Previous studies in Hawaii indicated that Ceratitis capitata (Wiedemann), Mediterranean fruit fly, became scarce at low elevations subsequent to accidental introduction of Bactrocear dorsalis (Hendel), oriental fruit fly. The conclusion was that competitive displacement, elevation, and parasites were major determinants in the ranges of these two fruit flies. Recently, commercial coffee, Coffea arabica L., was planted in former sugarcane. Saccharin officinarum L., fields at an elevation of 122 m on Kauai Island, HI. During a 3-yr period we studied colonization of fruits by C. capitata , B. dorsalis , and Biosteres arisanus (Sonan), a beneficial solitary wasp that attacks both species of fruit flies. During seasons 1 and 2, mean numbers of C. capitata were greater than those of B. dorsalis. Lack of an inverse correlation between numbers of the two tephritids emerging from fruits suggested that these species were not competitors. B. arisanus parasitization rates on the basis of live and dead parasitoids recovered from C. capitata and B. dorsalis pupae were modest. Studies during season 3 indicated B. arisanus parasitization rates were higher for C. capitata than those for B. dorsalis . Numbers of C. capitata and B. arisanus were correlated during both seasons, suggesting a density-dependent relationship between the most abundant host and the parasitoid. Fruit infestation data demonstrated that C. capitata exploits fruits at an earlier ripeness stage and emerges sooner from fruits than B. dorsalis. Analysis of three annual coffee crops indicated that C. capitata was the dominant fruit fly species in the coffee agroecosystem by the end of the season. This finding differs from previous studies, wherein B. dorsalis was dominant over C. capitata at low elevation.