The entomopathogenic fungus Beauveria brongniartii (Sacc.) Petch, the highly effective control agent against the cockchafer Melolontha melolontha, produces the secondary metabolite oosporein. Oosporein is well characterised as a metabolite with antibiotic activity against gram-positive bacteria. Nevertheless, the role of oosporein for the infection process of B. brongniartii on its host is still unclear. This choice-bioassay shows that oosporein has no repellent or toxic effect when ingested by larvae of M. melolontha and Galleria mellonella. Oosporein caused no retarded development of insects.