The incidence of parasitoids and entomopathogens in a larval population of Adoxophyes sp. in a tea field in Tsukuba, Ibaraki Prefecture, was determined. Three species of Braconids, one species of Ichneumonid, and one species of Tachinid were identified in the collected larvae. Three entomopathogenic viruses, an entomopoxvirus (EPV), a nuclear polyhedrosis virus and a granulosis virus, were isolated from the dead larvae. Overall, 87.0% of Adoxophyes sp. larvae were killed by parasitoids and entomopathogens. Ascogaster reticulatus and EPV were the most common parasitoids and pathogen and were responsible for 37.7% and 23.1% of the deaths in the Adoxophyes sp. larvae, respectively. Percent parasitism by A. reticulatus was highest in the first generation and then decreased progressively toward the fourth generation. EPV prevalence was low in the first generation and increased through the generations. Of 333 host larvae dying from viral infection, 12.0% of host larvae contained dead parasitoid larvae. some parasitoid larvae were able to emerge from virus-infected hosts, whereas these parasitoids died before or after pupation. The time to death of a parasitoid developing in virus-infected hosts appears to be closely related to the species of viruses.