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

Summary

• 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.