Relationships between polydnavirus gene expression and host range of the parasitoid wasp Campoletis sonorensis

To evaluate the relationship between immune suppression and host range six lepidopteran species were parasitized by the ichneumonid parasitoid Campole tis sonorensis. Parasitism inhibited the growth of permissive hosts (Heliot his virescens, Helicoverpa tea, and Trichoplusia ni), whereas growth of sem i-permissive (Spodoptera exigua, Agrotis ipsilon) and non-permissive hosts (Manduca sexta) was not significantly affected. The 29-36 kDa ovarian prote in (OP), responsible for transient immunosuppression in the permissive host H. virescens, bound to and was endocytosed by hemocytes of permissive and non-permissive hosts. Expression of the cysteine-rich polydnavirus gene, VH v1.4, was detected in all the hosts, but declined only in semi- and non-per missive hosts at later times after parasitization. The VHv1.4 protein bound to hemocytes of permissive and semi-permissive hosts; but did not bind to hemocytes of the non-permissive host, M. sexta. Melanization of larval hemo lymph was severely inhibited by parasitism in permissive hosts, but was una ffected in M. sexta. In the semi-permissive host, A. ipsilon, hemolymph mel anization was transiently inhibited while viral genes were expressed. In co nclusion, C. sonorensis OP transiently inhibits encapsulation in all hosts that were tested. The host range of C. sonorensis seems to be determined by whether or not the C. sonorensis ichnovirus (CsIV) is able to establish pe rsistent infections of parasitized larvae to provide long-term suppression of host immunity. (C) 2000 Elsevier Science Ltd. All rights reserved.