Derived from pupal ovarian tissue of spodoptera frugiperda. The cells are highly susceptible to Baculovirus infection and are used in the production of protein products genetically manipulated into Baculovirus vector systems. They were derived at the USDA Insect Pathology Laboratory from a cell line originating from pupal ovarian tissue of the fall army worm, Spodoptera frugiperda. Sf21 cells have greater range in size and have a doubling time of 24 hr compared to 48-72 hr for Sf9 cells