Male moth behaviour and perception in pheromone plumes

Abstract: Behaviour of male moths and electrophysiological responses of male pheromone-specific olfactory receptor neurones were studied in two model species, the oriental fruit moth Grapholita molesta and the turnip moth Agrotis segetum. The studies were aimed at elucidating the relative importance of different mating disruption mechanisms. In a wind tunnel study of G. molesta, behavioural response to a reference pheromone source was tentatively suppressed by pheromone released from a second treatment source. Manipulations of the treatment composition and concentration, revealed that the adaptation/habituation of the olfactory system had the biggest effect, followed by the false trail following mechanism, and that the complete blend was better than any reduced blend. In a study where A. segetum males were preexposed to a series of blends and concentrations of pheromone, the behavioural performance was significantly more affected than electroantennographic responses. Central nervous habituation is thus the most likely explanation to most of the observed behavioural effects. A comparison with field data in the literature showed that long-term adaptation/habituation is an unlikely explanation to the mating disruption effect observed in practical field applications. In a wind tunnel, a portable single-neurone recording unit was used to analyse pheromone plumes from female glands and different dispensers. Behavioural in-flight arrestment started occurring at concentrations that elicited maximum spiking activity in peripheral receptor neurones. Individual female pheromone release rates were measured in real time, and compared to the release rate from synthetic dispensers. A hitherto unknown degree of short-time variation in female pheromone release rate was revealed. With the help of a novel radar technique, up to 300 m long flight tracks of individual A. segetum males were recorded. Males tended to fly straight crosswind outside of pheromone plumes and up or downwind when in an area with pheromone.