Analytical studies of Spodoptera littoralis sex pheromone components by electroantennography and coupled gas chromatography–electroantennographic detection

In this paper we present analytical studies of the sex pheromone components of the Egyptian armyworm Spodoptera littoralis (Lepidoptera, Noctuidae) by electroantennography (EAG) and coupled gas chromatography-electroantennographic detection (GC-EAD). EAG responses in three different preparations, using an insectʹs head, an excised antenna and a live insect, have been recorded. EAG depolarizations of live insects were significantly higher than those elicited by the insectʹs head or the excised antenna. The responses were dose-dependent. Live insects also allowed regular pheromone stimulations for 40 min with only 38% decrease of the EAG initial depolarization. The synthetic pheromone blend elicited the highest EAG activity (2.0±0.3 mV), followed by the major compound (Z,E)-9,11-tetradecadienyl acetate (I) (1.54±0.1mV), and the minor components (Z)-9-tetradecenyl acetate (II), (E)-11-tetradecenyl acetate (III), tetradecyl acetate (IV) and (Z)-11-tetradecenyl acetate (V) (1.21-1.32 mV range). (Z,E)-9,12-tetradecadienyl acetate (VI), although not present in the pheromone blend of our strain, also showed an EAG activity (1.32±0.09 mV) similar to that of the monoenic components. GC-EAD responses confirmed the composition of the sex pheromone blend, the major response being elicited by the main component I followed by the other minor compounds II-V. The new dienic compound found in the female pheromone gland, (E,E)-10,12-tetradecadienyl acetate (VII), was not electrophysiologically active. Regarding sensitivity, the minimum amount detectable to elicit an antennal response in our GC-EAD system was 15 pg of the major component. In our system, which was built with cheap and easily available materials, no cooling of the effluent at the outlet of the chromatographic column is required.