Sublethal effects of chlorantraniliprole on molting hormone levels and mRNA expressions of three Halloween genes in the rice stem borer, Chilo suppressalis

Low concentrations of cyantraniliprole negatively affects the development of Spodoptera frugiperda by disruption of ecdysteroid biosynthesis and carbohydrate and lipid metabolism

In addition to the acute lethal toxicity, insecticides might affect population dynamics of insect pests by inducing life history trait changes under low concentrations, however, the underlying mechanisms remain not well understood. Here we examined systemic impacts on development and reproduction caused by low concentration exposures to cyantraniliprole in the fall armyworm (FAW), Spodoptera frugiperda, and the putative underlying mechanisms were investigated. The results showed that exposure of third-instar larvae to LC10 and LC30 of cyantraniliprole significantly extended larvae duration by 1.46 and 5.41 days, respectively. Treatment with LC30 of cyantraniliprole significantly decreased the pupae weight and pupation rate as well as the longevity, fecundity and egg hatchability of female adults. Consistently, we found that exposure of FAW to LC30 cyantraniliprole downregulated the mRNA expression of four ecdysteroid biosynthesis genes including SfNobo, SfShd, SfSpo and SfDib and one ecdysone response gene SfE75 in the larvae as well as the gene encoding vitellogenin (SfVg) in the female adults. We also found that treatment with LC30 of cyantraniliprole significantly decreased the whole body levels of glucose, trehalose, glycogen and triglyceride in the larvae. Our results indicate that low concentration of cyantraniliprole inhibited FAW development by disruption of ecdysteroid biosynthesis as well as carbohydrate and lipid metabolism, which have applied implications for the control of FAW.

Transcriptomic sequencing data illuminate insecticide-induced physiological stress mechanisms in aquatic non-target invertebrates

Pesticides are major agricultural stressors for freshwater species. Exposure to pesticides can disrupt the biotic integrity of freshwater ecosystems and impair associated ecosystem functions. Unfortunately, physiological mechanisms through which pesticides affect aquatic organisms are largely unknown. For example, the widely-used insecticide chlorantraniliprole is supposed to be highly selective for target pest species, i.e. Lepidoptera (butterflies), but its effect in aquatic non-target taxa is poorly studied. Using RNA-sequencing data, we quantified the insecticide effect on three aquatic invertebrate species: the caddisfly Lepidostoma basale, the mayfly Ephemera danica and the amphipod Gammarus pulex. Further, we tested how the insecticide-induced transcriptional response is modulated by biotic interaction between the two leaf-shredding species L. basale and G. pulex. While G. pulex was only weakly affected by chlorantraniliprole exposure, we detected strong transcriptional responses in L. basale and E. danica, implying that the stressor receptors are conserved between the target taxon Lepidoptera and other insect groups. We found in both insect species evidence for alterations of the developmental program. If transcriptional changes in the developmental program induce alterations in emergence phenology, pronounced effects on food web dynamics in a cross-ecosystem context are expected.

20E biosynthesis gene CYP306A1 confers resistance to imidacloprid in the nymph stage of Bemisia tabaci by detoxification metabolism

BACKGROUND

Difference in physiology level between the immature and mature stages of insects likely contribute to different mechanisms of insecticide resistance. It is well acknowledged that insect 20-hydroxyecdysone (20E) plays an important role in many biological processes in the immature stage, whether 20E confers insecticide resistance at this specific stage is still poorly understood. By gene cloning, reverse transcription quantitative real-time PCR, RNA interference (RNAi) and in vitro metabolism experiments, this study aimed to investigate the potential role of 20E-related genes in conferring imidacloprid (IMD) resistance in the immature stage of the whitefly Bemisia tabaci Mediterranean.

RESULTS

After identification of low to moderate IMD resistance in the whitefly, we found CYP306A1 of the six 20E-related genes was overexpressed in the nymph stage of the three resistant strains compared to a laboratory reference susceptible strain, but not in the adult stage. Further exposure to IMD resulted in an increase in CYP306A1 expression in the nymph stage. These results together imply that CYP306A1 may be implicated in IMD resistance in the nymph stage of the whitefly. RNAi knockdown of CYP306A1 increased the mortality of nymphs after treatment with IMD in bioassay, suggesting a pivotal role of CYP306A1 in conferring IMD resistance in the nymph stage. Additionally, our metabolism experiments in vivo showed that the content of IMD reduced by 20% along with cytochrome P450 reductase and heterologously expressed CYP306A1, which provides additional evidence for the important function of CYP306A1 in metabolizing IMD that leads to the resistance.

CONCLUSION

This study uncovers a novel function of the 20E biosynthesis gene CYP306A1 in metabolizing imidacloprid, thus contributing to such resistance in the immature stage of the insect. These findings not only advance our understanding of 20E-mediated insecticide resistance, but also provide a new target for sustainable pest control of global insect pests such as whitefly. © 2023 Society of Chemical Industry.

Comparative phosphoproteomics analysis provides insights into the responses of Chilo suppressalis to sublethal chlorantraniliprole exposure

BACKGROUND

Sublethal exposure to insecticides causes changes in insect behaviors and physiologies including feeding, mobility, communication, hormone homeostasis, development and fecundity, however, the underlying molecular mechanisms were largely unclear. Our previous studies revealed that sublethal chlorantraniliprole exposure disturbed the hormone homeostasis, reduced the weight and longevity and prolonged the developmental duration of Chilo suppressalis. In the present study, the potential phosphorylation modification regulation mechanisms in C. suppressalis in response to sublethal chlorantraniliprole exposure were explored using comparative and quantitative phosphoproteomics.

RESULTS

A total of 2640 phosphopeptides belonging to 1144 phosphoproteins were identified, among which 446 phosphopeptides derived from 303 unique phosphoproteins were differentially phosphorylated between the chlorantraniliprole-treated and control larvae. The phosphorylation levels of differentially phosphorylated phosphopeptides were further validated using parallel reaction monitoring (PRM). Functional classification and protein-protein interaction of the differentially phosphorylated proteins (DPPs) were analyzed. Generalized analysis of the DPPs and the differentially expressed genes (DEGs) identified in our previous study showed that sublethal chlorantraniliprole exposure significantly changed the transcription and phosphorylation levels of genes/proteins associated with carbohydrate and lipid metabolism, cytoskeleton, signal transduction, transcription, translation and post-translational modification, leading to the dysfunctions of energy metabolism, transcription regulation, protein synthesis and modification, and signal transduction in C. suppressalis. Further analysis of the phosphorylation motifs in DPPs revealed that the MAPKs, CDKs, CaMK II, PKA, PKC and CK II protein kinases might be directly responsible for the phosphoproteomics response of C. suppressalis to chlorantraniliprole treatment.

CONCLUSION

Our results provide abundant phosphorylation information for characterizing the protein modification in insects, and also provide valuable insights into the molecular mechanisms of insect post-translational modifications in response to sublethal insecticide exposure. © 2023 Society of Chemical Industry.

The loss of Halloween gene function seriously affects the development and reproduction of Diaphorina citri (Hemiptera: Liviidae) and increases its susceptibility to pesticides

The citrus industry has suffered severe losses as a result of Huanglongbing spread by Diaphorina citri. Controlling the population of D. citri is the key to preventing and controlling the spread of Huanglongbing. Ecdysteroids are key hormones that regulate insect development and reproduction. Therefore, the Halloween gene family involved in the ecdysone synthesis of D. citri is an ideal target for controlling the population growth of this insect. In this study, we successfully cloned four Halloween genes expressed during D. citri development. Silencing of one of the four genes resulted in a significant decrease in 20E titers in nymphs and significant decreases in the developmental, survival and emergence rates. Inhibiting Halloween gene expression in adults impeded the growth of the female ovary, diminished yolk formation, lowered vitellogenin transcription levels, and hence impaired female fecundity. This showed that Halloween genes were required for D. citri development and reproduction. DcCYP315A1 and DcCYP314A1 were highly expressed when D. citri was exposed to thiamethoxam and cypermethrin, and silencing these two genes made D. citri more sensitive to these two pesticides. Inhibition of DcCYP315A1 and DcCYP314A1 expression not only significantly delayed the development and reproduction of D. citri but also increased its susceptibility to pesticides. Therefore, these two genes are more suitable as potential target genes for controlling D. citri.

Mechanisms underlying the effects of low concentrations of chlorantraniliprole on development and reproduction of the fall armyworm, Spodoptera frugiperda

It is well known that sublethal dose of insecticides induces life history trait changes of both target and non-target insect species, however, the underlying mechanisms remain not well understood. In this study, the effects of low concentrations of the anthranilic diamide insecticide chlorantraniliprole on the development and reproduction of the fall armyworm (FAW), Spodoptera frugiperda, were evaluated, and the underlying mechanisms were explored. The results showed that exposure of FAW to LC₁₀ and LC₃₀ chlorantraniliprole prolonged the larvae duration, decreased the mean weight of the larvae and pupae, and lowered the pupation rate as well as emergence rate. The fecundity of female adults was also negatively affected by treatment with low concentrations of chlorantraniliprole. Consistently, we found that exposure of FAW to LC₃₀ chlorantraniliprole downregulated the mRNA expression of juvenile hormone (JH) esterase (SfJHE), leading to the increase of JH titer in larvae. We also found that treatment with low concentrations of chlorantraniliprole suppressed the expression of ribosomal protein S6 kinase1 (SfS6K1) in female adults, resulting in the downregulation of the gene encoding vitellogenin (SfVg). These results provided insights into the mechanisms underlying the effects of low concentrations of insecticides on insect pests, and had applied implications for the control of FAW.

Transcriptome analysis of fat accumulation in 3T3-L1 adipocytes induced by chlorantraniliprole

Introduction

Chlorantraniliprole is a diamide insecticide widely used in agriculture. Chlorantraniliprole has been previously found to increase the accumulation of triglycerides (fats) in adipocytes, however, the underlying molecular mechanism is unknown. The present study aimed to explore the molecular mechanisms of chlorantraniliprole-induced fat accumulation in 3T3-L1 adipocytes.

Methods

We measured the triglyceride content in chlorantraniliprole-treated 3T3-L1 adipocytes, and collected cell samples treated with chlorantraniliprole for 24 h and without any treatment for RNA sequencing.

Results

Compared with the control group, the content of triglyceride in the treatment group of chlorantraniliprole was significantly increased. The results of RNA sequencing (RNA-seq) showed that 284 differentially expressed genes (DEGs) were identified after treatment with chlorantraniliprole, involving 39 functional groups of gene ontology (GO) and 213 KEGG pathways. Moreover, these DEGs were significantly enriched in several key genes that regulate adipocyte differentiation and lipogenesis including Igf1, Rarres2, Nr1h3, and Psmb8.

Discussion

In general, these results suggest that chlorantraniliprole-induced lipogenesis is attributed to a whole-gene transcriptome response, which promotes further understanding of the potential mechanism of chlorantraniliprole-induced adipogenesis.

Differences in susceptibility to chlorantraniliprole between Chilo suppressalis (Lepidoptera: Crambidae) and two dominant parasitic wasps collected from Sichuan Province, China

Chilo suppressalis Walker (Lepidoptera: Crambidae) is one of the most destructive pests occurring in the rice-growing regions of Asia. Parasitoids, mainly egg parasitoids, have been of interest for several years even with practical used cases. Therefore, the potential impact of insecticides on natural enemies needs great attention. In this study, chlorantraniliprole was evaluated for its impact on C. suppressalis and two dominant parasitic wasps. Bioassays showed that chlorantraniliprole had negligible toxicity to Eriborus terebrans but was significantly toxic to Chelonus munakatae; the mortality exceeded 50% when the concentration reached 46.83 ng/cm². Enzyme assays suggested that the significantly different carboxylesterase activity may be involved in the high-level detoxification metabolism of E. terebrans. According to the results of enzyme gene correlation analysis, P450s may be the dominant factor in the detoxification metabolism of C. munakatae. In addition, the ryanodine receptor C-terminus of C. suppressalis (CsRyR), C. munakatae (CmRyR) and E. terebrans (EtRyR) were successfully cloned. Different amino acids at resistance mutation I4758 M between susceptible C. suppressalis (I) and parasitic wasps (M) may be related to susceptibility differences. Simulated docking showed that CsRyR and CmRyR can interact with chlorantraniliprole but not EtRyR. More interaction forces were formed between CsRyR and chlorantraniliprole than CmRyR. Furthermore, a Pi-Pi T-shape formed between 73PHE in CsRyR and the benzene ring in chlorantraniliprole. These results indicated that both detoxification metabolism and the target site could mediate the susceptibility difference between C. suppressalis and its parasitic wasps.

Review of molecular and biochemical responses during stress induced stimulation and hormesis in insects

The biphasic hormetic response to stress, defined by low-dose stimulation and high-dose inhibition is frequently observed in insects. Various molecular and biochemical responses associated with hormesis in insects have been reported in many studies, but no synthesis of all these findings has been undertaken. We conducted a systematic literature review, analyzing papers demonstrating phenotypic stimulatory effect(s) following exposure to stress where molecular or biochemical response(s) were also examined. Responses observed included stimulation of reproduction, survival and longevity, growth and development, and tolerance to temperature, chemical, or starvation and desiccation, in response to stressors including pesticides, oxidative stress, temperature, crowding and starvation, and radiation. Phenotypic stimulation ranged from <25% increased above controls to >100%. Reproductive stimulation was frequently <25% increased above controls, while stimulated temperature tolerance was frequently >100% increased. Molecular and biochemical responses had obvious direct connections to phenotypic responses in many cases, although not in all instances. Increased expression of heat shock proteins occurred in association with stimulated temperature tolerance, and increased expression of detoxification genes with stimulated pesticide or chemical tolerance, but also stimulated reproduction. Changes in the expression or activity of antioxidants were frequently associated with stimulation of longevity and reproduction. Stress induced changes in vitellogenin and juvenile hormone and genes in the IIS/TOR signalling pathway - which are directly responsible for regulating growth, development, and reproduction - were also reported. Our analysis showed that coordination of expression of genes or proteins associated with protection from oxidative stress and DNA and protein damage is important in the hormetic responses of insects.

Sublethal doses of broflanilide prevents molting in the fall armyworm, Spodoptera frugiperda via altering molting hormone biosynthesis

Broflanilide is a novel insecticide with a unique mode of action on the insect GABA receptor and is registered worldwide for the control of agricultural pests. It shows high efficacy in controlling the fall armyworm (FAW) Spodoptera frugiperda, which is a destructive pest to various crops. FAW was exposed to sublethal concentrations of broflanilide to determine its impact on insect development. Sublethal doses (LD₁₀ and LD₃₀) caused failure of ecdysis, reduced body length of larvae, malformation of pupae, and vestigial wing formation in adults. Also, broflanilide at LD₃₀ significantly reduced the amount of molting hormone (MH). After exposure to LD₁₀ or LD₃₀ broflanilide, expression of five Halloween genes, which participate in MH biosynthesis, were found to be altered. Specifically, the transcript levels of SfrCYP307A1 (Spook), SfrCYP314A1 (Shade) and SfrCYP315A1 (Shadow) in 3rd day larvae were significantly decreased as well as SfrCYP302A1 (Disembodied) and SfrCYP306A1 (Phantom) in 5th day pupae. In contrast, the transcript levels of SfrCYP302A1 in 3rd day larvae, SfrCYP307A1 and SfrCYP314A1 in 5th day pupae, and SfrCYP306A1, SfrCYP307A1 and SfrCYP315A1 in 0.5th day adults were significantly increased. Our results demonstrate that broflanilide caused the failure of ecdysis in FAW possibly by influencing the intake of cholesterol through inhibition of feeding and also via altering expression of genes important for MH biosynthesis.

20-Hydroxyecdysone (20E) signaling as a promising target for the chemical control of malaria vectors

With the rapid development and spread of resistance to insecticides among anopheline malaria vectors, the efficacy of current World Health Organization (WHO)-approved insecticides targeting these vectors is under threat. This has led to the development of novel interventions, including improved and enhanced insecticide formulations with new targets or synergists or with added sterilants and/or antimalarials, among others. To date, several studies in mosquitoes have revealed that the 20-hydroxyecdysone (20E) signaling pathway regulates both vector abundance and competence, two parameters that influence malaria transmission. Therefore, insecticides which target 20E signaling (e.g. methoxyfenozide and halofenozide) may be an asset for malaria vector control. While such insecticides are already commercially available for lepidopteran and coleopteran pests, they still need to be approved by the WHO for malaria vector control programs. Until recently, chemicals targeting 20E signaling were considered to be insect growth regulators, and their effect was mostly studied against immature mosquito stages. However, in the last few years, promising results have been obtained by applying methoxyfenozide or halofenozide (two compounds that boost 20E signaling) to Anopheles populations at different phases of their life-cycle. In addition, preliminary studies suggest that methoxyfenozide resistance is unstable, causing the insects substantial fitness costs, thereby potentially circumventing one of the biggest challenges faced by current vector control efforts. In this review, we first describe the 20E signaling pathway in mosquitoes and then summarize the mechanisms whereby 20E signaling regulates the physiological processes associated with vector competence and vector abundance. Finally, we discuss the potential of using chemicals targeting 20E signaling to control malaria vectors.

Knockdown of CYP301B1 and CYP6AX1v2 increases the susceptibility of the brown planthopper to beta-asarone, a potential plant-derived insecticide

The cytochrome P450 monooxygenases of insects play crucial roles in the metabolic detoxification of insecticides. Our previous finding showed that two cytochrome P450 genes, both CYP301B1 and CYP6AX1v2, in the BPH underwent overexpression due to β-asarone. In this study, we investigated the molecular characteristics, expression patterns and functions of these two cytochrome P450 genes. The results showed that CYP301B1 had the highest expression level in the eggs, while CYP6AX1v2 was expressed in macropterous female adults. Moreover, the expression level of CYP301B1 in the head was higher than that in the integument, fat body and gut. The expression level of CYP6AX1v2 in the fat body and gut was higher than that in head and integument. Importantly, silencing CYP301B1 and CYP6AX1v2 separately could increase the sensitivity, resulting in significant higher mortality of BPH following treatment with β-asarone. Our findings indicated that CYP301B1 and CYP6AX1v2 could contribute to the resistance of BPH to β-asarone, and these two genes may be involved in the detoxification metabolism of β-asarone in BPH.

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.