Post-copulatory male behaviour, sperm precedence and multiple mating in a solitary parasitoid wasp

Female Aphytis melinus (Hymenoptera: Aphelinidae), previously thought to be unreceptive after their first mating, mated multiply in the field at an incidence of at least 3·2-6·7%. In spring the adult sex ratio was female biased while in autumn it was male biased. Following copulation, male A. melinus guard females for an average of 149 s during which they display behaviour identical to that seen prior to copulation. Behavioural experiments using genetically marked pairs of males were set up to test several hypotheses concerning the adaptive significance of guarding and post-insemination displays. The behaviour seen during guarding probably keeps the female quiescent but does not influence the fate of second-male sperm. Second males that did not guard achieved equal paternity to those that did. Guarding and its associated post-copulatory behaviour helped 'switch off' female receptivity. The percentage of second males that managed to achieve intromission, if attempting to mate with a previously guarded female, dropped from 97 to 70%. Furthermore, males courting a previously guarded female scored significantly more contacts, unsuccessful mounts, time to achieve the successful mount, wingbeats, and time in the successful pre-coital mount. Last-male sperm precedence did not occur. Second males sired 30·5% of the progeny if the guarding male was immediately dislodged and 14·2% of the progeny if the first male was allowed to complete guarding. Thus by delaying rival male courtship through guarding, first male A. melinus decreased the chance that the female would mate again. Guarding also reduced the proportion of progeny sired by a second mating male.