Modification of the attractiveness of the primary pheromone component of the Egyptian cotton leafworm, Spodoptera littoralis (Boisduval) (Lepidoptera: Noctuidae), by secondary pheromone components and related chemicals

Abstract

Known components of the female sex pheromone of Spodoptera littoralis (Boisd.), tetradecyl acetate (I), (Z)-9-tetradecenyl acetate (IIA), (Z,E)-9, 11-tetradecadienyl acetate (III) and (Z,E)-9, 12-tetradecadienyl acetate (IV), and related compounds dispensed from polyethylene vials were used to bait water traps and funnel traps in lucerne fields in Crete. In comparison with the catches of males in traps baited with the primary component (III) alone, catches were increased by the addition of 1–100% of I in relation to the amounts of III, decreased by the addition of 5% or more of IIA and decreased by the addition of more than 5% of IV. The diene III was more attractive than any of the other three geometric isomers, although combining the Z,Z isomer (V) or the E,E isomer (VI) with III increased catches while the addition of the E,Z isomer (VII) decreased catches. The alcohols VIII and IX corresponding to the acetates III and IIA were not attractive but caused a marked reduction in trap catch when combined with III. The homologue of III (Z,E)-11-methyl–9, 11-tetradecadienyl acetate (X), was unattractive to males but increased trap catches when combined with III. 9-Tetradecynyl acetate (XI) exhibited neither attractant nor inhibitory activity, and similar results were obtained with ethyl cyclohexane carboxylate (XII) and 2-nonynal dimethyl acetal (XIII), compounds which have similar far-infrared spectra to that of diene III. The distributions of males landing on sticky board traps 70 cm in diameter baited with III or mixtures of III with I, IIA or IV showed that a greater percentage of the moths landed at the periphery of the traps baited with certain combinations of III with I and IV than on traps baited with III alone. Collection and analysis of the volatiles emitted by virgin females of different origins indicated that those from Crete produced I and III only, those from Israel produced I, III and IV, while those from Egypt produced I, III, IV and IIA and/or (E)-11-tetradecenyl acetate (IIB). The results are discussed in relation to previous work on S. littoralis and current theories on insect communication, and also in terms of their relevance to the practical field usage of pheromones in control of this pest.