Piperidine alkaloids in poison hemlock,Conium maculatumL. (Umbelliferae), are responsible for the plant's acute toxicity toward mammals and other vertebrates. Because of this property, these compounds are often assumed to be toxic to insect herbivores as well. One of these alkaloids, coniine, was bioassayed for toxicity, growth inhibition, and feeding deterrency in the polyphagous speciesHeliothis zea(Boddie) (Lepidoptera: Noctuidae). Contrary to expectations, coniine showed no biological activity towardH. zeaat the concentrations tested.