Studies on the attraction of Simulium damnosum s.l. (Diptera: Simuliidae) to its hosts. II. The nature of substances on the human skin responsible for atrractant olfactory stimuli.

In the Cameroon rain-forest, electric fan traps, baited with trousers which had been worn by men for several days, captured more females of S. damnosum s.l. than did traps baited with worn shirts of similar material. A number of human body fluids were used as bait, but only sweat appeared to contain the olfactory attractant(s). The fluid portion of filtered arm sweat attracted more flies than did the residue. The attractant substances from human skin would not dissolve directly in organic solvents, but when an artificial sweat solution was used to swab men's arms and legs, and this was then saturated with salt and shaken with an organic solvent, the extract was attractive to S. damnosum. Treatment of attractive worn cloths with dilute aqueous solutions of hydrochloric acid, sodium hydroxide or mercuric chloride greatly reduced their attractiveness. A number of organic compounds which occur on the human skin were found to be ineffective as attractants.