Responses of male aphids to the female sex pheromone in Megoura viciae Buckton

Oviparae of Megoura viciae Buckton release a sex pheromone from numerous plaques on their hind tibiae. Adult males react to this scent in a variety of ways: inactive males are aroused; males already walking orient to the odour source; and copulatory activity is increased. These responses are only evoked within a few centimetres of the stimulus source and decline rapidly as the stimulus is diluted. Male responsiveness to the pheromone is unchanging throughout the light phase (of LD 12 : 12), although they show a marked circadian locomotor rhythm. Their sensitivity develops early in adult life and thereafter remains high, decreasing only slightly before death. However, although very young adults will orient to a pheromone source, they do not show copulatory responses until they are sexually mature. Larval males neither respond to the pheromone nor possess the antennal receptors (secondary rhinaria) which are essential for the adult reaction. Mating, and attempted copulation with suitable objects (e.g. coloured beads), is dependent upon appropriate visual and tactile stimuli; it can occur in the absence of the pheromone but is enhanced by its presence. Habituation to the scent does not prevent copulation, and conversely, copulation does not affect subsequent responsiveness to the pheromone. Once copulation has begun the pheromone has no effect on the efficiency of insemination. Vigorous intergeneric responses to the pheromones of female M.viciae and Acyrthosiphon pisum Harris were observed.