As part of the development of a sterile insect technique (SIT) application for the Ethiopian fruit fly, Dacus ciliatus, we studied the mating behaviour of a laboratory-adapted strain (a 4-year-old colony kept for more than 40 generations) and a wild population. Effects of laboratory rearing and irradiation were assessed by carrying out mating compatibility and male mating competitiveness tests using a 1:1 ratio between irradiated (120 Gy) laboratory males and non-irradiated wild males. Mating behaviour was studied on host and non-host plants under field cage conditions. To assess the effect of mass rearing upon male performance, we repeated the mating competitiveness test using non-irradiated laboratory insects. The findings indicated a high degree of compatibility among the two populations and satisfactory competitiveness of the irradiated laboratory males (ca. 35%). The competitiveness of non-irradiated laboratory males was also ca. 35%, suggesting that no adverse effects resulted from their irradiation. Mating occurred only at twilight and mainly on the underside of leaves of non-host plants (lemon trees). Findings are discussed in view of their implications for a future application of SIT against this fruit fly pest.