Beauveria bassiana is naturally found in broiler chicken houses, and has been shown to be active against the lesser mealworm, Alphitobius diaperinus. The effectiveness of soil application of B. bassiana in emulsifiable oil-type formulation (Unioeste 4 isolate) to control the lesser mealworm in commercial poultry house was evaluated. The fungus was applied to the dirt floor of poultry house at 4.2 × 10 9 conidia/m 2 (treated aviary) and the insect population was assessed before and 96, 146 and 216 days after application (DAA). In the control aviary, no treatment was performed to control those insects. Molecular techniques were used to confirm the presence of the fungus in dead A. diaperinus. Significant treatment effects were observed, with 56% and 73% of insect population reduction on 96 and 146 DAA, respectively. However, on 216 DDA, insect population resumed to values close to those initially observed. In the control aviary, the population grew steadily, reaching almost 110% the initial population on 96 DAA, and close to 200% on 216 DDA. The results demonstrate the potential of the applied control strategy, even with a single application of the fungus; however, reapplications may be required after 3-6 months for more effective control.