Conophthorin enhances the electroantennogram and field behavioural response of Xylosandrus germanus (Coleoptera: Curculionidae) to ethanol

Ethanol acts as an attractant that aids Xylosandrus germanus (Blandford) in locating living but weakened hosts. Electroantennogram (EAG) and field trapping experiments were conducted with conophthorin and other selected semiochemicals that function as important olfactory cues for various ambrosia beetles to characterize their effect on the attraction of X. germanus to ethanol and to assess whether EAG responses provide an indication of behavioural activity. Thus, semiochemicals hypothesized to enhance (i.e. conophthorin), reduce (i.e. terpinolene, verbenone) or have a negligible (i.e. lineatin, sulcatol, retusol) effect on the attraction of X. germanus to ethanol were selected for comparative purposes. Ethanol plus conophthorin elicited larger EAG amplitudes than binary (1:1) mixtures of ethanol plus the remaining semiochemicals at dilutions of 0.001%, 0.01% and 1% per compound. Conophthorin also enhanced the attraction of X. germanus, Euwallacea validus (Eichhoff) and Cyclorhipidion pelliculosum (Eichhoff) to ethanol under field conditions. By contrast, terpinolene and verbenone reduced the attraction of X. germanus and other ambrosia beetles to ethanol. Semiochemicals that enhance (i.e. conophthorin) or reduce (i.e. terpinolene, verbenone) attraction by X. germanus may improve monitoring and/or management tactics. These results also suggest that EAG responses can indicate field behavioural activity and be useful for screening attractants for X. germanus.