The effects of the venom from A. glomeratus were examined on the morphology and contractility of cytoplasmic processes of granular cells and plasmatocytes as well as on the melanization of hemolymph of P. rapae crucivora, using an in vitro incubation system. In the presence of venom, both granular cells and plasmatocytes were capable of elongation or spreading as well as of retraction of their filopodia or lamellipodia, while retaining their normal surface morphology. This locomotive activity was also shown by plasmatocytes even in the presence of the venom. In addition, the venom had no influence on the melanin formation in the hemolymph. These negative results strongly confirmed that the venom was effective in suppressing the encapsulation reaction only to Apanteles eggs, but not to other foreign substances. One possibility why the venom is effective in keeping only these eggs from encapsulation by the host hemocytes will be discussed. none