LATENCIES OF BEHAVIORAL-RESPONSE TO INTERCEPTION OF FILAMENTS OF SEX-PHEROMONE AND CLEAN-AIR INFLUENCE FLIGHT TRACK SHAPE IN HELIOTHIS-VIRESCENS (F) MALES

1) Male Heliothis visescens moths flew up-wind to pulsed pheromone plu mes. Upon truncation of the pulsed plume males flew into clean air, tu rning their tracks crosswind (> 60 degrees relative to directly upwind direction at 0 degrees) within an average of 0.27 s, and were casting , perpendicular to the wind-line (90 degrees), within 0.43 s. 2) The c haracteristic casting flight in clean air consisted of left-right cros swind reversals, continuing for many seconds without further pheromona l stimulation. Males intercepting a single strand of pheromone during casting flight responded by surging upwind (track angles < 60 degrees) . The phasic surge lasted only 0.38 s before reverting to crosswind fl ight (> 60 degrees). 3) Average templates of responses in two and thre e dimensions were created. Males controlled their vertical deviations very tightly when in contact with pheromone but upon entering clean ai r, lateral and vertical excursions became much greater. 4) Males faile d 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 crosswin d casting. As the pulse frequency increased, the tracks became straigh ter and the single filament cast-surge-cast template could be viewed o nly sporadically when, for example, a male apparently failed to interc ept filaments.