Technical Abstract: A Paecilomyces fumosoroseus strain was mutagenized with ultraviolet radiation in order to obtain chitinase-overproducing mutants. Among 200 colonies, we choose one mutant (M84), which showed a larger and stable chitin hydrolysis-halo. Glucose consumption and biomass production were very similar for M84 and parental strains. The chitinase enzyme was inducible by chitin and repressed by glucose in both strains. When they were grown on a minimal medium plus colloidal chitin as sole carbon source, the parental and M84 strains yielded 198 and 690 umoles of N-acetylglucosamine, respectively. These results indicate that the mutant strain synthesized a chitinase with higher activity. Bioassays against Bemisia tabaci nymph showed that M84 incited a 2.0-fold higher incidence of disease compared to the parental P. fumosoroseus strain.