REPLICATION OF A MAMESTRA-BRASSICAE NUCLEAR POLYHEDROSIS-VIRUS IN A NEWLY ESTABLISHED MAMESTRA-BRASSICAE CELL-LINE

A continuous cell line, designated MbL-3, was newly established from m inced neonate larvae of the cabbage armyworm, Mamestra brassicae. This new cell line is heteroploid, containing triploid cells predominantly at the frequency of about 50%. Doubling time of the cell population i s 33 hrs. The Akutsu isolate of a Mamestra brassicae nuclear polyhedro sis virus (MbNPV) was examined for replication in 16 continuous cell l ines, including the cell line MbL-3, from seven lepidoptera species: M amestra brassicae, Pseudaletia separata, Spodoptera exigua, Spodoptera frugiperda, Spodoptera littoralis, Spodoptera litura and Plutella xyl ostella. Of these cell lines, only the MbL-3 cells supported a high re plication of the virus. Four other Mamestra cell lines and a P. separa ta cell line showed a low virus-susceptibility, while the other cell l ines were not permissive for the virus infection. Maximum infection ra te of MbL-3 cells to the Akutsu isolate was 23.4%. The growth kinetics of this virus isolate in MbL-3 cells showed that the virus was releas ed from infected cells 24 hrs p.i. and reached a maximal titer 96 hrs p.i. The number of polyhedral inclusion bodies (PIBs) reached a maximu m of 10(75) PIBs/ml 120 hrs p.i.