Male mating behavior and female-biased sex ratio of the Japanese gall-forming thrips Ponticulothrips diospyrosi (Thysanoptera: Phlaeothripidae)

We examined the sex ratio (proportion of males) and related life-history traits of adults of the Japanese gall forming thrips Ponticulothrips diospyrosi Haga et Okajima. A few foundresses started a gall in late April, and their progeny developed within the gall. Second generation adult males emerged sooner than females, guarded the female pupae II, and copulated within the gall after adult eclosion. Antagonistic interactions among males were not observed. There was a positive relationship between the mean number of foundresses and the mean sex ratio per gall, suggesting that the foundress could adjust the sex ratio of her clutch in response to the number of foundresses per gall. These life histories and observed female-biased sex ratios were in agreement with Hamilton's local mate competition model; however, partial nonlocalmating and the occasional high foundress number per gall possibly influenced the optimal sex ratio in this species.