HELICOVERPA-ZEA MALES (LEPIDOPTERA, NOCTUIDAE) RESPOND TO THE INTERMITTENT FINE-STRUCTURE OF THEIR SEX-PHEROMONE PLUME AND AN ANTAGONIST INA FLIGHT TUNNEL

We investigated the behavioural response of male Helicoverpa zea (Bodd ie) to the fine-scale structure of an odour plume experimentally modif ied 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-hexad ecanal (Z11-16:Ald) and (Z)-9-hexadecanal (Z9-16:Ald) in the ratio of 20:1. Sustained upwind flight in experimentally altered intermittent p lumes was dependent on concentration, as well as the frequency of gene ration of odour filaments. At a loading of 10 mu g of the major pherom one component, Z11-16:Ald, which gave an emission rate of approximatel y that released by a female H. zea, sustained upwind flight and source contact correlated positively with filament delivery rate, becoming s ignificant at a minimum filament delivery rate of 2/s. Decreases in up wind progress and source location were recorded at a loading of 1 mu g 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 (Z 11-16:OAc), was added to the attractive pheromone binary aldehyde blen d of H. zea at a proportion of 10% of the major pheromone component, a nd pulsed from the same source, there was a significant reduction in s ustained 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 th e synchronous arrival of odour filaments on the antenna needed for ant agonism of upwind flight.