Fourth larval instars of Metisa plana Walker were sprayed with conidial suspensions of Beauveria bassiana(Balsamo) Vuillemin containing 6.25 x 10^-6 conidial/ml. The mode of fungal infection was determined histologically. At 48 hours after inoculation, fungal hyphae penetrated the integument inside the trachea and via the nuclei of epidermal cells. Fungal hyphae infiltrated the fat bodies underlying the integument. At 72 hours after inoculation, the fat tissues were damaged by progressive colonization with hyphae. Subsequently, the hyphae invaded the muscle tissues, neural tissues, germ cavities, Malpighian tubules, gut musculature and epithelial cells, and finally colonized the gut lumen. Between 96 and 120 hours post inoculation, all internal organs of the bagworm were heavily colonized with hyphae, and the infected bagworms were already dead. Twenty-four hours after death, whitish mycelia began to emerge from the cuticle of the bagworm cadavers.