抄録
Drosophila simulans has been found for more than 10 years in Japan, mainly in suburban areas whereas its sibling species D, melanogaster tends to be found in houses. Seasonal activities of the two species were clearly different; In a typical hot summer the frequency of D. simulans decreased temporarily in August making two peaks in July and September. But in a cool summer the two peaks disappeared making a single peak in September or October. On the other hand, D. melanogaster showed higher activity in August in the hot summer but it occasionally shifted the active peak during the season avoiding competition with D. simulans. A nine year survey of D. simulans around the area of Mt. Fuji revealed that the species gradually invaded from the Pacific coast to the inland. Population size in autumn was strongly affected by the temperature of the Preceeding winter. Cold winters such as in 1977 and 1981 decreased the size drastically at every collection site.
