Abai, MR

6th International Congress of DipterologyMating behaviour of the parasitoid fly: Female choice forlarge males?Nakamura, S. & R. IchikiJapan International Research Center for Agricultural Sciences, Tsukuba 305-8686, JapanAlthough there have been many works on oviposition behaviour andstrategies of female parasitoids, studies on behaviour of male parasitoidsare very few. In most species of parasitoid wasps, females are usuallylarger than males, and the advantages of being larger are believed to berelatively less for males than females. Therefore, many studies onbehaviour and body size of parasitoids have focused only on those offemales. Parasitoid flies are not exceptional in this trend, but in Exoristajaponica (Diptera: Tachinidae), a gregarious endoparasitoid oflepidopteran larvae, males are on average larger than females. In thisspecies males try to overtake and grasp females without any specific prematingbehaviour. They usually grapple females on the ground, andfemales struggle vigorously to get rid of males. When a male seizes afemale, males can successfully copulate with females.We conducted an experiment on how male body size affected itsmating success. We divided males and females into three different bodysize groups and observed combinations of mating pairs. While large malescould mate with all sizes of females, smaller males had difficulties inmating with females larger than themselves. Large males could thuscontrol female resistance against male mating attempts and males enjoy theadvantage for being large. As E. japonica takes 5-6 hr for mating which islonger than reported mating durations of other species of tachinid flies, thislong duration could be a mating guard behaviour, even females of thisspecies are believed to mate only once in their life time. We also examineda possibility of multi-mating of females and discuss whether femalesintend to choose a large male for mating to increase their fitness.Key Words: parasitoids, Tachinidae, mating behaviour, sexual selection173