The parasitoid wasp Cotesia kariyai oviposits into larvae of the armyworm Mythimna (=Pseudaletia) separata. At this time, the coinjection of a polydnavirus and venom is prerequisite for successful parasitoid development. Polydnaviruses are responsible for developmental arrest and interference with the host's immune system; thereby they are called symbiont viruses of the parasitoid wasps. In this study, we demonstrated that C. kariyai polydnaviruses (CkPDVs) replicate in ovarian calyx cells of the host female wasps after pupation. In the course of the replication, DNA synthesis commences by one day after pupation, being followed by capsid protein synthesis. Almost one day after the initiation of the capsid protein synthesis, envelope proteins become visible in the lateral oviducts. Therefore, it is reasonable to assume that the complete virion of CkPDV is not composed simultaneously but requires gradual steps. none