Bioassays in 12×17×3-m field cages showed an airborne chemical was released from the hairpencils of the maleHeliothis virescens(F.) before mating. When receptors on the female antennae detected the pheromone during courtship, release of female sex pheromone ceased. Emission of the female sex pheromone was effectively terminated if the females were exposed to 50 male equivalents of hairpencil extract or to untreated 2-day-old (virgin) male tobacco budworms. Extracts of hairpencils made with ethyl ether were almost as effective as live males, but extracts made with carbon disulfide did not successfully suppress the production of the sex pheromone.