none Three main factors are responsible for the prepupal mortality of the olive fly: the quality of the olive fruits, frugivorous birds, and parasitoids. Protein and fat content of the fruits is important for the larval development. Larval mortality decreases by 17,2% resp. 0,79% if the protein content resp. the fat content increases by 1%. In oleasters, larval mortality is higher than in cultivated olives and this is primarily correlated with the protein content. Birds pick up about 4/5 of the oleaster fruits, particularly during the winter. Among the parasitoids which attack olive fly larvae in oleasters, the chalcid Pnigalio mediterraneus Ferr. & Del. is the most abundant species. Eupelmus urozonus Dalm. (chalcid) is rare, as is Opius concolor Szepl. (braconid). Some specimens of Cyrtoptyx dacicida Masi were also obtained, but from olives for oil only. Sex ratio of P. mediterraneus increases with fruit size, host feeding increases by 0.75% when 1% more 3rd instar larvae are parasitized, and each increase of the Dacus density by 1 3rd instar larva per 100 oleaster fruits is followed by an increase of 0.6 parasitoid.