A thoracic factor stimulates replication of Microplitis demolitor bracovirus

Abstract

Polydnaviruses (PDVs) are an unusual family of symbiotic DNA viruses, associated with parasitic wasps. The genome of PDVs is integrated in the wasp’s genome as a provirus and the virus only replicates in the ovary of female wasps. To date, PDVs have been described from two families of parasitic wasps: Ichneumonidae and Braconidae. PDVs bud through the calyx cell membrane into the oviduct lumen and are injected into host insects during parasitization. Prior studies show that PDVs are integrated into the genomes of every male and female of relevant wasp species. The formation of PDV virions in pupal wasp ovaries coincides with the appearance of melanization patterns in the pupal cuticle. Microplitis demolitor bracovirus (MdBV) is symbiotically associated with the braconid Microplitis demolitor. In this study, I characterized the timing and regulation of MdBV replication. My results indicated that MdBV replication begins one day after M. demolitor pupal ecdysis. A series of ligation experiments indicated that MdBV replication is stimulated by a factor produced in the pupal thorax. Radioimmunoassays further indicated that ecdysteroid titer of M. demolitor decreased from 5 ng in day one female pupa to 3 ng in day three female pupa.