Bodily stimulus gradients and precopulatory orientation in the midge, Culicoides melleus

. The male Culicoides melleus (Coquillett) (Diptera: Ceratopogonidae) is able to orientate extremely rapidly to the copulatory position on a C. melleus female and, remarkably, assumes an equivalent position on a mosquito female (Aedes taeniorhynchus). To test for possible similarity between the midge and mosquito females, the ability of their different bodily parts to stimulate sexual response from C. melleus males was assayed. Males were known to respond sexually to a contact pheromone. Males showed increasing response posteriorly on both female C. melleus and A. taeniorhynchus , and greater response to ventral positions than dorsal. Experiments involving transpositions of bodily parts of C. melleus females prove that orientation, at least in the later stages of precopulatory behaviour, is to cues on the female abdomen. It is suggested that the orientation behaviour of the C. melleus male is achieved in response to contact pheromone gradients on the female body.