The release of (9Z,11E)-9,11-tetradecadienyl acetate from dispensers placed 25 m apart in a cotton field was ineffective in causing mating disruption of the noctuid Spodoptera littoralis. Effective mating disruption was achieved by using a polymeric aerosol formulation containing the pheromone at 75 g a.i./ha placed at 500 release points per hectare and giving a daily release rate of 3 g/ha. It is concluded that to achieve effective mating disruption of S. littoralis it is necessary to deploy many dispensers placed closely together.