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 S imulium damnosum Theobald complex (Diptera: Simuliidae) from different sites in West Africa, was investigated by gas chromatographic analysi s of hexane extracts of the ovaries from wild-caught flies, bloodfed a nd maintained until gravid in the laboratory. The two compounds previo usly shown to be released from fresh eggs and associated with mediatio n of oviposition aggregation were found in S. leonense Boakye, Post & Mosha (Sierra Leone), S. yahense Vajime & Dunbar (Ghana), S. sanctipau li Vajime & Dunbar (Ghana), S. squamosum Enderlein (Cameroon), S. sirb anum Vajime & Dunbar (Ghana) and the Bioko form (island of Bioko, Equa torial Guinea). Coupled gas chromatography-mass spectrometry of the S. leonense, S. sanctipauli and the Bioko form extracts showed the two c ompounds to be identical in all three. Volatile emissions from freshly laid eggs of S. sanctipauli were similar to those previously describe d from S. leonense, and identical in chemical composition to gravid ov aries. No new compounds were detected in any ovary extracts or volatil e emissions examined, demonstrating that the composition of the aggreg ation pheromone is similar throughout the S. damnosum species complex. Analysis of S. leonense adults of different age groups and physiologi cal states showed that the compounds are detectable only in gravid ova ries at 2 or more days following the bloodmeal, suggesting that produc tion of the pheromone occurs during egg development. Demonstration of an oviposition aggregation pheromone common throughout the species com plex raises the possibility of developing an odour-baited trapping sys tem for blackflies, which could be employed across the large area of A frica where they are the vectors of onchocerciasis.