Electrophysiological and behavioural identification of host kairomones as olfactory cues for Culicoides impunctatus and C. nubeculosus

Electroantennograms (EAGs) were recorded from wild‐caught parous, female Culicoides impunctatus (Goetghebuer) in response to components of host odour. Nine synthetic compounds were found to be electrophysiologically active, eliciting EAGs which were significantly different from solvent control. An EAG hierarchy was established, in which 1‐octen‐3‐ol elicited the highest amplitude EAGs, followed by acetone, lactic acid and butanone. The overall responses to phenolic compounds were reduced compared to the non‐phenolics. Subsequent behavioural analyses of the effects of these compounds when tested singly revealed 1‐octen‐3‐ol, acetone and butanone to be attractive over specific stimulus doses. Exposure to supra‐optimal doses modified the insects’ behaviour; insects either ceased to respond or were repelled. Lactic acid was attractive at the lowest dose tested but was repellent at high doses. Behavioural responses to the phenolic components of host odour and lactic acid were similar, generally causing arrestment at low doses and repelling at the higher doses tested. A comparison of EAG profiles and behavioural assays between laboratory‐reared Culicoides nubeculosus (Meigen) and C. impunctatus suggested that the same kairomones are utilized by both species, with C. nubeculosus being less sensitive than C. impunctatus. The EAG hierarchy of C. nubeculosus to the four non‐phenolics was identical to that of C. impunctatus.