Latencies of behavioral response to interception of filaments of sex pheromone and clean air influence flight track shape in Heliothis virescens (F.) males

Male Heliothis virescens moths flew upwind to pulsed pheromone plumes. Upon truncation of the pulsed plume males flew into clean air, turning their tracks crosswind (> 60° relative to directly upwind direction at 0°) within an average of 0.27s, and were casting, perpendicular to the wind-line (90°), within 0.43 s. 2) The characteristic casting flight in clean air consisted of left-right crosswind reversals, continuing for many seconds without further pheromonal stimulation. Males intercepting a single strand of pheromone during casting flight responded by surging upwind (track angles < 60°). The phasic surge lasted only 0.38 s before reverting to crosswind flight (> 60°). 3) Average templates of responses in two and three dimensions were created. Males controlled their vertical deviations very tightly when in contact with pheromone but upon entering clean air, lateral and vertical excursions became much greater. 4) Males failed to sustain upwind flight to repetitively pulsed plumes generated at < 4 filaments/s. At the threshold frequency of 4 pulses/s we show that upwind flights were composed of reiterated surges followed by crosswind casting. As the pulse frequency increased, the tracks became straighter and the single filament castsurge-cast template could be viewed only sporadically when, for example, a male apparently failed to intercept filaments.