Odour quality discrimination for behavioural antagonist compounds in three tortricid species

The antennal and behavioural response of three tortricid species (Lepidoptera: Tortricidae) to their corresponding sex pheromones and known or putative behavioural antagonists was tested by electroantennography and in field trials. The species and their pheromones and known or proposed behavioural antagonist were lightbrown apple moth, Epiphyas postvittana (Walker) [pheromone: 95% (E)-11-tetradecenyl acetate (E11-14Ac) and 5% (E,E)-9,11-tetradecadienyl acetate (E9E11-14Ac); antagonist: (Z)-11-tetradecenyl acetate (Z11-14Ac)], codling moth, Cydia pomonella (L.) [pheromone: (E,E)-8,10-dodecadien-1-ol (codlemone); antagonist: (E,E)-8,10-dodecadienyl acetate (codlemone acetate)], and gorse pod moth, Cydia ulicetana (Haworth) [pheromone: (E,E)-8,10- dodecadienyl acetate (codlemone acetate); putative antagonist: (E,E)-8,10-dodecadien-1-ol (codlemone)]. In all three species, the antennal response to the antagonists was not significantly different from the antennal response to con-specific sex pheromone compounds. In the field trapping experiments, significantly fewer males of all three species were attracted to the respective pheromone when blended with the behavioural antagonist compound. However, this response varied between the species, with lightbrown apple moth and codling moth showing stronger responses to the antagonist compounds than gorse pod moth. Both lightbrown apple moth and codling moth males were able to discriminate between pure pheromone and pheromone blended with the antagonist when placed in traps side-by-side separated by ca. 10 cm. The presence of the behavioural antagonist not only affected the catch of males of both species within their own traps but also affected the catch in the neighbouring trap that contained con-specific sex pheromone; the catch of gorse pod moth was not reduced by the presence of codlemone in the neighbouring trap. These results suggest that strong behavioural antagonists such as codlemone acetate for codling moth and Z11-14Ac for lightbrown apple moth induce their inhibition effect at a substantial distance downwind from the odour source; however, most of those males that were able to overcome this inhibition effect at the early stage of orientation to odour source, were able to discriminate between the pheromone source and the pheromone source admixed with behavioural antagonist. Moderate behavioural antagonists such as codlemone for gorse pod moth did not elicit a discrimination effect.