Responses of male Helicoverpa zea to single pulses of sex pheromone and behavioural antagonist

Male Helicoverpa tea (Boddie) (Lepidoptera: Noctuidae) flying in a pheromon e plume respond to the loss of pheromone when they fly into a large pocket of clean air by going into crosswind casting flight in a mean of 0.48 s; 0. 62 s after re-contacting pheromone presented as a single pulse, they surge upwind in a kind of narrow zigzagging flight. After 0.36 s of surging, they lapse into casting flight once again in the clean air following the pulse. The addition of a known behavioural antagonist (Z)-11-hexadecenyl acetate (Z11-16:Ac), to the pheromone significantly increases the mean latency of t he response to a single pulse to 0.85 s. No other aspects of the surge were significantly changed by the presence of antagonist in the single pulse of pheromone. Thus, unlike males of the related species, Heliothis virescens, which show significant changes in track and course angles when antagonist is present in single pulses, only an increased latency of response to a fil ament containing antagonist occurred in H. zea males. The increased latency could act cumulatively when the male is exposed rapidly and repeatedly to filaments in a natural plume and explain the profound arrestment effect of the antagonist in such plumes. The latencies to casting and surging in resp onse to a pulse of pheromone blend are longer than those of the smaller spe cies, H. virescens, and may be due to size-related differences in manoeuver ability of H. zea vs. H. virescens.