Replication and serial passage of infectious Heliothis nucleopolyhedrosis virus in an established line of Heliothis zea cells

An established cell line derived from the ovary of adults of the cotton bollworm, Heliothis zea, supported growth of the Heliothis nucleopolyhedrosis virus (NPV). Typical NPV symptoms were obtained when infected cells were fed to neonatal bollworms; however, the cell line never produced free virions or inclusion bodies containing virions. Infectious virus was passed through the cell line 7 consecutive times, using only infected cells from the previous pass. Infectivity at the 7th serial-pass represented a dilution of >10⁻⁸ of the original inoculum.