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 times 10 ‐3 to 1 μg. In the bioassays, maximal repellencies occurred with 1 times 10˜ 2 to lOug. 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 l‐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 l‐octen‐3‐ol was reduced.