Landing responses of Anopheles gambiae elicited by oxocarboxylic acids

A wind tunnel bioassay and video system were used to observe Anopheles gambiae Giles sensu stricto (Diptera: Culicidae) landing on glass cylinders, heated to human skin temperature (34°C) and treated with aqueous solutions of oxocarboxylic acids. Six of nine compounds tested: 2‐oxobutanoic, 2‐oxo‐3‐methylbutanoic, 2‐oxopentanoic, 2‐oxo‐3‐methylpentanoic, 2‐oxo‐4‐methylpentanoic and 2‐oxohexanoic elicited significant landing responses in comparison to a water control. Landing responses appeared to be restricted to C4–C6, 2‐oxocarboxylic acids. A solution of 1 µg/µL of 2‐oxopentanoic acid elicited the highest level of response that was temperature dependent: significant numbers of landings occurred only within ± 2°C of human skin temperature. Chemical analysis by linked gas‐liquid chromatography/mass spectrometry of methyl‐oxime, trimethylsilyl derivatized samples of human sweat extracts revealed the presence of 2‐oxopropanoic (pyruvic) acid and three behaviourally active, branched chain acids: 2‐oxo‐3‐methylbutanoic, 2‐oxo‐3‐methylpentanoic and 2‐oxo‐4‐methylpentanoic.