Abstract: A histopathological study on Pieris rapae (L.) larvae infected by Verticillium lecanii (Zimm.) viegas showed that the fungi infected the insect body mainly by penetrating the cuticle. The conidia on the cuticle of P. rapae larvae germinated in 12 h after inoculation. The hyphae penetrated the cuticle of the 2nd and 3rd instar larvae in 24 h and pathogenesis started on their fat body in 48 h. The hyphae penetrated the cuticle of 4th and 5th instar larvae in 36 h. Some hyphae were observed inside the body in 48 h. Invasion of the hyphae upon the host tissues showed no significant selection. They grew in hemolymphs firstly and then entered the fat body and the muscle. As the hyphae grew, the mid gut and the malpighian tube and the silk gland were infected successively. Pathological changes occurred on all infected tissues and organs, including cuticle disintegration, malformation and dissolution of the fat body, loose muscle fibre layout, disappearance of cells of the midgut epithelium and vacuolization.

Key words: Pieris rapae, Verticillium lecanii; histopathologic changes