Search strategies of fruit flies in steady and shifting winds in the absence of food odours

Abstract. Flight behaviour by females of two species of fruit flies, Drosophila funebris and Drosophila immigrans , was videorecorded in a wind tunnel in still air and in wind with a constant or shifting direction. Flies which were deprived of food overnight took flight in the absence of food odours. Both species responded to the presented winds in agreement with two models that predict the shortest distance to an odour plume. According to these models, the shortest distance to an odour plume is travelled when insects fly at right angles to the wind with a steady direction. In winds shifting over more than 60, the shortest distance to an odour plume is achieved when insects fly parallel to the time-averaged wind direction. We propose a behavioural mechanism which accomplishes the observed flight directions taken by the two species of fruit flies in response to the tested wind regimes.