Helicoverpa zea males (Lepidoptera: Noctuidae) respond to the intermittent fine structure of their sex pheromone plume and an antagonist in a flight tunnel

We investigated the behavioural response of male Helicoverpa zea (Boddie) to the fine‐scale structure of an odour plume experimentally modified in a wind tunnel by using an air‐pulsing device. Male H. zea flew upwind to pulsed filaments of a binary pheromone blend of (Z)‐11‐hexadecanal (Z11‐16:Ald) and (Z)‐9‐hexadecanal (Z9‐16:Ald) in the ratio of 20:1. Sustained upwind flight in experimentally altered intermittent plumes was dependent on concentration, as well as the frequency of generation of odour filaments. At a loading of 10μg of the major pheromone component, Zll‐16:Ald, which gave an emission rate of approximately that released by a female H. zea , sustained upwind flight and source contact correlated positively with filament delivery rate, becoming significant at a minimum filament delivery rate of 2/s. Decreases in upwind progress and source location were recorded at a loading of 1 μg of Z11‐16:Ald. At this suboptimal dosage, a high filament generation rate of 10/s was necessary for significant upwind progress and source contact. When an interspecific compound: (Z)‐11‐hexadecenyl acetate (Z11‐16:OAc), was added to the attractive pheromone binary aldehyde blend of H. zea at a proportion of 10% of the major pheromone component, and pulsed from the same source, there was a significant reduction in sustained upwind progress and source location by males, indicating that Z11‐16:OAc is antagonistic to the upwind progress of H. zea. However, Z11‐16:OAc was less antagonistic when its filaments were isolated and alternated with pheromone filaments, indicating a strong effect of the synchronous arrival of odour filaments on the antenna needed for antagonism of upwind flight.