Similarity in oviposition aggregation pheromone composition within the Simulium damnosum (Diptera: Simuliidae) species complex

The oviposition aggregation pheromone of six species or forms of the Simulium damnosum Theobald complex (Diptera: Simuliidae) from different sites in West Africa, was investigated by gas chromatographic analysis of hexane extracts of the ovaries from wild-caught flies, bloodfed and maintained until gravid in the laboratory. The two compounds previously shown to be released from fresh eggs and associated with mediation of oviposition aggregation were found in S. leonense Boakye, Post and Mosha (Sierra Leone), S. yahense Vajime and Dunbar (Ghana), S. sanctipauli Vajime and Dunbar (Ghana), S. squamosum Enderlein (Cameroon), S. sirbanum Vajime and Dunbar (Ghana) and the Bioko form (island of Bioko, Equatorial Guinea). Coupled gas chromatography-mass spectrometry of the S. leonense, S. sanctipauli and the Bioko form extracts showed the two compounds to be identical in all three. Volatile emissions from freshly laid eggs of S. sanctipauli were similar to those previously described from S. leonense, and identical in chemical composition to gravid ovaries. No new compounds were detected in any ovary extracts or volatile emissions examined, demonstrating that the composition of the aggregation pheromone is similar throughout the S. damnosum species complex. Analysis of S. leonense adults of different age groups and physiological states showed that the compounds are detectable only in gravid ovaries at 2 or more days following the bloodmeal, suggesting that production of the pheromone occurs during egg development. Demonstration of an oviposition aggregation pheromone common throughout the species complex raises the possibility of developing an odour-baited trapping system for black flies, which could be employed across the large area of Africa where they are the vectors of onchocerciasis.