No abstract

Female Anopheles gambiae Giles mosquitoes were observed individually in a cage within a wind tunnel and their responses to pulses of carbon dioxide recorded on video tape. The range of concentrations tested revealed an 'activation' threshold concentration of carbon dioxide in the region of 0.01% above background. At this concentration, approximately 60% of the mosquitoes took off and flew upwind. Pulses of human breath, diluted with wind tunnel air to reproduce equivalent concentrations of carbon dioxide, elicited similar levels of response and the same 'activation' threshold concentration. These findings are discussed in relation to the activation of host-seeking mosquitoes.

A wind tunnel bioassay and video to observe mosquitoes landing on heated glass cylinders were used to test sweat and some derivatives for responses of Anopheles gambiae Giles (Diptera: Culicidae), a highly anthropophilic African species of malaria vector. Filter papers impregnated with human sweat and a diethyl ether extract from the filter papers elicited significantly more landings than a water control (P<0.001). The concentration of lactic acid in the extract was determined by GLC assay, but bioassays of an equivalent dose of lactic acid (from a commercial supplier) did not elicit landings. Chemical analysis of the extract by combined GLC/mass spectrometry indicated the presence of 73 compounds, of which 40 were tentatively identified. The major components of the extract were aliphatic carboxylic acids. An artificial blend of 22 carboxylic acids did not elicit landings. Bioassays of 2-oxopentanoic acid elicited significantly more, landings (P<0.001). The possible importance of oxo-carboxylic acids for host-seeking by anthropophilic mosquitoes is discussed and their use for trapping is suggested.