Toxicology Study Of Cycloxaprid On Lepidopteran Pests

Chronically,continuously and largely absurd application of traditional pesticides results in pesticide remanent and heavy resistance,so it is urgent to develop green pesticides.Cycloxaprid?CYC?is a new neonicotinoid independently developed in China,which has a well-documented bioactivity against the rice planthopper and other hemipteran pests.Lepidopteran pests often damage crops at the same time as hemipteran pests,but currently there is a lack of toxicological studies on CYC on lepidopteran pests.In order to make full use of CYC,improve economic efficiency and reduce the environmental pollution caused by the use of various pesticides,this paper carried out the toxicology study of CYC on lepidopteran pests.The main experiments and results are as follows:1.Bioactivity of CYC against lepidopteran pests.The LC₅₀s of CYC against 3^rd instar larvae of Ostrinia furnacalis,Helicoverpa armigera and Mythimna separate were determined to be 71.28?83.48 and 46.42 mg/L using the feeding bioassay.The LD₅₀s of CYC against 3^rdd instar larvae of O.furnacalis,H.armigera and M.separata were determined to be 521.44,797.87 and 175.92 ng/insect using the contact bioassay.The results demonstrated that lepidopteran pests are much less sensitive to CYC than hemipteran insects.2.The effect of feeding CYC on the transcriptome of O.furnacalis.A total of 384 up-regulated differentially expressed genes?DEGs?and 415 down-regulated DEGs were identified and more than half of the top 20 up-regulated genes encoded cuticular proteins.Real-time quantitative PCR?RT-qPCR?results showed that these genes were highly expressed in the cuticle.Therefore,cuticular protein genes may be the main reason for the insensitivity of lepidopteran pests to the feeding of CYC.3.The effect of body surface exposure to CYC on corn borer transcriptome.A total of 174up-regulated DEGs and 23 down-regulated DEGs were identified.Among the top 20 up-regulated DEGs,there were 11 genes related to cuticle formation and one gene encoded a detoxification enzyme.RT-qPCR results showed that genes related to cuticle formation were highly expressed in the cuticle.Therefore,genes related to cuticle formation may be the main reason for the insensitivity of lepidopteran pests to the body surface exposure to CYC.4.Toxicological analysis of CYC.First,the acetylcholine receptor from O.furnacalis had high sequence similarity with those from brown planthoppers and human and the amino acid residues involved in ligand binding were conserved.The administration of CYC did not cause the change of the gene expression level of the target.Therefore,it is speculated that the target is not responsible for the insensitivity of lepidopteran pests to CYC.Secondly,the pretreatment of detoxification enzyme inhibitors did not significantly improve the insecticidal activity of CYC,indicating that detoxification enzymes are not the main factor for the insensitivity of lepidopteran pests to CYC.Finally,the LD₅₀ value of CYC against O.furnacalis measured by injection method was 13.71 ng/insect,which was 38-fold different from that determined by contact method.This result demonstrated that the cuticle permeation is the main factor for the insensitivity of lepidopteran pests to CYC.The LD₅₀ value was determined to be 277.30ng/insect by synergistic application of CYC with a penetration enhancer?graphene oxide?,which increased the bioactivity by 1.88-fold.It shows that penetration enhancer can significantly improve the insecticidal activity of CYC on lepidopteran pests.