Plaque assay of baculoviruses employing an agarose-nutrient overlay.

Four baculoviruses produced visible plaques in the Spodoptera frugiperda cell line when cell monolayers were infected and overlayed with a simplified, agarose-nutrient formulation. Macroscopic plaques were first detected 4 days postinoculation, and by 10 days plaques ranging from 0.5 to 3 mm in diameter were seen. Dose-response experiments indicated that a single particle initiated the formation of a plaque, because a linear response was demonstrated with increased dosage.