Pheromone-modulated optomotor response in male gypsy moths, Lymantria dispar L.: Upwind flight in a pheromone plume in different wind velocities

1. Lymantria dispar males flying in a wind tunnel, up a plume of female sex pheromone, respond to increasing wind velocity by steering a course more precisely upwind. Even though the course angles steered are distributed unimodally about zero degrees (0°), the resulting track angles maintain a remarkably consistent bimodal distribution across all wind velocities tested (Fig. 4). 2. As the wind velocity increased, the moths maintained their average track angle and ground speed at fairly constant values (Figs. 2, 3). The males actively maintained these ‘preferred’ track angles and ground speeds by varying their air speed (Fig. 2) and course angles steered (Fig. 3). 3. The longitudinal component of image flow, the signal which hypothetically controls ground speed, remained relatively constant across all wind velocities (Fig. 5). The transverse component of image flow, which presumably controls steering increased significantly as the wind velocity increased (Fig. 5). There was no constant relationship between the transverse and longitudinal components of image flow; they appear to be used independently to control flight. 4. The males maintained the temporal aspects of their zigzagging flight tracks with remarkable consistency (Table 1). The duration between turns remained nearly the same across all wind velocities, lending support to a hypothetical CNS counterturning generator.