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Abstract
Microgastroid wasps (Hymenoptera: Braconidae) are endoparasitoids that primarily parasitize larval stage Lepidoptera. Bracoviruses (BVs) are endogenized nudiviruses that wasps have coopted for functions in successfully parasitizing hosts. Viral genes are expressed in wasp ovaries during BV replication resulting in formation of virions which wasps deliver to hosts during parasitism. BVs are descended from nudiviruses (Family: Nudiviridae), an understudied group of insect pathogens. BVs retain viral replication genes that were first identified and characterized in baculoviruses (Family: Baculoviridae), sister group to nudiviruses. Microplitis demolitor is a microgastroid wasp that carries Microplitis demolitor bracovirus (MdBV) and parasitizes larval stages of the moth Chrysodeixis includens. Some genes shared with baculoviruses retain conserved roles in MdBV, however not all conserved genes have been studied. There remain many uncharacterized viral genes for which there are no functional predictions. This study had four objectives: 1) Conduct a proteomic analysis of MdBV virions, 2) functionally analyze a gene named HzNVorf64-like, 3) characterize MdBV genes that are homologs of oral infectivity factors that are present both in baculoviruses and nudiviruses and 4) characterize MdBV genes that are predicted integrases. In this research I separated MdBV viral nucleocapsids from envelopes and performed proteomics on both fractions and found that most baculovirus-like gene products were localized to the same fraction in MdBV as they are in baculoviruses. Gene products from unknown viral genes were assigned to nucleocapsid, envelope, or both fractions based on my data. I focused on HzNVorf64-like (MdBVe46), a betanudivirus gene homolog that produces a 46kDa product assigned to the viral envelope. I found that MdBVe46 is required for viral envelope formation and infection of C. includens. I next focused on baculovirus oral infectivity factors (PIFs), envelope proteins that are conserved in MdBV (p74/pif-0, pif-1, pif-2, pif-3, pif-4, pif-5-1, pif-5-2, pif-5-3, pif-6 and vp91/pif-8). Functional assays indicated that select PIFs play important roles in MdBV infection and morphogenesis. I looked at viral tyrosine recombinases conserved in MdBV (vlf-1a, vlf-1b-1, vlf-1b-2, int-1, int-2), including 4 uncharacterized nudivirus-like genes (k425_451, k425_468, k425_475, HzNVorf93-like). I found that all integrases and two unknowns (k425_475, HzNVorf93-like) are involved in processing MdBV proviral DNA.