A newly isolated densonucleosis virus from Pseudoplusia includens (Lepidoptera: Noctuidae)

An icosahedral DNA virus isolated from the soybean looper, Pseudoplusia includens, was characterized. Purified virus had a diameter of 20 ± 1 nm and negatively stained preparations showed a trend to form linear to three-dimensional crystals. The virus had a sedimentation coefficient of 120 ± 3 S and a buoyant density of 1.40 ± 0.01 g/cm³. The DNA content of the virus was 37.8 ± 0.1% and the absorption spectrum showed it to be a typical nucleoprotein. Viral DNA in situ was shown to be single-stranded by staining the virus with acridine orange as well as by reaction to formaldehyde. Evidence of inverted terminal repetition of the DNA was observed by electron microscopy. The terminal repetition comprises ca. 6–7% of the genome. The molecular weight of the ssDNA was 2.0 ± 0.1 × 10⁶ as determined by agarose gel electrophoresis or 2.1 ± 0.1 × 10⁶ as determined by electron microscopy. Four virion proteins with molecular weights of 46.5 ± 0.1, 54.0 ± 0.1, 64.0 ± 0.2, and 87.0 ± 0.1 × 10³ were detected by 9% SDS-polyacrylamide gel electrophoresis. Double-diffusion tests showed the virus to be serologically related but not identical to DNV-1. Ultrathin sections showed that the nucleus of the hemocyte, muscle, hypodermal, and fat body cells contained virus-like particles. The chromatin of an infected nucleus always underwent a margination and the nucleoplasm was often replaced largely by virions.Data indicate that the virus belongs to the Densovirus of the family Parvoviridae.