Electrophysiological and behavioural studies of the biting midge, Culicoides impunctatus Goetghebuer (Diptera, Ceratopogonidae): interactions between some plant-derived repellent compounds and a host-odour attractant, 1-octen-3-ol

Electroantennogram (EAG) and Y-tube bioassays have been used to demonstrate the repellent properties of five plant compounds with host-seeking parous female Culicoides impunctatus Goetghebuer. The compounds were methyl salicylate and allyl-, butyl- phenyl- and 2-phenylethyl isothiocyanate. EAG thresholds were 1 x 10(-3) to 1 mu g. In the bioassays, maximal repellencies occurred with 1 x 10(-2) to 10 mu g. When each compound was combined with 1-octen-3-ol, a confirmed host-odour attractant for C.impunctatus females, additive effects were recorded in EAG assays and in bioassays, all of the compounds either reduced or reversed the attractancy of 1-octen-3-ol. Of the isothiocyanates, allyl isothiocyanate was the most potent and when combined with 1-octen-3-ol in field trials, the attractant effect of 1-octen-3-ol was reduced.