Effects of light levels and plume structure on the orientation manoeuvres of male gypsy moths flying along pheromone plumes

The upwind zigzag flights of male gypsy moths (Lymantria dispar L.; Lepidoptera: Lymantriidae) along narrow, ribbon‐like and wide, turbulent plumes of pheromone were examined in a wind tunnel at light levels of 450 and 4 lux. Under all conditions tested males flew upwind zigzag paths. In 450 lux, males flying along turbulent plumes had the highest ground speeds and the widest crosswind excursions between counterturns, compared to slow flight and a narrow zigzag of males along a ribbon plume. In a turbulent plume, males flew more slowly and had narrower zigzags in 4 than in 450 lux. Across most treatments of plume structure and light level, the rate of transverse image flow and the frequency of counterturning remained relatively constant. The effects of light levels on orientation are not readily reconcilable with a model in which moths in low light levels would head more towards crosswind, thereby enhancing the rate of transverse image flow and the perception of wind‐induced drift.