Transmitted infectious diseases mosquito-borne diseases such as malaria, dengue fever and Zika fever kill more than 770,000 people worldwide each year. Understanding how mosquitoes find people has long been a challenge in controlling the spread of these diseases. However, little is known about how mosquitoes integrate multiple signals, including visual information and carbon dioxide, to approach a target.
In this context, a research team led by the Georgia Institute of Technology and the Massachusetts Institute of Technology it worked automatic derivation of a animated model governing mosquito flight by applying Bayesian inference statistical methods to extensive amounts of data recording mosquito movements.
Bayesian inference is a statistical technique that probabilistically determines the most likely model parameters based on observed data. Using this method, the researchers were able to construct a mathematical model that could reproduce the experimental results with high accuracy, compressing the mosquitoes’ behavior to fewer than 30 parameters.
“The big question was: How do mosquitoes find a human target?” explains Cheng-Yi Fei, a postdoctoral researcher at MIT. “There have been previous experimental studies on what signals might be important, but none of them have been particularly quantitative.”
Mosquitoes have two ways of flying
The research team released two females Aedes aegypti mosquitoes into a closed experimental space and recorded their flight paths with an accuracy of 0.01 seconds using two infrared cameras. The data obtained from a total of 20 experiments exceeds 53 million points and over 400,000 flight paths have been recorded. This represents the largest dataset ever collected for a study to quantitatively measure mosquito flight.
The experiment began by photographing mosquitoes flying around people wearing gloomy clothes. This observation revealed it Aedes aegypti mosquitoes focused their approach on human heads. This was a fundamental discovery that served as the starting point for the entire study.
The researchers then experimented with people wearing black on one side and white on the other. They found that although carbon dioxide and body odor were emitted equally from both sides of the body, the mosquitoes’ flight trajectories were concentrated only on the black side. Although strange at first glance, this result clearly showed that visual stimuli play an vital role in the search for targets in a windless environment.
Moreover, detailed analysis of mosquitoes flying in a stimulant-free environment showed that their flight patterns can be broadly divided into two types. One was the lively state, in which they actively explored space, maintaining a speed of about 0.7 meters per second. The second was the idle state in which they flew with almost no thrust. The idle state is believed to be a stage of preparation for landing and was more frequently observed near the ceiling of the experimental space.
Analysis of mosquitoes’ responses to visual stimuli showed that mosquitoes are attracted to gloomy objects and snail-paced down when they come within about 40 centimeters. However, without additional cues such as body odor, humidity, or heat, the mosquitoes often flew away even after approaching their target. This suggests that visual stimuli alone are not sufficient to induce landing and blood sucking.
The response to carbon dioxide sources was completely different. Mosquitoes that came within about 40 centimeters of the carbon dioxide source suddenly slowed down to 0.2 m/s and began flying chaotically, swaying with no clear direction. Numerical simulations also showed that mosquitoes can detect carbon dioxide concentrations as low as 0.1 percent, and their detection range extends to about 50 centimeters from the source.
Moreover, the mosquitoes’ response changed even more dramatically when visual stimuli and carbon dioxide were simultaneously administered. Mosquitoes began to circle around the target, and significantly more mosquitoes clustered near the target than when either stimulus was used alone.