Cysteine protease that plays an essential role in host liquefaction to facilitate horizontal transmission of the virus. May participate in the degradation of foreign protein expressed by the baculovirus system. Endopeptidase of broad specificity, hydrolyzing substrates of both cathepsin L and cathepsin B. Synthesized as an inactive proenzyme and activated by proteolytic removal of the inhibitory propeptide. Optimal pH is 4.0, also active at neutral pHs. Belongs to the peptidase C1 family.