This study describes some of the effects of calyx and venom fluids of Apanteles kariyai on the morphology and the filopodial function of Pseudaletia separata granular cells, using scanning electron microscopy and an in vitro incubation system. Calyx fluid contained virus-like particles, which were shown to be round or oval with a smooth surface and a size of about 225 nm in diameter under the scanning electron microscopy. When granular cells were incubated in the presence of either calyx or venom fluids, their filopodia elongated extensively at the cell periphery just like the control. However, incubation of cells with both calyx and venom fluids greatly inhibited filopodial elongation and further caused a remarkable cytolysis during the incubation time. Calyx fluid seems to require components of the venom fluid to have inhibitory effects on the initial cellular defence reaction of host larvae. In this paper, the possible roles of calyx and venom fluids in suppression of the hemocytic reaction of host will be discussed. none