Scramble competition polygyny in the coreid bug (Colpula lativentris)

The mating system of the coreid bug, Colpula lativentris, was studied, and compared with those in other hemipteran bugs. Copulating pairs formed a compact aggregation on a shoot of the Japanese knotweed, Polygonum cuspidatum, and there continued copulation and feeding for more than one day. This aggregation was defined as “a shoot aggregation”. Other than this aggregation composed of copulating pairs, there were loose aggregations on the ground composed of males and females not in copula. This loose aggregation was defined as “a ground aggregation”. Males searched for receptive females mostly in a ground aggregation. Sex ratio was constant and variance of sex ratio was also very small in any shoot aggregations and in large ground aggregations. However, in small ground aggregations, sex ratio was strongly male biased and variance of sex ratio was fairly large. This was because receptive females tended to leave a small ground aggregation and join a large one. These results suggest that a male can attain higher mating success in a larger ground aggregation.