Apoptosis was observed in Spodoptera litura cell line Sl zsu 1 induced by Autographa californica multicapsid nuclear polyhedrosis virus ( Ac MNPV).Apoptotic cell death appeared at 10￣12 h after infection

and peak mortality was approximately 95%￣100%. The Apoptosis was found in the Sl zsu 1 cells infected with budded virions but not in the cells transfected with viral DNA or infected with polyhedrin derived virions. Ac MNPV GP64 membrane fusion protein encoded by gp 64 gene is the major envelope glycoprotein of the budded virion

and is the earliest viral factor touching cells when cells were attacked by budded virion. A hypothesis was proposed that Ac MNPV GP64 membrane fusion protein gene might be a primary apoptosis inducer according with our experimental results and literature analysis. An experimental program has been designed to prove the hypothesis.