PLAQUE-ASSAY FOR SPODOPTERA-EXIGUA AND AUTOGRAPHA-CALIFORINICA NUCLEAR POLYHEDROSIS VIRUSES IN A NEWLY ESTABLISHED CELL-LINE OF THE BEET ARMYWORM, SPODOPTERA-EXIGUA

The nuclear polyhedrosis viruses of Spodoptera exigua (SeNPV) and Auto grapha californica (AcNPV) produced plaques in a newly established cel l line of the beet armyworm, Spodoptera exigua. Plaques were composed of infected cells containing many polyhedra and were visible without a ny staining procedure. Dose-response assays showed a direct correlatio n between the number of plaques and the inoculum size. Growth kinetic studies of the two viruses, using the developed plaque assay system, r evealed that the release of extracellular viruses began 6 hrs post inf ection (p.i.) and the titer reached a plateau 48 hrs p.i. The sensitiv ity of this plaque assay system was 100 times greater for the heterolo gous AcNPV than for the homologous SeNPV.