Moment-to-moment flight manoeuvres of the female yellow fever mosquito (Aedes aegypti L.) in response to plumes of carbon dioxide and human skin odour.

Odours are crucial cues enabling female mosquitoes to orient to prospective hosts. However, their in-flight manoeuvres to host odours are virtually unknown. Here we analyzed in 3-D the video records of female Aedes aegypti mosquitoes flying in a wind tunnel in response to host odour plumes that differed in spatial structure and composition. Following a brief (~0.03 s) encounter with CO(2), mosquitoes surged upwind and, in the absence of further encounters, counterturned without displacing upwind. These patterns resemble moth responses to encounter and loss of a filament of pheromone. Moreover, CO(2) encounters induced a highly regular pattern of counterturning across the windline in the horizontal (crosswind) and vertical planes, causing the mosquito to transect repeatedly the area where CO(2) was previously detected. However, despite the rapid changes across all three axes following an encounter with CO(2), the angular velocities remained remarkably constant. This suggests that during these CO(2)-induced surges mosquitoes stabilize flight through sensors, such as the halteres and Johnston organs, sensitive to Coriolis forces. In contrast to the instantaneous responses of the mosquito CO(2), a brief encounter with a filament of human skin odour did not induce a consistent change in mosquito flight. These differential responses were reflected in further experiments with broad plumes. A broad homogeneous plume of skin odour induced rapid upwind flight and source finding, whereas a broad filamentous plume of skin odour lowered activation rates, kinetic responses and source finding compared with homogeneous plumes. Apparently, yellow fever mosquitoes need longer continuous exposure to complex skin-odour blends to induce activation and source finding.