The presence of a host-searching stimulant (kairomone) forMicroplitis croceipes, a braconid parasite ofHeliothisspp. in the commercial formulation and four preformulation stages of theHeliothisNPY, Elcar was investigated. A petri dish bioassay was used to determine kairomonal activity of Elcar at three concentrations (1.0, 0.5, and O.1g in 100 ml of water). “Cremed” diseasedHeliothislarvae, the supernatant resulting from centrifugation of “cremed” larvae, formulated inert ingredients, and purifiedHeliothisNPY were also bioassayed at a concentration of 1 g in 100 ml of water. There was no searching response to the purified NPY, inert additives, or the lowest concentration of Elcar, but responses were observed to the high and medium concentrations of Elcar, the supernatant, and the “cremed” larvae. These data indicate the presence of kairomonal substance(s) in Elcar, and suggest that virus purification during the formulation process may reduce the potential kairomone activity.