The effects of source dosage, flight altitude, wind speed, and ground pattern on the sex pheromone‐mediated flight manoeuvres of male lightbrown apple moth, Epiphyas postvittana (Walker)

Abstract

The flight tracks (plan view) of male Epiphyas postvittana flying in a sex pheromone plume in a wind tunnel were recorded. With increasing source dosages (10, 100, 300 μg), males steered a more upwind course, with corresponding track angles more upwind, and had smaller intertrack reversal distances (i.e., they showed less lateral movement). Although net ground speed tended to increase with increasing source dosage, the effect was not significant. Increased wind speed (from 20 to 40 cm sec‐1) resulted in little change in the apparent track of the males, but males increased their airspeed and steered a course more upwind in response to the increased downwind push and crosswind drift. Flight altitudes (source suspended at 5, 12.5, and 20 cm above the floor of the tunnel), had little effect on most flight parameters, except for ground speed and airspeed, which increased with increasing altitude, and which in turn resulted in increases in intertrack reversal distances. Finally, males steered a more upwind course and had a higher net upwind velocity when flying over a ground pattern of longitudinal black and white stripes than over a ground pattern of lateral black and white stripes. Across all treatments, the frequencies of turning back and forth across the windline were similar. These results are consistent with those observed in several other species of moths, and suggest that the pheromone‐mediated flight of male E. postvittana is shaped by optomotor anemotaxis (the use of visual images to steer a resultant track and ground speed with respect to the wind) and by a behavioural mechanism that governs the rhythmic counterturning.