Faunal and Ecological Surveys on Drosophilid Flies in Iriomote-jima, a Subtropical Island of Japan

A total of 80 drosophilid species representing 16 genera were collected during our surveys in Iriomote-jima. About 65% of them were subtropical or tropical species, about 30% were inhabitants of subtropical to temperate areas, and the rests were cosmopolitan species. Fruits, flowers, fungi and leaves were observed to be used by drosophilids for breeding. This island was rich in fruit feeders but poor in herbage feeders compared with temperate areas. Habitat selection and seasonal fluctuations were studied by trap collections using fermenting banana as baits. Drosophilid species collected by this method were mainly fruit feeders. They were subdivided into three groups, species living mainly in forests, those in domestic areas, and those in open land, domestic areas, and/or forest canopy. Many species decreased in number of individuals from February to May or June, but some species increased during this period. In most species, reproductively mature females were collected even in winter, suggesting that they do not have hibernal reproductive diapause. However, females of Drosophila daruma collected from autumn to winter usually had undeveloped ovaries ; this species may enter reproductive diapause.