EFFECTS OF PHEROMONE PLUME STRUCTURE AND VISUAL-STIMULI ON THE PHEROMONE-MODULATED UPWIND FLIGHT OF MALE GYPSY MOTHS (LYMANTRIA-DISPAR) IN A FOREST (LEPIDOPTERA, LYMANTRIIDAE)

The pheromone-modulated upwind flight of Lymantria dispar males respon ding to different pheromone plume structures and visual stimuli design ed to mimic trees was video recorded in a forest. Males flying upwind along pheromone plumes of similar structure generated tracks that were similar in appearance and quantitatively similar in almost all parame ters measured, regardless of the experimentally manipulated visual sti muli associated with the pheromone source. Net velocities, ground spee ds, and airspeeds of males flying in point-source plumes were slower t han those of males flying in the wider, more diffuse plumes issuing fr om a cylindrical baffle. The mean track angle of males flying in plume s issuing from a point source was greater (oriented more across the wi nd) than that of males flying in plumes issuing from a transparent cyl indrical baffle. Males flying in point-source plumes also turned more frequently and had narrower tracks overall than males responding to pl umes from a cylindrical baffle. These data suggest that L. dispar male s orienting to pheromone sources (i.e., calling females) associated wi th visible vertical cylinders (i.e. , trees) use predominantly olfacto ry cues to locate the source and that the structure of the pheromone p lume markedly affects the flight orientation and the resultant track.