Abstract: The entomopathogenic fungus Beauveria bassiana is known to interact with insects inseveral ways. The present work reports the results of observations on the potential of Beauveriabassiana strain ATCC 74040 against the Mediterranean fruit fly, Ceratitis capitata, with specialregard to disturbance effects on oviposition behaviour. A commercial formulation (Naturalis) anddifferent fungal preparations (pure conidia, hyphae, culture supernatants) were applied to orangefruits offered to ovipositing medflies. A significantly lower number of fly visits and ovipositionpunctures were recorded on fruits treated with Naturalis and with pure conidia than on controlfruits. The observed effects are examined on the basis of additional proteomic and genomicobservations, and the potential molecular implications of the rodlet layer of aerial conidia arediscussed.