Abstract: Diachasmimorpha longicaudata is a solitary larval-pupal endoparasitoid of several fruit flies that has been introduced to many countries as biocontrol agent of tephritid pests. The species has been reared in Italy under quarantine conditions to test its reliability in biological control programmes against fruit flies. Laboratory bioassays aimed at evaluating the behavioural response of D. longicaudata toward Bactrocera oleae infested or non infested olives have been carried out in the last two years. Data obtained through two different behavioural experiments demonstrated that the parasitoid can perceive olfactory and visual cues coming from fruits, especially from infested ones. In bioassays performed in arenas, naïve and experienced females were able to discriminate infested and non infested fruits showing also a noticeable ability in recognizing different fruit size by visual stimuli. Experiments conducted in Y-tube olfactometer revealed a remarkable response of naïve females to infested olives while experienced females preferred the pure air, showing a probable bias by the factitious host. Further research has to be planned in order to study other possible stimuli coming from the insect pest as well as from olive leaves and fruits. Moreover, additional bioassays should be performed on non-frugivorous tephritid flies before field releasing attempts, in order to avoid possible negative side effects.