Dietary Stress From Plant Secondary Metabolites Contributes to Grasshopper (Oedaleus asiaticus) Migration or Plague by Regulating Insect Insulin-Like Signaling Pathway

The diverse roles of insulin signaling in insect behavior

In insects and other animals, nutrition-mediated behaviors are modulated by communication between the brain and peripheral systems, a process that relies heavily on the insulin/insulin-like growth factor signaling pathway (IIS). Previous studies have focused on the mechanistic and physiological functions of insulin-like peptides (ILPs) in critical developmental and adult milestones like pupation or vitellogenesis. Less work has detailed the mechanisms connecting ILPs to adult nutrient-mediated behaviors related to survival and reproductive success. Here we briefly review the range of behaviors linked to IIS in insects, from conserved regulation of feeding behavior to evolutionarily derived polyphenisms. Where possible, we incorporate information from Drosophila melanogaster and other model species to describe molecular and neural mechanisms that connect nutritional status to behavioral expression via IIS. We identify knowledge gaps which include the diverse functional roles of peripheral ILPs, how ILPs modulate neural function and behavior across the lifespan, and the lack of detailed mechanistic research in a broad range of taxa. Addressing these gaps would enable a better understanding of the evolution of this conserved and widely deployed tool kit pathway.

The Survival and Physiological Response of Calliptamus abbreviatus Ikonn (Orthoptera: Acrididae) to Flavonoids Rutin and Quercetin

Insect-resistant substances from plants are important natural resources that human beings can potentially develop and use to control pests. In this study, we explored the adverse effects of rutin and quercetin on grasshopper (Calliptamus abbreviatus), as well as the insect's physiological response to these substances in laboratory and field experiments. These two plant compounds exhibited toxic effects on C. abbreviatus, with quercetin showing a stronger toxicity, indicated by a lower survival, slower development, and higher induced gene expression and activities of UDP-glucuronosyltransferase, cytochrome P450s, superoxide dismutase, peroxidase and catalase, compared to rutin. These compounds, especially quercetin, have the potential to be developed as biopesticides to control grasshoppers.

The insecticidal effect of the botanical insecticide chlorogenic acid on Mythimna separata (Walker) is related to changes in MsCYP450 gene expression

The oriental armyworm Mythimna separata (Walker) (Lepidoptera: Noctuidae) can feed on the leaves of many crops, resulting in vast areas of damage and severe losses. Therefore, this insect has become a significant agricultural pest in north Asia. In this study, we fed 3^rd instar larvae with artificial diets containing different concentrations of chlorogenic acid and found a significant lethal effect and the mortality increased with increasing chlorogenic acid concentration. Next, we measured the sublethal effect of chlorogenic acid at LC₂₀ on the growth and development of M. separata larvae. The durations of the 4^th and 5^th instar were longer than those of the control group (prolonged by 0.8 and 0.6 days, respectively), and the 6^th instar was shorter (by 1.1 days). The total survival rate, pupation rate, eclosion rate, sex ratio, and oviposition amount in the LC₂₀ chlorogenic acid-treated group were significantly lower than those in the control group. Furthermore, transcriptome analysis of 3^rd instar larvae fed various concentrations of chlorogenic acid revealed that several MsCYP450 genes were significantly up-regulated, and this finding was further validated by qRT-PCR. In addition, various concentrations of chlorogenic acid and different treatment times significantly affected the enzyme activity of CYP450 in 3^rd instar larvae. Importantly, dietary ingestion of dsMsCYP450 significantly reduced the mRNA level of MsCYP450 genes and increased mortality in the presence of chlorogenic acid. Our results revealed that MsCYP6B6, MsCYP321A7, and MsCYP6B7-like play an essential role in the detoxification of chlorogenic acid by M. separata. This study provides evidence of control effect by botanical insecticide chlorogenic acid on M. separata, and potential detoxification mechanism mediated by P450 of botanical insecticide in arthropods.

Molecular characterization of insulin receptor (IR) in oriental fruit moth, Grapholita molesta (Lepidoptera: Tortricidae), and elucidation of its regulatory roles in glucolipid homeostasis and metamorphosis through interaction with miR-982490

As an intermediate molecule in the Insulin/Insulin-like growth factor signalling pathway (IIS), the insulin receptor (IR) plays vital roles linking nutritional signals to the downstream regulation of metabolic homeostasis, development, metamorphosis, reproduction and stress responses. In the present study, we describe the molecular characteristics of IR in the cosmopolitan fruit boring pest, Grapholita molesta, and its predicted posttranscription regulator miR-982490, and elucidate its regulatory roles in glucolipid homeostasis and metamorphosis. Phylogenetic and domain analyses indicate that lepidopteran IRs normally cluster within families, and that four main domains are conserved in GmIR and those of other Lepidoptera. Bio-informatic prediction, synchronic expression profile evaluation and dual luciferase reporter assays indicated negative regulation of GmIR by miR-982490. Injection of miR-982490 agomir into fifth instar larvae yielded effects similar to dsGmIR injection, resulting in enhanced levels of trehalose and triglyceride in haemolymph, and reduced pupation success and pupal weight, both of which could be rescued by co-injection of dsGmIR and miR-982490 antagomir. We infer that GmIR regulates glucolipid homeostasis and affects G. molesta metamorphosis via interactions with its posttranscriptional regulator miR-982490. This study expands our understanding of the regulatory network of IIS in insect nutritional homeostasis and development.

Effects of gallic acid and Zn, Cu, and Ni on antioxidant enzyme activities of Hyphantria cunea larvae infected with Bacillus thuringiensis

The effects of copper, nickel, and zinc and the potent antioxidant gallic acid on the antioxidant enzyme activities of Hyphantria cunea larvae infected with Bacillus thuringiensis subsp. kurstaki have been identified in this study. With metal exposure, all the enzyme activities have increased. Antagonistic effects were observed in the combination of gallic acid with all three metals on the activities of superoxide dismutase and catalase. In glutathione peroxidase activity, an antagonistic effect was observed in gallic acid plus nickel group, while there was a synergistic effect for gallic acid plus zinc and gallic acid plus copper. Activities of these enzymes in larvae exposed only to the metals increased in the infected groups; while exposure to gallic acid alone elicited a decrease. As a consequence, it was found that enzyme activities were affected by both metals and gallic acid and infection.

Growth Performance and Enzymatic Response of the Grasshopper, Calliptamus abbreviatus (Orthoptera: Acrididae), to Six Plant-Derived Compounds

Plant-derived compounds are sources of biopesticides for the control of insect pests. We compared the growth performance and enzymatic response of the grasshopper Calliptamus abbreviatus Ikonn to six plant-derived compounds (rutin, quercetin, nicotine, matrine, azadirachtin, and rotenone) in laboratory and field trials. When exposed to the six compounds, C. abbreviatus had significantly reduced growth and survival. All the compounds significantly induced an elevated level of reactive oxygen species, indicating oxidative damage. The activity of detoxifying enzymes, including cytochrome P450s, carboxylesterase, glutathione-S-transferase, and UDP-glucuronosyltransferase, and the antioxidant enzymes, including superoxide dismutase, catalase, and peroxidase, all significantly increased after exposure to the six compounds. These data suggest that the six plant-derived compounds had negative effects on C. abbreviatus. Of the six compounds, matrine, azadirachtin, and rotenone were more toxic to C. abbreviatus, followed by nicotine, quercetin, and rutin. These results show the potential of these compounds as botanical pesticides, which can be applied for the biological control of the grasshopper C. abbreviatus.

Phenotypic and Transcriptomic Response of the Grasshopper Oedaleus asiaticus (Orthoptera: Acrididae) to Toxic Rutin

Rutin, a widely distributed phytochemical flavonoid, can be used to control insect pests. In this study, we studied the growth performance of the grasshopper Oedaleus asiaticus Bey-Bienko given xenobiotic rutin using feeding experiments and transcriptomic analysis. O. asiaticus had reduced body size, lower survival rate, and reduced growth performance when fed with xenobiotic rutin. Rutin-fed nymphs had large variation in gene expression profiles, with a total of 308 genes significantly upregulated and 287 genes downregulated. The upregulated genes were significantly enriched in stress resistance-, immune-, and detoxification-related biological processes and the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways. Downregulated genes mainly involved cuticle biosynthesis and nutrition metabolism-related pathways. The quantitative real-time PCR (qRT-PCR) analysis of 15 candidate genes also produced results consistent with the transcriptome data. These results suggested that grasshoppers’ capacity for biosynthesis and nutrition metabolism decreased, and stress resistance and metabolized capacity to toxic substances were significantly induced when O. asiaticus was fed on xenobiotic rutin. Rutin, as a phytotoxin, had detrimental effects and induced changes in gene expression profiles for O. asiaticus. This study can provide a molecular basis and offer future opportunities for the development of rutin-related insecticides and their application to grasshopper control.