Bioassays were carried out under controlled conditions (27 ± 2°C, 80 ± 5% RH, and a photoperiod of 12:12 [L:D] h) to evaluate the effect of eight strains of the entomopathogenic fungus Beauveria bassiana upon larvae, pupae, and adult females of the Mexican fruit fly, Anastrepha ludens (Loew). Mortality of the immature stages was low, 2–8% in larvae and 0% in pupae. However, very high levels of mortality were obtained for adult flies, with values of 100, 98, and 98% for the strains Bb16, Bb24, and Bb 26, respectively. LC₅₀ values for these three strains ranged from 3.12 × 10⁶ to 9.07 × 10⁶ conidia/ml. Lethal time 50 (LT₅₀) was 2.8, 3.7, and 4.2 d for Bb16, Bb26, and Bb24 strains, respectively, with an average LT₅₀ of 4.4 d across all strains. The fungal mycelium emerged through the soft parts of the exoskeleton, such as the wing bases, mouth, intersegmental regions of the legs, and membranous regions of the abdomen, coxae, and neck. Maximum percentage sporulation ranged from 66.4 to 74.7% for the three most virulent strains.