The major component of the sex pheromone of female Spodoptera littoralis, (Z,E)-9,11-tetradecadienyl acetate (1), elicited all steps of the male behavioral sequence, i.e., wing fanning and taking flight, oriented upwind flight and arrival to the middle of the tunnel, close approach and contact with the source. The activity was equivalent to that elicited by virgin females. In the range of doses tested, the dosage of 1 had no significant effect on the number of source contacts. Male response was significantly affected by light intensity, being optimum at 3 lux. Activity of the minor components (Z)-9-tetradecenyl acetate (2), (E)-11-tetradecenyl acetate (3), tetradecyl acetate (4), (Z)-11-tetradecenyl acetate (5), and (Z,E)-9,12-tetradecadienyl acetate (6) was significantly lower than that of the major component when assayed individually. In multicomponent blends compound 4 appeared to strongly decrease the number of males arrested at the source, the effect being particularly important when compound 5 was present in the blend. Results of single sensillum experiments confirmed the existence of two main physiologically distinct sensillar types. The most common type of sensilla contained a neuron that responded specifically to compound1. A second type of sensilla, located laterally on the ventral sensory surface, contained two receptor neurons responding to compound 6 and to (Z)-9-tetradecenol. Among short sensilla, one hair responded to compound 4 and could represent a minor sensillar type. No sensory neuron was found to detect the other minor pheromone compounds 2, 3, and 5.