Impact of deletion of the Lymantria dispar nucleopolyhedrovirus PEP gene on viral potency: expression of the green fluorescent protein prevents larval liquefaction

The Lymantria dispar multicapsid nucleopolyhedrovirus (LdMNPV) is an effective biological control agent of the gypsy moth, L. dispar, but is not in general use because the high cost of production limits availability. In an effort to generate a more cost efficient LdMNPV biopesticide, two recombinant baculoviruses were generated to evaluate the impact of deleting the polyhedral envelope protein (PEP) gene on viral potency. One of these baculoviruses had the PEP gene inactivated by insertional mutagenesis with the green fluorescent protein (GFP) gene from Aequorea victoria (vGFP: PEP-); and the other contained a partial deletion of the PEP gene from the LdMNPV viral genome (vPEP-). Both recombinant baculoviruses produced polyhedra that were lacking a polyhedral envelope and displayed an unusually pitted surface as analyzed by scanning and transmission electron microscopy. Polyhedra produced by vGFP:PEP- were considerably smaller than those produced by vPEP- or wild-type virus. Although vPEP- and vGFP:PEP- polyhedra exhibited abnormal phenotypes, bioassay results indicated that there was no significant difference in the potency of these polyhedral envelope-lacking polyhedra in comparison to wildtype polyhedra. In addition, expression of GFP prevented virus-induced larval liquefaction upon death, and the deletion of PEP prevented lysis of infected cells in culture.