Physiological Entomology zyxwvuts (1990) 15, 275-283 Physiology of interspecific chemical communication in Heliothis moths zyxw THOMAS A. CHRISTENSEN, SABRINA C. GEOFFRION and JOHN G zyxwvuts . HI LDEBRAND University of Arizona, Tucson, Arizona, U.S.A. Arizona Research Laboratories, Division of Neurobiology, zy Abstract. Electroantennograms were recorded from the antennae of adult male and female corn earworms, Heliothis zea (Boddie). A total of seventeen female moth sex pheromone components from several species were tested. Of these, two components elicited significantly greater responses than the other fifteen. These were (2)-11- hexadecenal, a conspecific component, and (2)-9-tetradecenal, a component found in the pheromone blend of a sympatric species H. virescens (F.) that inhibits attraction of H.zea males. The results from dose-response and selective adaptation studies indicate that there are separate populations of receptors for these two chemical signals on the antenna of male H.zea. The more sensitive population is selective for (2)-11-hexadecenal, while the less sensitive one responds to (Z)-9- tetradecenal. These findings provide a physiological basis by which H.zea males can distinguish the interspecific repellent from the conspecific pheromone blend. It is likely that this discrimination con- tributes to reproductive isolation between these two species. Key words. Electroantennogram, sex pheromones, corn earworm, Heliothis zea, tobacco budworm, Heliothis virescens, Lepidoptera, Noctuidae. Introduction Moths belonging to the genus Heliothis (Lepidoptera, Noctuidae) are among the most adaptable and therefore devastating agricultural pests in North, Central and South America (reviewed in Fitt, 1989). Consequently, for many years scientists have studied sex pheromone communication in the corn earworm H.zea (Boddie), and the tobacco budworm Correspondence: Dr Thomas A. Christensen, ARLDN, 611 Gould-Simpson, University of Arizona, Tucson, AZ 85721, U.S.A. H.virescens (F.) in an attempt to control their numbers through mating disruption (Campion, 1984). Several field studies showed that when traps were baited with virgin females of both species, the result was a reduction in the number of corn earworm males captured (Haile er a l . , 1973; Roach, 1975; Carpenter et al., 1984). More recently it has been demonstrated that when using separate traps for each species, the negative influence of the tobacco budworm pheromone blend on trap catches of corn ear- worm males can be minimized by placing the tobacco budworm traps downwind of the corn earworm traps (Lopez & Witz, 1988). Using synthetic pheromone blends identified from the 275