Effects Of Rice Volatiles Induced By The Brown Planthopper On Trichogramma Japonicum

Herbivore-induced plant volatiles(HIPVs)play an important regulatory role in the complex multi-level nutritional interactions in nature.HIPVs can not only regulate the host selection behavior of herbivorous insects,the predation or parasitism behavior of natural enemies,but also affect the physiological and biochemical characteristics of adjacent plants.Revealing the key role of plant volatiles in the tritrophic nutrition relationships between plant and herbivorous insect and natural enemy has great practical significance for the development of green pest control strategies in farmland.Previous studies in our laboratory have found that the striped rice stem borer,Chilo suppressalis(Walker)adults prefer to lay eggs on rice plants damaged by Nilaparvata lugens(St(?)l),and rice plants(Oryza sativa)damaged by N.lugens have interference or repellent effects on Trichogramma japonicum,an egg parasitoid of C.suppressalis.However,the biochemical mechanism mediating the parasitic behavior of the parasitoids is still unclear.In this paper,a series of ecological experiments were conducted on the tritrophic nutrition relationships between N.lugens,C.suppressalis,and T.japonicum mediated by rice volatiles.On this basis,further biochemical and molecular experiments were conducted to elucidate the mechanism of rice volatiles induced by brown planthopper affect the parasitic behavior of T.japonicum.The specific research results are as follows:1)The selection behavior of T.japonicum to different treated rice plants was studied by Y-tube olfactometer selection test.The results showed that the rice plants damaged by oviposition of C.suppressalis attracted T.japonicum,and the rice plants damaged by N.lugens repelled T.japonicum.T.japonicum had no selection preference between the rice plants damaged by both C.suppressalis and N.lugens and the healthy rice plants,that is,the rice volatiles induced by N.lugens disturbed the localization ability of T.japonicum to the host.2)The parasitism rate of T.japonicum infestans on C.suppressalis eggs on different treated rice plants was studied by cage experiment.The results showed that compared with the parasitism rate of C.suppressalis eggs on healthy rice plants,the parasitism rate of T.japonicum on C.suppressalis eggs on rice plants damaged by N.lugens decreased by 14.7 %.The presence of N.lugens can significantly reduce the risk of C.suppressalis eggs being parasitized by T.japonicum,which provides a “shelter” for C.suppressalis eggs from parasitism.3)The effects of key compounds on T.japonicum were investigated by GC-MS analysis and functional verification experiments.The results showed that there were significant differences in rice volatiles amongst different treatments.Eight compounds with significant differences were screened from rice plants treated with different pests.Then they were quantitatively analyzed.The effects of different concentrations of compounds on the selection behavior of T.japonicum were determined by Y-tube olfactometer test.The results showed D-limonene and Dodecane had a significant repulsion effect on parasitic wasps under high concentrations,while they had a significant attraction effect on parasitic wasps under low concentrations.Linalool has a repellent effect on parasitic wasps under high concentrations;Methyl salicylate,Decanal and Hexadecane have attractive effects on parasitic wasps under specific concentrations.Referring to the actual proportion of each component in the volatiles of different treated rice plants,six functional compounds were configured into mixtures in the experiment.These mixtures were basically consistent with the regulatory effects of the corresponding treated rice plants on the chemotaxis of parasitic wasps.4)The related pathways and genes of terpene synthesis were studied by rice transcriptome analysis and q RT-PCR.The results showed that different insect infested can cause rice transcriptional response.Through KEGG functional enrichment analysis,it was found that some genes related to glycolysis / gluconeogenesis pathway and terpene skeleton synthesis pathway were significantly up-regulated.These pathways are related to the synthesis of D-limonene,Linalool and Methyl salicylate.Seven differentially expressed genes related to the synthesis of terpenes were screened out for q RT-PCR verification.The results showed that the expression trend of the genes was the same as that in RNA-seq.In summary,the rice volatiles induced by N.lugens affect the recognition and localization of C.suppressalis eggs by T.japonicum,and provide a shelter for C.suppressalis eggs to avoid natural enemies.In addition,this study revealed the key role of HIPVs in the tritrophic relationship of plant-pest-natural enemy,and provided a basis for formulating green control strategies for pests in paddy fields.