THE SPATIAL-DISTRIBUTION OF ENDEMIC AND INTRODUCED FLOWER-BREEDING SPECIES OF DROSOPHILA (DIPTERA, DROSOPHILIDAE) DURING THEIR EARLY HISTORY OF ENCOUNTER ON THE ISLAND OF HAWAII

The spatial distribution of two flower-breeding drosophilids (an endem ic, Scaptomyza caliginosa Hardy and an exotic, Drosophila floricola St urtevant) is reported for morning and evening censuses of four sites a t one locality on the island of Hawaii. The increase in the relative f requency of the introduced species over the last 10 years appears to b e due to the increase in the number of adult D. floricola and not a re duction in number of endemic adult S. caliginosa. The analysis indicat es that the two species are sympatric and adults occupy the same indiv idual blossoms of morning glory. Afternoon and evening aggregation beh avior of adult S. caliginosa may explain some variation in the joint d istribution of the two species. Although there is some evidence for th e adults using different blossoms, there is considerable overlap of ad ults of the two species in the same blossoms and it is concluded that the potential for larval-larval competition between the two species is high.