PLAQUE-ASSAY AND REPLICATION OF TIPULA IRIDESCENT VIRUS IN SPODOPTERA-FRUGIPERDA OVARIAN-CELLS

A plaque assay was developed for the study of Tipula iridescent virus (TIV) replication using a cell line derived from the fall army worm Sp odoptera frugiperda (Sf9). Infection and plaque formation were monitor ed with time by phase contrast microscopy, video and fluorescent light microscopy. Structure of virions, viroplasmic centres and organelles of infected cells; were examined by transmission electron microscopy ( TEM). After 4 h postinfection, plaques were visibly detected within th e cell monolayer by the presence of localized cell damage and producti on of numerous vesicular-like cytoplasmic structures. Quantitation of virions present per A(260) unit of TIV preparation was determined by T EM. The number of visible plaques corresponded to virus concentration and 1 A(260) produced approximate to 10(5) plaques. DNA hybridization analysis revealed no gross differences in genomic DNA from TIV propaga ted in either Sf9 cells or wax moth Galleria mellonella larvae. These findings indicate that Sf9 is permissive for replication of TIV and su perior by some parameters to other cell lines currently in use for the study of host cell/TiV interactions.