The entomopathogenic fungus Beauveria bassiana (Hypocreales: Cordycipitaceae) is widely used as a biological control agent, yet its efficacy against orthopteran pests remains poorly characterized. In this study, we evaluated the susceptibility of second-, third-, and fourth-instar nymphs of the Italian locust, Calliptamus italics (Orthoptera: Acrididae), to B. bassiana strain PPRI5339 under controlled laboratory conditions. Nymphs were exposed to six conidial concentrations (1 × 10³ to 1 × 10⁸ conidia/mL) via treated food, with mortality recorded over 10 days. The fungus caused significant, dose- and time-dependent mortality across all instars. Second-instar nymphs exhibited the highest susceptibility, with an LC₅₀ of 5.8 × 10⁵ conidia/mL and an LT₅₀ of 3.1 days at the highest concentration. Susceptibility decreased with advancing developmental stage; fourth-instar nymphs required higher concentrations and longer exposure to achieve comparable mortality (LC₅₀ = 2.3 × 10⁶ conidia/mL; LT₅₀ = 4.5 days). Cox proportional hazards analysis confirmed that the mortality hazard was significantly lower for third (HR = 0.66) and fourth (HR = 0.51) instars compared to second instars (HR = 1.00). These results demonstrate that B. bassiana is pathogenic to C. italicus, with pronounced stage-dependent susceptibility.