none Females of the larval parasitoid Apanteles kariyai (Watanabe) (Hymenoptera: Braconidae) are arrested on fecal pellets of Acantholeucania loreyi (Duponchel) (Lepidoptera: Noctuidae) larvae. Upon subsequent antennal contact with an A. loreyi larva, females sting it with their ovipositor. However, such stinging did not result in any offspring. The allelochemical involved in feces has been identified and is identical to a kairomone of the host Pseudaletia separata (Lepidoptera: Noctuidae). In contrast to A. loreyi , P. separata is a suitable host for A. kariyai , and oviposition in P. separata results in offspring production. The allelochemical mediating the interaction between A. loreyi and A. kariyai is discussed in the context of current allelochemical terminology.