Characterization of polydnavirus-encoded mRNA in parasitized armyworm larvae

We have isolated five cDNA clones encoding Cotesia kariyai polydnavirus (CkPDV) mRNAs transcribed in parasitized host larvae of Pseudaletia separata. One of the cDNAs encoding the longest 2.0 kb CkPDV mRNA was sequenced and characterized. Southern hybridization analyses using the cloned cDNA as a probe showed that CkPDV mRNA was homologous to one of CkPDV DNA segments, 5.6 kbp DNA segment A. The 2.0-kb mRNA was demonstrated as being expressed in the parasitized host larvae by Northern-blot analyses. When specific host tissues were examined, the 2.0-kb mRNA was detected mainly in haemocytes. This RNA increased in relative abundance after 2 and 4 h post-parasitization when the immune response of host haemocytes appeared compromised.