The aim of this study was to evaluate pathogenicity and effect of four isolated native and a strain of Isaria fumosorosea on beet armyworm, Spodoptera exigua (Hübner), and corn earworm, Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae). Bioassays in a laboratory used neonate larvae of beet armyworm and corn earworm reared on artificial diet, which were inoculated by spraying or immersing with suspensions of 1 × 10⁸ ml^-1 conidia of I. fumosorosea, and subsequently incubated at 26°C, 65 ± 5% relative humidity, and 14:10 light: dark hours. Isolated HIB-30 killed the most immersed corn earworms, but fewest beet armyworms. HIB-30 most disrupted metamorphosis, 40%, by immersing beet armyworms, while HIB-29 and Pfr-612 least interrupted metamorphosis (8%), by spraying and immersing, respectively.