PHYSIOLOGY AND MORPHOLOGY OF PHEROMONE-SPECIFIC SENSILLA ON THE ANTENNAE OF MALE AND FEMALE SPODOPTERA-LITTORALIS (LEPIDOPTERA, NOCTUIDAE)

The physiology, morphology and distribution of pheromone receptors on the antennae of both sexes of Spodoptera littoralis Boisd. (Lepidoptera: Noctuidae) were investigated by electroantennogram screening, single sensillum recordings and scanning electron microscopy. The electroantennogram recordings showed maximal responses to (Z,E)-9,11-tetradecadienyl acetate in males and to (Z)-7-dodecenyl acetate in females. In subsequent single sensillum recordings, receptor cells specific for the two known phermone components, (Z,E)-9,11-tetradecadienyl acetate and (Z,E)-9,12-tetradecadienyl acetate, as well as for the behavioural antagonist (Z)-9-tetradecenol, were found in both sexes. The sensitivity of the pheromone receptors to their respective stimuli was the same in the sexes, while the number of pheromone-specific sensilla was much lower in the female. In the male, two physiologically distinct sensillum types were differently distributed over the antennal surface. The most numerous type, containing only one receptor neurone specific for (ZE)-9,11-tetradecadienyl acetate, was evenly distributed over the ventral antennal surface, while a sensillum type containing one neurone responding to (Z,E)-9,12-tetradecadienyl acetate and one neurone specific for (Z)-9-tetradecenol was only found among more laterally situated sensilla. This distribution was not observed in the female.