Host location byAedes aegypti(Diptera: Culicidae): a wind tunnel study of chemical cues

Abstract

Lactic acid, carbon dioxide and human sweat stimuli were presented singly and in combination to female Aedes aegypti (Linnaeus) within a wind-tunnel system. The take-off, flight, landing and probing responses of the mosquitoes were recorded using direct observation and video techniques. The analyses determined the nature of the response to different stimuli and the concentration ranges within which specific behaviours occurred. A threshold carbon dioxide concentration for taking-off of approximately 0.03% above ambient was detected. Lactic acid and human sweat samples did not elicit take-off when presented alone, however, when they were combined with elevated carbon dioxide, take-off rate was enhanced in most of the combinations tested. Flight activity was positively correlated with carbon dioxide level and some evidence for synergism with lactic acid was found within a narrow window of blend concentrations. The factors eliciting landing were more subtle. There was a positive correlation between landing rate and carbon dioxide concentration. At the lowest carbon dioxide concentration tested, landing occurred only in the presence of lactic acid. Within a window of low to intermediate concentrations, landing rate was enhanced by this combination. At the highest carbon dioxide concentration, landing was however inhibited by the presence of lactic acid. The sweat extract elicited landings in the absence of elevated carbon dioxide. This indicated the presence of chemical stimuli, other than lactic acid, active in the short range. Probing occurred only at low carbon dioxide concentrations and there was no probing when lactic acid alone was tested. There was however probing in the presence of combined stimuli, the level of response seemed to be positively correlated with the ratio of carbon dioxide and lactic acid concentrations.