Divergent molecular evolution in glutathione S-transferase conferring malathion resistance in the oriental fruit fly, Bactrocera dorsalis (Hendel)

Odorant Binding Protein Expressed in Legs Enhances Malathion Tolerance in Bactrocera dorsalis (Hendel)

Bactrocera dorsalis is a highly invasive species and is one of the most destructive agricultural pests worldwide. Organophosphorus insecticides have been widely and chronically used to control it, leading to the escalating development of resistance. Recently, odorant binding proteins (OBPs) have been found to play a role in reducing insecticide susceptibility. In this study, we used RT-qPCR to measure the expression levels of four highly expressed OBP genes in the legs of B. dorsalis at different developmental stages and observed the effect of malathion exposure on their expression patterns. The results showed that OBP28a-2 had a high expression level in 5 day old adults of B. dorsalis, and its expression increased after exposure to malathion. By CRISPR/Cas9 mutagenesis, we generated OBP28a-2-/- null mutants and found that they were more susceptible to malathion than wild-type adults. Furthermore, in vitro direct affinity assays confirmed that OBP28a-2 has a strong affinity for malathion, suggesting that it plays a role in reducing the susceptibility of B. dorsalis to malathion. Our findings enriched our understanding of the function of OBPs. The results highlighted the potential role of OBPs as buffering proteins that help insects survive exposure to insecticides.

Characterization of three glutathione S-transferases potentially associated with adaptation of the wheat blossom midge Sitodiplosis mosellana to host plant defense

BACKGROUND

Insect glutathione S-transferases (GSTs), a multifunctional protein family, play a crucial role in detoxification of plant defensive compounds. However, they have been rarely investigated in Sitodiplosis mosellana, a destructive pest of wheat worldwide. In this study, we characterized for the first time a delta (SmGSTd1) and two epsilon GST genes (SmGSTe1 and SmGSTe2) and analyzed their expression patterns and functions associated with adaptation to host plant defense in this species.

RESULTS

Expression of these SmGST genes greatly increased in S. mosellana larvae feeding on resistant wheat varieties Kenong1006, Shanmai139 and Jinmai47 which contain higher tannin and ferulic acid, the major defensive compounds of wheat against this pest, compared with those feeding on susceptible varieties Xinong822, Xinong88 and Xiaoyan22. Their expression was also tissue-specific, most predominant in larval midgut. Recombinant SmGSTs expressed in Escherichia coli could catalyze the conjugation of 1-chloro-2,4-dinitrobenzene, with activity peak at pH around 7.0 and temperature between 30 and 40 °C. Notably, they could metabolize tannin and ferulic acid, with the strongest metabolic ability by SmGSTe2 against two compounds, followed by SmGSTd1 on tannin, and SmGSTe1 on ferulic acid.

CONCLUSION

The results suggest that these SmGSTs are important in metabolizing wheat defensive chemicals during feeding, which may be related to host plant adaptation of S. mosellana. Our study has provided information for future investigation and development of strategies such as host-induced gene silencing of insect-detoxifying genes for managing pest adaptation. © 2023 Society of Chemical Industry.

Mitochondrial coding genes mediate insecticide tolerance in the oriental fruit fly, Bactrocera dorsalis (Hendel)

The oriental fruit fly, Bactrocera dorsalis (Hendel), an invasive insect pest infesting fruits and vegetables, possesses a remarkable capacity for environmental adaptation. The investigation of behind mechanisms of the stress adaptability in B. dorsalis holds significantly practical relevance. Previous studies on the molecular mechanism underlying stress resistance in B. dorsalis have predominantly focused on nuclear-coding genes, with limited exploration on organelle-coding genes. In this study, we assessed alterations in the mitochondrial physiological parameters of B. dorsalis under exposure to malathion, avermectin, and beta-cypermethrin at LD50 dosages. The results showed that all three insecticides were capable of reducing mitochondrial complex IV activity and ATP content. Expression patterns of mitochondrial coding genes across different developmental stages, tissues and insecticide exposures were analyzed by RT-qPCR. The results revealed that these mitochondrial coding genes were expressed in various tissues and at different developmental stages. Particularly noteworthy, atp6, cox2, and cytb exhibited substantial up-regulation in response to malathion and avermectin treatment. Furthermore, RNAi-mediated knockdown of atp6 and cox2 resulted in the increased toxicity of malathion and avermectin against B. dorsalis, and cox2 silencing was also associated with the decreased complex IV activity. These findings suggest that atp6 and cox2 most likely play pivotal roles in mediating tolerance or resistance to malathion and avermectin in B. dorsalis. Our results provide novel insights into the role of mitochondrial coding genes in conferring tolerance to insecticides in B. dorsalis, with practical implications for controlling this pest in the field.

Preparation, purification, and biochemical of fat-degrading bacterial enzymes from pig carcass compost and its application

BACKGROUND

A lot of kitchen waste oil is produced every day worldwide, leading to serious environmental pollution. As one of the environmental protection methods, microorganisms are widely used treating of various wastes. Lipase, as one of the cleaning agents can effectively degrade kitchen waste oil. The composting process of pig carcasses produces many lipase producing microorganisms, rendering compost products an excellent source for isolating lipase producing microorganisms. To our knowledge, there are no reports isolating of lipase producing strains from the high temperature phase of pig carcass compost.

METHODOLOGY

Lipase producing strains were isolated using a triglyceride medium and identified by 16S rRNA gene sequencing. The optimal fermentation conditions for maximum lipase yield were gradually optimized by single-factor tests. The extracellular lipase was purified by ammonium sulfate precipitation and Sephadex G-75 gel isolation chromatography. Amino acid sequence analysis, structure prediction, and molecular docking of the purified protein were performed. The pure lipase's enzymatic properties and application potential were evaluated by characterizing its biochemical properties.

RESULTS

In this study, a lipase producing strain of Bacillus sp. ZF2 was isolated from pig carcass compost products, the optimal fermentation conditions of lipase: sucrose 3 g/L, ammonium sulfate 7 g/L, Mn2+ 1.0 mmol/L, initial pH 6, inoculum 5%, temperature 25 ℃, and fermentation time 48 h. After purification, the specific activity of the purified lipase reached 317.59 U/mg, a 9.78-fold improvement. Lipase had the highest similarity to the GH family 46 chitosanase and molecular docking showed that lipase binds to fat via two hydrogen bonds at Gln146 (A) and Glu203 (A). Under different conditions (temperature, metal ions, organic solvents, and surfactants), lipase can maintain enzymatic activity. Under different types of kitchen oils, lipase has low activity only for 'chicken oil', in treating other substrates, the enzyme activity can exceed 50%.

CONCLUSIONS

This study reveals the potential of lipase for waste oil removal, and future research will be devoted to the application of lipase.

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

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

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.

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.

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.

The metabolic resistance of Nilaparvata lugens to chlorpyrifos is mainly driven by the carboxylesterase CarE17

The involvement of carboxylesterases (CarEs) in resistance to chlorpyrifos has been confirmed by the synergism analysis in Nilaparvata lugens. However, the function of specific CarE gene in chlorpyrifos resistance and the transcriptional regulatory mechanism are obscure. Herein, the expression patterns of 29 CarE genes in the susceptible and chlorpyrifos-resistant strains were analyzed. Among them, CarE3, CarE17 and CarE19 were overexpressed in the resistant strain, and knockdown of either CarE gene by RNA interference significantly increased the susceptibility to chlorpyrifos. Remarkably, knockdown of CarE17 reduced the enzymatic activity of CarE by 88.63 % and showed a much greater effect on increasing chlorpyrifos toxicity than silencing other two CarE genes. Overexpression of CarE17 in Drosophila melanogaster decreased the toxicity of chlorpyrifos to transgenic fruit flies. Furthermore, the region between - 205 to + 256 of CarE17 promoter sequence showed the highest promoter activity, and 16 transcription factors (TFs) were predicted from this region. Among these TFs, Lim1β and C15 were overexpressed in the resistant strain. Knockdown of either TF resulted in reduced CarE17 expression and a decrease in resistance of N. lugens to chlorpyrifos. These results indicate that the constitutive overexpression of Lim1β and C15 induces CarE17 expression thus conferring chlorpyrifos resistance in N. lugens.

Evaluations of two glutathione S-transferase epsilon genes for their contributions to metabolism of three selected insecticides in Locusta migratoria

The insect-specific epsilon class of glutathione S-transferases (GSTEs) plays important roles in insecticide detoxification in insects. In our previous work, five GSTEs were identified in Locusta migratoria, and two recombinant GSTEs, rLmGSTE1 and rLmGSTE4, showed high catalytic activity when 1-chloro-2,4-dinitrobenzene (CDNB) was used as a substrate. In this work, we further investigated whether these two GSTEs could metabolize three insecticides including malathion, deltamethrin and DDT. Using ultra-high-performance liquid chromatography tandem mass spectrometry (UHPLC/MS) method, we found that rLmGSTE4, but not rLmGSTE1, can metabolize malathion and DDT. Malathion bioassays of L.migratoria after the expression of LmGSTE4 was suppressed by RNA interference (RNAi) showed increased insect mortality from 33.8% to 68.9%. However, no changes in mortality were observed in deltamethrin- or DDT-treated L.migratoria after the expression of LmGSTE4 was suppressed by RNAi. Our results provided direct evidences that LmGSTE4 participates in malathion detoxification in L.migratoria. These findings are important for understanding the mechanisms of insecticide resistance in L.migratoria and developing new strategies for managing the insect populations in the field.

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

BACKGROUND

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

RESULTS

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

CONCLUSION

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

Assessment of attractancy and safeness of (E)-coniferyl alcohol for management of female adults of Oriental fruit fly, Bactrocera dorsalis (Hendel)

BACKGROUND

Bactrocera dorsalis is a devastating pest on fruits and vegetables because the adult female is the key factor that determines the population density of offspring and the degree of host damage. Unfortunately, there is still a lack of effective female attractants for behavioral control. Males of B. dorsalis fed on methyl eugenol (ME) were shown to be more sexually attracted to females and, therefore, were more successful in mating over ME-deprived males.

RESULTS

In the current study, we demonstrated that (E)-coniferyl alcohol (E-CF), one of the ME metabolites in males, was highly attractive to sexually-mature females in laboratory bioassays. During the dusk courtship period, mature females showed the highest response to E-CF. However, there were no significant differences in olfactory responses to E-CF between virgin and mated mature females. Moreover, no obvious signs and symptoms of toxicity or death were observed in mice during a 14-day acute oral toxicity test. Toxicologically, no significant changes were observed in body weight, water intake, food consumption and absolute and relative organ weights between control and treated groups of healthy-looking mice, implying that E-CF could be regarded as non-toxic. Furthermore, cytotoxicity assessment revealed that E-CF was non-toxic against human fetal lung fibroblast 1 (HFL1), human breast cancer (MDA-MB-231), mouse embryonic hepatocytes (BNL-CL.2) and Spodoptera frugiperda ovary (SF-9) cell lines.

CONCLUSIONS

E-CF proved to be an effective, promising and eco-friendly lure to B. dorsalis females. Therefore, this study may facilitate the development of novel control strategies against B. dorsalis in the field.

Regulation of GSTu1-mediated insecticide resistance in Plutella xylostella by miRNA and lncRNA

The evolution of resistance to insecticides is well known to be closely associated with the overexpression of detoxifying enzymes. Although the role of glutathione S-transferase (GST) genes in insecticide resistance has been widely reported, the underlying regulatory mechanisms are poorly understood. Here, one GST gene (GSTu1) and its antisense transcript (lnc-GSTu1-AS) were identified and cloned, and both of them were upregulated in several chlorantraniliprole-resistant Plutella xylostella populations. GSTu1 was confirmed to be involved in chlorantraniliprole resistance by direct degradation of this insecticide. Furthermore, we demonstrated that lnc-GSTu1-AS interacted with GSTu1 by forming an RNA duplex, which masked the binding site of miR-8525-5p at the GSTu1-3′UTR. In summary, we revealed that lnc-GSTu1-AS maintained the mRNA stability of GSTu1 by preventing its degradation that could have been induced by miR-8525-5p and thus increased the resistance of P. xylostella to chlorantraniliprole. Our findings reveal a new noncoding RNA-mediated pathway that regulates the expression of detoxifying enzymes in insecticide-resistant insects and offer opportunities for the further understanding of the mechanisms of insecticide and drug resistance.

The development of insecticide resistance in insect pests is a worldwide concern and a major problem in agriculture. Understanding the genetics of insecticide resistance is critical for effective crop protection. Plutella. xylostella (L.), a major pest of cruciferous crops, has developed resistance to almost all kinds of insecticide, and has become one of the most resistant pests in the world. Overexpression of detoxification enzymes is closely associated with insecticide resistance, but researches on their regulatory mechanism are still very limited. Here, GSTu1 was identified to be upregulated in several chlorantraniliprole-resistant P. xylostella populations and was confirmed to be involved in chlorantraniliprole resistance by direct degradation of this insecticide. Further, lnc-GSTu1-AS transcribed from the opposite DNA strand to GSTu1 was identified to be able to enhance the mRNA stability of GSTu1 by blocking miRNA activity, and thus increased the resistance of P. xylostella to chlorantraniliprole. The results provide further insights into the mechanisms underlying metabolic resistance.

Activator protein-1 mediated CYP6ER1 overexpression in the clothianidin resistance of Nilaparvata lugens (Stål)

BACKGROUND

Nilaparvata lugens, a destructive rice pest in Asia, has developed resistance to many insecticides, including the neonicotinoid clothianidin. CYP6ER1 plays an important role in N. lugens resistant to clothianidin, but only limited information on the transcriptional regulation of CYP6ER1 overexpression in clothianidin resistance is available.

RESULTS

In this study, the transcription factor activator protein 1 (AP-1) was found to be overexpressed in a clothianidin-resistant strain of N. lugens and several field resistant populations. RNA interference-mediated silencing of NlAP-1 significantly decreased CYP6ER1 expression and increased the susceptibility of N. lugens to clothianidin. Additionally, NlAP-1 was highly expressed in egg and adult stages, and in midguts, and NlAP-1 was upregulated and induced to a greater extent in the clothianidin-resistant strain after exposure to clothianidin. Finally, dual-luciferase reporter assays confirmed the interaction between NlAP-1 and the two predicted binding sites in the CYP6ER1 promoter.

CONCLUSION

NlAP-1 bound the -1388 to -1208-bp region of the CYP6ER1 promoter, enhancing its activity and then regulate the expression of CYP6ER1. These findings enhance our knowledge of the transcriptional regulation of the P450 genes that mediate insecticide resistance in insect pests. © 2021 Society of Chemical Industry.

The effects of quercetin combined with nucleopolyhedrovirus on the growth and immune response in the silkworm (Bombyx mori)

Flavonoids are secondary metabolites that help plants resist insect attack. It can resist insect attack by inhibiting insect immune defense, and pathogens can also inhibit insect immune defense. It is speculated that the combination of flavonoids and pathogens may inhibit the immune defense and have stronger toxicity to silkworm. In this study, the combined treatment of quercetin with Bombyx mori nuclear polyhedrosis virus (BmNPV) had significant negative effects on the growth and survival of silkworm compared with BmNPV group. The detoxifying enzyme activity of BmNPV group was significantly increased at 96 h, while the activity of the combined treatment group was significantly decreased with the increase of quercetin exposure time (72 or 96 h). The activity of antioxidant enzymes also showed a similar trend, that was, the activity of antioxidant enzymes in the combined treatment group also decreased significantly with the increase of quercetin exposure time, which led to the increase of reactive oxygen species content. The silkworm cells would produce lipid peroxidation, malondialdehyde content was significantly increased, so that the expression of immune-related genes (the antimicrobial peptide, Toll pathway, IMD pathway, JAK-STAT pathway, and melanin genes) were decreased, leading to the damage of the immune system of silkworm. These results indicated that quercetin combined with BmNPV could inhibit the activities of protective enzymes and lead to oxidative damage to silkworm. It can also affect the immune response of the silkworm, and thus resulting in abnormal growth. This study provides the novel conclusion that quercetin accumulation will increase the susceptibility of silkworm to pathogens.

The glutathione S-transferase (PxGST2L) may contribute to the detoxification metabolism of chlorantraniliprole in Plutella xylostella(L.)

The diamondback moth (Plutella xylostella L.), is an economic pest of cruciferous plants worldwide, which causes great economic loss to cruciferous plants production. However, the pest has developed resistance to insecticides. One of such insecticides is chlorantraniliprole. The study of the mechanisms underlying resistance is key for the effective management of resistance. In this study, a comparative proteomics approach was used to isolate and identify various proteins that differed between chlorantraniliprole-susceptible and -resistant strains of P. xylostella. Eleven proteins were significantly different and were successfully identified by MALDI-TOF-MS. Metabolism-related proteins accounted for the highest proportion among the eleven different proteins. The function of the PxGST2L protein was validated by RNAi. Knockdown of PxGST2L reduced the GST activity and increased the toxicity of chlorantraniliprole to the diamondback moth. The resistance ratio of diamondback moth to chlorantraniliprole was reduced from 1029 to 505. The results indicated that PxGST2L is partly responsible for chlorantraniliprole insecticide resistance in DBM. Our finding contributes to the understanding of the mechanism underlying resistance to chlorantraniliprole in the DBM, to develop effective resistance management tactics.

Functional identification and characterization of GST genes in the Asian gypsy moth in response to poplar secondary metabolites

The Asian gypsy moth, Lymantria dispar, as one of the most important forest pests in the world, can feed on more than 500 species of host plants, causing serious damage to the forests. Poplar is one of the favorite host plants of L. dispar. The present study aimed to explore the effects of poplar secondary metabolites on the growth and detoxification function of L. dispar larvae. We also aimed to study the expression of glutathione S-transferase (GST) genes in different developmental stages and in response to treatment with secondary metabolites. Six kinds of main secondary metabolites and three groups of characteristic mixed secondary metabolites were selected as follows: Caffeic acid, salicin, rutin, quercetin, catechol, flavone, mixture 1 (salicin and flavone), mixture 2 (salicin, caffeic acid and catechol), and mixture 3 (flavone, caffeic acid and catechol) according to the content changes of secondary metabolites in poplar. The thirteen GST genes were selected as candidate genes to study the expression of GST genes in different developmental stages and after treatment with secondary metabolites using quantitative real-time reverse transcription PCR. The LdGSTe4 and LdGSTo1 genes could be induced by secondary metabolites and were screened to explore their detoxification function against secondary metabolites using RNA interference technology. The results showed that salicin and rutin significantly induced the expression of LdGSTe4 and LdGSTo1. Under the stress of secondary metabolites, LdGSTe4 silencing affected the adaptability of L. dispar larvae to salicin and rutin. LdGSTe4 silencing resulted in a significant decrease in the body weight of L. dispar, but had little effect on the relative growth rate, relative consumption rate, efficiency of conversion of ingested food, efficiency of conversion of digested food, and approximate digestibility, as well as the survival rate and development time. These results provide a deeper understanding of the adaptive mechanism of L. dispar to host plants, form the foundation for the further research into the host resistance mechanism, and identify target genes for breeding resistant transgenic poplar.

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.

Activation of the NR2E nuclear receptor HR83 leads to metabolic detoxification-mediated chlorpyrifos resistance in Nilaparvata lugens

Increased production of detoxification enzymes appears to be the primary route for insecticide resistance in many crop pests. However, the mechanisms employed by resistant insects for overexpression of detoxification genes involved in insecticide resistance remain obscure. We report here that the NR2E nuclear receptor HR83 plays a critical role in chlorpyrifos resistance by regulating the expression of detoxification genes in the brown planthopper (BPH), Nilaparvata lugens. HR83 was highly expressed in the fat body and ovary of adult females in chlorpyrifos-resistant BPHs. Knockdown of HR83 by RNA interference showed no effect on female fecundity, whereas caused a decrease of resistance to chlorpyrifos. This treatment also led to a dramatic reduction in the expression of multiple detoxification genes, including four UDP-glycosyltransferases (UGTs), three cytochrome P450 monooxygenases (P450s) and four carboxylesterases (CarEs). Among these HR83-regulated genes, UGT-1-3, UGT-2B10, CYP6CW1, CYP4CE1, CarE and Esterase E4-1 were over-expressed both in the fat body and ovary of the resistant BPHs. Functional analyses revealed that UGT-2B10, CYP4CE1, CarE and Esterase E4-1 are essential for the resistance of BPH to chlorpyrifos. Generally, this study implicates HR83 in the metabolic detoxification-mediated chlorpyrifos resistance and suggests that the regulation of detoxification genes may be an ancestral function of the NR2E nuclear receptor subfamily.

Susceptibility of Dermanyssus gallinae from China to acaricides and functional analysis of glutathione S-transferases associated with beta-cypermethrin resistance

Dermanyssus gallinae poses a significant threat to poultry production, and the resistance to pyrethroids has been identified worldwide. Periodic monitoring of acaricide resistance in D. gallinae is very important for its control, and molecular mechanism associated with beta-cypermethrin resistance in D. gallinae is not fully clear. Results showed, four field isolates of CBP-1, CBP-2, CBP-5 and CBY-1 from China remained either susceptible or with decreased susceptibility (resistance ratio < 5.0) to phoxim, amitraz, propoxur and carbaryl. Four field isolates of CBP-1, CBP-3, CBY-2 and CBH-1 had developed high or extremely high level of resistance (resistance ratio ≥ 40.0) to beta-cypermethrin or permethrin. Detoxification enzyme activity of GSTs was significantly higher in beta-cypermethrin resistant (RS) than susceptible strain (SS), indicating that GSTs are probably involved in beta-cypermethrin resistance in D. gallinae. The recombinant GSTs (rGST-1, 2, 3) showed a pronounced activity toward the conjugates of 1-chloro-2, 4 dinitrobenzene (CDNB) and glutathione (GSH), with rGST-1 presenting the highest enzymatic activity. Constitutive over-expression of Deg-GST-2 was detected in RS strain, and GSTs genes were all inducible with the treatment of beta-cypermethrin in SS and RS strains. More importantly, knocking down Deg-GST-2 gene expression by RNAi increased the susceptibility of RS strain to beta-cypermethrin. HPLC analysis indicated that rGST-1 protein could metabolize phoxim directly, but rGSTs could not directly metabolize beta-cypermethrin. Our results indicated that some field isolates of D. gallinae from China had developed high level of resistance to pyrethroids, and elevated GSTs activity as well as increased GSTs expression levels were involved in beta-cypermethrin resistance, but the three evaluated GSTs did not play a direct role in the metabolism of beta-cypermethrin.