FLIGHT RESPONSES OF TSETSE-FLIES (GLOSSINA) TO OCTENOL AND ACETONE VAPOR IN A WIND-TUNNEL

Female Glossina morsitans morsitans Westwood were video-recorded in a wind-tunnel as they entered, in crosswind flight, a broad plume of either octenol or acetone (two components of ox odour). Both odours produced upwind turning responses (in-flight anemotaxis) to a range of concentrations, with thresholds at around 10(-8) mg l-1 for octenol and 10(-6) mg l-1 for acetone. Kinetic responses were unaffected by octenol at low concentrations, but flight speed was significantly reduced and sinuosity (degrees-m-1) and angular velocity (degrees-s-1) significantly increased by concentrations at or above those in ox breath; for acetone, these effects were apparent but inconsistently related to concentration. It is concluded that octenol and acetone vapour are used by tsetse flies to locate hosts by upwind anemotaxis, probably combined with kinetic responses. The behavioural basis for the 'repellency' of high octenol concentrations in the field is discussed in the context of the virtual loss of upwind anemotaxis to octenol at the highest concentration tested in the tunnel (30 x ox breath).