Laboratory experiments on the disruption of mating in the Egyptian cotton leafworm Spodoptera littoralis (Boisduval) (Lepidoptera: Noctuidae) by excesses of female pheromones

Abstract

The courtship of Spodoptera littoralis (Boisd.) was studied in closed cages containing an excess of the female sex pheromones (Z,E)-9, 11-tetradecadienly acetate (III) or (Z)-9-tetradecenyl acetate (IIA). High levels of III or IIA were obtained by using polyethylene vials loaded with 5, 1 or 0·1 mg of pheromone. Vials containing 10 or 1 μg released low levels of pheromone. Excess pheromone reduced mating; at high levels of III and IIA, only 15% and 42% of pairs, respectively, mated, compared with 92% of control pairs. Some 45% of courtships in control cages did not end in copulation, and in half of these the female rejected the male by giving a rapid flick of the wings. A detailed examination of unsuccessful courtships showed that an excess of III or IIA disrupted female courtship behaviour. At the higher levels of pheromone, no female wing-lifted to show acceptance of the male and only a few rejected the male by wing-flicking. Significantly more females took to flight in cages containing III, whilst in cages with IIA females either took to flight or remained still. These changes in behaviour were still apparent in courtships where the female was calling and the male gave a full brush display. It is suggested that both III and IIA block olfactory reception of the male brush pheromone. An excess of either pheromone increased the proportion of male courtships of non-calling females. IIA had no other appreciable effect on male behaviour, but III also significantly reduced full brush displays during courtship, increased the period of flight preceding hovering and increased partial brush extension during flights that did not lead to courtship.