Identification of compounds produced by male hairpencil glands of corn earworm, Helicoverpa zea and their role in male autodetection and female mate acceptance

Abstract

Heliothine moths represent some of the world's most important agricultural pest species. Helicoverpa zea (Corn Earworm) and Heliothis virescens (Tobacco Budworm) cause billions in damage and control costs worldwide each year. Given their economic importance, sex pheromones of many species have been studied for the development of management techniques such as trapping for population monitoring. The majority of pheromones identified and studied to date have been female-produced sex pheromones. Less emphasis has been placed on male sex pheromones, associated with abdominal hairpencil structures that often function in courtship or to attract females. The present study examines the composition, detection and behavioural role of male H. zea hairpencil compounds in male autodetection and in courtship. Comparative examination of the hairpencil effluvia of H. zea and H. virescens did not reveal distinct differences in pheromone blend composition produced by males of these species. Electrophysiological testing demonstrated broad antennal neuron response in both males and females of H. zea to nine key stimuli, with sexual dimorphism present in each species. Behavioural assays suggested that odours released by male hairpencils are important in mate acceptance by female H. zea and may play a role in mate choice and species isolation. Wind tunnel observations indicated that key H. zea hairpencil odours (hexadecanyl acetate and octadecanyl acetate) also function in mate competition, antagonising responses of downwind conspecific males following a synthetic female sex pheromone plume. This finding provides insight regarding male–male detection and response to hairpencil compounds in H. zea.