Permissiveness of lepidopteran hosts is linked to differential expression of bracovirus genes

Polydnaviruses in the genus Bracovirus (BV) are associated with parasitoid wasps in the family Braconidae. BV-carrying wasps rely on their associated viruses to parasitize permissive hosts but also occasionally oviposit into host species that are non-permissive. Here, we studied Microplitis demolitor and M. demolitor bracovirus (MdBV) in Chrysodeixis includens, a permissive host, and Trichoplusia ni, which is usually non-permissive. M. demolitor laid eggs and injected MdBV into both hosts but almost no wasp offspring developed in T. ni. MdBV DNA similarly persisted in both host species, but deep sequencing data showed that transcript abundance for most viral genes was higher in C. includens than T. ni. Overall, our results identify lower expression of MdBV genes as an important factor in the non-permissiveness of T. ni. However, certain genes with functions in immunosuppression were sufficiently expressed to have similar effect in T. ni and C. includens.