The mechanism of how endoparasitoids avoid the host's cellular immune reaction is not well known. Evidence is presented here for the existence of a Helix pomatia lectin binding protein (HpLBP) on Macrocentrus cingulum extraembryonic membrane and its involvement in the protection of embryos against encapsulation by its host Ostrinia furnaclis. HpLBP is present in eggs, embryos and larvae and is located on the outmost layer of the extraembryonic membrane. While Sephadex A-25 beads and immature Macrocentrus eggs coated with follicular cells were encapsulated, Macrocentrus embryos were not after they were transplanted separately into naive O. furnaclis larvae. Moreover, embryos became encapsulated after being coated with anti-HpLBP serum. Furthermore, encapsulation of agarose-H. pomatia lectin beads decreased significantly after the beads were coated with HpLBP. However, encapsulation of the HpLBP-coated agarose beads increased and the extent of encapsulation was enhanced significantly when the HpLBP-coated beads were pre-incubated with anti-HpLBP antibody.