The mosquito fungal pathogen Culicinomyces clavisporus was found to be sensitive to the antibiotics hygromycin B and phleomycin but resistant to kanamycin and geneticin. Protoplasts were genetically transformed to give strains resistant to phleomycin and hygromycin B. The results show that multiple integrations of transforming DNA can occur and that heterologous fungal gene expression signals are functional in C. clavisporus .