Apoptosis was observed in Spodoptera litura cells (Sl zsu 1) infected with Trichoplusia ni multicapsid nuclear polyhedrosis virus( Tn MNPV) and in Trichoplusia ni cells(Tn 5B1 4) infected with Heliothis armigera singlecapsid nuclear polyhedrosis virus( Ha SNPV) for the first time. Apoptotic cell death of Sl zsu 1 cells started about 10 h after infection and progressed from 10 to 24 h.Peak mortality of Sl zsu 1 cells at 24 h after infection was approximately 95% to 100%. Apoptotic cell death of Tn 5B1 4 cells started at about 24 h after infection and peak motality of the cells at 48 h after infection was about 60%.Occlusion bodies were visible in about 10% of Tn 5B1 4 cells infected with Ha SNPV. Apoptotic response of the two cells progressed and intensified when the cells were infected by the viruses at increasing multiplicit of infection (MOI) (from 0 1 to 5)

and peak motality of Sl zsu 1 and Tn 5B1 4 cells were approximately 95% and 60% respectively when the cells were infected by the viruses at a MOI of 5 or more than 5. Apoptosis was found in Sl zsu 1 and Tn 5B1 4 cells infected with budded virus(BV) containing inoculum rather than transfected with viral DNA. These results indicate that host cell factors play a role in blocking or interfering with apoptotic processes; there is host specificity in the p 35 gene suppressed apoptosis;some structure proteins of baculovirus might initiate apoptotic cell death.