Laboratory studies on the olfactory behaviour of Anopheles quadriannulatus

The host preference of Anopheles quadriannulatus Theobald (Diptera: Culicidae), the zoophilic member of the malaria mosquito complex Anopheles gambiae Giles, was investigated in a dual-choice olfactometer. Naive female mosquitoes were exposed to CO2, acetone, 1-octen-3-ol, and skin emanations from cows and humans in various combinations. Their behavioural responses were recorded when they had entered one of either upwind traps from where the odours were being released. The mosquitoes did not respond to CO2 when released at human or cattle equivalent concentrations. Too few mosquitoes responded to acetone to allow for a statistical analysis. The combination of CO2+ 1-octen-3-ol was repellent. Cow odour alone was slightly attractive, but there was a synergistic attractive effect of cow odour + CO2. Surprisingly, the mosquitoes were attracted to human odour, and in a choice situation human odour was selected above cow odour + CO2. Anthropophilic An. gambiae Giles s.s. was repelled by cow odour + CO2 in contrast to An. quadriannulatus. In a choice situation, both mosquito species selected human odour above cow odour + CO2. The implications of these results are discussed in the light of recent behavioural data from the field.