Compensation for height in the control of groundspeed byDrosophila in a new, ?barber's pole? wind tunnel

Abstract

1. All experiments were performed on freely flyingDrosophila in a new, horizontal wind tunnel where the visual input was provided by the apparent axial movement of rotating helical patterns surrounding the cylindrical working section. The flies were flown upwind along a narrow plume of attractant odour in the mid-line of the tunnel so their visual input was specified. 2. When the pattern was at a constant distance from the flies they controlled their groundspeed by flying at an airspeed such that there was a constant angular velocity of image movement rather than a constant frequency of stripe alternation over their eyes. They thus flew at the same groundspeed regardless of wind speed. 3. When the distance of the pattern from the flies changed in a step, the flies adjusted their airspeed at the change so as to keep a relatively constant groundspeed. They did this by changing the angular velocity of image movement that they held constant. 4. When the distance of the pattern from the flies changed gradually, on a cone rather than in a step, the flies did not adjust the angular velocity of image movement that they held constant. Their groundspeed thus did not remain constant. 5. It is suggested that the flies used parallax cues, from the different apparent angular velocities visible juxtaposed on either side of a step in pattern distance, to adjust the angular velocity of image movement that they held constant.