Present addresses: Natural Resources Institute, The University of Greenwich, Central Avenue, Chatham Maritime, Kent ME4 4TB, U.K. and 2University of Maryland, School of Medicine, Anatomy and Neurobiology, HSF 256, Baltimore, Maryland 21201, U.S.A.
Electroantennogram and behavioural responses of the malaria vector Anopheles gambiae to human-specific sweat components
Article first published online: 20 DEC 2001
Medical and Veterinary Entomology
Volume 15, Issue 3, pages 259–266, September 2001
How to Cite
Costantini, C., Birkett, M. A., Gibson, G., Ziesmann, J., Sagnon, N'F., Mohammed, H. A., Coluzzi, M. and Pickett, J. A. (2001), Electroantennogram and behavioural responses of the malaria vector Anopheles gambiae to human-specific sweat components. Medical and Veterinary Entomology, 15: 259–266. doi: 10.1046/j.0269-283x.2001.00297.x
- Issue published online: 20 DEC 2001
- Article first published online: 20 DEC 2001
- Anopheles gambiae;
- 7-octenoic acid;
- (E)-3-methyl-2-hexenoic acid;
- odour-baited entry trap;
- malaria mosquito;
- (Z)-3-methyl-2-hexenoic acid;
- wind tunnel;
- Burkina Faso
Abstract. Afrotropical malaria vectors of the Anopheles gambiae complex (Diptera: Culicidae), particularly An. gambiae sensu stricto, are attracted mainly to human hosts. A major source of human volatile emissions is sweat, from which key human-specific components are the carboxylic acids (E)- and (Z)-3-methyl-2-hexenoic acid and 7-octenoic acid. Electrophysiological studies on the antennae of An. gambiae s.s. showed selective sensitivity to these compounds, with a threshold at 10−6 g comparable to that of known olfactory stimulants 1-octen-3-ol, p-cresol, isovaleric acid, and lower than threshold sensitivity to l-lactic acid and the synthetic mosquito repellent N,N-diethyltoluamide (DEET). A combination of the acids released at concentrations > 10−5 g in wind tunnel bioassays significantly reduced the response to CO2, the major attractant released by human hosts, for strains of An. gambiae s.s. originating from East and West Africa.
Field trials with odour-baited entry traps (OBETs) in Burkina Faso showed that 7-octenoic acid significantly increased (by 1.7-fold) the catch of females of An. gambiae sensu lato (comprising two sibling species: An. arabiensis Patton and An. gambiae s.s.) in OBETs baited with CO2, whereas combinations of the acids significantly reduced the catch in CO2-baited traps (by 2.1-fold) and in whole human odour-baited traps (by 1.5-fold). The pure (E) and (Z) geometric isomers of 3-methyl-2-hexenoic acid gave comparable results to the (E/Z) isomer mixture. These results provide the first experimental evidence that human-specific compounds affect the behaviour of highly anthropophilic An. gambiae s.l. mosquitoes. The compounds appear to inhibit the ‘upwind flight’ response to known long-range attractants, and may serve either to ‘mask’ the attractants present or, more probably, to ‘arrest’ upwind flight when mosquitoes arrive at a host under natural conditions. In the final approach to hosts, vectors are known to reduce their flight speed and increase their turning rate, to avoid overshooting the source. In our experimental apparatus, these changes in flight behaviour would reduce the number of mosquitoes entering the ports of the collection devices.