The braconid wasp Microplitis demolitor carries Microplitis demolitor bracovirus (MdBV) and parasitizes the larval stage of several noctuid moths. A key function of MdBV in parasitism is suppression of the host's cellular immune response. Prior studies in the host Pseudoplusia indudens indicated that MdBV blocks encapsulation by preventing two types of hemocytes, plasmatocytes and granulocytes, from adhering to foreign targets. The other main immune response mediated by insect hemocytes is phagocytosis. The goal of this study was to determine which hemocyte types were phagocytic in P indudens and to assess whether MdBV infection affects this defense response. Using the Bacterium Escherichia coli and inert polystyrene beads as targets, our results indicated that the professional phagoncyte in P indudens is granulocytes. The phagoncytic responses of granulocytes were very similar to those of High Five cells that prior studies have suggested are a granulocyte-like cell line. MdBV infection dose-dependently disrupted phagoncytosis in both cell types by inhibiting adhesion of targets to the cell surface. The MdBV glc 1.8 gene encodes a cell surface glycoprotein that had previously been implicated in disruption of adhesion and encapsulation responses by immune cells. Knockdown of gk1.8 expression by RNA interference (RNAi) during the current study rescued the ability of MdBV-infected High Five cells to phagoncytize targets. Collectively, these results indicate that gk1.8 is a key virulence determinant in disruption of both adhesion and phagoncytosis by insect immune cells. none