Heliothis virescens; HYMENOPTERAN-PARASITES; Campoletis sonorensis; Gene structures of virus involved in immunosuppression of host Campoletis sonorensis; ASSOCIATIONS-; Polydnavirus; Gene structures of virus involved in immunosuppression of lepidopteran host; LEPIDOPTERAN-HOSTS; Heliothis virescens; Gene structures of virus involved in immunosuppression of host For successful parasftization, the female Campoletis sonorensis endoparasftic wasp injects a polydnavirus into its host, Heliothis virescens, during oviposition. Viral gene expression induces immunosuppression and alters development of the host. We report here that three abundantly expressed genes, VHvl.l, WHvl.O, and WHvl.6, describe a polydnavirus "cysteine-rich" gene family which may be important In inducing these host manifestations. These genes have a similar primary gene structure and their proteins contain cysteine motifs characteristic of snail ion-channel ligands, the w-conotoxins. Like the w-conotoxins, the intercysteine amino acid residues are hypervariable with only three Identical amino acids In all motifs. The conservation of this domain in the three viral genes may reflect an important functional role for these viral proteins in the parasitization of H. virescens. The three genes also contain introns similar in sequence at comparable positions in their 5' untranslated leaders and coding sequences. VHvl.l contains two cysteine motifs, and each motif is interrupted by an intron at the same position as in the cysteine motifs of WHvl.O and WHvl.6. lntron 2 sequences of WHvl.O and WHvl.6 are 92% identical, while the immediately flanking axon sequences encoding the cystelne motifs are only 76% identical. none