Disruption of the baculovirus core gene ac78 results in decreased production of multiple nucleocapsid-enveloped occlusion-derived virions and the failure of primary infection in vivo.

•Ac78 is critical but is not essential for BV production.•Ac78 plays a role in the formation of M-ODVs.•Ac78 is essential for AcMNPV to initiate primary infection in T. ni.•Ac78 residues 2–25 and 64–88 play important roles in its function.•Ac78 predominately localizes to the ODV envelope and contains an INM-SM.