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Mosquitoes

National Museum of American History

Mosquitoes Preserved in Plastic

National Museum of American History

Kill All the Mosquitoes?!

Smithsonian Magazine
New gene-editing technology gives scientists the ability to wipe out the carriers of malaria and the Zika virus. But should they use it?

Can Mosquitoes Fight Malaria?

Smithsonian Magazine

We may not have flying cars, and our shower curtains inevitably turn moldy after several months, but, to their credit, scientists can engineer a mosquito resistant to Plasmodium, the pathogen that causes malaria in people. Molecular biologists now can manufacture a gene that blocks the infection from fully forming, and inject it into a batch of mosquito eggs. To track the gene's success over generations, the researchers include a marker that, when active, gives each altered offspring a bulging pair of neon green eyes.

The idea behind these tiny green lights was that they might help researchers control the disease that kills more than a million people a year—particularly in impoverished nations. This notion gained strength a few years ago, when a group of researchers found that mosquitoes carrying Plasmodium laid fewer eggs and lived shorter lives than those that buzzed about infection free. It stood to reason, then, that genetically altered insects—called "transgenic" mosquitoes—would, in the long-run, fair better than their wild cousins.

Inside labs around the world, however, this logic did not always hold true. Scientists filled cages half with wild and half with transgenic mosquitoes. Several life cycles later, they censused the insect population and found that, at best, the cages remained half-filled with green eyes. More often, the wild eyes had it.

Recently, a group of researchers at Johns Hopkins University tried again—with a twist. Instead of feeding the mosquitoes regular blood, as the previous experiments had, the Hopkins group fed the insects blood infected with Plasmodium. "Indeed, as generations passed, the proportion of transgenic mosquitoes increased," says Marcelo Jacobs-Lorena, a co-author of the study, which appeared in the Mar. 19 Proceedings of the National Academy of Science. After nine generations, some 70 percent of the population flashed those glowing greens. "Under these conditions," he says, "they were fitter."

Among infectious disease researchers, such a finding would seem packed with promise. "The first reaction is, well, here you go," says Jacobs-Lorena. But the excitement is tempered by several reservations. The first is whether the work could translate to human blood (in the experiment, the mosquitoes fed on infected mice). Jacobs-Lorena believes it would, but even so, releasing genetically altered insects into the wild could also let loose a furious ethical debate.

A more immediate problem exists, however. In wild populations, only 10 to 20 percent of mosquitoes transmit the disease, says parasitologist Hilary Hurd of Keele University, in England, who was not affiliated with the study. Sure, green eyes become the norm in populations that begin with an even roster of altered mosquitoes. But, when outnumbered greatly, could enough malaria-resistant mosquitoes pass on their genes to make a difference? "I am doubtful," says Hurd, a skepticism echoed by Jacobs-Lorena.

It would help matters if some force could drive the desired gene through the population. "That's the biggest remaining burden," says Jacobs-Lorena, "to find this so-called 'drive mechanism.'" Relief for this burden could be getting closer—despite coming from a lab across the country studying not mosquitoes but fruit flies. A group of researchers in California has found a way to make certain genes spray through a population at a rate greater than chance.

Put generally, the highly technical method "uses some trick to cause the death of a chromosome that doesn't carry the element"—in this case, the malaria-resistant gene—says Bruce A. Hay of the California Institute of Technology, who co-authored the study published in the Apr. 27 Science. The researchers call this trickster chromosome Medea, named for Euripides' tragic heroine who killed her own children to spite the husband who abandoned her. When Hay and his colleagues infused some fruit flies with Medea and put them in a cage with unaltered flies, every insect showed signs of the element within 10 or 11 generations. "The average fitness of wild type chromosomes goes down whenever Medea is in the population," he says.

The two studies already have struck a romance: "I think this is quite promising," says Jacobs-Lorena. "If one can transfer this technology to mosquitoes, that could be quite powerful." Researchers would have to create a tight lock between Medea, the driver, and the transgene, the passenger carrying the critical briefcase. "If one could do this in an area relatively quickly, with the driver helping to move [the transgene] rapidly, you have an opportunity to break the cycle of infection," says Hay. "Once Plasmodium has nowhere to replicate, then it's gone."

Those are two big "ifs," and the researchers say they have several generations of studies to go through before removing any doubt. But in time—perhaps in as few as five years, says Hay—the two might even have themselves a swarm of bugs with beautiful green eyes. A healthy swarm.

Mosquitoes Can Smell Your Sweat

Smithsonian Magazine

When a mosquito lands and your arm and starts taking a drink, it's not just an unhappy accident. Mosquitoes use an array of chemical neuroreceptors to track down their next blood meal. Now, researchers have identified a key receptor that detects the lactic acid in human sweat, a finding that could eventually help people avoid becoming fast food for the insects.

In particular, researchers looked at Aedes aegypti, one mosquito species that has adapted to dining on human blood and also happens to be a transmitter of many tropical diseases, according to the new study in the journal Current Biology. When mosquitoes hunt down human blood to complete their breeding cycle, they do it pretty methodically.

First, reports Deborah Netburn at The Los Angeles Times, carbon dioxide receptors alert them to the presences of a mammal from up to 30 feet away. Coming in for a closer look, it’s believed another group of receptors let the mosquito know that the animal is human. A closer inspection of body heat confirms that we are living, breathing animals full of tasty blood. Once the mosquito lands, receptors on her legs confirm that her prey is indeed human telling her it’s alright to plunge her syringe-like proboscis into your flesh.

Matt DeGennaro, a study co-author and mosquito neurobiologist at Florida International University, tells Netburn all those neuroreceptors are a cacophony of signals telling the mosquito to feast.

“At this moment they are experiencing all the cues at once, and it must be very intoxicating,” he says. “The mosquito is thinking, ‘I don’t care if you are going to swat me, I’m going to bite you.’”

Researchers have long hypothesized that there must be a receptor that helps the mosquitoes home in on the scent of humans in particular. In previous research, DeGennaro and his colleagues used CRISPR/Cas-9 gene-editing technology to remove one suspected olfactory receptor, called Orco, from a population of mosquitoes and then the team watched how they behaved.

While the insects had trouble differentiating between humans and other animals, they were still attracted to vertebrates. Also, the loss of Orco meant the bugs lost their aversion to DEET, the most commonly used and effect mosquito repellent on the market.

That meant the key receptor was still to be identified. For this new study, they focused on a receptor called Ir8a, found in the antenna of the insect. Removing that receptor from the mosquitoes genes led to insects that didn’t respond to the scent of lactic acid, a main component unique to human sweat as well as other chemicals that make up human odor. Their ability to sense carbon dioxide and heat, however, remained intact.

The study provides sound evidence that mosquitoes cue in on humans by using a suite of neuroreceptors, confirming the long-held hypothesis. “People have been looking for more than 40 years,” DeGennaro says in Cell Press statement. “Even in the 1960s, scientists knew it was sweat and lactic acid, but no one knew how those were sensed. Back then, mosquito scientists didn’t have genetics.”

Knocking out Ir8a isn’t perfect, but it does have a pretty major impact on mosquito behavior. “Removing the function of Ir8a removes approximately 50 percent of host-seeking activity,” DeGennaro says in a different statement. “Odors that mask the Ir8a pathway could be found that could enhance the efficacy of current repellents like DEET or picaridin. In this way, our discovery may help make people disappear as potential hosts for mosquitoes.”

It’s likely that Ir8a isn’t the only receptor that helps mosquitoes find us, Laura Duvall of The Rockefeller University in New York tells Nell Greenfieldboyce at NPR. “Mosquitoes are so good at finding us because they’re paying attention to many different components of human odor — including the acidic volatiles that we produce,” she says.

But the more we understand what chemicals the insects are paying attention to, the better we can become at thwarting them. For instance, we could make better traps that lure the blood-suckers away from our backyards or create a spray that masks the smell of human sweat.

Keeping mosquitoes away isn’t just a matter of keeping our backyards tolerable. In many parts of the world, mosquitoes are vectors of diseases like malaria, dengue and yellow fever, leading to about 725,000 human deaths each year.

This “Sweaty” Billboard Kills Mosquitoes

Smithsonian Magazine

Zika virus is spreading like a swarm of mosquitoes—since 2007, the World Health Organization reports, 66 countries have experienced transmission of the disease, and the WHO recently declared the microcephaly and other neurological disorders it’s believed to cause a public health emergency. But one group of Brazilian marketing agencies think they can stop its spread with an unlikely tool, the BBC reports: A billboard that secretes human-like “sweat,” then traps and kills mosquitoes.

It’s called The Mosquito Killer Billboard, and its premise is both disgusting and deceptively simple. On the device’s website, which includes free blueprints for those who might want to make one of its own, its inventors explain the premise. The billboard emits a solution containing carbon dioxide and lactic acid that mimics human sweat and breath, attracting mosquitoes from a distance of up to nearly two and a half miles. Fluorescent lights make it even more attractive to mosquitoes and take advantage of the bugs’ need for a fixed point of light to navigate. When mosquitoes make it to the billboard, they’re lured inside, where they dehydrate and die.

So far, two billboards (appropriately showcasing a Zika awareness message) have been installed in Rio de Janeiro. The BBC reports that the collective behind the anti-mosquito ads won’t be selling ad space on the billboards. But at least one expert worries that the innovation could backfire. Chris Jackson, an ecologist and pest control specialist at the University of Southampton, told the BBC that since the billboards are so good at sucking mosquitoes in, they could actually endanger people in proximity to the billboard who could become the target of hungry bugs.

The idea is just one of a spate of creative solutions coming out in the wake of a virus that could infect up to four million people by the end of the year. Earlier this month, Massachusetts General Hospital’s Consortium for Affordable Medical Technologies (CAMTech) hosted a Zika Innovation Hackathon that yielded ideas like a mobile app that helps hunt down mosquito larvae and a water buoy that automatically dispenses larvicide.

Over 50 engineers, global health specialists and students participated in a similar event at Johns Hopkins a few days later, and the ideas they came up with are just as brilliant and weird. Potential Zika solutions included mosquito trap surveillance systems, Zika-proof clothing, sporting event banners that also scare off bugs and even “Never Will Bite,” a body and laundry soap that could one day make mosquito prevention part of people’s everyday routine.

While a single billboard or bar of soap is unlikely to stop Zika’s deadly march any time soon, every prevented bite represents one less potential victim of the virus. And with mosquitoes implicated in the spread of other deadly diseases, like dengue and malaria, there’s no time like the present to take full advantage of human ingenuity in the war against mosquito-borne illness.

Mosquitoes' Sperm Can Detect Smells

Smithsonian Magazine

Female mosquitoes have a powerful olfactory system—it helps them sniff out sweaty victims and potential mates. Their "odorant receptors," the special chemical sensors that detect smells, are found on their antenna. But, according to new research, male mosquitos—or at least their gametes—rely on this sense, as well. These same odorant receptors are also present on the insect's sperm. 

The researchers were quite surprised at this discovery. They were originally clued in on the receptors' existence when they found molecules in males that are normally associated with females. Narrowing down the hunt for those receptors, they pinpointed them as occurring in the testes. While testing mosquito sperm's reaction to different chemicals, they found that the sperm began to excitedly flail about when it came into contact with certain chemical concotions. The sperm tails, it turned out, contained odorant receptors. 

Female mosquitoes store sperm inside thier body, in a special container called the spermathecae, after mating. There, the sperm waits dormant until the females find a prerequisite blood meal for producing her eggs. The researchers think that the receptors on the sperm might chemically clue those cells in that it's time to kick into action, once all the pieces are in place for fertilization. "There are reports that within one day after insemination, the sperm begin swimming around in the spermathecae," the researchers said in a statement. "There must be one or more signals that activate this movement and our findings suggest that odorant receptors may be the sensor that receives these signals."

The team decided to take a look at a few other insect species, and found that both wasp and fruit fly sperm also carry their own odorant receptors. Given the essential role smell seems to play in ensuring the next generation of disease-carrying mosquitoes or insect pests comes into being, the researchers wonder if the sperm might hold a clue for controlling some of those populations. 

Here, the researchers talk a bit more about their work: 

Genetically-Modified Mosquitoes Could Help Fight Malaria

Smithsonian Magazine

From yeast to salmon, gene-editing technology has made tremendous leaps in the last few years.

Now, two unrelated groups of researchers say they have developed new ways to fight the spread of malaria by genetically modifying the mosquitos that spread the deadly parasite. One solution prevents mosquitos from being infected with malaria and the other makes infected mosquitos infertile.

Malaria is easily one of the most deadly diseases in the world, killing 500,000 people and sickening hundreds of millions more every year, according to the World Health Organization. While there are medications to treat malaria, the best way to prevent it is to stave off mosquito bites.

In recent years, however, researchers started experimenting with ways to prevent malaria transmission at the source, using a new gene-editing technique called CRISPR, which allows scientists to edit genetic sequences rapidly and precisely.

Researchers at the University of California just published one possible solution: Insert a modified gene into mosquitoes that makes them incapable of carrying the malaria parasite, Maggie Fox reports for NBC News.

"This opens up the real promise that this technique can be adapted for eliminating malaria," study co-author Anthony James tells Fox. "We know the gene works. The mosquitoes we created are not the final brand, but we know this technology allows us to efficiently create large populations."

Not only did the mosquitoes in the study become malaria-resistant, but they were able to pass the gene to 99.5 percent of their offspring. That means that within a few generations, they could spread the gene to wild mosquitoes, effectively creating a natural barrier to malarial infection, Fox writes.

Meanwhile, scientists at the Imperial College London were working on a similar CRISPR project. But while the scientists at the University of California were trying to alter the mosquitos, this team wanted to wipe them out, Michelle Roberts reports for the BBC.

Led by molecular biologist Tony Nolan and vector biologist Andrea Crisanti, the mosquitoes created by London-based researchers could still carry and transmit the parasite. But they were infertile, according to their study published in Nature Biotechnology.

If the bugs were allowed to interbreed with wild mosquitoes, the species could eventually be driven into extinction, Fox writes. While some experts are worried that wiping out one species of mosquitoes could harm the environment, Nolan argues that the species his team is experimenting with is just one of 800 in all of Africa and eliminating it wouldn’t upset the balance of nature.

While it will be decades before anyone might consider releasing any of these mosquitoes into the wild, these studies raise some intriguing questions about CRISPR’s potential.

A Blood-Monitoring Device Inspired by Mosquitoes

Smithsonian Magazine

The mosquito is responsible for more deaths than any other animal on earth, thanks to its habit of spreading diseases like malaria and dengue fever. But studying the mosquito’s bloodsucking jab might just help scientists save lives at risk from another disease: diabetes.

Researchers at the University of Calgary in Canada have developed an “e-mosquito,” a device that pierces the skin like a mosquito’s mouthparts and extracts a tiny amount of blood from a capillary to use for glucose testing. Embedded in a watch-like band, the e-mosquito can be programmed to automatically prick the skin multiple times a day and analyze the results, relieving people with diabetes of the need to test their blood glucose in the traditional way, by sticking their finger and wiping the blood on a test strip. People with diabetes have to monitor their blood sugar levels carefully; people with type 1 diabetes sometimes prick their fingers up to eight times a day.

“The idea is to get rid completely of finger-pricking and the logistics around finger-pricking, which are really bothersome,” says Martin Mintchev, the senior researcher on the project. “For children, in particular, and the elderly, and blind people, this is a very cumbersome exercise several times a day.”

Mintchev and his team have been working on the e-mosquito for a decade. The material they originally used for the actuator – the part of the device that moves the needle – made it large and bulky. But the invention of a new material called shape memory alloy, a composite metal that contracts or expands with electric current, proved a boon. A tiny amount of shape memory alloy can provide a strong force, which allowed the team to miniaturize the device to its current watch-like size.

“It can penetrate the skin with much greater force, and greater controllability, and a minimal use of electricity,” Mintchev says. Plus, like a mosquito bite, it's almost painless.

A rendering of the construction of the e-mosquito. (University of Calgary)

The current prototype consists of a “watch” top with the actuator, a battery, and LED display and several other components, with an attached bottom cartridge with the needle and test strips. Though the current prototype fits on the wrist, in theory the device could be strapped almost anywhere on the body. There will be challenges before the device is ready for the market, though. Right now, while the e-mosquito can reliably hit a capillary, it doesn’t always bring enough blood to the surface for testing. In this sense, it’s truly similar to a mosquito, which rarely leaves behind a pool of blood on the surface of the skin. Mintchev and his team could equip the device with a larger needle, but that would defeat the idea of the device being tiny and painless. So what they hope to do instead is develop a needle that doubles as a sensor. The needle would penetrate the skin and the sensor would check the blood while still embedded, then transmit the results wirelessly.

“The technology of today has the ability to do this,” Mintchev says. “It requires a bit more work from us, of course.”

They’re also interested in seeing whether the device can work alongside an artificial pancreas, a device which continuously and automatically monitors glucose levels and delivers insulin. The first artificial pancreas was approved by the FDA last year; Mintchev and his team wonder if the e-mosquito technology could somehow be combined with newer models to provide better continuous monitoring.

Mintchev says a consumer-ready e-mosquito might be on the market in as little as three years, depending on FDA approval. Right now he estimates the cost of using the device as about twice as much as using traditional finger-pricking and glucose strip technology. But with time that cost may go down, he says.

“I’m sure that when mass produced it will become really competitive to traditional finger pricking,” he says.

A device that helps people with diabetes eliminate finger-pricking has been something of a holy grail for scientists. Many people with diabetes need to test their glucose every few hours, even during sleep. Apple is said to be secretly conducting feasibility trials of an optical sensor that can measure glucose levels noninvasively by shining a light through the skin, reportedly pouring hundreds of millions of dollars into the project. Google is working on its own continuous glucose monitor. But developing successful continuous glucose-monitoring devices, invasive or not, is a notoriously difficult endeavor. A former diabetes industry consultant, John L. Smith, has written an entire book on the failures of various continuous glucose-monitoring technologies, in which he describes tiny needle technologies like e-mosquito as “[a] recurrent technological theme” that has been tried many times over the years but has yet to bear fruit.

For the sake of the 1.25 million Americans with type 1 diabetes, here’s hoping the e-mosquito has a more successful outcome. 

Insecticide-Treated Nets May Create Super Mosquitoes

Smithsonian Magazine

Evolution’s mechanisms keep life on Earth mutable, adaptable and alive. But it also presents a stumbling block when we humans attempt to control nature. When confronted with penicillin, bacteria develop resistance to the formerly miraculous drug and its successors. When challenged repeatedly with the same potent herbicides, weeds become dreaded superweeds. Now, our efforts to drive back malaria-carrying mosquitoes have created bloodsuckers unaffected by insecticides. 

Since 2000, deaths from malaria worldwide have fallen by 47 percent, according to the World Health Organization’s World Malaria Report. Much of that success in sub-Saharan Africa, where the brunt of that toll is exacted, can be attributed to the use of insecticide-treated nets. The Guardian reports that access to such nets in the region rose from 3 percent in 2002 to 49 percent in 2013. The article, written in December, states that the WHO report "estimates that 214m long-lasting insecticidal nets will have been delivered to the area by the end of this year, bringing the total number distributed in the area over the past two years to 427m."

That kind of firepower gets met by the inevitable mosquito march for survival. The malaria-carrying mosquito species Anopheles coluzzii has apparently interbred with another species Anopheles gambiae. The hybrids carry genes that give them resistance to the most commonly used insecticides, reports Arielle Duhaime-Ross for The Verge

Alarmingly, the rise of insecticide-treated nets in Mali coincides neatly with the development of this resistance, researchers found. They published their work in Proceedings of the National Academy of Sciences U.S.A.

It could be that the hybrid mosquitos who happened to have specific mutations were better able to survive and proliferate despite the nets. "[A] man-made change to the environment — the use of nets — has actually driven hybridization between two species, ultimately leading to an 'improved' mosquito," one of the study’s authors, Gregory Lanzaro of the University of California, Davis, told The Verge. Duhaime-Ross writes:

The findings shouldn’t cause anyone to stop using nets in areas with high rates of malaria; nets are still widely considered the frontline tool of malaria control. But Lanzaro believes that there's an urgent need for new methods for malaria mosquito vector control. Scientists are exploring the use of bacteria to kill mosquito larvae, Lanzaro says. And "work is underway to use genetic methods to kill or alter mosquitoes."

Epidemiologists had predicted this development years ago and urged the WHO to come up with strategies to address and even preempt resistance. Declan Butler reported for Nature in 2011 that those recommendations include alternating what types of insecticides are sprayed, using combinations of sprays and developing new classes of insecticides. 

The news—along with reports that Ebola’s presence may complicate malaria eradication efforts in West Africa—only serves to underscore the difficulty of combating diseases. Just when we think we’ve found an exploitable weakness, evolution changes the game.

Artist's Brook, Hoit Sketching, Mosquitoes Biting Furiously

Cooper Hewitt, Smithsonian Design Museum
Grassy bank at right with artist sketching under a tree. Stream with wooden bridge, center, and tree at left.

Saltmarsh Mosquito

NMNH - Education & Outreach
This object is part of the Education and Outreach collection, some of which are in the Q?rius science education center and available to see.

Why Some Summers Are So Appealing For Mosquitoes

Smithsonian Magazine

As you pack your bags for the cottage or campground this weekend, don’t forget to bring light clothes with long sleeves — and a truckload or two of insect repellent. Spring has come and gone, so welcome to mosquito season.

How much we enjoy summer in North America depends a lot on how many mosquitoes there are waiting for us outside. Their bites are itchy and their drone annoying, but there’s also concern that mosquitoes carrying dangerous diseases are knocking on our door.

So what makes some years worse than others?

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You don’t have to be an entomologist to notice that the mosquito population size can vary from year to year and place to place. Last June, I couldn’t set foot outside my Ottawa home without being bitten. Meanwhile, Winnipeg was experiencing its lowest mosquito count in four decades.

This year is far from mosquito-free, but I can at least enjoy peace for about 10 minutes before they find me.

What causes mosquito populations to balloon and shrink? In short, it’s a combination of weather and climate — mosquitoes are very sensitive to their environment.

Will your weekend be itchy or not? (Shutterstock)

Temperature and rainfall are two major predictors of mosquito abundance, and this is for a good reason: These two factors have a massive effect on their survival and ability to reproduce.

How much it rains at one time, when it rains, how long a cold or warm spell lasted and when it happened all matter when it comes to predicting what kind of mosquito season lies ahead.

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Mosquitoes, like most insects, are cold-blooded, or ectothermic. Unlike us, their body temperature closely matches the temperature of the environment (air or water) around them. If it is cold outside, they are cold. If it is warm outside, they are warm. Any time spent outside of their comfort zone can slow or stop their development or even cause them to be injured and die.

In order for most mosquito larvae to grow, temperatures need to be above a threshold, which varies, depending on the species, but is typically around seven to 16 degrees Celsius.

Since the larvae are entirely aquatic, they also need a source of standing water (like your flower pot) that will remain until they are ready to emerge as adults.

This means cold or dry conditions that hit at the right time during larval development in the spring or summer can drastically reduce the number of adult mosquitoes looking for a meal a week or two later.

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We love to hate mosquitoes, but the vast majority of mosquito species do not directly impact our lives.

Mosquitoes, like most insects, are outrageously diverse: There are more than 3,000 species of mosquitoes buzzing about on this planet, and only a handful of those species actively hunt humans.

And even then, only female mosquitoes feed on blood. The much more reasonable males instead drink flower nectar.

Unfortunately, some of these mosquito species are also far from being just a mild annoyance, as they can carry dangerous diseases. In Canada and the United States, we often hear about the threat of West Nile virus, which is carried by local mosquito species and can lead to serious health complications like coma and paralysis in a minority of cases.

One of the best predictors of West Nile infection rates in Ontario is the minimum temperature reached during February. If the coldest temperatures in February are warmer than usual, more people become infected with West Nile virus during the summer months.

In tropical regions, people instead contend with malaria, yellow fever, dengue, chikungunya and Zika viruses. These viruses are all spread by mosquitoes, are severely debilitating and cause hundreds of thousands of deaths each year.

When Hurricane Harvey hit Texas in September 2017, the flooding increased the mosquitoes’ breeding habitat. So, the state sprayed 240,000 hectares around Houston to help prevent an increase in mosquito-borne disease.

The fact that mosquitoes carry these diseases, rather than the mosquitoes themselves, led the Gates Foundation to label mosquitoes the deadliest animals on the planet.

Two of the worst offenders for spreading disease are the yellow fever mosquito (Aedes aegypti) and the Asian tiger mosquito (Aedes albopictus), which typically live in tropical and subtropical regions where it stays warm and humid. The range of these mosquitoes also extends well into the continental U.S., particularly in the southern and eastern states. However, they simply cannot survive northern climates with long and cold winters.

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Suitably low winter temperatures typically keep tropical and subtropical insect species from becoming permanently established in areas closer to the poles with cold winters. Over the past few decades, however, climate change has led to documented changes in insect distribution patterns, including the collapse of southern range limits of bumblebees and the northward movement of many insect ranges.

As winters become more mild, the northern limits of mosquito ranges may also be shifting. Movement of the northern range limits are thought to happen because milder winters allow species that can’t usually hack it in the cold to squeak through winter alive, reproduce and establish themselves in a new location.

The Asian tiger mosquito, which can transmit the Zika virus, has been spotted in southern Ontario in Canada. (Shutterstock)

Mosquito trapping programs are active around the globe, precisely because monitoring and responding to mosquito populations is critical to global health. In the last few years (2016-2018), adults of both the yellow fever mosquito and the Asian tiger mosquito were found in Windsor, Ont. (near the southernmost point of Canada), which suggests that these dangerous vectors could be a serious health concern in northern climates in the future.

Thankfully, none of the individual mosquitoes caught in Windsor have tested positive for any viruses.

In an era of climate change, it’s increasingly essential that we understand what environmental factors determine where insects can and will live, and how well they do. Understanding how insects respond to climate is absolutely critical to our food security and global health.

Only when we are armed with this information can we accurately predict the spread of invasive agricultural pests or disease vectors, like the bloodsucking mosquitoes that even entomologists despise.

Feeding Mosquitoes Diet Drugs Makes Them Stop Biting

Smithsonian Magazine

While it sometimes seems like mosquitoes swarm humans simply to make our lives miserable, they actually ruin our evening strolls and barbecues because they’re hungry. A female mosquito needs to slurp up a belly full of blood to produce her clutch of eggs and her hunger hormones drive her to seek out bare arms and ankles.

But Thomas Lewton at NPR reports that a group of researchers have come up with a novel solution for mosquito control: by restricting the insects’ hunger using diet drugs, they’ve found they can keep the pests from bugging people.

Neurobiology researcher Leslie Vosshall of Rockefeller University, co-author of a new study in the journal Cell, and her team noticed that after taking a blood meal, female mosquitoes didn’t seem interested in feeding for several days afterwards. Since hunger follows the same hormonal pathways in many species, they decided to see if human diet drugs could quiet the mosquitoes’ urge for blood. In particular, reports Matthew Warren at Nature, the team suspected neuropeptide Y receptors (NPY), which are part of the food-seeking pathway for many species including humans, might be involved, so they chose drugs that target NPY.

“On a lark we thought, ‘Let’s go for it. Let’s do the craziest experiment possible and get some human diet drugs and see if they work on mosquitoes,’” Vosshall tells Lewton. “It was surprising that it worked so well.”

To study the effects of the drugs, the team mixed powdered diet drugs with a solution containing the molecule ATP found in most animals that mosquitoes are strongly attracted to, and fed it to female Aedes aegypti mosquitoes, reports NPR’s Lewton. They then presented the mosquitoes with bare human arms and even tempted them with a previously worn nylon stocking, both of which would normally attract large number of the bloodsuckers. But the mosquitoes remained uninterested in food for days after drinking the diet solution.

But that was only half the study. The team then sought to find out which protein in the mosquitoes was reacting with the drug, causing them to feel full. Nature’s Warren reports they cultivated 49 different protein tissues found in the insects and looked at which reacted to the drug. One in particular, the NPY-like receptor 7 (NPYLR7), stood out from the rest. The team then used CRISPR gene-editing techniques to create a mosquito that could not produce NPYLR7. The diet drugs had not impact the gene-edited mosquitoes, suggesting that receptor is where the appetite suppressing action is happening.

But using a human diet drug to control mosquitoes won’t fly outside the lab. First, it would be unsafe to humans and other animals to release those chemicals into the environment. And second, the patents for those diet drugs are owned by pharmaceutical companies, meaning it's unlikely any useful compound inspired by the drugs could be manufactured cheaply. So the team went through a high-speed screening of 265,000 compounds to find ones that would activate the NPYLR7 receptor. Out of that, they found 24 good candidates and one, compound 18, that worked best. Like with the diet drugs, after being exposed to compound 18, the mosquitoes lost interest in biting humans.

“When they’re hungry, these mosquitoes are super motivated. They fly toward the scent of a human the same way that we might approach a chocolate cake,” Vosshall says in a press release. “But after they were given the drug, they lost interest.”

It will take lots of time before compound 18 is ready for primetime, if it makes it to market at all. The team envisions some sort of feeders where the female insects would drink the chemical-laden solution rather than blood and stop biting for several days. It’s also possible that the same chemical could work on ticks and other insects that feed on humans.

Vosshall says this approach has some advantages. Other techniques—like releasing sterilized male mosquitoes or genetically modified males, which leads to the local extinction of the mosquitoes—could have adverse impacts on the environment. The diet drug method has the advantage of limiting the population of mosquitoes without eradicating them and doing unintended harm to local ecosystems.

But Vosshall is knows her new method isn’t a silver bullet. “No single approach has ever worked and will ever work by itself. So we view our idea as a method of behavioral control that can integrate with the other ideas floating around, whether it’s insecticides or GMO mosquitoes,” she tells Ed Cara at Gizmodo. “But anyone claiming that their technology is going to eradicate mosquitoes—it’s just not going to work that way. Nature is just much too smart.”

Genes Make Some People More Attractive to Mosquitoes

Smithsonian Magazine

Are you a human mosquito magnet? Your genes may be to blame, according to a study of twins that suggests your DNA is the main factor that makes some people much more appetizing to the pesky insects. The good news is that identifying the genes involved could help scientists devise ever more effective mosquito repellents. 

An estimated 20 percent of people are especially attractive to mosquitoes. Puzzled scientists have explored many reasons why mosquitoes seem to prefer some people to others. Possibilities include a person's blood type, metabolism, exercise levels and even clothing color. Previous studies have even shown that Anopheles gambiae, a malaria-carrying scourge in Africa, is more attracted to pregnant women. Diet is another oft-cited culprit, but no solid link between certain foods and mosquito bites has been shown—despite the persistent but unproven claims that intake of garlic or beer will repel or attract the insects.

One thing science can agree on is that body odor seems to play a significant role. “The mosquito's sense of smell is the primary method used to select which human to feed on,” says James Logan of the London School of Hygiene & Tropical Medicine. “There is an enormous amount of data to support the fact that how attractive you are to mosquitoes is determined by body odor.” Now, by studying human twins, Logan and colleagues have found that the specific body odors that affect mosquitoes appear to have a genetic basis.

His team conducted experiments with sets of twin sisters who volunteered to be mosquito bait for the betterment of science—18 pairs of identical twins and 19 pairs of non-identical twins. Non-identical, or fraternal, twins share far fewer genes than identical twin pairs. To test their mosquito-attracting mojo, the twins each placed a hand into one branch of a Y-shaped tube. Then dengue mosquitoes (Aedes aegypti) were released into the third branch, where they could sense the human odors and fly down to bite whichever twin they found most attractive. 

While the identical twins proved equally attractive to mosquitoes, some of the non-identical twins were far less likely to be bitten than their siblings. This matches previous work showing that identical twins are more likely to have the same body odor than fraternal twins, Logan says. According to their tests, the measured level of heritability for this trait—the amount of total variability in body odor that can be attributed to genetics—was quite high. The results suggest that genes may play as big a role in determining whether our smell attracts mosquitoes as they do in regulating our height or IQ. Other possible factors to account for mosquito attractiveness, including diet and cleanliness, were largely controlled for during the study.

The team's findings, published today in PLOS ONE, could prove a valuable weapon in the fight against these pests and the many diseases they transmit. Current repellents such as DEET aren't foolproof, and some mosquitoes can become immune to DEET in just a few hours.

Finding the genes that govern certain body odors may help scientists develop more targeted types of mosquito repellants, and the authors have identified one promising place to search. The major histocompatibility complex (MHC) genes are believed to control odor cues associated with genetic similarity—perhaps to help avoid inbreeding by deterring humans from being attracted to a close relative. Those same genes may somehow trigger odors that either attract or repel mosquitoes, the authors theorize.

“Once we identify the genes involved, we may be able to screen populations to better predict the likely level of risk of being bitten, which is directly correlated to transmission of diseases like malaria and dengue," says Logan. If the genes are linked to a repellent odor, "we may also be able to develop a drug which would up-regulate the production of natural repellents by the skin and therefore minimize the need for topical repellents.” 

Why Mosquitoes Find Your Warm Blood So Appealing

Smithsonian Magazine

When his mosquitoes refuse to feed, Willem Laursen dons a pair of pantyhose.

“The smell [of feet] really attracts them,” says the Brandeis University biologist, who wraps his hosiery in a ring around the insects’ blood-filled feeding discs. “When you go outside, they go straight toward your ankles.”

Wild mosquitoes may harbor a seemingly insatiable thirst for blood, but their lab-grown counterparts—taken out of their natural habitats and penned in teeny, artificially lit chambers—sometimes struggle to rustle up an appetite. To keep the bugs at fighting weight, Laursen and his colleagues ply them with a suite of sensory cues, intended to mimic what they’d come across outdoors: warmth from a heated metal disc; puffs of carbon dioxide from exhaled breath; the alluring funk of human sweat emanating from unwashed nylon stockings.

The lab’s latest crop of mosquito mutants, however, have proved even tougher to coax than usual. Laursen and his colleagues have genetically modified the bloodsuckers to stop expressing a molecular thermostat called IR21a in their antennae, stunting their ability to home in on heat—and leaving them less prone to sup on servings of warm human blood.

The team’s findings, published today in the journal Science, represent the first time researchers have pinpointed some of the genes and cells responsible for mosquitoes’ attraction to heat. Understanding these molecular targets could someday aid the development of mosquito repellents or traps to bait the disease-transmitting bugs, which can carry the pathogens that cause malaria, dengue, Zika and more.

Although mosquitoes (pictured) and fruit flies are separated by about 200 million years of evolution, they share a lot of the same machinery, including molecular temperature sensors. (Courtesy of Willem Laursen)

“Everybody knows that mosquitoes are annoying—they bite, and they’re everywhere,” says Sarah Zohdy, an infectious disease ecologist who wasn’t involved in the study. “But we still have some question marks about the basic underlying mechanisms that drive them. This really elegant study … addresses that gap in knowledge.”

For mosquitoes, nothing screams dinner like a body brimming with fresh, warm blood. But for a bug to actually buzz in for a bite, a whole slew of signals must first fall into place. Kicking things off are what Laursen calls the long-range cues—things like body odor and plumes of carbon dioxide that can entice the insects from several feet away. Once they come within a couple inches, the short-range triggers like temperature and humidity start to come into play, paving a clear path to a patch of delectable skin.

In the past several years, mosquito researchers have made big strides in determining what helps the bugs sense chemical cues from afar. But what keeps the insects on track as they gear up for landing has been “harder to pin down,” Laursen says.

To suss out the mosquitoes’ temperature-sensing strategy, a team led by Laursen and fellow Brandeis biologists Chloé Greppi and Paul Garrity turned to an unlikely source of inspiration: fruit flies. Though separated from mosquitoes by some drastic dietary differences and about 200 million years of evolution, fruit flies still share a lot of molecular machinery with their distant, bloodsucking cousins, Garrity says. One important difference? A lot of the temperature sensitivity in fruit flies has been worked out.

Anopheles gambiae mosquitoes are capable of carrying the parasite that causes malaria, Plasmodium falciparum. (Courtesy of Willem Laursen)

This evolutionarily minded strategy has actually been used before. In 2015, another group of researchers modified the mosquito genome to disrupt each of two genes that help fruit flies detect heat. But neither of the mutations appeared to quell the mosquitoes’ thirst for warm blood.

That finding was initially puzzling, Garrity says. The most traditional (and simplest) way to conceptualize heat-seeking behavior is through a set of cells or receptors that respond to increased temperature. “But there are two ways to be attracted to a warm object,” he says. “You can either seek out where the temperature is warmer, or be repelled by where the temperature starts to drop.”

So the researchers turned their attention instead to IR21a, a receptor that helps fruit flies sense, and ultimately migrate toward, cooler temperatures to keep from overheating. Genetically engineered to lack IR21a, Anopheles gambiae mosquitoes were no longer attracted to miniature heaters warmed to 98.6 degrees, a target that unaltered mosquitoes go bonkers for.

Mosquitoes without IR21a also showed less interest in warmed-up blood, offered to them in a heated disc attached to the top of their mesh cage—a setup that also provided the insects’ main source of food. (A cheaper but more bothersome option is for lab members to simply take turns sticking their forearms into the enclosure.)

To keep the mutant mosquitoes fed outside of these experiments, Laursen and his lab mates will bring the bugs extra blood, or blow into their cage to spike the air with carbon dioxide. They also frequently break out the pantyhose, though some members of the lab have proved more potent mosquito magnets than others. (They keep score on a whiteboard; Laursen is currently tied for second place.)

A mutant mosquito (green eyes) that lacks the IR21a receptor, which helps it navigate toward warmth, shown with a normal mosquito (red eyes) (Courtesy of Willem Laursen)

The team’s experiments suggest that, at the molecular level, IR21a functions pretty much the same in fruit flies and mosquitoes. But while it helps fruit flies avoid the heat, it makes mosquitoes navigate toward it. Mosquitoes, it seems, repurposed an evolutionarily ancient gene into a new cellular circuit—and flipped its function on its head. “Instead of just worrying about thermoregulation, mosquitoes are now using these temperature sensors to hunt humans,” says Laura Duvall, a mosquito behavior expert at Columbia University who wasn’t involved in the study.

Disabling IR21a, however, isn’t enough to completely flummox a hungry bloodsucker. When the researchers placed their bare hands on top of the mutant mosquitoes’ cages, the insects still flocked upward for a taste.

“Mosquitoes are exquisitely good at finding us,” Duvall says. With so many different sensory cues tickling the fancy of these bugs, “targeting a single pathway is never going to be enough … to disrupt that ability.”

But in fleshing out the list of lures that draw mosquitoes to humans, researchers may be on their way to developing more powerful repellents, including some that could discombobulate the bugs’ navigation skills.

Alternatively, a whole slew of these triggers could be combined into an ultra-appealing trap that seduces the insects away from skin. “This is a really attractive approach,” Duvall says. “It could have a huge impact. If you could reduce the number of interactions between mosquitoes and humans ... you could prevent all the diseases that those animals spread.”

Graphene-Coated Fabric Causes Mosquitoes to Buzz Off

Smithsonian Magazine

Graphene holds plenty of superlative titles in the materials world: it’s the strongest, thinnest and most conductive material on earth. Those traits together mean the thin, one-atom-thick sheets of carbon molecules can be applied in lots of ways. Many scientists are optimistic that graphene will one day enhance—or replace—metals and plastics in our daily lives. Swapping silicon with graphene in electronics can effectively create super batteries. It also shows promise in medicine, it can filter water and it can even take a classic little black dress to the next level.

But can graphene repel mosquitoes? It sure can, researchers show in a new study published in the Proceedings of the National Academy of Sciences.

According to a press release, researchers at Brown University were working on lining fabric with graphene oxide—a type of graphene that can be made into thin nanosheets to coat things—to see if it could block chemical exposures. When they brainstormed other uses for graphene-lined clothing, mosquitoes came to mind. The scientists suspected that the insect’s proboscis wouldn’t be able to penetrate the graphene barrier.

To see if it worked, the team recruited volunteers willing to risk a few bites from Aedes aegypti mosquitoes. Participants put their arm in a mosquito-filled chamber, either with bare skin, skin covered with a thin layer of cheese cloth or skin covered by the graphene coated fabric.

While the bare-skinned and cheese cloth-covered participants got hammered by the mosquitoes, those wearing the graphene fabrics didn’t get a single bite.

The mosquitoes didn’t have enough force to push their needle-like proboscis through the graphene oxide, which protected the volunteers. Not only that but insects wouldn’t even land on the fabric, suggesting something else was going on, explains Cintia Castilho, the study’s lead author and a chemical engineer at Brown University.

“With the graphene, the mosquitoes weren’t even landing on the skin patch—they just didn't seem to care,” she says in a statement. “We had assumed that graphene would be a physical barrier to biting, through puncture resistance, but when we saw these experiments we started to think that it was also a chemical barrier that prevents mosquitoes from sensing that someone is there.”

The team then dabbed a little sweat on the outside of the fabric, which immediately drew in the bloodsuckers. The team suspects that besides offering a physical barrier to the bites, the graphene also blocks the chemical cues coming off of human skin. (That makes sense because mosquitoes can detect sweat; earlier this year, researchers confirmed that some mosquitoes including Aedes aegypti have receptors that detect lactic acid and other components in perspiration.)

The fabric does have some limitations. When graphene oxide is dry, mosquitoes can’t produce enough force to puncture it. When the material gets wet, however, their needle-like mouthparts slip right through.

Another version of graphene oxide with reduced oxygen content (rGO) does provide bug-bite protection when it gets wet, but it loses one of graphene oxide’s best qualities.

“Graphene oxide is breathable, meaning you can sweat through it, while rGO isn’t,” says Robert Hurt, the study’s senior author and an engineer at Brown University. “So our preferred embodiment of this technology would be to find a way to stabilize GO mechanically so that is remains strong when wet. This next step would give us the full benefits of breathability and bite protection.”

It’s unlikely that graphene-lined clothes will make it to market anytime soon. Even though carbon—graphene’s only component—is the fourth most common element in the universe, it is currently very difficult to make in large quantities, report Les Johnson and Joseph E. Meany at The American Scientist. Currently, producing even small amounts involves complex machines and multi-step reactions using dangerous chemicals.

In 2017, researchers at Kansas State found a way to produce graphene using small detonations, a process that may be scalable and other processes look promising as well. But it may take a decade, or several decades, before we’re able to produce enough graphene to revolutionize our computers, lighten our airplanes and make mosquitoes to buzz off.

This Sweet-Smelling Herb Can Ward Away Mosquitoes

Smithsonian Magazine

If you hate the pungent odor of most mosquito repellents, there might be a very sweet-smelling alternative. Researchers have identified two mosquito-repelling chemicals naturally found in sweetgrass, an aromatic herb that some Native American peoples have traditionally used to ward off the pesky insects.

In one test, distilled sweetgrass oil even matched the repellent potency of DEET, the current gold standard for anti-mosquito effectiveness.

Stopping mosquito bites is about more than enjoying a barbecue in peace. It's a serious human health issue—as vectors for diseases such as malaria and yellow fever, mosquitoes kill more humans than murderers do. There are some unusual ideas for how to ward off the pests, including silencing the bacteria on your skin, but most people are still in search of a safe and effective topical repellent they can use when needed. Sweetgrass (Hierochloe odorata) is the latest in a line of traditional, natural repellents to be examined by chemist Charles Cantrell and his colleagues at the USDA's Natural Products Utilization Research Unit at the University of Mississippi.

“We're always looking for new leads for discovering new biopesticides,” says Cantrell. “Traditional or folk remedies have been a good source of leads for natural things that may be effective in repelling insects. We've looked at beautyberry, we've looked at breadfruit from the Hawaiian Islands, which is one that you burn, and we've looked at Jatropha from India, which is another one you burn. They've all kind of led us in different directions chemically, and sweetgrass has another different chemistry.”

Despite concerns about its toxicity to humans and potential environmental damage, DEET remains the gold standard for repelling mosquitoes, ticks, fleas and other pests. The main reason, Cantrell says, is that it not only works, but it also lasts for a long time.

“You see that the market is being flooded with natural products, essential oil-based insect repellents,” he says. “There are some that work, but there are a lot of them that may only work for 20 or 30 minutes. What we're ideally looking for is something natural and nontoxic that's just as effective as DEET, that will work as an effective repellent for 10 or 12 hours like DEET.” So far, finding a natural product with the same staying power has been challenging, which is why Cantrell's lab has been exploring so many different plants.

Sweetgrass had many ceremonial uses among Native Americans. Some people wore braids of it around their necks or adorned their homes with the aromatic plant to help repel mosquitoes. Because of these uses, Cantrell theorized that the plant's sweet smell must include bug-repellent chemicals that waft off the plant in nature.

His team extracted sweetgrass's essential oils via steam distillation and then put it to the test. They presented mosquitoes with vials containing a feeding agent much like human blood. Each vial was covered with a thin membrane that was then treated with a variety of repellents, including the sweetgrass oil and, for comparison, DEET.

The scientists watched the mosquitoes' biting behavior and even satisfyingly smashed the insects on paper to see which false bloods they had ingested. Sweetgrass oil performed very well—matching the repellency of DEET, the team reported this week at the 250th American Chemical Society National Meeting & Exposition in Boston.

The team then broke down sweetgrass oil into its chemical components using nuclear magnetic resonance spectroscopy and mass spectrometry to reveal two chemicals that appeared to be responsible for the plant's repellent powers—coumarin and phytol.

Scientific literature on essential oils had previously suggested that phytol can play a repellent role. And coumarin has actually been commonly used as an insect repellent for many years—though it's never been marketed as one.

“You may remember that for a long time there was a buzz surrounding Avon's Skin-So-Soft, which many people are convinced had repellent properties,” Cantrell says. “Avon never made any such claims because Skin-So-Soft wasn't registered as a repellent, it was formulated for skin care. But the general consensus of people who looked at the product was that coumarin was acting as a repellent." Avon now makes skin produces that are branded as repellents, but those don't contain coumarin, because the chemical is not registered as a repellent with the EPA.

It's still unclear whether coumarin will prove to have the same long-lasting effectiveness as DEET, so Cantrell plans to subject sweetgrass oils to further study. He's quick to note, too, that showing there is sound science behind the herb's bug-busting properties doesn't mean that all traditional repellents will have merit. “When you look at these traditional remedies, those people certainly didn't bat 1,000,” Cantrell notes. “But we have had good luck with some of them, and they've really been fun projects.”

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