THE specificities of oligophagous insects to groups of related plants have been postulated and demonstrated in several instances to be mediated by secondary plant substances of limited distribution (reviewed by Dethier¹ and Fraenkel^2,3). These substances are variously called attractants, token stimuli, or phagostimulants when they serve in such capacity and are generally tested on the feeding stages of the insects concerned by applying the substances on various artifices such as filter paper, pith disks, non-host leaves or agar gel diets. The insects are then allowed to discriminate the presence of the attractants by biting or feeding.