Fog and dense gas disrupt mosquito flight due to increased aerodynamic drag on halteres

Chemical insecticide foggers have long been used to control mosquito populations and reduce the spread of malaria, West Nile virus, and dengue fever. In this study, we show that simple fogs of water droplets, devoid of chemicals, are effective at obstructing the flight of Anopheles freeborni mosquitoes. Using high-speed video, we film the flight of mosquitoes in denser-than-air fluids such as fogs produced by household humidifiers and heavy gas. In gases with more than twice the density of air, mosquitoes cannot maintain flight stability, but pitch and roll uncontrollably until they fall to the ground. We here show that the increased drag of denser-than-air flight environments is sufficient to render a mosquito׳s gyroscopic sensors and wingbeat controllers, their halteres, ineffective. Anomalous drag forces are estimated with steady and unsteady drag analyses. We glue masses of 10 ng to each haltere, equivalent to 0.0005% the mass of the mosquito. Mosquitoes with such a minor treatment executed flight patterns, similar to mosquitoes in fog, indicating a mosquito׳s haltere are highly tuned to aerodynamic properties of normal air, making them sensitive to contaminants. The failure of mosquito flight in fog reveals potential new methods for mosquito control that do not require insecticide-laced particles.