Olfactory sensitivities of mosquitoes with different host preferences (Anopheles gambiae s.s., An. arabiensis,An. quadriannulatus,An. m. atroparvus) to synthetic host odours

Responses of antennal olfactory cells associated with sensilla trichodea were recorded in females of four Anopheles species (Diptera, Culicidae) with different host preferences: the anthropophilic An. gambiae s.s., the opportunistic An. arabiensis, and the zoophilic An. quadriannulatus and An. maculipennis atroparvus. Stimuli were vapours of synthetic host-odours: ethanoic, propanoic, butanoic, 3-methyl propanoic, 4-methyl butanoic acid, 1-octen-3-ol, and 3- and 4-methyl phenol. On stimulation with fatty acids and phenols either excitation or inhibition of spike activity was found, whereas responses to 1-octen-3-ol were invariably excitatory. The odour spectra of the cells could include activating as well as inhibiting substances. Differences in host preferences may be reflected in the numbers of olfactory cells responding to different odours and/or in the sensitivities of these cells. In An. gambiae more cells were excited by fatty acids than in An. arabiensis and An. m. atroparvus, whereas inhibition occurred more often in the latter two species. In addition, the fatty acid-excited cells in An. gambiae were more sensitive to these substances than in An. m. atroparvus and An. quadriannulatus. On the contrary, in the latter two species cells were more responsive to 1-octen-3-ol. In An. arabiensis, responses of stimulus-excited cells were intermediate between those in the anthropophilic and zoophilic species.