CcOBP2 plays a crucial role in 3-carene olfactory response of the parasitoid wasp Chouioia cunea.

Chouioia cunea (Yang) is a pupal parasitoid wasp and this species is able to seek host insects depending on its olfactory system. However, the molecular mechanism of the olfactory system in the C. cunea is still limited. To identify putative semiochemicals bound to CcOBP2, a protein specifically expressed in antennae, 14 compounds from the pupae of H. cunea and 11 common volatile compounds from plants were selected for competitive fluorescence binding assay. The result of the binding assay showed that five compounds were able to bind toCcOBP2. The electroantennogram (EAG) demonstrated that the antennae had a significant response to the 3-Carene, a bicyclic monoterpene, and C. cunea could be obviously attracted by this compound. The behavioral response to 3- carene was dramatically weakened when CcOBP2 was specifically knocked down. The molecular docking result indicated that several amino acids especially Ile-81, Val-122, Phe-123 of CcOBP2 were responsible for binding to 3-Carene. Furthermore, there was a repellent effect on the host H. cunea with the treatment of the 3-Carene. This study illustrated that CcOBP2 might be a crucial protein involved in the olfactory signaling pathway and the 3-Carene, secreted from plants, could probably have a potential role in repelling pests as well as attracting natural enemies.