THE REGULATION OF DISTANCE TO DUMMY FLOWERS DURING HOVERING FLIGHT INTHE HAWK MOTH MACROGLOSSUM-STELLATARUM

1. While collecting nectar in hovering flight the European hawk moth M acroglossum stellatarum efficiently regulates its distance relative to flowers that are shaken by wind. This can be demonstrated in laborato ry experiments by moving dummy flowers (blue cardboard disks) towards and away from the feeding animal (Fig. 1). 2. Distance regulation is p redominantly mediated by visual cues. Mechanoreceptors on the probosci s appear to contribute little to the response. 3. Movements of dummy f lowers can be simulated by expanding and contracting a pattern project ed onto a screen. With this technique we investigated the dynamical pr operties of the servo mechanism underlying distance regulation. The sy stem behaves as a bandpass filter with corner frequencies of 0.15 and 5 Hz (Figs.2,3). 4. When a high-speed ramp-like movement of the flower is simulated, there is an asymmetry in the response. During simulated approach the reaction is phasic-tonic with a pronounced overshoot at the beginning, during simulated retraction it remains tonic (Fig.5B,C) . 5. During distance regulation the animals compensate for the speed o f the edge of the projected pattern. Distance regulation improves subs tantially when the number of stimulated elementary movement detectors is increased through increasing the number of contour lines by project ing concentric rings instead of a homogeneous disk (Figs.7, 8).