Parasitization rates of eggs of oriental fruit fly,Dacus dorsalisHendel, byBiosteres arisanus(Sonan), and larvae of melon fly,Dacus cucurbitaeCoquillett. byPsytallia fletcheri(Silvestri) in mature green to fully ripe papaya fruits on trees and in fully ripe fruits on the ground was studied. Parasitization of oriental fruit fly eggs byB. arisanuswas greater in fully ripe fruits than in one-quarter to half-ripe fruits on trees;B. arisanusnever parasitized oriental fruit fly eggs in mature green to color-break fruits. No difference was observed in the density of emergentB. arisanusadults from oriental fruit fly pupae recovered from fully ripe fruits on trees and on the ground. Parasitization of melon fly larvae byP. fletcheriwas observed in only one fully ripe, fallen fruit. Results in relation to the effect of host plants on the foraging behavior of adult parasitoids and to the biological control of oriental fruit fly and melon fly in an agricultural ecosystem were discussed.