Identification And Expression Of Chemosensory Genes In Bradysia Odoriphaga And Its Olfactory Behavioral Responses To Host Volatiles

The chive maggot Bradysia odoriphaga Yang et Zhang(Diptera: Sciaridae)is a devastating agricultural pest which can damage host roots and cause crop failures.B.odoriphaga feeds on plants from seven families,including Liliaceae,Cucurbitaceae,and Compositae,and is also a potential pest of mushrooms.Third-instar larvae of B.odoriphaga,the most serious stage of damage.At present,the control of chive root maggot relies mainly on chemical pesticides.Pesticides are not the most effective treatment because of widespread drug resistance,slow toxicity and their association with many problems,such as pesticide residues and food safety.As an alternative to chemical insecticides,non-pesticide control methods are urgently needed for application as an efficient and environment-friendly control strategy.The shared host plant volatiles and chemosensory genes of B.odoriphaga may together play crucial roles for insects to identify their host.However,the responses of B.odoriphaga to host volatiles remain unclear.In this study,we investigated the electrophysiological and behavioral responses of B.odoriphaga to different host volatiles and identified its chemosensory genes,which represent two critical factors of olfactory recognition.1.In our study,57 chemosensory genes,including 51 odorant binding proteins(OBPs)and 6 chemosensory proteins(CSPs),were identified based on transcriptomes of larvae and pupae.Compared with previous adult transcriptomes,11 BodoOBPs were specifically expressed in adults,and 6 BodoOBPs were specifically expressed in larvae and pupae.BodoCSP2 and BodoCSP3 were exclusively expressed in the adult stage.Expression profiles of new genes in adult tissues and the enrichment differences of chemosensory genes between larvae and adults provided targets for further research on the binding ability to host volatiles.2.Electroantennography(EAG)and behavioral bioassays were performed on 12 volatiles shared in Allium and Pleurotus.Hexanal evoked in both male and female adults extremely significant EAG responses and has significant impacts on the behavior of B.odoriphaga(attract or repel at different concentrations).In behavioral assays,3rd-instar larvae and female adults can be significantly repelled by methyl propyl disulfide,1-octen-3-ol or hexanal at the concentration of 100 mg/mL.Third-instar larvae and female adults were significantly attracted by limonene with a concentration of 10 and 100 mg/mL,respectively.In short,our results provided the targets for further study of chemosensory gene functions and the potential substances in new ecofriendly pest management.