Fine-scale resolution of closely spaced pheromone and antagonist filamentsby flying male Helicoverpa zea

The limits of a male moth's ability to resolve closely spaced odor filament s have been investigated. Male Helicoverpa tea normally respond to their co nspecific sex pheromone blend by exhibiting an upwind flight, which culmina tes in source contact by at least 50% of the bioassayed individuals. When l oaded onto the same filter paper source containing this hitherto attractive pheromone blend, or onto a separate filter paper and co-emitted from the s ame pipette source with pheromone, (Z)-11-hexadecenyl acetate severely redu ced upwind flight and source contact by male H. zea. A similar level of upw ind flight inhibition was recorded when the antagonist (Z)-11-hexadecenyl a cetate was emitted from its own point source placed 1 mm upwind of the pher omone point source, both plumes being simultaneously emitted in a continuou s mode to form a confluent strand. However, (Z)-11-hexadecenyl acetate was less effective in reducing upwind flight and source contact when it was iso lated and pulsed from its own source, placed 1 mm either upwind, downwind o r cross-wind of a pipette source from which pheromone was simultaneously be ing pulsed, such that both filaments were separated in time by 0.001-0.003 s. These results suggest that male H. zea are able to distinguish between o dor sources separated by as little as 1 mm in space and 0.001 s in time.