Polydnavirus replication at ovarian calyx in Cotesia plutellae and endocrine impact

Polydnaviruses are a group of insect DNA viruses mutually associated with host endoparasitoids classified in Ichneumonidae or Braconidae. The virus genome is segmented and located in the wasp chromosome(s) as a provirus. The viral replication occurs only in the female reproductive organ during pupal stage. An endoparasitoid wasp, Cotesia plutellae, contains a polydnavirus called CpBV. Its viral replication began at late pupal stage of the female wasp. Quantitative real-time PCR suggests that the viral replication consisted of amplification of the viral genome and subsequent its excision from the wasp chromosome(s). Application of pyriproxyfen (a juvenile hormone agonist) completely inhibited the viral replication whereas RH5992 (an ecdysteroid agonist) stimulated the viral replication. Inverse PCR and immunoblotting assays show that pyriproxyfen delayed the replication, but RH5992 accelerated the viral production. Expression sequence tag (EST) of ovarian tissues generated by 454 pyrosequencing suggest several putative genes related with CpBV replication. Some of these genes were expressed only at day 4 pupal stage, at which CpBV was replicated. These gene expressions appened to be susceptible to the hormonal treatments. These result suggest that effects of JH (pyriproxyfen) and Ecd (RH5992) on polydnavirus replication at ovarian calyx in Cotesia plutellae.