Co-replication of a reovirus and a polydnavirus in the ichneumonid parasitoid Hyposoter exiguae

A recently established colony of the ichneumonid parasitoid, Hyposoter exig uae, was found to carry both a reovirus (HeRV) and a polydnavirus (HePDV). Morphogenesis of these viruses was observed in all cells comprising the ova rian calyx epithelium, apparently without detrimental effect to the parasit oid. While polydnavirus replication in H. exiguae was restricted to the cal yx region, HeRV was detected in ovarioles, oviducts, midguts, malpighian tu bules, and accessory glands associated with the male reproductive system. I n addition, HeRV was able to infect the fat body of parasitized host larvae and to establish a persistent infection in vitro. Electron microscopy reve aled that both viruses were released into the calyx fluid compartment exclu sively by budding, a phenomenon rarely observed among the Reoviridae; HeRV envelopes thus obtained, however, appeared to be subsequently shed within t he oviducts. HeRV particles were concentrated to near homogeneity by differ ential centrifugation; mature virions consisted of seven to eight structura l polypeptides and 10 dsRNA genome segments. Prominent spikes were observed at the vertices of icosahedral core particles. Most, but not all, individu als comprising the H. exiguae colony appeared to be infected with HeRV, sug gesting a commensal relationship between wasp and virus: however, while thi s association is of obvious benefit to the virus, it seems unlikely that an y advantage accrues to the parasitoid which carries it. (C) 2000 Academic P ress.