IDENTIFICATION OF ELECTROPHYSIOLOGICALLY-ACTIVE COMPOUNDS FOR THE MALARIA MOSQUITO, ANOPHELES-GAMBIAE, IN HUMAN SWEAT EXTRACTS

Human sweat samples were chemically fractionated into acid and non-aci d components. The most abundant volatile compounds present in the frac tions were identified by linked gas chromatography mass spectrometry. The acid fractions were found to be composed of a range of twenty alip hatic and three aromatic carboxylic acids ranging, on average, from 0. 02 to 20 mu g per mi of sweat sampled. Non-acid fractions were found t o contain: 6-methyl-5-hepten-2-one, 1-octen-3-ol, decanal, benzyl alco hol, dimethylsulphone, phenylethanol, phenol and dr-methylphenol, coll ectively amounting to 0.1 and 3 mu g per mi of sweat. The major compon ent of sweat was found to be L-lactic acid which constituted from 1 to 5 mg/ml. Using the intact antennae of the anthropophilic malaria vect or mosquito Anopheles gambiae Giles, the peripheral olfactory activiti es of compounds identified in the sweat fractions were investigated by electroantennography (EAG). Short-chain saturated carboxylic acids, m ethanoic, ethanoic, propanoic, butanoic, pentanoic and hexanoic acids were found to elicit significantly larger EAG responses than longer ch ain saturated carboxylic acids from female An.gambiae. For a given dos e the largest amplitude EAG response was elicited by methanoic acid. P entanoic acid elicited larger EAG responses than either butanoic or he xanoic acids. Two non-acidic compounds, 1-octen-3-ol and 4-methylpheno l, were found to elicit significant dose-dependent EAG responses from female An.gambiae. 1-Octen-3-ol elicited larger EAG responses than dr- methylphenol for a given dose, but both compounds elicited smaller EAG responses than the same dose of C-1-C-6 straight-chain aliphatic carb oxylic acids. The possible behavioural significance of the FAG-active compounds identified in human sweat samples is discussed.