On the Flight of Mimela testaceipes between Sward and Forest, in Relation to its Internal Conditions (Coleoptera, Scarabaeidae)

A field observation was carried out on flying adults of Mimela testaceipes MOTSCHULSKY, a serious pest on grass and conifers, at a heavily injured sward near coniferous forest in northern Hokkaido, Japan, through the whole flight season, from late July to late August, 1979. The flight activity in a day was concentrated at dusk from 30 to 50 minute after sunset, and the daily abundance of flying chafer was very variable during the season. Independently of wind directions two main tracks of flight were recognized. One is a track toward the forest observed in the early to middle flight season, and the other an opposite one, namely toward sward in the middle to late season. Males were found among the population flying toward forest in early flight season, and not found in the population toward sward. The females flying toward forest are composed of 1) newly-emerged females, including some barren ones, mostly found in the early flight season, 2) postoviposition females, containing no or only a few eggs, mostly found in the middle season, and 3) mature females, containing many fully-formed eggs, mostly found in the middle and late season. It is difficult to understand the reason why a lot of mature females leave sward, the oviposition site of the species, and fly to forest. The females flying toward sward are composed of only mature ones, mostly mated and containing 25-60 fully-formed eggs. The coniferous forest, on which aggregation of chafers was observed, may be important as a site of feeding, mating and egg-developing especially for newly-emerged chafers. A process of the adult behavior of Mimela testaceipes was presumed and was compared with that of Melolontha melolontha L. in Switzerland given by SCHNEIDER (1952). As a conclusion it is pointed out that the mass flight of mature females toward sward may be one of the main causes of the concentric occurence of larvae in sward.