Infestation rates of the Mediterranean fruit fly,Ceratitis capitata(Wiedemann), and the oriental fruit fly,Dacus dorsalisHendel, were studied in a 13-km2area of Kula, Maui, in Hawaii from 1978 to 1981 by counting fruits on trees and collecting and holding fruits in the laboratory for adult eclosion. The number of trees in the area, number of fruits per tree, percent infestation of the fruits, number of parasitoids, and number of pupae reared per infested fruit were examined. Loquats, peaches, and figs produced the largest number of flies. Other minor fruits produced relatively small numbers of flies. MoreC capitatathanD. dorsaliswere recorded from peach fruits at the higher elevations than at the lower elevations. Eclosion data showed that both fruit fly species developed successfully together in individual peach fruits, the larvae of one species causing no apparent reduction in the number of larvae of the other species in those fruits.