Cardiochiles nigriceps Viereck (Hymenoptera, Braconidae) is an endophagous parasitoid of the tobacco budworm, Heliothis virescens (F.) (Lepidoptera, Noctuidae). Parasitized host larvae show a complex array of pathological symptoms. The most evident alterations registered are the suppression of the immune response and the developmental arrest of host mature larvae, which, when parasitized, fail to pupate and provide the required nutritional resources to the developing parasitoid larva. Most of these syndromes observed in parasitized host larvae are induced by C. nigriceps polydnavirus (CnPDV) infection. CnPDV, like all the other members of the peculiar virus family Polydnaviridae, actively replicates only in the calyx region of the wasp’s ovary while in the host tissues replication is not observed. However, CnPDV genes are actively expressed in various host tissues and their expression is associated to major parasitoid-induced host alterations. The present study analyses gene expression of CnPDV in tobacco budworm larvae parasitized by C. nigriceps, starting from a few hours after parasitoid oviposition. The screening of CnPDV genomic libraries and of cDNA libraries, prepared with RNA poly A + from parasitized host larvae, allowed the isolation of various viral genomic clones and of their corresponding cDNAs. Different viral genes have been cloned, fully sequenced and characterized so far. The expression of these CnPDV genes in different host tissues and organs has been analyzed by Northern blot experiments and in situ hybridization. A functional analysis, both in vivo and in vitro, of CnPDV gene products has been undertaken.

Index terms: host regulation; gene expression; physiological interactions; Braconidae

---