Genetic sexing strains (GSS) are being developed for use in sterile insect technique programs against the Mediterranean fruit fly, Ceratitis capitata (Wiedemann). Among other important factors, the utility of these new strains depends on the ability of laboratory-reared males to compete efficiently with wild males in mating with wild females in the field. The current study evaluated the mating ability of a new GSS, Cast 191, in competition with wild males. A well-known GSS, Seib 6–96, was also included in the test. The effect of irradiation on the mating competitiveness of the Cast 191 strain was assessed. The results showed that nonirradiated Cast 191 males outcompeted wild males, whereas irradiated males performed as well as wild counterparts. Although Seib 6–96 males performed less efficiently than Cast 191, they did not differ from their own performance reported 2 yr ago. Mating duration of Cast males, either irradiated or not, was not significantly different from the mating duration of wild males. Seib 6–96 had shorter mating duration times than wild and Cast males. These results demonstrated, besides an effect of irradiation on male mating success, a good mating performance of the strain Cast 191.