Antennal perception of oilseed rape, Brassica napus (Brassicaceae), volatiles by the cabbage seed weevil Ceutorhynchus assimilis (Coleoptera: Curculionidae)

The response of the Ceutorhynchus assimilis antenna to volatiles in air entrainment-derived extracts of oilseed rape, Brassica napus, was studied using coupled gas chromatography (GC)-electroantennography (EAG) and coupled GC-single cell recording (SCR). By means of these techniques and coupled gas chromatography-mass spectrometry (GC-MS). 25 active compounds were identified, including isoprenoids and compounds derived from fatty acids and amino acids. Some of the latter, the isothiocyanates and goitrin, and probably indole and benzyl cyanide, are catabolites of glucosinolates. The electrophysiological activity of the identified compounds was confirmed by EAG using a physiologically discriminating dose, and by SCR studies. The importance of the combined use of the EAG and SCR techniques was demonstrated, since specific olfactory cells were located for five compounds that did not elicit significant EAG responses. The majority of the olfactory cells from which single cell recordings were obtained showed very high specificity, and in numerous recordings there were consistent pairings of specific cell types.