on prior research, this study used microinjection of synthetic miR-310s mimics into DDT-resistant 91-R flies and observed both a significant transcriptional repression of computationally-predicted endogenous target P450 detoxification genes, Cyp6g1 and Cyp6g2, and also a concomitant increase in DDT susceptibility. Additionally, co-transfection of D. melanogaster S2 cells with dual luciferase reporter constructs validated predictions that miR-310s bind to target binding sites in the 3ʹ untranslated regions (3ʹ-UTR) of both Cyp6g1 and Cyp6g2 in vitro. Findings in the current study provide empirical evidence for a link between reduced miRNA expression and an insecticidal resistance phenotype through reduced targeted post-transcriptional suppression of transcripts encoding proteins involved in xenobiotic detoxification. These insights are important for understanding the breadth of adaptive molecular changes that have contributed to the evolution of DDT resistance in D. melanogaster.

Dietary antioxidants impact DDT resistance in Drosophila melanogaster

Insects experience a diversity of subtoxic and/or toxic xenobiotics through exposure to pesticides and, in the case of herbivorous insects, through plant defensive compounds in their diets. Many insects are also concurrently exposed to antioxidants in their diets. The impact of dietary antioxidants on the toxicity of xenobiotics in insects is not well understood, in part due to the challenge of developing appropriate systems in which doses and exposure times (of both the antioxidants and the xenobiotics) can be controlled and outcomes can be easily measured. However, in Drosophila melanogaster, a well-established insect model system, both dietary factors and pesticide exposure can be easily controlled. Additionally, the mode of action and xenobiotic metabolism of dichlorodiphenyltrichloroethane (DDT), a highly persistent neurotoxic organochlorine insecticide that is detected widely in the environment, have been well studied in DDT-susceptible and -resistant strains. Using a glass-vial bioassay system with blue diet as the food source, seven compounds with known antioxidant effects (ascorbic acid, β-carotene, glutathione, α-lipoic acid, melatonin, minocycline, and serotonin) were orally tested for their impact on DDT toxicity across three strains of D. melanogaster: one highly susceptible to DDT (Canton-S), one mildly susceptible (91-C), and one highly resistant (91-R). Three of the antioxidants (serotonin, ascorbic acid, and β-carotene) significantly impacted the toxicity of DDT in one or more strains. Fly strain and gender, antioxidant type, and antioxidant dose all affected the relative toxicity of DDT. Our work demonstrates that dietary antioxidants can potentially alter the toxicity of a xenobiotic in an insect population.

Transcriptional Response of ATP-Binding Cassette (ABC) Transporters to Insecticide in the Brown Planthopper, Nilaparvata lugens (Stål)

The ATP-binding cassette (ABC) transporter superfamily is one of the largest groups of proteins and plays a non-negligible role in phase III of the detoxification process, which is highly involved in the response of insects to environmental stress (plant secondary metabolites and insecticides). In the present study, in Nilaparvata lugens, we identified 32 ABC transporters, which are grouped into eight subfamilies (ABCA–H) based on phylogenetic analysis. The temporal and spatial expression profiles suggested that the nymphal stages (1st–5th) and adult males showed similarity, which was different from eggs and adult females, and NlABCA1, NlABCA2, NlABCB6, NlABCD2, NlABCG4, NlABCG12, NlABCG15, and NlABCH1 were highly expressed in the midgut and Malpighian tubules. In addition, ABCG12, which belongs to the ABC transporter G subfamily, was significantly upregulated after exposure to sulfoxaflor, nitenpyram, clothianidin, etofenprox, chlorpyrifos, and isoprocarb. Moreover, verapamil significantly increased the sensitivity of N. lugens to nitenpyram, clothianidin, etofenprox, chlorpyrifos, and isoprocarb. These results provide a basis for further research on ABC transporters involved in detoxification in N. lugens, and for a more comprehensive understanding of the response of N. lugens to environmental stress.

Transposable elements contribute to the genomic response to insecticides in Drosophila melanogaster

Most of the genotype–phenotype analyses to date have largely centred attention on single nucleotide polymorphisms. However, transposable element (TE) insertions have arisen as a plausible addition to the study of the genotypic–phenotypic link because of to their role in genome function and evolution. In this work, we investigate the contribution of TE insertions to the regulation of gene expression in response to insecticides. We exposed four Drosophila melanogaster strains to malathion, a commonly used organophosphate insecticide. By combining information from different approaches, including RNA-seq and ATAC-seq, we found that TEs can contribute to the regulation of gene expression under insecticide exposure by rewiring cis-regulatory networks.

This article is part of a discussion meeting issue ‘Crossroads between transposons and gene regulation’.

A review of DDT resistance as it pertains to the 91-C and 91-R strains in Drosophila melanogaster

While insecticide resistance presents a challenge for those intent on controlling insect populations, these challenges have also generated a set of tools that can be used to ask fundamental biological questions about that resistance. Numerous species of insects have evolved resistance to multiple classes of insecticides. Each one of these species and their respective resistant populations represent a potential tool for understanding the molecular basis of the evolution of resistance. However, in-laboratory maintenance of resistant insect populations (and their comparative susceptible populations) suitable for asking the needed set of questions around the molecular consequences of long-term pesticide exposure requires a significant, in places prohibitive, level of resources. Drosophila melanogaster (hereafter referred to as Drosophila) is a model insect system with populations easily selected with pesticides and readily maintainable over decades. Even within Drosophila, however, few populations exist where long-term pesticide selection has occurred along with contrasting non-selected population. As such, the Drosophila 91-C and 91-R populations, which exhibit insecticide resistance to DDT (91-R), compared to a non-selection population (91-C), represent a unique resource for the study of high level DDT resistance. Moreover, with the availability of "omics" technologies over the past several decades, this paired population has emerged as a useful tool for understanding both the molecular basis of pesticide resistance and the molecular consequences of long-term pesticide exposure. In this review, we summarize the studies with these aforementioned populations over the past several decades, addressing what has been learned from these efforts.

Impacts of Sub-lethal DDT Exposures on microRNA and Putative Target Transcript Expression in DDT Resistant and Susceptible Drosophila melanogaster Strains

Ten constitutively differentially expressed miRNAs were previously described between DDT-resistant 91-R and -susceptible control Drosophila melanogaster strains, and among their predicted target genes were those associated with metabolic DDT resistance mechanisms. The present study evaluated the inducibility of miRNA expression and putative downstream regulation of cytochrome P450s in response to DDT exposure in a time-dependent manner in 91-R and the susceptible Canton-S strain. Specifically, RT-qPCR analysis showed that DDT exposures led to the significant down-regulation (repression) of miR-310-3p, miR-311-3p, miR-312-3p, miR-313-3p, and miR-92a-3p levels in Canton-S. This is contrasted with the lack of significant changes in 91-R at most time-points following DDT exposure. The levels of expression among miRNAs exhibited opposite expression patterns compared to their corresponding putative target cytochrome P450s at the same time points after DDT exposure. Collectively, results from this study suggest that miR-310-3p, miR-311-3p, miR-312-3p, miR-313-3p, and miR-92a-3p might have a potential role in the control of DDT detoxification through the post-transcriptional regulation of target cytochrome P450s in Canton-S. Conversely, the lack of significant changes of these same miRNAs in 91-R following DDT-exposure suggests a possible adaptive mutation that removes repressive control mechanisms. These data are important for the understanding impact of adaptive changes in miRNA expression on post-transcriptional regulatory mechanism involved in the evolution of DDT resistance in 91-R.