Behavioural response of Prostephanus truncatus (Horn) (Coleoptera: Bostrichidae) to the individual components of its pheromone in a flight tunnel: Discrimination between two odour sources

The flight response of P. truncatus to its major pheromone component (T1), minor pheromone component (T2), and a 1:1 mixture of T1 and T2 was investigated in a wind tunnel. Single-source and two-choice experiments were conducted to determine which of the two components is more important in the medium-close-range (≥ 100 cm) behaviour of the beetle. In single-source experiments, either of the two components could attract the beetles, and the mixture was only slightly, but not significantly, more attractive than either of the components. In two-choice flight experiments, P. truncatus were able to discriminate between two simultaneously presented odour sources separated by 12.5 cm, and displayed significant preference for the mixture, or T2 over T1, suggesting that T2 may be more important than T1 in the medium-close-range behaviour of P. truncatus. These results contrast with some previously published data and possible reasons are discussed. There were no differences in the sex ratios of beetles attracted to the three pheromone treatments (T1, T2, or the mixture), suggesting that neither of the two components specifically functions as a sex attractant. The results are discussed in relation to the existing concepts for the multicomponent sex pheromones produced by females of many moth species.