The response of newly established cell lines of Spodoptera littoralis to group I and group II baculoviruses.

Autographa californica multiple nucleopolyhedrovirus (AcMNPV) and Spodoptera littoralis multiple nucleopolyhedrovirus (SpliMNPV) belong to group I and group II nucleopolyhedroviruses, respectively and can replicate in a wide range of insect species. In this study, the ability of newly established S. littoralis cell lines to support replication of AcMNPV and SpliMNPV was examined. The microscopic observations showed that the S. littoralis cells infected with AcMNPV exhibited morphological changes such as cells breaking into small bodies and forming apoptosis-like bodies post-infection. Nuclear DNA fragmentation was observed in all AcMNPV-infected cell lines through DNA gel electrophoresis analysis. Therefore, the virus replication was unsuccessful in most of cells, which were able to abort the virus replication. On the other hand, cells that were infected with SpliMNPV did not show similar morphological changes and no small bodies were formed. In addition, SpliMNPV succeeded to infect the cells, replicate, and form viral occlusion bodies inside the infected cells. In suspension culture, S. littoralis cells, which were infected with AcMNPV, accumulated as composed balls in shaker flasks after infection overnight, with cell density decreasing dramatically. In contrast, there was no cell clumping seen in the infected cells with SpliMNPV and the uninfected cells. In conclusion, the newly established embryonic S. littoralis cells were highly susceptible to SpliMNPV, whereas the cells were non-permissive to AcMNPV, yet they still underwent programmed cell death.