Heliothis zea (Boddie) larvae fed cowpea seedlings produced volatile semiochemicals to which Microplitis demolitor Wilkinson responded in a wind tunnel. However, most M. demolitor females reared from H. zea larvae fed an artificial diet were not responsive at emergence to the same volatile semiochemicals. A preflight contact with frass from H. zea fed cowpea was needed to stimulate a response of sustained flight in a wind tunnel. Chilling the parasitoid pupae rendered most of the emerging females unresponsive to volatile semiochemicals. none