After watching hundreds of mosquitoes buzzing around one of their colleagues and collecting 20 million data points, Georgia Tech and Massachusetts Institute of Technology researchers have created a mathematical model that predicts how and where female mosquitoes will fly to feast on humans.
The new study is the first to visualize mosquito flight patterns and provides hard data for improving capture and control strategies. In addition to being a nuisance, mosquitoes transmit diseases such as malaria, yellow fever, and Zika, which cause more than 700,000 deaths every year.
The researchers also designed an interactive, public website to show the paths and behaviors.
The team used 3D infrared cameras to see how the insects moved around inanimate objects based on visual cues and carbon dioxide. Then they put a person in a chamber, dressed him in various shades of clothing, and tracked mosquito trajectories.
The study is published in Science Advances and focused on female Aedes aegypti mosquitoes (also called yellow fever mosquitoes), which are found throughout the southeastern United States, California, and around the world.
Based on their data, the researchers said they don't think mosquitoes swarm because they're following the pack. Each appeared to pick up on the cues independently, then find themselves at the same place at the same time.
"It's like a crowded bar," said David Hu , a professor in Georgia Tech's George W. Woodruff School of Mechanical Engineering and the School of Biological Sciences. "Customers aren't there because they followed each other into the bar. They're attracted by the same cues: drinks, music, and the atmosphere. The same is true of mosquitoes. Rather than following the leader, the insect follows the signals and happens to arrive at the same spot as the others. They're good copies of each other."
The study included three experiments that varied visual cues and carbon dioxide. In the first, the researchers used a black sphere as a target. It attracted the mosquitoes, but only when they were flying toward the object. Once they arrived, they didn't stick around, often fluttering past.
When the researchers swapped the black target with something white and added carbon dioxide, mosquitoes slowly found the source, but only if they were nearby. Hu noticed the insects doing a "double take" before settling in around the source.
Introducing a black sphere and CO2 at the same time proved to be the most irresistible scenario: the mosquitoes swarmed, stayed, and attacked.
"Previous studies had shown that visual cues and carbon dioxide attract mosquitoes. But we didn't know how they put those cues together to determine where to fly," said Christopher Zuo, who conducted the study as a Georgia Tech master's student. "They're like little robots. We just had to figure out their rules."
Once he learned about their attraction to motionless clues, Zuo donned various outfits and stepped into a mosquito chamber. He dressed in all black, all white, or a combination.
Zuo stretched out his arms and let dozens of insects circle him as cameras captured their trajectories. The data was sent to MIT, which determined the mostly likely rules that generated those flight patterns.
The yellow fever mosquitoes flew around Zuo just as if he was an inanimate object. The biggest swarms were around his head and shoulders, the species' typical attraction points.
Luo wore a long-sleeved sweatshirt, pants, and head covering in the chamber. He said he wasn't bitten very often.
The team's interactive website and data-driven model show how mosquitoes turn, speed up, and slow down based on visual cues and CO2. Users can toggle between visual cues and colors, carbon dioxide, both, or neither and see how up to 20 mosquitoes will react. They can also upload an image of their choice as the target.
The researchers hope their findings can lead to better pest control.
"One tactic is using suction traps that rely on steady cues, such as continuous CO2 release or constant light sources, to attract mosquitoes," Zuo said. "Our study suggests using them intermittently, then activating suction at intervals, might be better. That's because mosquitoes don't tend to stick around their target when both clues aren't used at the same time."
Zuo and Hu were joined by mechanical engineering Ph.D. candidate Soohwan Kim. Other co-authors are MIT's Chenyi Fei and Alexander Cohen, as well as Ring Carde of the University of California at Riverside.
