Earlier studies have suggested that successful parasitism by certain braconid parasitoids may depend on the presence in host insect larvae of both polydnavirus and venom. We have shown that venom from the braconid parasitoid, Cotesia melanoscela, was required for in vivo persistence of polydnavirus DNA in host larvae. In parallel studies using an in vitro system, we observed that in the presence of venom nucleocapsids were released into the cytoplasm and subsequently uncoated at nuclear pores; in the absence of venom, this sequence of events was not observed. none