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The extent of DNA base sequence homology between entomopoxviruses (EPVs) from Lepidoptera, Orthoptera, and the vertebrate poxvirus Vaccinia was investigated by DNA-DNA hybridization. α-32P-Labeled DNA from Amsacta moorei EPV, Melanoplus sanguinipes EPV, and Vaccinia virus strain WR was hybridized with the DNA from six different entomopoxvirus isolates. Based on the thermal denaturation temperature of hybrid DNA molecules, approximately 54% base sequence homology was detected between Amsacta moorei and Euxoa auxiliaris EPV DNAs. Extensive DNA hybridization was detected between α-32P-labeled Melanoplus sanguinipes EPV DNA and DNA from Arphia conspirsa and Phoetaliotes nebrascensis entomopoxviruses. No base sequence homology was detected between vaccinia DNA and DNA from any of the entomopoxvirus isolates used in this study.

The structural proteins of Amsacta moorei, Euxoa auxiliaris , and Melanoplus sanguinipes entomopoxviruses (EPVs) were separated by electrophoresis on sodium dodecyl sulfate (SDS)-polyacrylamide gels. More than 35 structural proteins were detected in each virus. Based on the distribution and the variation in the molecular weights of the virus structural proteins little homology was detected between the EPVs and vaccinia virus. The molecular weight of Amsacta EPV occlusion body matrix protein (110,000) was determined by SDS-acrylamide gel electrophoresis. The occlusion body matrix protein of Amsacta EPV occluded virus isolated from infected E. acrea larvae was rapidly degraded at p H 10.6 to peptides of approximately 94,000 and 60,000 daltons. After 2 hr incubation at alkaline p H, Amsacta EPV occlusion body protein was degraded to approximately 56,000 daltons. Proteolysis of occlusion body protein was inhibited by SDS. No proteolytic degradation was detected in occlusion body matrix protein isolated from Amsacta EPV infected BTI-EAA cells. Amino acid analysis indicates that entomopoxvirus occlusion body matrix protein consists of approximately 20% acidic amino acids and 9% of the sulfur-containing amino acids cysteine and methionine.

Laboratory studies demonstrated that neonate larvae of the white cutworm, Euxoa scandens, are susceptible to infection with nuclear polyhedrosis viruses of Mamestra brassicae (MbNPV), Euxoa messoria (EmNPV), Agrotis segetum (AsNPV), and Autographa californica (AcNPV). Among these viruses, MbNPV and EmNPV were found to be the most virulent and AcNPV the least virulent. Comparative LC50 values of MbNPV, EmNPV, AsNPV, and AcNPV were 21, 25, 45, and 1075 polyhedra/mm2 of diet, respectively. The difference between the LC50 values of MbNPV and EmNPV was not significant. The Heliothis NPV was found to be nonvirulent to all E. scandens larvae. Restriction endonuclease analysis of viral DNAs before and after passage through E. scandens larvae confirm that true cross-transmission occurred.

A pox virus was isolated from a field-collected larva of the army cutworm, Euxoa auxiliaris . Death of diseased larvae usually occurred 16–18 days after infection when from 1 to 1.5 million polyhedral inclusion bodies per milligram of larval tissue were recovered. The primary site of viral replication appeared to be the cytoplasm of fat body cells; limited infection occurred in the tracheal matrix and gut musculature. Within the fat body, oval immature virions bounded by double membranes were observed budding from viroplasms. After further maturation but before they were occluded in a protein matrix, these virions contained brick-shaped cores. Mature virions, which measured 165 × 260 nm and were loosely bounded by a wavy membrane, were occluded in polyhedra that averaged 3.7 × 4.7 μ.

A nonoccluded virus was isolated from larvae of the army cutworm, Euxoa auxiliaris. Infected larvae became lethargic and shrunken, and death usually occurred 12–20 days after infection. The primary site of viral infection and replication appeared to be the nuclei of midgut epithelial cells; however, virus replication also occurred in cells of the tracheal matrix and in muscle. Nuclei in early stages of the infection contained large granular areas with the chromatin scattered near the nuclear membrane. These areas differentiated into viral particles that measured 24 nm and formed crystalline arrays, occasionally 10 μm long. Disruption of the nuclear membrane liberated these arrays of particles into the cytoplasm. Fluorescence microscopy studies indicated that the viral particles contained DNA. The crystalline arrays were Feulgen positive. The virus also infected larvae of the armyworm, Pseudaletia unipuncta, and corn carworm, Heliothis zea, in laboratory tests.