With superimposed oviposition of oriental fruit flies, Dacus dorsalis Hendel, or Mediterranean fruit flies, Ceratitis capitata (Wiedemann), in either sequence in fresh guava fruit in the laboratory, following oviposition by the other species, oriental fruit flies completely or almost completely suppressed the development of Mediterranean fruit flies. When oviposition in the same guava was not super-imposed but limited to separate areas for each of the 2 species, suppression of Mediterranean fruit flies by oriental fruit flies also was manifested, albeit not as drastically. This suppression generally was not demonstrated when eggs of both species were seeded simultaneously on artificial larval medium.