Identification of electrophysiologically‐active compounds for the malaria mosquito, Anopheles gambiae , in human sweat extracts

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Abstract
Human sweat samples were chemically fractionated into acid and non‐acid components. The most abundant volatile compounds present in the fractions were identified by linked gas chromatography mass spectrometry. The acid fractions were found to be composed of a range of twenty aliphatic and three aromatic carboxylic acids ranging, on average, from 0.02 to 20 ig per ml of sweat sampled. Non‐acid fractions were found to contain: 6‐methyl‐5‐hepten‐2‐one, l‐octen‐3‐ol, decanal, benzyl alcohol, dimethylsulphone, phenylethanol, phenol and 4‐mefhylphenol, collectively amounting to 0.1 and 3 |ig per ml of sweat. The major component 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 vector mosquito Anopheles gambiae Giles, the peripheral olfactory activities of compounds identified in the sweat fractions were investigated by electroantennography (EAG). Short‐chain saturated carboxylic acids, methanoic, ethanoic, propanoic, butanoic, pentanoic and hexanoic acids were found to elicit significantly larger EAG responses than longer chain saturated carboxylic acids from female An.gambiae. For a given dose the largest amplitude EAG response was elicited by methanoic acid. Pentanoic acid elicited larger EAG responses than either butanoic or hexanoic acids. Two non‐acidic compounds, l‐octen‐3‐ol and 4‐methylphenol, were found to elicit significant dose‐dependent EAG responses from female An.gambiae. 1 ‐Octen‐3‐ol elicited larger EAG responses than 4‐methylphenol for a given dose, but both compounds elicited smaller EAG responses than the same dose of C ] ‐C 6 straight‐chain aliphatic carboxylic acids. The possible behavioural significance of the EAG‐active compounds identified in human sweat samples is discussed.

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