Electrophysiological And Behavioural Responses Of Adult Plutella Xylostella(Lepidoptera:Plutellidae)to Mentha Spicata(Lamiaceae) Secondary Substance

The long-term and extensive use of chemical pesticides has resulted in the diamondback moth Plutella xylostella(L.)becoming one of the most resistant pests.There is an urgent need for green and environmentally-friendly integrated management technology systems for the sustainable control of the diamondback moth.Secondary substances produced by non-host plants are effective in repelling,poisoning and inhibiting the growth of insects.In this paper,we used headspace collection,GC-EAD,GC-MS,EAG,Y-tube olfactometer,LC-MS,proboscis extension reflex and field oviposition assays to screen volatile and non-volatile secondary metabolites from the non-host plant Mentha spicata.Our results provide a theoretical basis for controlling the P.xylostella damage by remotely regulating the orientation of this species and/or changing the surface chemistry of host plants.We showed the olfactory responses of P.xylostella adults to intact and mechanically damaged M.spicata plants.Damaged M.spicata have a strong repellent effect on both female and male adults of P.xylostella.Indoor behavioral experiments showed repellent indices of 80% and 53.33%,respectively.The field oviposition assays showed the oviposition repellent index was 71.32% which can achieve an extremely significant repellent effect on females.The intact M.spicata had no significant repellent effect on both sexes of P.xylostella.We screened and identified volatiles with repellent activities against P.xylostella from M.spicata.The 2,4-dimethylheptane,4-methyloctane and myrcene in the secondary substance volatiles of M.spicata had significant repellent effects on the adult P.xylostella.Myrcene had the strongest repellent effect followed by 2,4-dimethylheptane,and 4-methyloctane.At a concentration of 500 μg/μl,the indoor behavioral repellent indices of myrcene to adult females and males of P.xylostella were 83.3% and 80.0%,respectively.The field oviposition repellent index to female adults was 41.38%.The indoor behavioral repellent indices of 2,4-dimethylheptane to female and male adults were 83.3% and 76.6%,respectively.The field oviposition repellent index was 36.08%.The indoor behavioral repellent index of 4-methyloctane to both sexes adults was 56.7% and the field oviposition repellent index was only 24.73%.We also screened and identified non-volatiles with repellent activity against P.xylostella from M.spicata.A total of 40 non-volatile substances were detected from M.spicata extract amongst which rutin and theophylline had significant repellent effects on the oviposition of female adults of P.xylostella.At a concentration of 100 mmol/L,the oviposition repellent indices of rutin and theophylline suspension to the female adults of P.xylostella were 37.87% and 27.81%,respectively.The results of this study further clarify the repellent mechanism of M.spicata secondary substance against P.xylostella from the aspects of olfactory and taste responses.We also characterized the efficacy of these compounds in controlling the P.xylostella damage by remotely regulating the orientation of this species and/or changing the surface chemistry of host plants.