We report the identification of the southwestern corn borer,Diatraea grandiosella Dyar (Lepidoptera: Pyralidae), female sex attractant pheromone as a mixture of (Z)-9-hexadecenal, (Z)-11-hexadecenal, and (Z)-13-octadecenal in the ratio 21.5∶70.6∶7.9. Initially, six 16- and 18-carbon aldehydes includingn-hexadecanal, (Z)-9-octadecenal, (Z)-11-octadecenal, and the three above were isolated from female gland rinses and evaluated as potential pheromone components by GLC-MS and laboratory bioassays. By laboratory flight chamber and field tests, the stated mixture of (Z)-9-hexadecenal, (Z)-11-hexadecenal, and (Z)-13-octadecenal was shown to be as effective as the female for male attraction. Electrophysiological studies confirmed the requirement for these three compounds, but not forn-hexadecanal, (Z)-9-octadecenal, and (Z)-11-octadecenal.