A microsporidian pathogen was first isolated from the larvae of beet armyworm,Laphygma exigua. The microsporidian invaded primarily midgut, fat body and Malpighian tubules of the host. The pathogen was highly virulent to three lepidopteron,Laphygma exigua, Pieris rapae and Helicoverpa armigera, and could be transmitted vertically to their offspring by either contamination of the surface of eggs (transovum)or via an ovarian infection (transovarian) in the female host, and the horizontal transmission was by t...