Hundreds of hungry mosquitoes, a student volunteer and a mesh suit helped us figure out how these deadly insects reach their targets

“Four minutes is too long.”

This is the note that undergraduate student Chris Zuo sent me with photos of countless mosquito bites on his bare skin. This complete massacre was not the result of a camping trip gone wrong. He had spent this limited time in a room with 100 hungry mosquitoes while wearing nothing but a mesh suit that was thought would have protected him.

Thus began our three-year journey to understand the behavior of a deceptively simple insect, the mosquito. This may sound like a sadistic teacher’s plan, but, in reality, we did everything by the rules. Our university’s institutional review board approved our procedures, ensuring that Chris was safe and not under any restraints. The mosquitoes were disease free and native to our home state of Georgia. And this session resulted in the first and last bites received during the study.

In addition to my role as a student torturer, I am an author and professor at Georgia Tech with over 20 years of experience studying animal movement.

Mosquitoes are the most dangerous animal in the world. The diseases they carry, from malaria to dengue, cause more than 700,000 deaths per year. More people have died from mosquitoes than from wars.

The world spends $22 billion a year on billions of gallons of insecticides, millions of pounds of larvicide, and millions of insecticide-treated bed nets – all to combat a tiny insect that weighs 10 times less than a grain of rice and has just 200,000 neurons.

Yet people are losing the war against mosquitoes. These insects are evolving to thrive in cities and spreading disease more quickly with climate change. How can such simple animals find us so easily?

Scientists know that mosquitoes have very poor eyesight and rely on chemical signals to compensate for it. However, knowing what attracts a mosquito is not enough to predict its behavior. You may know that a heat-seeking missile is attracted to heat, but you still won’t know how a missile works.

Enter Chris and his self-sacrifice in the mosquito room. By tracking the flight of many mosquitoes around it, we hoped to determine how they made decisions in response to its presence. Understanding how mosquitoes respond to humans is a first step to controlling them.

How Mosquitoes Focus on Their Meal

Out of 3,500 species of mosquitoes, more than 100 species are classified as anthropophilic, meaning they prefer humans for lunch. Some species of mosquitoes will find a person among a whole herd of cattle to suck human blood.

This is quite an achievement considering that mosquitoes are little flyers. They stop flying in a light breeze of 2 to 3 mph, the same air speed generated by the swing of a horse’s tail. In calmer conditions, mosquitoes use their tiny brains to track human warmth, humidity and odors carried downwind.

Carbon dioxide, a byproduct of respiration in all living animals, is particularly attractive. Mosquitoes notice carbon dioxide as well as you notice the stench of a full dumpster, detecting it up to 30 feet from a host, where concentrations drop to a few parts per million, like a few cups of dye in an Olympic swimming pool.

Mosquitoes’ vision isn’t much help when they’re looking for their next blood meal. Their two compound eyes have several hundred individual lenses called ommatidia, each about the width of a human hair. They produce a somewhat blurry mosaic or pixelated image. Thanks to the laws of optics, mosquitoes can only discern an adult-sized human from a few meters away. With their vision alone, they cannot distinguish a human from a small tree. They inspect every dark object.

Collection of flight path data

The challenge of studying mosquito flight is that, like teenagers who talk trash, most of what they do is meaningless noise. Mosquitoes flying in an empty room largely randomly change the speed and direction of their flight. We needed many flight paths to reduce noise.

One of our collaborators at the University of California, Riverside, biologist Ring Cardé, told us that in the 1980s, scientists conducted “bite studies” by stripping down to their underwear and swatting mosquitoes that landed on their naked bodies. He said nudity avoids confusing variables, such as the color of a shirt’s fabric.

Chris and I looked at each other. Sit naked and wait to become prey for mosquitoes? Instead, we designed the mesh suit that Chris originally wore in the mosquito room. But after seeing Chris’ bites, we needed a better solution.

Instead, Chris washed the long-sleeved clothes with unscented detergent and wore gloves and a mask. Fully protected, Chris just had to wait while a swarm of mosquitoes invaded him.

The US Centers for Disease Control and Prevention introduced us to the Photonic Sentry, a camera that tracks hundreds of flying insects in a room simultaneously. It records 100 frames per second at 5mm resolution for a space like a large studio. In just a few hours, Chris and another graduate student, Soohwan Kim, generated more data on mosquito flights than had been measured before in human history.

Jörn Dunkel, Chenyi Fei and Alex Cohen, our mathematician collaborators at MIT, explained to us that the geometry of Chris’ body was still too complicated to study the mosquitoes’ reactions. Mathematicians excel at simplifying complex problems down to their essence. Chenyi suggested we go easy on Chris – why not replace him with a simple mannequin: a black Styrofoam ball on a stick combined with a carbon dioxide canister.

Over the next two years, Chris filmed the mosquitoes mercilessly circling the Styrofoam mannequins. Then he vacuumed up the mosquitoes, trying not to get bitten.

Decipher the trajectories

A mosquito flies like an airplane: it turns left or right, accelerates or brakes. We determined a mosquito’s flight behavior based on its speed, location, and direction relative to the target, as the first step in creating our behavior model.

Our confidence in our behavioral rules increased as we read more trajectories, ultimately using 20 million mosquito positions and velocities. This idea of ​​incorporating observations to support a mathematical hypothesis is a 200-year-old idea called Bayesian inference. We illustrated the behavior of the mosquitoes that we had observed in a web application.

Using our model, we showed how different targets cause mosquitoes to fly differently. Visual targets cause flybys, where mosquitoes fly over the target. Carbon dioxide causes double takes, where mosquitoes slow down near the target. The combination of a visual cue and carbon dioxide creates high-speed orbit patterns.

Until now, we had only used experiments with polystyrene spheres to train our model. The real test was whether one could predict mosquito flights around a human. Chris returned to the room, this time wearing white clothes and a black hat, making himself a target. Our model successfully predicted the distribution of mosquitoes around it. We identified danger zones, where there was a high chance of a mosquito circling around.

Predicting mosquito behavior is a first step in thwarting them. In mosquito-prone areas, people design homes with features that prevent mosquitoes from following human signals and entering. Similarly, mosquito traps suck in mosquitoes when they get too close but still allow between 50% and 90% of mosquitoes to escape. Many of these designs are based on trial and error. We hope that our study will provide a more accurate tool for designing methods to capture or deter mosquitoes.

When Chris’ mother attended his master’s defense, I asked her what she thought about her son using himself as mosquito bait. She said she was very proud. Me too – and not just because I’m relieved Chris didn’t ask me to take his place in the mosquito room.

This article is republished from The Conversation, an independent, nonprofit news organization that brings you trusted facts and analysis to help you make sense of our complex world. It was written by: David Hu, Georgia Institute of Technology

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David Hu does not work for, consult, own shares in, or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond his academic appointment.