In the stink bug, Megacopta punctatissima, which forms mating aggregations, male mating behaviors and the copulatory success of males were examined in experimental populations with 4 different sex ratios. In the male-biased sex ratio, more males tended to stay in "copulatory aggregations" including at least a mating pair rather than in "non-copulatory aggregations" including no mating pair, despite a scarcity of non-copulating females in such aggregations. However, when copulating females were included, there were more females in the copulatory aggregations than those in the non-copulatory aggregations. Therefore, the results appear to suggest that males also regarded copulating females as potential mates. Males which had immigrated to an aggregation showed a higher copulatory success than resident males in the aggregation at a male-biased sex ratio. Moreover, males showed a large variation in mating success, and those which had a higher mating success tended to stay in aggregations of female-biased sex ratios. These results suggest that females may choose their mates in mating aggregations, and that the choice may influence male mating success more acutely in a male-biased sex ratio.
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