Plant responses induced by Adoxophyes honmai oviposition in host tea plants and non-host Arabidopsis thaliana

Abstract

In the tea ecosystem, tea plants are exposed to attack by the smaller tea tortrix, Adoxophyes honmai Yasuda (Lepidoptera: Tortricidae). Ascogaster reticulata Watanabe (Hymenoptera: Braconidae) is a solitary egg-larval parasitoid wasp that uses chemical cues from tea leaves to search for its host habitat. However, wasp responses to volatiles from egg-laden tea leaves, and plant signaling in response to oviposition by A. honmai, which also recruits parasitoids, are still unknown. Therefore, in this study, we examined wasp responses to volatiles from tea leaves treated with A. honmai egg or reproductive system (RS) homogenate. Although wasps did not show preference for volatiles of host egg-masses or RS homogenates themselves, they preferred egg-laden and RS-treated leaf volatiles to intact leaf volatiles. These results indicate that host plant responses involved in volatile emission attract wasps. Thus, we also investigated plant innate responses induced by A. honmai oviposition. Multiple defense related genes, including JA- and ET-signaling genes, were induced on RS-treated tea leaf. We also investigated gene expression profiles of the SA, JA and ET pathways in a nonhost plant, Arabidopsis thaliana. In A. thaliana, expression of SA and ET-signaling genes was induced by egg treatment, but that of JA-signaling genes was down-regulated. These results suggest that volatile compounds induced by JA pathway may attract A. reticulata to host plant tea leaves.