Chemical communication in heliothine moths. III. Flight behavior of male Helicoverpa zea and Heliothis virescens in response to varying ratios of intra- and interspecific sex pheromone components

Helicoverpa zea males flew upwind and successfully contacted the source when presented with 2-component blends consisting of their principal conspecific sex pheromone component, (Z)-11-hexadecenal, plus small amounts of (Z)-9-tetradecenal, a key secondary component in the Heliothis virescens blend which has heretofore been considered antagonistic to H. zea pheromone-mediated behavior. Neurophysiological studies of H. zea antennal receptor neurons and central interneurons had suggested that this unexpected antagonistic effect on behavior might occur. When the amount of (Z)-9-tetradecenal in the blend reached 15% relative to the principal component its effect did become antagonistic with significantly more H. zea males remaining quiescent. Five-to-fifteen percent (Z)-9-tetradecenal is emitted by H. virescens in its pheromone blend, levels that evoked optimal upwind flight and source contact in H. virescens males. As suggested by studies of H. virescens antennal receptor neurons, H. virescens males were unresponsive to the reciprocal inter-specific blend, comprised of (Z)-11-hexadecenal plus various percentages of (Z)-9-hexadecenal. Receptors that allow such mutual replacement of compounds might permit significant shifts in pheromone systems; a single mutation that drastically alters the female sex pheromone blend could still be carried in a population due to the successful attraction of normal males by mutant females.