The olive fruit fly [Bactrocera (Dacus) oleae (Rossi) (Diptera: Tephritidae)] adult diet since its development in the 1960's regularly incorporates antibiotic. Considering recent findings on the importance and function of the indigenous microbial flora of insects, the effects of antibiotic removal were measured on the survival and egg laying of wild flies derived from McPhail trappings and from field infested olive fruits. In the first case wild flies fed no antibiotic laid significantly greater numbers of eggs for two generations (in 5 out of 10 and 2 out of 10 counting dates for G1 and G2 respectively), while there were no significant differences in survival in either test (P = 0.221 for P generation, P = 0.988 for G1 generation from McPhail traps, P = 0.056 for flies from infested fruits). Percent egg-pupa recovery and adult emergence were not significantly affected by lack of antibiotic. An antibiotic-free strain has been maintained for eight generations, showing acceptable performance when compared to the long-reared standard 'Laboratory' strain. Overall results suggest the feasibility of an adult diet free of antibiotic without negative effects on colony survival and performance.