Effect of Campoletis sonorensis ichnovirus cys-motif proteins on Heliothis virescens larval development

Polydnaviruses are obligate symbionts of some parasitic hymenopteran wasps responsible for modifying the physiology of their host lepidopteran larvae to benefit the endoparasite. Injection of Campoletis sonorensis ichnovirus (CsIV) into Heliothis virescens larvae alters larval growth, development and immunity but genes responsible for alterations of host physiology are not well described. Recent studies of polydnavirus genomes establish that these genomes encode families of related genes expressed in parasitized larvae. Here we evaluate five members of the CsIV cys-motif gene family for their ability to inhibit growth and development of lepidopteran larvae. To study the function of cys-motif proteins, recombinant proteins were produced from baculovirus expression vectors and injected or fed to H. virescens larvae in diet. rVHv1.1 was identified as the most potent protein tested causing a significant reduction in growth of H. virescens and Spodoptera exigua larvae. H. virescens larvae ingesting this protein also exhibited delayed development, reductions in pupation and increased mortality. Increased mortality was associated with chronic sub-lethal baculovirus infections. Taken together, these data indicate that the cys-motif proteins have pleiotropic effects on lepidopteran physiology affecting both development and immunity.