Olfactory receptors on the antennae of the malaria mosquito Anopheles gambiae are sensitive to ammonia and other sweat-borne components

Electrophysiological studies on female An. gambiae s.s. mosquitoes revealed a receptor neuron within a subpopulation of the antennal grooved-peg sensi lla sensitive to the odour of incubated sweat, but not responding to fresh sweat. This receptor neuron was sensitive to ammonia as well, a sweat-borne component which attracts female An. gambiae in a windtunnel bioassay. Neur ons innervating a different subpopulation of grooved-peg sensilla did not s how a response to incubated sweat. In the latter sensilla, however, one typ e of neuron responded to water or water containing solutions, while another receptor neuron was inhibited when stimulated with dry air, ether or ethan ol. Neurons innervating sensilla trichodea, a more abundant antennal type o f olfactory sensillum, did not respond to fresh or incubated sweat at the d oses offered. However, receptor neurons within the sensilla trichodea respo nded with excitation to several sweat-borne components. A subpopulation of the sensilla trichodea was innervated by neurons sensitive to geranyl aceto ne. A second subpopulation housed receptor neurons sensitive to indole. 3-M ethyl-1-butanol and 6-methyl-5-hepten-2-one evoked excitation of receptor n eurons within both subpopulations of sensilla trichodea. Neurons were most sensitive to indole and geranyl acetone with a threshold of 0.01%. These fi ndings are discussed in the context of host-seeking behaviour. (C) 2001 Els evier Science Ltd. All rights reserved.