Carbon dioxide, visual information and certain cues from the environment lead mosquitoes to their targets. New research led by a team of scientists from the Georgia Institute of Technology and the Massachusetts Institute of Technology points to the elements that direct a mosquitoes’ flight and their uncanny ability to hone in on people.
The research was conducted with the larger goal of controlling the spread of mosquito-borne infectious diseases such as malaria, dengue and Zika, which claim more than 770,000 lives worldwide each year.
The team of scientists conducted experiments, involving colour-coded clothing, a controlled environment and a couple of striped mosquitoes. They succeeded in deriving a dynamical model governing mosquito flight. They arrived at this model by applying a statistical method based on Bayesian inference to vast amounts of data that recorded mosquito movements.
Bayesian inference is a statistical technique that probabilistically finds the parameters of a plausible model from observed knowledge or data. This probability gets refined as more and more information becomes available. Using this method, the researchers were able to construct a mathematical model that could reproduce experimental results with high precision while compressing mosquito behaviour to fewer than 30 parameters.
“The biggest question was how mosquitoes find their human targets,” explains Cheng-Yi Fei, a postdoctoral researcher at MIT. “There had been previous experimental studies on what cues were important, but few had taken a quantitative approach.”
Charting the Mosquito Flight
The study involved flying female striped mosquitoes into an enclosed space and recording their flight trajectories in 0.01-second increments using two infrared cameras. In total, they obtained over 53 million data points from 20 experiments, with more than 400,000 flight trajectories. This was the largest data set ever obtained in a study that quantitatively measured mosquito flight.
The experiment began by photographing mosquitoes flying around the subjects, who were dressed in dark-coloured clothing. This observation revealed that the stingless mosquitoes were frequently approaching the heads of the subjects. This was the discovery that became the starting point for the entire study.
Dark Matter
Next, the same experiment was carried out with a change of clothing. The subjects wore black on one side of the body and white on the other. The researchers found that although carbon dioxide and body odour were emitted equally from both sides, the mosquitoes’ flight trajectories were concentrated only on the black side. This result, according to researchers, demonstrated that visual stimuli played an important role in the search for targets in a windless environment.
Detailed analysis of mosquitoes flying in an unstimulated space also revealed that flight patterns fall into two main categories. One is an “active state”, in which the mosquito actively explores space while maintaining a speed of about 0.7 m/second, and the other is an “idle state”, in which the mosquito flies as if drifting and using almost no thrust. The idle state is considered to be a preparatory stage for landing, and was observed more frequently near the ceiling of the experimental space.