Two delta class glutathione S-transferases involved in the detoxification of malathion in Bactrocera dorsalis (Hendel)

Comparative toxicity and enzymatic detoxification responses in Spodoptera frugiperda (Lepidoptera: Noctuidae) to two insecticides

The fall armyworm (FAW), Spodoptera frugiperda Smith (Lepidoptera: Noctuidae), poses a significant threat to food security, necessitating effective management strategies. While chemical control remains a primary approach, understanding the toxicity and detoxification mechanisms of different insecticides is crucial. In this study, we conducted leaf-dipping bioassays to assess the toxicity of quinalphos and beta-cypermethrin·emamectin benzoate (β-cyp·EMB) on S. frugiperda larvae. Additionally, we assessed the response of alterations in CarE, GST, MFO, and AChE activities to sublethal concentrations of these insecticides over various treatment durations. Results indicated that β-cyp·EMB exhibited higher toxicity than quinalphos in S. frugiperda. Interestingly, the highest activities of GST, CarE, MFO, and AChE were observed at 6 h exposure to LC10 and LC25 of β-cyp·EMB, surpassing equivalent sublethal concentrations of quinalphos. Subsequently, GST and CarE activities exposure to β-cyp·EMB steadily decreased, while MFO and AChE activities exposure to both insecticides was initially decreased then increased. Conversely, two sublethal concentrations of quinalphos notably enhanced GST activity across all exposure durations, with significantly higher than β-cyp·EMB at 12-48 h. Similarly, CarE activity was also increased at various durations. Our research has exhibited significant alterations in enzyme activities exposure to both concentration and duration. Furthermore, Pearson correlation analysis showed significant correlations among these enzyme activities at different treatment durations. These findings contribute to a better understanding of detoxification mechanisms across different insecticides, providing valuable insights for the rational management of S. frugiperda populations.

The Fat Body-Specific GST Gene SlGSTe11 Enhances the Tolerance of Spodoptera litura to Cyantraniliprole and Nicotine

Spodoptera litura is a significant agricultural pest, and its glutathione S-transferase (GST) plays a crucial role in insecticide resistance. This study aimed to investigate the relationship between the SlGSTe11 gene of S. litura and resistance to cyantraniliprole and nicotine. Transcriptome analysis revealed that SlGSTe11 is highly expressed mainly in fat bodies, with a significant increase in SlGSTe11 gene expression under induction by cyantraniliprole and nicotine. The ectopic expression of the SlGSTe11 gene in transgenic fruit flies resulted in a 5.22-fold increase in the tolerance to cyantraniliprole. Moreover, compared to the UAS-SlGSTe11 line, the Act5C-UAS>SlGSTe11 line laid more eggs and had a lower mortality after nicotine exposure. RNAi-mediated inhibition of SlGSTe11 gene expression led to a significant increase in the mortality of S. litura under cyantraniliprole exposure. In vitro metabolism experiments demonstrated that the recombinant SlGSTe11 protein efficiently metabolizes cyantraniliprole. Molecular docking results indicated that SlGSTe11 has a strong affinity for both cyantraniliprole and nicotine. These findings suggest that SlGSTe11 is involved in the development of resistance to cyantraniliprole and nicotine in S. litura.

Dynamics of Bactrocera dorsalis Resistance to Seven Insecticides in South China

Bactrocera dorsalis is a highly invasive and destructive pest distributed worldwide. Chemical insecticides remain the primary measure for their control; however, this species has already developed resistance to several insecticides. In recent years, there have been several reports of monitoring B. dorsalis resistance in China, but continuous monitoring results are lacking and do not even span a decade. In this study, we monitored the dynamics of resistance to seven insecticides among 11 geographically distinct Chinese populations of B. dorsalis (2010-2013; follow-up in 2023). The 11 populations were found to adapt rapidly to antibiotic insecticides (spinosad, emamectin benzoate, and avermectin), reaching high levels of insecticide resistance in several areas. Overall, a decreasing trend in resistance to organophosphorus insecticides (chlorpyrifos and trichlorfon) was observed, whereas pyrethroid (beta-cypermethrin and cyhalothrin) resistance trends were observed to both increase and decrease. The monitoring of field resistance among different B. dorsalis populations over the duration of this study is important for improving the efficiency and sustainability of agricultural pest management, and the results provide a scientific basis for the development of more effective resistance management strategies.

Heterologous expression and characterization of two delta glutathione S-transferases genes involved in imidacloprid metabolism in Grapholita molesta

Glutathione S-transferases (GSTs) are multifunctional enzymes, and insect GSTs play a pivotal role in the metabolism of insecticides. Grapholita molesta is a worldwide pest that causes substantial economic losses to the fruit industry. However, it remains unclear how imidacloprid, a commonly used insecticide in orchards, is metabolized by G. molesta. In the present study, the synergist diethyl maleate (DEM), which inhibits the GST activity, exhibited a 22-fold synergistic ratio against imidacloprid. Two new GST genes, GmGSTD2 (OR096251) and GmGSTD3 (OR096252), were identified and successfully cloned, showing the highest expression in the Malpighian tubes. Knockdown of GmGSTD2 and GmGSTD3 by RNA interference, increased the mortality of G. molesta from 28% to 47% following imidacloprid treatment. Both recombinant GmGSTD2 and GmGSTD3 proteins exhibited 1-chloro-2,4-dinitrobenzene (CDNB) activity and could be inhibited by imidacloprid in vitro, with maximum inhibition was 60% for GmGSTD2 and 80% for GmGSTD3. These results suggested that GSTs participate in the metabolism of imidacloprid with GmGSTD2 and GmGSTD3 playing key roles in this process.

Functional Analysis of Insecticide Inhibition and Metabolism of Six Glutathione S-Transferases in the Rice Stem Borer, Chilo suppressalis

The glutathione S-transferases (GSTs) are important detoxifying enzymes in insects. Our previous studies found that the susceptibility of Chilo suppressalis to abamectin was significantly increased when the CsGST activity was inhibited by glutathione (GSH) depletory. In this study, the potential detoxification mechanisms of CsGSTs to abamectin were explored. Six CsGSTs of C. suppressalis were expressed in vitro. Enzymatic kinetic parameters including Km and Vmax of recombinant CsGSTs were determined, and results showed that all of the six CsGSTs were catalytically active and displaying glutathione transferase activity. Insecticide inhibitions revealed that a low concentration of abamectin could effectively inhibit the activities of CsGSTs including CsGSTd1, CsGSTe4, CsGSTo2, CsGSTs3, and CsGSTu1. However, the in vitro metabolism assay found that the six CsGSTs could not metabolize abamectin directly. Additionally, the glutathione transferase activity of CsGSTs in C. suppressalis was significantly increased post-treatment with abamectin. Comprehensive analysis of the results in present and our previous studies demonstrated that CsGSTs play an important role in detoxification of abamectin by catalyzing the conjugation of GSH to abamectin in C. suppressalis, and the high binding affinities of CsGSTd1, CsGSTe4, CsGSTo2, CsGSTs3, and CsGSTu1 with abamectin might also suggest the involvement of CsGSTs in detoxification of abamectin via the noncatalytic passive binding and sequestration instead of direct metabolism. These studies are helpful to better understand the detoxification mechanisms of GSTs in insects.

Suppressing the expression of glutathione S-transferase gene GSTd10 increases the sensitivity of Zeugodacus cucurbitae against β-cypermethrin

Zeugodacus cucurbitae Coquillett (Diptera: Tephritidae) is an agriculturally and economically important pest worldwide that has developed resistance to β-cypermethrin. Glutathione S-transferases (GSTs) have been reported to be involved in the detoxification of insecticides in insects. We have found that both ZcGSTd6 and ZcGSTd10 were up-regulated by β-cypermethrin induction in our previous study, so we aimed to explore their potential relationship with β-cypermethrin tolerance in this study. The heterologous expression of ZcGSTd6 and ZcGSTd10 in Escherichia coli showed significantly high activities against 1-chloro-2,4-dinitrobenzene (CDNB). The kinetic parameters of ZcGSTd6 and ZcGSTd10 were determined by Lineweaver-Burk. The Vmax and Km of ZcGSTd6 were 0.50 μmol/min·mg and 0.3 mM, respectively. The Vmax and Km of ZcGSTd10 were 1.82 μmol/min·mg and 0.53 mM. The 3D modelling and molecular docking results revealed that β-cypermethrin exhibited a stronger bounding to the active site SER-9 of ZcGSTd10. The sensitivity to β-cypermethrin was significantly increased by 18.73% and 27.21%, respectively, after the knockdown of ZcGSTd6 and ZcGSTd10 by using RNA interference. In addition, the inhibition of CDNB at 50% (IC50) and the inhibition constants (Ki) of β-cypermethrin against ZcGSTd10 were determined as 0.41 and 0.33 mM, respectively. The Ki and IC50 of β-cypermethrin against ZcSGTd6 were not analysed. These results suggested that ZcGSTd10 could be an essential regulator involved in the tolerance of Z. cucurbitae to β-cypermethrin.

Overexpression of an Integument Esterase Gene LbEST-inte4 Infers the Malathion Detoxification in Liposcelis bostrychophila (Psocoptera: Liposcelididae)

Liposcelis bostrychophila, commonly known as booklouse, is an important stored-product pest worldwide. Studies have demonstrated that booklices have developed resistance to several insecticides. In this study, an integument esterase gene, LbEST-inte4, with upregulated expression, was characterized in L. bostrychophila. Knockdown of LbEST-inte4 resulted in a substantial increase in the booklice susceptibility to malathion. Overexpression of LbEST-inte4 in Drosophila melanogaster significantly enhanced its malathion tolerance. Molecular modeling and docking analysis suggested potential interactions between LbEST-inte4 and malathion. When overexpressed LbEST-inte4 in Sf9 cells, a notable elevation in esterase activity and malathion tolerance was observed. HPLC analysis indicated that the LbEST-inte4 enzyme could effectively degrade malathion. Taken together, the upregulated LbEST-inte4 appears to contribute to malathion tolerance in L. bostrychophila by facilitating the depletion of malathion. This study elucidates the molecular mechanism underlying malathion detoxification and provides the foundations for the development of effective prevention and control measures against psocids.

Molecular and functional characterization of an antenna-enriched glutathione S-transferase BminGSTd3 involved in undecanol degradation in the citrus fruit fly, Bactrocera minax (Enderlein) (Diptera Tephritidae)

Bactrocera minax is a disastrous pest of citrus crops in China. Numerous studies focused on the molecular mechanism of odorant perception of B. minax, but the molecular mechanism of odorant degradation remains unclear. Glutathione S-transferases (GSTs) are considered as a class of odorant-degrading enzymes involved in degrading odorant molecules in insects' olfactory system. Here, we identified a delta-class GST gene, BminGSTd3, from B. minax. It was predominantly expressed in adult's olfactory organ antennae. The bacterially expressed recombinant BminGSTd3 was able to catalyze the conjugation of glutathione (GSH) with 2, 4-dinitrochlorobenzene (CDNB). Spectrophotometric analysis showed that undecanol can inhibit catalytic activities of BminGSTd3. Metabolic assays exhibited that undecanol can be depleted by BminGSTd3. Undecanol is believed to be an important B. minax sex pheromone component. The other components of the pheromone remain unclear. To understand how BminGSTd3 specifically recognizes undecanol, a 3D model of BminGSTd3 was constructed by homology modeling. Molecular docking based on this model revealed that E64 and S65 are the key amino acids recognizing undecanol, and this was proven by site-directed mutagenesis and intrinsic fluorescence assays. We suggest that BminGSTd3 is an undecanol metabolizing GST in B.minax, and E64 and S65 may serve as the key binding sites.

Identification and Functional Analysis of an Epsilon Class Glutathione S-Transferase Gene Associated with α-Pinene Adaptation in Monochamus alternatus

Alpha-pinene is one of the main defensive components in conifers. Monochamus alternatus (Coleoptera: Cerambycidae), a wood borer feeding on Pinaceae plants, relies on its detoxifying enzymes to resist the defensive terpenoids. Here, we assayed the peroxide level and GST activity of M. alternatus larvae treated with different concentrations of α-pinene. Meanwhile, a gst gene (MaGSTe3) was isolated and analyzed. We determined its expression level and verified its function. The results showed that α-pinene treatment led to membrane lipid peroxidation and thus increased the GST activity. Expression of MaGSTe3 was significantly upregulated in guts following exposure to α-pinene, which has a similar pattern with the malonaldehyde level. In vitro expression and disk diffusion assay showed that the MaGSTe3 protein had high antioxidant capacity. However, RNAi treatment of MaGSTe3 did not reduce the hydrogen peroxide and malonaldehyde levels, while GST activity was significantly reduced. These results suggested MaGSTe3 takes part in α-pinene adaptation, but it does not play a great role in the resistance of M. alternatus larvae to α-pinene.

Cuticular competing endogenous RNAs regulate insecticide penetration and resistance in a major agricultural pest

BACKGROUND

The continuously developing pesticide resistance is a great threat to agriculture and human health. Understanding the mechanisms of insecticide resistance is a key step in dealing with the phenomenon. Insect cuticle is recently documented to delay xenobiotic penetration which breaks the previous stereotype that cuticle is useless in insecticide resistance, while the underlying mechanism remains scarce.

RESULTS

Here, we find the integument contributes over 40.0% to insecticide resistance via different insecticide delivery strategies in oriental fruit fly. A negative relationship exists between cuticle thickening and insecticide penetration in resistant/susceptible, also in field strains of oriental fruit fly which is a reason for integument-mediated resistance. Our investigations uncover a regulator of insecticide penetration that miR-994 mimic treatment causes cuticle thinning and increases susceptibility to malathion, whereas miR-994 inhibitor results in opposite phenotypes. The target of miR-994 is a most abundant cuticle protein (CPCFC) in resistant/susceptible integument expression profile, which possesses capability of chitin-binding and influences the cuticle thickness-mediated insecticide penetration. Our analyses find an upstream transcriptional regulatory signal of miR-994 cascade, long noncoding RNA (lnc19419), that indirectly upregulates CPCFC in cuticle of the resistant strain by sponging miR-994. Thus, we elucidate the mechanism of cuticular competing endogenous RNAs for regulating insecticide penetration and demonstrate it also exists in field strain of oriental fruit fly.

CONCLUSIONS

We unveil a regulatory axis of lnc19419 ~ miR-994 ~ CPCFC on the cuticle thickness that leads to insecticide penetration resistance. These findings indicate that competing endogenous RNAs regulate insecticide resistance by modulating the cuticle thickness and provide insight into the resistance mechanism in insects.

Functional analysis of an overexpressed glutathione S-transferase BdGSTd5 involved in malathion and malaoxon detoxification in Bactrocera dorsalis

Glutathione S-transferases (GSTs) are one of the three detoxification enzyme families. The constitutive and inducible overexpression of GSTs genes plays an important role in insecticide resistance. Previous study showed that malathion resistance was polygenic, and elevated GSTs activity was one of the important factor participating in malathion resistance of Bactrocera dorsalis (Hendel), a serious economic pest worldwide. BdGSTd5 overexpression was inducible upon exposure to malathion. However, the involvement of BdGSTd5 in malathion resistance has not been clarified. In this study, we found that BdGSTd5 sequence harbored the conserved region of delta class GSTs, which were overexpressed in malathion resistant strain of B. dorsalis compared to malathion susceptible strain. The highest mRNA expression level of BdGSTd5 was found in 1-day-old adult, and the levels decreased with aging. The dsBdGSTd5 injection effectively silenced (73.4% reduction) the expression of BdGSTd5 and caused significant increase in susceptibility to malathion with a cumulative mortality increasing of 13.5% at 72 h post malathion treatment (p < 0.05). Cytotoxicity assay demonstrated that BdGSTd5 was capable of malathion detoxification. Molecular docking analysis further indicated the interactive potential of BdGSTd5 with malathion and its toxic oxide malaoxon. The recombinant BdGSTd5 exhibited glutathione-conjugating activity toward 1-chloro-2, 4-dinitrobenzene and malathion and malaoxon metabolic capacity with significant reduction (p < 0.05) of the peak areas by 90.0% and 73.1%, respectively. Taken together, the overexpressed BdGSTd5 contributes to malathion metabolism and resistance, which detoxify the malathion in B. dorsalis via directly depleting malathion and malaoxon.

Genome-wide screening and expression of glutathione S-transferase genes reveal that GSTe4 contributes to sensitivity against β-cypermethrin in Zeugodacus cucurbitae

Glutathione S-transferases (GSTs) are an essential multifunctional protein family with common detoxifying enzymes. In this study, 34 GST genes were identified from the melon fly, Zeugodacus cucurbitae, one of the most destructive pests worldwide. These GSTs include 32 cytosolic genes and two microsomal genes. Furthermore, these cytosolic GSTs were classified into six classes: 11 delta, 13 epsilon, three theta, one sigma, two zeta, and two omega. Most of these showed dynamic expression during the developmental stage, some of which showed stage-specific expression. The expression in various adult tissues showed that most of them were expressed in anti-stress-related tissues. The transcriptional response of the delta and epsilon families was determined when Z. cucurbitae was exposed to three insecticides, abamectin, dinotefuran, and β-cypermethrin. Seven genes were significantly up-regulated by abamectin exposure. Moreover, five and four genes were significantly up-regulated with dinotefuran and β-cypermethrin exposure, respectively, demonstrating their involvement in the detoxification of these such toxic substances in Z. cucurbitae. One example of these genes, ZcGSTe4, was randomly selected to explore its function in response to β-cypermethrin exposure. Over-expressed ZcGSTe4 in E. coli showed significant tolerance to β-cypermethrin, and RNAi-mediated suppression of ZcGSTe4 also increased the sensitivity of melon fly to this agent. This study provides a foundation for further studies on the mechanism of detoxification metabolism in the melon fly.

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

BACKGROUND

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

RESULTS

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

CONCLUSION

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

Chromosome-level genome assembly reveals potential epigenetic mechanisms of the thermal tolerance in the oriental fruit fly, Bactrocera dorsalis

The oriental fruit fly, Bactrocera dorsalis (Hendel), has very strong ecological adaptability and phenotypic plasticity. Here, the genome of B. dorsalis was assembled into 549.45 Mb sequences with a contig N50 length of 12.81 Mb. Among, 95.67 % assembled genome sequences were anchored on six chromosomes with an N50 length of 94.63 Mb. According to the basic characteristics of the sex chromosomes of Tephritidae, the X chromosome of B. dorsalis was identified. Significant gene expansions were detected in several important gene families related to adaptability. In particular, we annotated 50 histone modification enzymes (HMEs) in this genome. A comparative transcriptome analysis indicated that 12 HME genes were differentially expressed in two thermo-tolerant strains (heat and cold). Interestingly, four and seven of the 12 HME genes responded to heat shock or cold hardening, respectively. These evidences suggested that the histone modification as an epigenetic modification may be involved in the thermal tolerance of B. dorsalis, but with different regulation mechanisms in thermal acclimation and hardening. The high quality genome of B. dorsalis provides an invaluable resource for further functional genomic study. Moreover, comparative genomic analysis will shed insights on revealing the mechanisms of adaptive evolution in this fly.

CYP4G100 contributes to desiccation resistance by mediating cuticular hydrocarbon synthesis in Bactrocera dorsalis

The oriental fruit fly Bactrocera dorsalis (Hendel) is expanding its distribution to higher latitudes. Our goal in this study was to understand how B. dorsalis adapts to higher latitude environments that are more arid than tropical regions. Cuticular hydrocarbons (CHCs) on the surface of the epicuticle in insects act as a hydrophobic barrier against water loss. The essential decarbonylation reaction in CHC synthesis is catalysed by CYP4G, a cytochrome P450 subfamily protein. Hence, in B. dorsalis it is necessary to clarify the function of the CYP4G gene and its role in desiccation resistance. CYP4G100 was identified in the B. dorsalis genome. The complete open reading frame (ORF) encodes a CYP4 family protein (552 amino acid residues) that has the CYP4G-specific insertion. This CYP4G gene was highly expressed in adults, especially in the oenocyte-rich peripheral fat body. The gene can be induced by desiccation treatment, suggesting its role in CHC synthesis and waterproofing. Silencing of CYP4G100 resulted in a decrease of CHC levels and the accumulation of triglycerides. It also increased water loss and resulted in higher desiccation susceptibility. CYP4G100 is involved in hydrocarbon synthesis and contributes to cuticle waterproofing to help B. dorsalis resist desiccation in arid environments.

Sublethal Dose of β-Cypermethrin Impairs the Olfaction of Bactrocera dorsalis by Suppressing the Expression of Chemosensory Genes

The oriental fruit fly, Bactrocera dorsalis, is one of the most destructive fruit insect pests. β-cypermethrin has been widely used in the orchard to control this major insect. Based on the resistance monitoring in 2011, B. dorsalis developed significant resistance against β-cypermethrin in fields. This indicated that the B. dorsalis has been exposed to sublethal concentrations of β-cypermethrin in the field for a long time. Thus, it is urgent to understand the sublethal effects of β-cypermethrin on this fly to guide the rational use of an insecticide. According to the olfactory preference assays and electroantennogram (EAG) recording, the B. dorsalis after β-cypermethrin exposure (LD₃₀ = 10 ng/fly) severely decreased the ability to perceive the tested odorants. Moreover, we then performed quantitative real-time PCR and found the chemosensory genes including odorant receptor co-receptor (BdorORco) and ionotropic receptor co-receptors (BdorIRcos) were obviously suppressed. Our results demonstrated that the sublethal dose of β-cypermethrin impairs the olfaction of the pest insects by suppressing the expression of chemosensory genes (BdorORco and BdorIRcos), which expanded our knowledge of the sublethal effects of the pesticide on insects.

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.

Metabolism and antioxidant activity of SlGSTD1 in Spodoptera litura as a detoxification enzyme to pyrethroids

Glutathione S-transferase (GSTs) are members of multifunction enzymes in organisms and mostly known for their roles in insecticide resistance by conjugation. Spodoptera litura (Fabricius) is a voracious agricultural pest widely distributed in the world with high resistance to various insecticides. The function of GSTs in the delta group of S. litura is still lacking. Significantly up-regulation of SlGSTd1 was reported in four pyrethroids-resistant populations and a chlorpyrifos-selected population. To further explore its role in pyrethroids and organophosphates resistance, the metabolism and peroxidase activity of SlGSTD1 were studied by heterologous expression, RNAi, and disk diffusion assay. The results showed that K_m and V_max for 1-chloro-2,4-dinitrobenzene (CDNB) conjugating activity of SlGSTD1were 1.68 ± 0.11 mmol L⁻¹ and 76.0 ± 2.7 nmol mg⁻¹ min⁻¹, respectively. Cyhalothrin, beta-cypermethrin, and chlorpyrifos had an obvious inhibitory effect on SlGSTD1 activity, especially for fenvalerate, when using CDNB as substrate. Fenvalerate and cyhalothrin can be metabolized by SlGSTD1 in E. coli and in vitro. Also, silencing of SlGSTd1 significantly increased the toxicity of fenvalerate and cyhalothrin, but had no significant effect on the mortality of larvae treated by beta-cypermethrin or chlorpyrifos. SlGSTD1 possesses peroxidase activity using cumene hydroperoxide as a stress inducer. The comprehensive results indicate that SlGSTD1 is involved in fenvalerate and cyhalothrin resistance of S. litura by detoxication and antioxidant capacity.

Monarda didyma Hydrolate Affects the Survival and the Behaviour of Drosophila suzukii

Simple Summary

During the steam distillation of aromatic plants, two main fractions are usually obtained: the hydrophobic essential oils and the hydrophilic fraction commonly known as hydrolate (HY). The essential oils are largely used in several industry fields, including the agricultural industry as biopesticides. Residual HYs, instead, are often discarded as by-products of little or no value. Our research pointed out that also HYs have biological activity, suggesting their potential use in plant-based strategy for the pest control. In more detail, we investigated the insecticidal properties of the hydrolate from Monarda didyma, scarlet beebalm, towards Drosophila suzukii. Using specific molecular and behavioural assays, we showed that M. didyma hydrolate affected the fitness and behaviour of D. suzukii, providing new insights in the D. suzukii control strategies through M. didyma hydrolate.

Abstract

Drosophila suzukii (Matsumara) is an herbivorous pest whose control in the field with conventional chemical is particularly difficult and has important drawbacks. Here, we investigated the insecticidal properties of hydrolate from Monarda didyma, scarlet beebalm, an aromatic herb in the Lamiaceae family. The identification of volatile organic compounds (VOCs) by CG–MS systems revealed that thymol (38%) and carvacrol (59%) were the most abundant VOCs in the hydrolate. M. didyma hydrolate did not show fumigant toxicity. Conversely, in contact assays, M. didyma hydrolate showed a LC₅₀ of 5.03 µL mL⁻¹, 48 h after the application on D. suzukii adults. Expression of detoxification genes increased in flies that survived the LC₅₀ application. Furthermore, toxicity persisted for 7 days after the treatment in the survival evaluation. Artificial diet assays with 100 and 1000 µL mL⁻¹ of M. didyma hydrolate resulted in a significant decrease in total food intake in both male and female D. suzukii adults. In addition, electropenetrography (EPG) showed that the D. suzukii females’ feeding behaviour was altered in hydrolate-treated diets. The hydrolate also caused a significant reduction in the number of eggs laid in two different oviposition assays. Overall, our findings provide a new perspective for the improvement of D. suzukii control strategies through M. didyma hydrolate.

The role of Glutathione-S-transferases in phoxim and chlorfenapyr tolerance in a major mulberry pest, Glyphodes pyloalis walker (Lepidoptera: Pyralidae)

Glyphodes pyloalis Walker is a destructive pest on mulberry trees and poses a significant threat to the sericultural industry in China. Phoxim and chlorfenapyr are two commonly used insecticides in mulberry fields. Glutathione-S-transferases (GSTs) comprise a multifunctional protein superfamily that plays important roles in the detoxification of insecticides and xenobiotic compounds in insects. However, whether GSTs participate in the tolerance of phoxim and chlorfenapyr in G. pyloalis is still unknown. To better understand the mechanism of insecticide tolerance in G. pyloalis, the enzymatic activity of GSTs was evaluated under phoxim and chlorfenapyr exposure, respectively. GST enzyme activity was significantly increased after 12, 36 and 48 h of phoxim treatment and 12, 24, 36 and 48 h of chlorfenapyr treatment. Subsequently, eighteen GST genes were identified from the larvae transcriptome of G. pyloalis. Among these, ten GpGSTs had GSH-binding sites and fifteen GpGSTs had variable hydrophobic substrate-binding sites. The expression levels of Delta-GpGST and Epsilon-GpGST genes were significantly influenced by phoxim and chlorfenapyr treatment, and by the time post insecticide application. Furthermore, after silencing GpGST-E4, the mortality rate of G. pyloalis larvae was increased when they were exposed to chlorfenapyr, but it did not significantly alter when the larvae were exposed to phoxim. Our results indicated the vital roles of GpGSTs in the tolerance of insecticides and this action depends on the categories of insecticides. The present study provides a theoretical basis for elucidating insecticide susceptibility and promotes functional research on GST genes in G. pyloalis.

Multi-insecticide resistant malaria vectors in the field remain susceptible to malathion, despite the presence of Ace1 point mutations

Insecticide resistance in Anopheles mosquitoes is seriously threatening the success of insecticide-based malaria vector control. Surveillance of insecticide resistance in mosquito populations and identifying the underlying mechanisms enables optimisation of vector control strategies. Here, we investigated the molecular mechanisms of insecticide resistance in three Anopheles coluzzii field populations from southern Côte d’Ivoire, including Agboville, Dabou and Tiassalé. All three populations were resistant to bendiocarb, deltamethrin and DDT, but not or only very weakly resistant to malathion. The absence of malathion resistance is an unexpected result because we found the acetylcholinesterase mutation Ace1-G280S at high frequencies, which would typically confer cross-resistance to carbamates and organophosphates, including malathion. Notably, Tiassalé was the most susceptible population to malathion while being the most resistant one to the pyrethroid deltamethrin. The resistance ratio to deltamethrin between Tiassalé and the laboratory reference colony was 1,800 fold. By sequencing the transcriptome of individual mosquitoes, we found numerous cytochrome P450-dependent monooxygenases – including CYP6M2, CYP6P2, CYP6P3, CYP6P4 and CYP6P5 – overexpressed in all three field populations. This could be an indication for negative cross-resistance caused by overexpression of pyrethroid-detoxifying cytochrome P450s that may activate pro-insecticides, thereby increasing malathion susceptibility. In addition to the P450s, we found several overexpressed carboxylesterases, glutathione S-transferases and other candidates putatively involved in insecticide resistance.

Insecticide-based mosquito control has saved millions of lives from malaria and other vector-borne diseases. However, the emergence and increase of insecticide resistant Anopheles populations seriously threaten to derail malaria control programmes. Surveillance of insecticide resistance and understanding the underlying molecular mechanisms are key for choosing effective vector control strategies. Here, we characterised the degree and mechanisms of resistance in three malaria vector populations from Côte d’Ivoire. Our key finding was that these multi-insecticide resistant malaria vectors largely remained susceptible to malathion, despite the presence of a mutation in the target enzyme of this organophosphate insecticide that would typically confer resistance. Intriguingly, we found overexpression of metabolic P450 enzymes that are known to detoxify insecticides and activate pro-insecticides such as malathion. It is highly probable that, here, we observed P450-mediated negative cross-resistance for the first time in Anopheles field populations. Negative cross-resistance merits further investigation as advantage could be taken of this phenomenon in the fight against multi-resistant malaria vectors.

SlGSTE9 participates in the stability of chlorpyrifos resistance in Spodoptera litura

BACKGROUND

Spodoptera litura is an important agricultural pest and has developed serious resistance to multiple insecticides. The resistance level to several insecticides is reported to be unstable, but the mechanism is less reported.

RESULTS

Chlorpyrifos and phoxim resistance level in a field-collected population of S. litura declined continuously from the first to the tenth generation and remained stable at the 11th and 12th generations without insecticide exposure. Synergist experiment showed that diethyl maleate and piperonyl butoxide significantly increased mortality to chlorpyrifos and phoxim in the first and sixth generations, but not in the 12th generation. The expression of 31 identified glutathione S-transferase (GST) genes in the third-instar larvae of S. litura in the first, sixth and 12th generations was determined, and eight genes were seen to decrease significantly in the sixth and 12th generations compared with the first generation. SlGSTe9 was selected for further functional study as it had higher abundance and significantly higher expression in the chlorpyrifos-resistant population than in the susceptible population. The recombinant protein of SlGSTE9 showed metabolism activity to chlorpyrifos in vitro and in Escherichia coli, but not to phoxim. Silencing of SlGSTe9 increased the cumulative mortality to chlorpyrifos significantly. SlGSTE9 also showed antioxidant activity to cumene hydroperoxide.

CONCLUSION

Our results suggest that SlGSTe9 is directly involved in chlorpyrifos resistance stability, but not in phoxim. SlGSTE9 may also participate in insecticides resistance by relieving the oxidase stress induced by insecticides. © 2021 Society of Chemical Industry.

Structural and Functional Characterization of One Unclassified Glutathione S-Transferase in Xenobiotic Adaptation of Leptinotarsa decemlineata

Arthropod Glutathione S-transferases (GSTs) constitute a large family of multifunctional enzymes that are mainly associated with xenobiotic or stress adaptation. GST-mediated xenobiotic adaptation takes place through direct metabolism or sequestration of xenobiotics, and/or indirectly by providing protection against oxidative stress induced by xenobiotic exposure. To date, the roles of GSTs in xenobiotic adaptation in the Colorado potato beetle (CPB), a notorious agricultural pest of plants within Solanaceae, have not been well studied. Here, we functionally expressed and characterized an unclassified-class GST, LdGSTu1. The three-dimensional structure of the LdGSTu1 was solved with a resolution up to 1.8 Å by X-ray crystallography. The signature motif VSDGPPSL was identified in the “G-site”, and it contains the catalytically active residue Ser14. Recombinant LdGSTu1 was used to determine enzyme activity and kinetic parameters using 1-chloro-2, 4-dinitrobenzene (CDNB), GSH, p-nitrophenyl acetate (PNA) as substrates. The enzyme kinetic parameters and enzyme-substrate interaction studies demonstrated that LdGSTu1 could catalyze the conjugation of GSH to both CDNB and PNA, with a higher turnover number for CDNB than PNA. The LdGSTu1 enzyme inhibition assays demonstrated that the enzymatic conjugation of GSH to CDNB was inhibited by multiple pesticides, suggesting a potential function of LdGSTu1 in xenobiotic adaptation.

Evolution of tolerance to chlorpyrifos causes cross-tolerance to another organophosphate and a carbamate, but reduces tolerance to a neonicotinoid and a pharmaceutical

Exposure to pesticides is a major stressor in freshwater ecosystems. While populations can evolve tolerance to pesticides and thereby ensure their persistence in contaminated environments, this may have important consequences for their sensitivity to other pollutants. Indeed, tolerance to one pollutant may both increase (as a cost of tolerance) or decrease (cross-tolerance) the sensitivity to other pollutants. Despite the increasing concern of pharmaceuticals in waterbodies, no patterns of pesticide-induced (cross-)tolerance have been studied. We conducted 48 h acute toxicity assays with a range of concentrations of different pollutants to determine how the evolution of tolerance to the insecticide chlorpyrifos affects the sensitivity to other pesticides and a pharmaceutical in the water flea Daphnia magna, a keystone zooplankton species in aquatic food webs. We capitalized on an experimental evolution trial with chlorpyrifos, hence could unambiguously identify any patterns in increased tolerance or sensitivity to the other pollutants as a direct result of the evolution of tolerance to chlorpyrifos. We found that evolution of tolerance to chlorpyrifos conferred cross-tolerance to another organophosphate, namely malathion (mean change in EC_50,48h: factor 3.1), and to the carbamate carbaryl (factor 1.7), confirming that a shared mode of action favours the evolution of cross-tolerance. While the evolution of tolerance to chlorpyrifos did not affect the sensitivity to the pyrethroid esfenvalerate, it increased the sensitivity to the neonicotinoid imidacloprid as shown by the decrease in EC_50,48h (factor 0.6). Notably, we demonstrated for the first time that the evolution of tolerance to a pesticide increased the sensitivity to a pharmaceutical, namely fluoxetine (decrease in EC_50,48h with factor 0.7), thereby identifying an overlooked cost of tolerance to a pesticide. Given the increasing exposure to pesticides and pharmaceuticals, our results highlight that considering cross-tolerance and costs of tolerance is crucial in risk assessment of both pesticides and pharmaceuticals in aquatic ecosystems.

Evaluation of Reference Genes for Quantitative Reverse Transcription Polymerase Chain Reaction in Bactrocera dorsalis (Diptera: Tephritidae) Subjected to Various Phytosanitary Treatments

Simple Summary

In this study, seven internal reference genes (G6PDH, GAPDH, RPL-32, Rpl-13, Rps-3, α-tub, and 18S) of Bactroceradorsalis under different quarantine treatments (heat treatment, cold treatment, methyl bromide fumigation, and irradiation) were screened. Finally, the most stable internal reference gene was selected, which laid a foundation for the further study of its resistance mechanisms to some abiotic stresses.

Abstract

Bactrocera dorsalis is a major pest that causes serious damage to many fruits. Although phytosanitary treatment methods have been developed for Bactrocera control, there is a lack of information related to the gene expression pattern of B. dorsalis subjected to phytosanitary treatment conditions. Prior to quantitative reverse transcription polymerase chain reaction analysis of the most stable reference genes in B. dorsalis (Diptera: Tephritidae), B. dorsalis third-instar larvae were exposed to various phytosanitary treatments; seven candidate reference genes (18S, G6PDH, GAPDH, RPL-13, RPL-32, RPS-3, and α-Tub) were amplified and their expression stabilities were evaluated using geNorm, NormFinder, BestKeeper, and RefFinder algorithms. Different reference genes were found under different stress conditions. G6PDH was the most stable gene after heat treatment. After cold treatment, α-Tub exhibited the highest expression stability. G6PDH expression stability was the highest after fumigation with methyl bromide. RPL-32 showed the highest expression stability after irradiation treatment. Collectively, RefFinder analysis results revealed G6PDH and RPL-32 as the most suitable genes for analyzing phytosanitary treatment in B. dorsalis. This study provides an experimental basis for further gene expression analyses in B. dorsalis subjected to various phytosanitary treatments, which can aid in the development of novel phytosanitary treatments against insect pests.

Transcriptional response of detoxifying enzyme genes in Bombyx mori under chlorfenapyr exposure

The silkworm, Bombyx mori (B. mori) is an important economic insect which ingests mulberry leaves and products the silk in industry. Chlorfenapyr is a new halogenated pyrrole insecticide which has been promoted for the control of mulberry insect pests in China. However, the detoxification mechanism of the silkworm to chlorfenapyr has not been investigated yet. In the present study, we first estimated the LC₃₀ dose of chlorfenapyr for 3rd instar B. mori larvae, and then, in order to characterise the chlorfenapyr detoxification mechanism, the transcriptomes of chlorfenapyr-treated and untreated 3rd instar B. mori larvae were compared using RNA-sequencing. In total, 146, 533, 126 and 148, 957, 676 clean reads were obtained from insecticide-treated and control silkworm larvae, respectively, and these reads generated 10, 954 genes. The transcriptional profile of silkworm larvae was significantly influenced by chlorfenapyr treatment. A total of 1196 differentially expressed genes (DEGs) were identified in insecticide-treated and control B. mori larvae, in which 644 genes were upregulated and 552 genes were downregulated. Results showed that multiple DEGs were enriched in detoxication-related gene ontology (GO) terms and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways. Eleven detoxifying enzyme genes which differentially expressed were screened, and their expression patterns were validated by qRT-PCR. Furthermore, we successfully knocked down all differentially upregulated detoxifying enzyme genes, and a bioassay showed that the mortality of chlorfenapyr-treated silkworm larvae was significantly higher after silencing these genes than in groups injected with dsGFP. The present study reveals the molecular basis of silkworm detoxification to chlorfenapyr exposure, and provides new insights into the management of insecticide damage in the silkworm.

Functional Analysis of SlGSTE12 in Pyrethroid and Organophosphate Resistance in Spodoptera litura

Glutathione S-transferase genes in the epsilon group were reported to function in insecticide resistance. SlGSTE12 was validated to be overexpressed in pyrethroid- and organophosphate-resistant populations of Spodoptera litura compared to a susceptible population. A functional study of heterologously expressed SlGSTE12 showed that K_m and V_max for 1-chloro-2,4-dinitrobenzene (CDNB) conjugating activity were 0.70 ± 0.18 mmol L^-1 and 90.6 ± 9.4 nmol mg^-1 min^-1, respectively. β-Cypermethrin and cyhalothrin showed much weaker inhibition of SlGSTE12 activity to CDNB conjugation than fenvalerate, chlorpyrifos, and phoxim. Ultrahigh-performance liquid chromatography analysis showed that SlGSTE12 had significant metabolism activity to fenvalerate and phoxim both in vitro and in Escherichia coli, especially to chlorpyrifos, and slight metabolism activity toward cyhalothrin only in vitro. Silencing of SlGSTE12 by RNAi increased the mortality to fenvalerate, cyhalothrin, and chlorpyrifos significantly. SlGSTE12 also had a significant antioxidant ability against cumene hydroperoxide. Our study suggested that SlGSTE12 could metabolize phoxim, fenvalerate, cyhalothrin, and especially chlorpyrifos. SlGSTE12 might also participate in pyrethroid and organophosphate resistance by antioxidant activity.

The adipokinetic hormone signaling system regulates the sensitivity of Bactrocera dorsalis to malathion

The neuropeptide adipokinetic hormone (AKH) binds to the AKH receptor (AKHR) to regulate carbohydrate and lipid metabolism. It also participates in the insect anti-stress response. We used RT-qPCR to detect the expression levels of 39 neuropeptides in malathion-susceptible (MS) and malathion-resistant (MR) strains of Bactrocera dorsalis. AKH and AKHR were highly expressed in the MR strain. Using a malathion bioassay and RNA interference (RNAi), we demonstrated that AKHR is involved in the susceptibility of B. dorsalis to malathion. We found significantly reduced expression of two detoxification enzyme genes (glutathione-S-transferase, GST and α-esterase, CarE) after AKHR RNAi. Based on our previous data, GSTd10 and CarE6 participate the direct metabolism of malathion in this fly, which is also verified by a malathion metabolism assay by HPLC using the crude enzymes in the current study. These results suggest that AKHR plays an important role in affecting malathion susceptibility via detoxification enzyme genes.

Genome-wide identification of long non-coding RNAs (lncRNAs) associated with malathion resistance in Bactrocera dorsalis

BACKGROUND

Long non-coding RNAs (lncRNAs) play important roles in the regulation of biological processes and have been identified in many species including insects. However, the association between lncRNAs and pesticide resistance in insect species such as Bactrocera dorsalis is unknown.

RESULTS

RNA-seq was performed on malathion resistant (MR1) and susceptible (MS) strains of B. dorsalis and a total of 6171 lncRNAs transcripts were identified. These included 3728 lincRNAs, 653 antisense lncRNAs, 1402 intronic lncRNAs, and 388 sense lncRNAs. A total of 40 and 52 upregulated lncRNAs were found in females and males of the MR1 strain compared to 54 and 49 in the same sexes of the MS strain, respectively. Twenty-seven of these lncRNAs showed the same trend of expression in both females and males in the MR1 strain, in which 15 lncRNAs were upregulated and 12 were downregulated. RT-qPCR results indicated that the differentially expressed lncRNAs were associated with malathion resistance. The lnc15010.10 and lnc3774.2 were highly expressed in the cuticle of the MR1 strain, indicating that these two lncRNAs may be related to malathion resistance. RNAi of lnc3774.2 and a bioassay showed that malathion resistance was possibly influenced by changes in the B. dorsalis cuticle.

CONCLUSION

LncRNAs of B. dorsalis potentially related to the malathion resistance were identified. Two lncRNAs appear to influence malathion resistance via modulating the structure, or components, of the cuticle. © 2021 Society of Chemical Industry.

Bioinformatic and immunological investigation of Per a 5 (delta class GST) allergen from Periplaneta americana

INTRODUCTION

GSTs are multifunctional enzymes involved in cellular detoxification and present as potent allergens in several sources. Present study investigates allergenic relevance of GST from P. americana and determine its cross reactive potential with other indoor allergen sources.

METHODS

Computational analysis with FASTA and ConSurf webserver was performed to determine potentially cross reactive allergens. Further, Per a 5 gene was cloned in pET 22b+ vector and expressed in E.coli BL21 cells and the rPer a 5 protein was purified using Ni-NTA affinity chromatography. Enzymatic activity of rPer a 5 was assessed using CDNB and cumene hydroperoxide. ELISA and immunoblot were performed using cockroach hypersensitive patient's sera. Functional activity of rPer a 5 was evaluated by basophil activation test. Inhibition studies were carried out with D. pteronyssinus, A. alternata and C. lunata extracts.

RESULTS

Per a 5 demonstrates highest sequence similarity with delta class GST of Blattella germanica (94.9%). It also exhibits significant sequence similarity (50-58%) with mite, fungal and helminth allergenic GSTs. ConSurf analysis reveals high degree of evolutionary similarity in N terminal region of Per a 5, especially at GST dimerization interface. The purified rPer a 5 protein resolved at 27 kDa on SDS-PAGE. The rPer a 5 protein exhibits GST activity and possess upto 65% immunoreactivity with cockroach hypersensitive patient's sera in ELISA and immunoblot. It upregulates expression of CD203c on basophils signifying its biological ability to activate effector cells. rPer a 5 significantly inhibits corresponding GSTs in P. americana, D. pteronyssinus, A. alternata and C. lunata with EC₅₀ values of 15.5 ng. 38.38 ng, 41.4 ng and 61.66 ng, respectively.

CONCLUSION

Recombinant delta class GST of P. americana is a clinically relevant allergen showing upto 65% immunoreactivity with hypersensitive patient's sera. Per a 5 GST allergen showed phylogenetic similarity with dust mite, fungal and birch allergens thereby demonstrating allergen cross reactivity.

The determination of Plutella xylostella (L.) GSTs (PxGSTs) involved in the detoxification metabolism of Tolfenpyrad

BACKGROUND

Insect glutathione S-transferases (GSTs) play a crucial role in insecticide detoxification. However, there remains a distinct lack of information regarding the role of GSTs in the detoxification of Tolfenpyrad (TFP) in insects.

RESULTS

Real-time quantitative PCR showed significant upregulation of PxGSTs after exposure to TFP for 6 h. An in vitro inhibition assay showed that TFP could inhibit PxGSTδ, PxGSTε and PxGSTσ, and the most pronounced inhibitory effect was on PxGSTσ. Metabolism assays displayed that PxGSTσ was superior to other test PxGSTs in metabolizing TFP. The molecular docking of TFP and PxGSTσ revealed that the H-bond provided by the sidechains of Tyr107 and Tyr162 were key to the detoxification of TFP by PxGSTσ. Further tests using mutant PxGSTσ proteins at the sites of Tyr107 (PxGSTσY107A) and Tyr162 (PxGSTσY162A) corroborated that the individual replacement of Tyr107 and Tyr162 could greatly weaken the binding and metabolic abilities to TFP.

CONCLUSION

Metabolic interactions between the Plutella xylostella (L.) GSTs (PxGSTs) and TFP were deciphered. This study illustrates the molecular metabolism mechanism of PxGSTσ towards TFP and provides theoretical underpinnings for the design and optimization of novel TFP-like insecticides. © 2020 Society of Chemical Industry.

A glutathione S-transferase (BdGSTd9) participates in malathion resistance via directly depleting malathion and its toxic oxide malaoxon in Bactrocera dorsalis (Hendel)

BACKGROUND

The oriental fruit fly, Bactrocera dorsalis (Hendel), is a widespread agricultural pest that has evolved resistance to many commonly used insecticides including malathion. Glutathione S-transferases (GSTs) are multifunctional enzymes that metabolize insecticides directly or indirectly. The specific mechanism used by GSTs to confer malathion resistance in B. dorsalis is unclear.

RESULTS

BdGSTd9 was identified from B. dorsalis and was expressed at twice the level in a malathion-resistant strain (MR) than in a susceptible strain (MS). By using RNAi of BdGSTd9, the toxicity of malathion against MR was increased. Protein modelling and docking of BdGSTd9 with malathion and malaoxon indicated key amino acid residues for direct binding in the active site. In vitro assays with engineered Sf9 cells overexpressing BdGSTd9 demonstrated lower cytotoxicity of malathion. High performance liquid chromatography (HPLC) analysis indicated that malathion could be broken down significantly by BdGSTd9, and it also could deplete the malathion metabolite malaoxon, which possesses a higher toxicity to B. dorsalis. Taken together, the BdGSTd9 of B. dorsalis could not only deplete malathion, but also react with malaoxon and therefore enhance malathion resistance.

CONCLUSION

BdGSTd9 is a component of malathion resistance in B. dorsalis. It acts by depleting both malathion and malaoxon. © 2020 Society of Chemical Industry.

Sublethal Effects of Triflumezopyrim on Biological Traits and Detoxification Enzyme Activities in the Small Brown Planthopper Laodelphax striatellus (Hemiptera: Delphacidae)

The small brown planthopper [Laodelphax striatellus (Fallén) (Hemiptera, Delphacidae)] is one of the most destructive insect pests of rice and has developed strong resistance to several kinds of chemical insecticides. Triflumezopyrim, a novel mesoionic insecticide developed by Corteva Agriscience (formerly DuPont Crop Protection), has efficient biological activity in controlling sucking insects, such as the planthopper. However, the effects of triflumezopyrim on the growth and reproduction of L. striatellus have not been reported. In this study, an F₅ generation was obtained by conducting five rounds of insecticide screening on a sensitive L. striatellus strain (F₀ generation). An age-stage life table procedure was used to evaluate the effects of a sublethal concentration (LC₅₀) of triflumezopyrim on the biological parameters of L. striatellus. Compared with those of the F₀ generation, the intrinsic rate of increase (r), the finite rate (λ), and the net reproductive rate (R₀) of the F₅ generation were significantly decreased; nevertheless, the average duration of life (T) was not significantly affected. The results of detoxification enzyme activity assays indicated that the glutathione S-transferase and cytochrome P450 monooxygenase (P450) activities in the F₅ generation were significantly higher than those in the F₀ generation. The contents of vitellogenin (Vg) and vitellogenin receptor (VgR) were also detected, and the results indicated that the contents of Vg and VgR in the F₅ generation were significantly decreased compared to those in the F₀ generation. Furthermore, we detected the relative expression of ecdysone receptor (EcR), Vg, and VgR in the F₀ and F₅ generations and found that the relative expression levels of Vg and VgR in the F₅ generation female adults were obviously lower than those in the F₀ generation (P < 0.05), whereas the relative expression of EcR was slightly increased, although the difference was not significant (P > 0.05). Based on these results, a sublethal concentration (median lethal concentration, LC₅₀) of triflumezopyrim may inhibit the generational growth and reproduction of L. striatellus. Moreover, our results may provide a reference for further studies of the suitability and resistance mechanisms of L. striatellus subjected to a sublethal dose of triflumezopyrim.

Genomic and transcriptomic analyses of glutathione S-transferases in an endoparasitoid wasp, Pteromalus puparum

Pteromalus puparum is a gregarious pupal endoparasitoid with a wide host range. It deposits eggs into pierid and papilionid butterfly pupae. Glutathione S-transferases (GSTs) are a family of multifunctional detoxification enzymes that act in xenobiotic metabolism in insects. Insect genome projects have facilitated identification and characterization of GST family members. We identified 20 putative GSTs in the P. puparum genome, including 19 cytosolic and one microsomal. Phylogenetic analysis showed that P. puparum GSTs are clustered into Hymenoptera-specific branches. Transcriptomic data of embryos, larvae, female pupae, male pupae, female adults, male adults, venom glands, carcass, salivary glands, and ovaries revealed stage-, sex-, and tissue-specific expression patterns of GSTs in P. puparum. This is the most comprehensive study of genome-wide identification, characterization, and expression profiling of GST family in hymenopterans. Our results provide valuable information for understanding the metabolic adaptation of this wasp.

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.