Effect of age and mating status on the mating behaviour and pheromone titre in alfalfa blotch leafminer females Agromyza frontella (Diptera: Agromyzidae)

The receptivity of 1- to 7-day-old virgin Agromyza frontella (Rondani) females did not change with age. In bioassays the cadavers of newly-emerged virgins (< 1 day old) elicited less courtship from males than those of older virgin females, but no differences were noted between cadavers of 1- to 6-day-old virgins. Females mated on the day of emergence and showed behavioural changes that reduced further encounters with males, although about 50% subsequently mated a second time. In bioassays, males in the presence of cadavers of mated females exhibited less mating behaviour than when presented cadavers of similar-aged virgins. The levels of 3,7-dimethylnonadecane, the female sex pheromone, increased with age in virgin females, but following mating the titre decreased and remained low for the remainder of the female's life. The apparent discrepancy between certain bioassay results and the observed pheromone titres are discussed within the context of available information on semiochemically-mating in Diptera.