none Preparation of an artificial oviposition substrate (AOS) from agarose and host hemolymph for oviposition by a parasitic wasp, Microplitis croceipes (Cresson), is described. Natural hosts for this endoparasitoid are larvae of Heliothis, spp. Infusion of hemolymph from Heliothis zea (Boddie) into a drop of solidified agar induced females of M. croceipes to oviposit into the material. Ovipositional response to dilution of host hemolymph was determined. The factor or factors that stimulated oviposition were moderately heat sensitive, dialyzable, and unaffected by treatment with protease or pancreatic trypsin or hexane extraction. Hemolymph from Manduca sexta (L.) was less effective than H. zea hemolymph. Ths AOS will facilitate in vitro efforts to rear M. croceipes, because of dissection of host larvae is no longer necessary and many eggs can be collected easily.