a1 London School of Hygiene and Tropical Medicine, London, WClE 7HT, UK
a2 Rothamsted Experimental Station, Harpenden, Herts., AL5 2JQ, UK
Gravid females of Culex quinquefasciatus Say from a laboratory strain originating in Nigeria orientated to a source of the main volatile pheromone component, erythro-6-acetoxy-5-hexadecanolide, isolated from the apical droplets of the egg rafts. Significantly more egg rafts were laid around polystyrene discs treated with the synthetic compound than around untreated discs, and modification of the chemical structure destroyed its biological activity. The response was found at a dose of 0·02μg of the synthetic compound, which is equivalent to one-sixteenth of the total acetoxyhexadecanolide found in an egg raft, and above. Although the apical droplets were contaminated by bacteria, these did not contribute to the production of the acetoxyhexadecanolide, which was present in the eggs before they were laid. It is concluded that the pheromone is released slowly from the apical droplets into the air above the water surface, attracting other gravid females to oviposit around previously laid egg rafts, and there is evidence of attraction over a distance of 5·5 cm.
(Received September 14 1984)