Responses of the biting midge Culicoides impunctatus to acetone, CO2 and 1-octen-3-ol in a wind tunnel

Responses of host-seeking female Culicoides impunctatus (Goetghebuer) (Diptera: Ceratopogonidae) to acetone, carbon dioxide and 1-octen-3-ol were measured in a wind tunnel. Carbon dioxide, presented as a filamentous plume, increased upwind flight in a dose-dependent manner, up to 0.09% concentration. A homogenous CO2 plume elicited similar upwind responses at concentrations up to 0.09%, whereas higher plume concentrations (> 0.1%) induced erratic responses with a suppression of upwind flight. Bovine equivalent concentrations of acetone (1.5 x 10(-6) g/l) and 1-octen-3-ol (1.3 x 10(-8) g/l) failed to induce any significant upwind response when tested alone. In the presence of CO2, however, 1-octen-3-ol showed highly significant increases in upwind responses at concentrations of 1.3 x 10(-10)-10(-8) g/l. Mixtures of CO2 + acetone also enhanced upwind flight at 1.5 x 10(-9) g/l. High tunnel concentrations of both 1-octen-3-ol and acetone inhibited upwind responses. These findings are discussed in relation to host finding by C. impunctatus and known mechanisms by which upwind flight is initiated and arrested at high odour concentrations.