This is a report to demonstrate a pathogenicity enhancement by two microbial agents. Baculovirus pathogenicity was attenuated with larval development of both lepidopteran species: the beet armyworm, Spodoptera exigua, and the diamondback moth, Plutella xylostella. The addition of an entomopathogenic bacterium, Xenorhabdus nematophila Kl, to the baculovirus treatment significantly enhanced the viral pathogenicity in both lepidopteran species. The synergistic pathogenicity may result from their independent pathogenic targets in the insects.