Replication and serial passage of a singly enveloped baculovirus of Orgyia leucostigma in homologous cell lines.

A singly enveloped nuclear polyhedrosis virus (SNPV) of the white-marked tussock moth, Orgyia leucostigma, was successfully grown in four continuous cell lines developed from minced neonate larvae of this insect. Level of infection in two cell lines, IPRI-OL-12 and IPRI-OL-13, was 65-90%, but in the other two, IPRI-OL-4 and IPRI-OL-9, it was about 3%. Polyhedral inclusion bodies (PIBs) appeared in the nuclei of cells within 24 h postinoculation. Cytopathological changes and morphogenesis of the virus, as revealed by light and electron microscopy, were in general typical of an SNPV. However, some of the PIBs contained very few virions, and some were fractured. Rate zonal centrifugation of alkali-released occluded virions further confirmed the singly enveloped characteristics of the virus. The SNPV was serially passaged 60 times each in OL-12 and OL-13 cells. Percentage infected cells and PIB production stayed generally high throughout serial passaging in OL-13 cells, but declined sharply after the 41st passage in OL-12 cells. PIBs from the 4th passage of the virus in OL-12 cells were tested and found to be pathogenic to O. leucostigma larvae.