Olfactory antennal responses of the vine weevil Otiorhynchus sulcatus to plant volatiles

Electroantennograms (EAGs) were recorded from the vine weevil, Otiorhynchus sulcatus F. (Coleoptera: Curculionidae) to a broad range of volatile plant compounds. The response profile is restricted to a small number of volatiles that evoke substantial EAGs. Large EAG responses were particularly found among green leaf volatiles (GLV) such as (E)-2-hexenol-1, (Z)-3-hexenol-1, hexanol-1, hexanal, and heptanal. Other plant volatiles eliciting responses in the weevils' antenna are 2,5-dimethylpyrazine, hexylamine, benzylalcohol, 1,2-dimethoxybenzene, o-cresol, myrtenol, 3-methylcyclohexanol, gamma-hexalactone, and gamma-heptalactone. EAG responses to terpenes were generally weak. Many of the monoterpenes are characteristic for the odour of conifers, a group of plants which tend to be avoided by adult vine weevils. The EAG response to several GLV and benzene derivatives in three geographically distinct populations of the vine weevil differed, suggesting between-population variation in receptor sensitivities for several compounds under test. The GLV-composition of the odour profile of potential food plants may be an important criterion for a polyphagous insect like the vine weevil to be used in host-plant selection, since compounds in this odour group dominate so strongly the EAG response profile. In multiple food-choice situations the weevils are known to prefer certain plant species and we hypothesize that they combine GLV information with that of more specific plant volatiles, thereby promoting attraction or avoidance.