Induction of Cytochrome P450 Activity by the Interaction of Chlorantraniliprole and Sinigrin in the Spodoptera exigua (Lepidoptera: Noctuidae)

Inducible Cytochrome P450s in the Fat Body and Malpighian Tubules of the Polyphagous Pests of Spodoptera litura Confer Xenobiotic Tolerance

Cytochrome P450 plays vital roles in detoxifying xenobiotics. In this study, SlCYP340A and SlCYP340L expression in the Spodoptera litura fat body and SlCYP332A1, SlCYP6AB12, SlCYP6AB58, SlCYP6AB59, and SlCYP6AN4 expression in the Malpighian tubules were significantly upregulated after cyantraniliprole exposure, and SlCYP6AB58 and SlCYP6AB59 expression levels were simultaneously increased in the Malpighian tubules after gossypol treatment. Drosophila ectopically expressing candidate P450 genes showed that SlCYP332A1, SlCYP6AB12, SlCYP6AB59, SlCYP6AN4, and SlCYP340A conferred cyantraniliprole tolerance. The overexpression of SlCYP6AB58 and SlCYP6AB59 in Drosophila increased the number of eggs laid under the gossypol treatment. Moreover, the knockdown of SlCYP332A1, SlCYP6AB12, SlCYP6AB59, SlCYP6AN4, and SlCYP340A increased S. litura mortality under the cyantraniliprole treatment. Homology modeling and molecular docking results suggested that candidate P450 has the potential to bind with cyantraniliprole. These results indicate that the CYP3 and CYP4 genes participate in cyantraniliprole detoxification and that SlCYP6AB59 may be simultaneously involved in the gossypol tolerance of S. litura.

Knockdown of CYP9A9 increases the susceptibility to lufenuron, methoxyfenozide and a mixture of both in Spodoptera exigua

Lufenuron (LUF) and Methoxyfenozide (MET) as Insect Growth Regulators (IGRs) contribute to the current control of the catastrophic crop pest, Spodoptera exigua (Lepidoptera, Noctuidae). Yet S. exigua has evolved resistance to LUF and MET, which is possibly mediated by cytochrome P450 monooxygenases (P450s), particularly from the CYP3 clade family, as it plays a key role in the detoxification of insecticides. However, a mixture of LUF and MET (MML) (optimal ratio: 6:4) remains highly insecticidal. Here, we analysed the response of S. exigua to sublethal concentrations of LUF, MET, and MML via transcriptomics. Twelve differentially expressed genes (DEGs) encoding CYP3 clade members were observed in transcriptomes and CYP9A9 was significantly upregulated after treatment with LUF, MET, and MML. Further, CYP9A9 was most highly expressed in the midgut of L4 S. exigua larvae. RNAi-mediated knockdown of CYP9A9 reduced the activity of CYP450 and increased the susceptibility of S. exigua larvae to LUF, MET, and MML. Thus, CYP9A9 plays a key role in the detoxification of LUF, MET, and MML in S. exigua. These findings provide new insights into insecticidal actions of IGRs, which can be applied to the establishment of novel pest management strategies.

Two P450 genes, CYP6SN3 and CYP306A1, involved in the growth and development of Chilo suppressalis and the lethal effect caused by vetiver grass

Chilo suppressalis is a widely distributed pest occurring in nearly all paddy fields, which has developed high level resistance to different classes of insecticides. Vetiver grass has been identified as a dead-end trap plant for the alternative control of C. suppressalis. In this study, two cytochrome P450 monooxygenase (P450) genes, CsCYP6SN3 and CsCYP306A1, were identified and characterized, which are expressed at all developmental stages, with the highest expression in the midguts and fat bodies of 3rd instar larvae. Vetiver significantly inhibited the expression levels of CsCYP6SN3 and CsCYP306A1 in 3rd larvae after feeding. RNA interference showed that silencing CsCYP6SN3 and CsCYP306A1 genes dramatically reduced the pupation rate and pupa weight. Feeding on vetiver after silencing CsCYP6SN3 and CsCYP306A1 led to higher mortality compared with feeding on rice. In conclusion, these findings indicated that the expression levels of CsCYP6SN3 and CsCYP306A1 were associated with the lethal effect of vetiver against C. suppressalis larvae and functional knowledge about these two detoxification genes could provide new targets for agricultural pest control.

Evaluation of tolerance to λ-cyhalothrin and response of detoxification enzymes in silkworms reared on artificial diet

A representative silkworm rearing mode of Ⅰ-Ⅲ instars reared on artificial diet and Ⅳ-Ⅴ instars reared on fresh mulberry leaves has been recognized in some sericultural areas of China. Under this rearing mode, silkworms are prone to be poisoned by pesticide residues on mulberry leaves at the Ⅳ and Ⅴ instar stages. As one of the most widely applied insecticides, λ-cyhalothrin was used to study the insecticide tolerance of silkworm reared on artificial diet (referred as the AD group). Our results showed that the newly ecdysized Ⅳ instar larvae in the AD group were less tolerant to λ-cyhalothrin compared to the mulberry leaves reared group (referred as the ML group). After continuous exposure to trace λ-cyhalothrin, the weight gain and the survival rate of silkworms were significantly lower in the AD group than those in the ML group, even though compensatory growth was observed in the control of the AD group. Histopathology and ultrastructure of fat body showed that λ-cyhalothrin induced more severe cell injuries in the AD group, such as shrunken nucleus, dilatation of endoplasmic reticulum, and mitochondrial swelling. The transcription levels of detoxification related genes (CYP4M5, CYP6AB4, CarE2, CarE5, GSTe1 and GSTe3) and the enzyme activities of P450s, CarEs and GSTs were inducible by trace λ-cyhalothrin in a time-specific manner, and the data showed that the response of P450 enzyme activity was retarded in the AD group, indicating a potential reason for a higher sensitivity to λ-cyhalothrin. Our results provided a new clue for the study of the relationship between feed nutrition and detoxification ability, and also provided an important reference for the development of modern silkworm rearing mode.

Sublethal effects of chlorantraniliprole on Paederus fuscipes (Staphylinidae: Coleoptera), a general predator in paddle field

Paederus fuscipes is a general predator in rice fields and a non-target organism of chlorantraniliprole, an effective insecticide for insect-pest control in paddy fields. Pesticide hazards to non-target organisms have been a growing global problem for decades. This study was designed to evaluate the toxicity of chlorantraniliprole at lethal and sublethal levels against P. fuscipes larvae and adults. The LC₅₀ of chlorantraniliprole against P. fuscipes adults and larvae were respectively 535.49 and 111.24 mg a.i. L^-1, which is higher than the dosage recommended for use in the field (59.38 mg a.i. L^-1), but the LC₃₀ and LC₁₀ for larvae are lower than the recommended field dose which showed that the sublethal effects on immature stages are inevitable. Treatment at larval stage with LC₃₀ of chlorantraniliprole significantly elongated the pre-imaginal developmental and pre-oviposition periods. Also, adults exposed directly to chlorantraniliprole oviposited significantly less number of eggs in both LC₁₀ and LC₃₀ treatments. Furthermore, the larval predation efficiency and female bodyweight were also reduced due to exposure to sublethal doses. Meanwhile, the activities of antioxidant (SOD, POD and CAT) and detoxification (P450, AChE and GST) enzymes were also significantly affected by the exposure to these sublethal concentrations. These findings showed that sublethal doses of chlorantraniliprole adversely influenced P. fuscipes development and physiology, and therefore its use as part of integrative pest management should be given further considerations.

Comparative analysis of the detoxification gene inventory of four major Spodoptera pest species in response to xenobiotics

The genus Spodoptera (Lepidoptera: Noctuidae) comprises some of the most polyphagous and destructive agricultural pests worldwide. The success of many species of this genus is due to their striking abilities to adapt to a broad range of host plants. Superfamilies of detoxification genes play a crucial role in the adaption to overcome plant defense mechanisms mediated by numerous secondary metabolites and toxins. Over the past decade, a substantial amount of expression data in Spodoptera larvae was produced for those genes in response to xenobiotics such as plant secondary metabolites, but also insecticide exposure. However, this information is scattered throughout the literature and in most cases does not allow to clearly identify candidate genes involved in host-plant adaptation and insecticide resistance. In the present review, we analyzed and compiled information on close to 600 pairs of inducers (xenobiotics) and induced genes from four main Spodoptera species: S. exigua, S. frugiperda, S. littoralis and S. litura. The cytochrome P450 monooxygenases (P450s; encoded by CYP genes) were the most upregulated detoxification genes across the literature for all four species. Most of the data was provided from studies on S. litura, followed by S. exigua, S. frugiperda and S. littoralis. We examined whether these detoxification genes were reported for larval survival under xenobiotic challenge in forward and reverse genetic studies. We further analyzed whether biochemical assays were carried out showing the ability of corresponding enzymes and transporters to breakdown and excrete xenobiotics, respectively. This revealed a clear disparity between species and the lack of genetic and biochemical information in S. frugiperda. Finally, we discussed the biological importance of detoxification genes for this genus and propose a workflow to study the involvement of these enzymes in an ecological and agricultural context.

The fitness advantages of bistrifluron resistance related to chitin synthase A in Spodoptera litura (Fab.) (Noctuidae: Lepidoptera)

BACKGROUND

Spodoptera litura is one of the major agricultural pests in China, and it has developed serious resistance to many traditional chemical insecticides. In the present study, the bistrifluron-resistant (Bis-SEL) strain accompanied by a higher oviposition, 113.8-fold RR compared to the bistrifluron-susceptible (Bis-UNSEL) strain, was obtained by bidirectional screening. A comparison of their gonad coefficiency and genes related to oviposition or resistance was used to elucidate the resurgence mechanism.

RESULTS

The ovarian index, oviposition, and potential egg production in the Bis-SEL strain of female adults were significantly higher than those in the Bis-UNSEL strain, and the length of ovariole in the Bis-SEL strain was also significantly elongated. The protein contents of vitellogenin (Vg) and vitellogenin receptor (VgR) in the Bis-UNSEL strain were lower than those in the Bis-SEL strain, consistent with their gene expressions levels, and there was a significantly positive linear correlation between Vg and VgR protein contents, further confirming that resistant strains have high reproductive fitness. Moreover, the chitin synthase A in the Bis-SEL strain was clearly up-regulated, and a mutation (H866Y) near the QRRRW in the catalytic domain caused a rise in the hydrogen bond between UDP-GlcNAc and chitin synthase, and its chitin content was higher than that in the Bis-UNSEL strain. Nevertheless, the sensitivity of the Bis-SEL strain to bistrifluron was significantly recovered when it was knocked down though RNA interference.

CONCLUSION

The fitness advantages of bistrifluron resistance may be related to the up-regulation and mution of chitin synthase A. © 2021 Society of Chemical Industry.

The expression of Spodoptera exigua P450 and UGT genes: tissue specificity and response to insecticides

Cytochrome P450 and UDP-glucosyltransferase (UGT) as phase I and phase II metabolism enzymes, respectively, play vital roles in the breakdown of endobiotics and xenobiotics. Insects can increase the expression of detoxification enzymes to cope with the stress from xenobiotics including insecticides. However, the molecular mechanisms for insecticide detoxification in Spodoptera exigua remain elusive, and the genes conferring insecticide metabolisms in this species are less well reported. In this study, 68 P450 and 32 UGT genes were identified. Phylogenetic analysis showed gene expansions in CYP3 and CYP4 clans of P450 genes and UGT33 family of this pest. P450 and UGT genes exhibited specific tissue expression patterns. Insecticide treatments in fat body cells of S. exigua revealed that the expression levels of P450 and UGT genes were significantly influenced by challenges of abamectin, lambda-cyhalothrin, chlorantraniliprole, metaflumizone and indoxacarb. Multiple genes for detoxification were affected in expression levels after insecticide exposures. The results demonstrated that lambda-cyhalothrin, chlorantraniliprole, metaflumizone and indoxacarb induced similar responses in the expression of P450 and UGT genes in fat body cells; eight P450 genes and four UGT genes were co-up-regulated significantly, and no or only a few CYP/UGT genes were down-regulated significantly by these four insecticides. However, abamectin triggered a distinct response for P450 and UGT gene expression; more P450 and UGT genes were down-regulated by abamectin than by the other four compounds. In conclusion, P450 and UGT genes from S. exigua were identified, and different responses to abamectin suggest a different mechanism for insecticide detoxification.

Molecular identification of four novel cytochrome P450 genes related to the development of resistance of Spodoptera exigua (Lepidoptera: Noctuidae) to chlorantraniliprole

BACKGROUND

The beet armyworm, Spodoptera exigua, is an omnivorous insect that damages a variety of crops worldwide. Chlorantraniliprole is a new diamide insecticide that acts on the ryanodine receptors in insects. The aim of this study was to explore key genes related to the development of chlorantraniliprole resistance in S. exigua.

RESULTS

Transcriptomes were compared between beet armyworms from a susceptible laboratory strain (Sus-Lab) and Sus-Lab screened with LC₂₅ sublethal doses of chlorantraniliprole for six generations (SE-Sel). Ten of 11 cytochrome P450 genes with upregulated expression verified by quantitative reverse transcription polymerase chain reaction (qRT-PCR) in SE-Sel strains were detected in SE-PZ16 and SE-ZY16, two extremely resistant field populations. In addition, expression of four new cytochrome P450 genes, CYP9A21v1, CYP9A21v2, CYP9A21v3 and CYP9A21v4, was shown in the two field populations and was significantly higher in the SE-Sel strain than in the Sus-Lab strain (P < 0.05). Their full-length and protein tertiary structures were also cloned and predicted. The function of CYP9A21v3 was analysed by RNA interference, and the relative expression of CYP9A21v3 in the SE-ZY16 population after feeding on dsRNA was lower than in the control group. Moreover, mortality rates in insects treated at the LC₅₀ of chlorantraniliprole after dsRNA feeding were significantly higher than in the control group 24 h after treatment (P < 0.05).

CONCLUSION

Overexpression of CYP9A21v3 may be a primary factor in the development of chlorantraniliprole resistance in beet armyworms. © 2018 Society of Chemical Industry.

Monitoring and biochemical characterization of beta-cypermethrin resistance in Spodoptera exigua (Lepidoptera: Noctuidae) in Sichuan Province, China

The beet armyworm Spodoptera exigua, a major pest affecting numerous cultivated crops in China, has developed a serious resistance to many traditional chemical insecticides. The resistance levels of the field-collected populations from different districts in Sichuan Province, China, to nine insecticides were detected with a diet-incorporation bioassay. Compared to the Lab-ZN strain, five (in 2014) and three (in 2016) field populations displayed either high or extremely high levels of resistance to beta-cypermethrin. All the field populations collected in 2014 were susceptible to emamectin benzoate, hexaflumuron, methoxyfenozide, chlorantraniliprole, cyantraniliprole and indoxacarb but exhibited low or moderate levels of resistance to abamectin. The resistances of field populations collected in 2016 were significantly higher than two years earlier, especial for chlorantraniliprole and cyantraniliprole with RRs rising from 173.4- to 582.6-fold and 175.3- to 287.6-fold, respectively, even though the field populations had retained moderate or low levels of resistance to chlorpyrifos and hexaflumuron. The synergism experiment revealed that the resistance of the LS16 population to beta-cypermethrin may be mainly related to cytochrome P450 monooxygenases (P450s), which was responsible for the highest increase ratio of 37.97-fold, for piperonyl butoxide, rather than either carboxylesterase (CarE) or glutathione S-transferase (GST). The cytochrome P450 ethoxycoumarin O-deethylase activity of the LS16 population was also the strongest among the treatments (P < 0.05). Non-denaturing polyacrylamide gel electrophoresis (native PAGE) indicated that enhanced E11, E13 and E15-E16 bands in the LS16 population likely contribute to the development of resistance to beta-cypermethrin.

Identification and Functional Analysis of a Novel Cytochrome P450 Gene CYP9A105 Associated with Pyrethroid Detoxification in Spodoptera exigua Hübner

In insects, cytochrome P450 monooxygenases (P450s or CYPs) are known to be involved in the detoxification and metabolism of insecticides, leading to increased resistance in insect populations. Spodoptera exigua is a serious polyphagous insect pest worldwide and has developed resistance to various insecticides. In this study, a novel CYP3 clan P450 gene CYP9A105 was identified and characterized from S. exigua. The cDNAs of CYP9A105 encoded 530 amino acid proteins, respectively. Quantitative real-time PCR analyses showed that CYP9A105 was expressed at all developmental stages, with maximal expression observed in fifth instar stage larvae, and in dissected fifth instar larvae the highest transcript levels were found in midguts and fat bodies. The expression of CYP9A105 in midguts was upregulated by treatments with the insecticides α-cypermethrin, deltamethrin and fenvalerate at both LC₁₅ concentrations (0.10, 0.20 and 5.0 mg/L, respectively) and LC₅₀ concentrations (0.25, 0.40 and 10.00 mg/L, respectively). RNA interference (RNAi) mediated silencing of CYP9A105 led to increased mortalities of insecticide-treated 4th instar S. exigua larvae. Our results suggest that CYP9A105 might play an important role in α-cypermethrin, deltamethrin and fenvalerate detoxification in S. exigua.