Identification Of Olfactory Genes And Their Sex Pheromone Perception In Larvae Of Hypantria Cunea

The fall webworm(Hyphantria cunea Drury)is a worldwide quarantine pest insect.The larvae of H.cunea feeding on various host plants has caused serious damage to the local forets,landscaping and ornamental trees in the affected areas,resulting in great economic and ecological losses.The olfactory system is important for behavioral activities of insects to recognize relevant odor information in the complex environment.And the chemical perception is crucial for insects’ reproduction and regeneration.The olfactory system of H.cunea adult has been systematically studied,however,the olfactory genes of H.cunea larvae and its responses to sex pheromones remain poorly understood.In this study,the transcriptome of the head of H.cunea larvae was conducted and the olfactory candidate genes were identified.Then,the sequence allignment of olfactory candidate genes was analysed between the H.cunea larvae and adult.The binary-choice assay was employed to exame the responses of H.cunea larvae to the adult sex pheromones.Meanwhile,the expression level of odorant-binding proteins in H.cunea larvae,involved in sex pheromones,were analyzed by fluorescence quantitative PCR.The main results are as follows:(1).Identification of olfactory genes in larvae of H.cuneaThe olfactory genes were identified based on transcriptomic and genomic data from H.cunea,the identified olfactory genes include 46 odorant-binding proteins(OBPs),38 chemosensory proteins(CSPs),13 odorant receptors(ORs),17 ionotropic receptors(IRs),53 gustatory receptors(GRs),2 sensory membrane proteins(SNMPs)and the candidate genes of odor-degrading enzymes oxidase which include 3 aldehyde oxidase genes(AOXs),30 carboxylesterase genes(CXEs),34 glutathione S-transferase genes(GSTs)and 60 cytochrome P450 genes(CYPs).(2).Sequence allignment of olfactory candidate genes between the H.cunea larvae and adultBased on the genome and transcriptome data from H.cunea adult and larvae,the types and number of olfactory genes were examed.Here,17 OBPs,21 CSPs,5 ORs,13 IRs and47 GRs were newly discovered in larvae.Among them,PBP1,PBP2,PBP3,GOBP1,GOBP2 and Orco genes are expressed simultaneously in larvae and adults,while PRs genes are only expressed in adults.The phylogenetic tree analysis of IRs genes showed that the newly identified IR22 and IR23 clustered into IR8 a and IR25 a branches,respectively.the phylogenetic tree analysis of GRs showed that the newly identified GR31 clustered into the CO2 receptor family,and GR10 and GR19 clustered into the sugar receptor family.(3).Behavioural response of H.cunea larvae to sex pheromoneThe behavior response of H.cunea larvae to sex pheromoneo were analyzed in the binarychoice assay.The results showed that the dose difference of mixed sex pheromones components led to different behavior response,and the H.cunea larvae showed more preference to mixed sex pheromones components at the dose of 10 ng,rather than 3ng or30 ng.Then the behavior response of H.cunea larvae to single sex pheromones components was further determined.The results showed that larvae had obviously preference to Z9,Z12-18 ald,Z9,Z12,Z15-18 Ald,instead of Z3,Z6-9S,10R-epoxy-21 Hy or 1-Z3,Z6-9S,10Repoxy-21 Hy.(4).The expression level of odorant-binding proteins in H.cunea larvae involved in sex pheromonesTwo highly selective sex pheromone components(Z9,Z12-18 ald,Z9,Z12,Z15-18Ald)were chosed to attract H.cunea larvae,and then the expression level of different OBP genes were analyzed by fluorescence quantitative PCR.The results show that the expression level of twelve OBP genes was significantly up-regulated after treated with Z9,Z12-18 Ald.After Z9,Z12,Z15-18 Ald induction,six genes were found to be up-regulated.Among them,GOBP2,OBP2,OBP9,OBP29,OBP34,OBP36 were significantly up-regulated after these two treatments.In conclusion,the olfactory genes of H.cunea larvae was systematically analyzed in this study.And the sequence similarities of olfactory genes between larval and adult was also identified.Moreover,the perception ability of H.cunea larvae to sense sex pheromones was confirmed in the study.This research has laid the foundatin for relucidating the olfactory mechanism of H.cunea larvae and these OBPs might represent meaningful targets for developing behavioral interference control strategies against H.cunea.