To keep mosquitoes away from your deck or patio without slathering your skin in bug repellent, get the Thermacell Radius Zone Mosquito Repellent Gen 2.0. After 45 hours researching a category full of marketing hype and debunked methods (including popular options like citronella candles), we found that the Radius stands out by actually being effective. Its rechargeable six-and-a-half-hour battery lasts long enough to odorlessly keep a bedroom-sized area mosquito-free for an entire evening—as long as there’s no breeze.
Our pick: Thermacell Radius Zone Mosquito Repeller Gen 2.0
In addition to the Radius Gen 2.0, Thermacell makes several other effective spatial repellents (mosquito control methods that cover an entire area instead of just one person), but none can match the Radius’s ease of use. Its long-lasting 40-hour repellent cartridges, automatic shutoff timer, and rechargeable lithium-ion battery make it much more convenient than butane-cartridge options, which don’t last nearly as long. Compared with other methods of mosquito control, the Radius is more effective and more user friendly overall.
Runner-up: Thermacell MR450 Armored Portable Mosquito Repeller
If you prefer a more durable and portable option, we like the Thermacell MR450 Armored Portable Mosquito Repeller. Like the Radius, the MR450 has proven mosquito-repelling capabilities, but it lacks some of the Radius’s finer touches, including the rechargeable battery, the timer, and the long-lasting repellent cartridge. Instead, like most of Thermacell’s products, the MR450 runs on a butane cartridge and uses four-hour repellent pads, both of which are less convenient than the Radius’s features. The butane is easier to burn through and harder to replace, versus simply recharging a battery. The pads last for far less time than cartridges, and it’s harder to tell when they’re used up. In a large catalog of similar Thermacell products, the MR450 stands out with a more rugged design and a few minor convenience features, but if you’re okay with the compromises of using butane and pads, Thermacell offers some similar models worth considering.
Budget pick: Pic Mosquito Repelling Coils
For a less expensive option, we recommend Pic’s Mosquito Repelling Coils. Like the Thermacell options, the coils effectively clear an area of mosquitoes, and for their seven-hour burn time their price is a fraction of that of our other picks. But they’re not as portable or durable as our picks, their burning ends are not as safe to leave unattended, and they emit a smoke with an odor that some people find unpleasant.
The catch with any of these spatial repellents is that they lose efficacy in windy conditions. But they’re still the best bet, since many popular mosquito control methods—including bug zappers and citronella candles—don’t actually work. A few additional methods of mosquito control are worth considering, including simply running a fan, and of course, using the most predictably effective option, a spray repellent in conjunction with permethrin-treated clothing.
Why you should trust us
While researching this guide we spoke with Joe Conlon, technical advisor of the American Mosquito Control Association, a position he has held since 2000. Conlon’s experience with mosquitoes is wide ranging and has spanned nearly four decades. Since 1981 he has been a medical entomologist, and in that time he has presented more than 350 invited papers on vector control to various universities, medical and public-health associations, and national, regional, and state mosquito-control groups. In addition, he has conducted vector-control operations or on-site consultations in 34 countries. He has published at least 20 articles on vector control in refereed journals and more than 70 articles in trade publications.
For questions on repellent safety and the EPA’s pesticide approval process, we spoke with Lawrence Feller, senior consultant to Scientific Coordination, an organization that assists companies with the development and approval of EPA-regulated products. Feller is also a contributor to the Insect Repellents Handbook. He spoke with us on behalf of Thermacell, one of his clients.
We also read as much as we could on mosquito repellents, traps, and other control products, focusing our attention on information from the AMCA as well as a number of studies, such as ones found in the Journal of Insect Science, Acta Tropica, and the Journal of Medical Entomology.
Who this is for
Everyone should have an interest in avoiding mosquito bites. According to the Centers for Disease Control and Prevention, “Vectorborne diseases are a large and growing public health problem in the United States.” This category includes those diseases transmitted by mosquitoes, such as West Nile virus and Zika. As we found in research for our guide to the best bug repellent, and confirmed again in the research for this guide, the best course of prevention is to use an effective spray repellent.
This guide is for those times—the many times—when covering yourself head to toe in bug spray isn’t practical. We wanted to find a product that would effectively reduce mosquito bites when you’re hosting a backyard barbeque, lounging on the patio, or having a picnic in a park. Everyone occasionally wants to briefly enjoy an outdoor space without being bitten, and without having to deal with applying a spray repellent—our objective for this guide was to find something that would make that possible.
Spatial repellents, like all of our picks in this guide, are effective in still conditions but basically useless if it’s windy. The AMCA’s Joe Conlon told us, “There is an effectiveness there, as long as you’re not sitting in a place with a stiff breeze.” Think of the dispersed repellent as if it were smoke, and you can visualize how it can simply blow away. This drawback also means that a spatial repellent is not a good choice for someone in motion—if you’re taking a walk in the woods or mowing the lawn, a spray repellent applied to your body and clothing is more effective. The good news is, mosquitoes are weak flyers and have a hard time flying into even gentle breezes—which is why we list a simple room fan among other options you might consider.
How we picked
When you’re looking at our selection criteria for these devices, it helps to understand how the leading scientists in the field view the problem of mosquito control. One point that the AMCA’s Joe Conlon stressed in our interviews was: “People have just got to understand that there’s no easy solution to this whole thing.” Mosquitoes are famously resilient, and with at least 175 species recognized in the US alone, there is a lot that people don’t yet know about their behavior. Add in the variables of the local environment where a spray, repellent, pesticide, or any other product is in use, and it’s easier to understand why there isn’t one single solution that works 100 percent of the time in 100 percent of the possible environments.
With that in mind, though, we identified a few attributes that an effective mosquito control product should ideally have. After poring over the research, talking to Conlon, and setting our expectations realistically, we settled on a handful of objectives we wanted our recommendations to meet:
Offer proven effectiveness: The product needs to have proven efficacy based on a credible study—preferably more than one. Conlon warned us against relying on anecdotal evidence when evaluating options: “You can’t take internet testimonials at face value. Period.” We found many well-marketed products with positive reviews whose effectiveness has been completely (and repeatedly) debunked by the scientific community. “There is a lot of nonsense out there,” Conlon told us. And as the authors of a Journal of Insect Science study write, “the most egregious danger to the consumer is the false comfort that some repellents give them protection against Ae. aegypti [mosquitoes] when they actually offer none.” In our research, this concern allowed us to eliminate a number of popular control methods, including citronella candles, anti-mosquito bracelets, and sonic options.
Repel rather than trap: Repelling mosquitoes produces more consistent results than trapping them. As Conlon notes on the AMCA website, studies on traps have yielded mixed results.1 He told us that with current trap designs, if given the choice, a mosquito will always head toward a human over the attractant in the trap. “If you put one of these things in your yard, if you happen to be between the breeding habitat and the mosquitoes, you’re going to get fed upon. They’re not going to bypass you and go to these traps. And they’re going to keep coming.”
A study in Acta Tropica looked at three different traps and found that they “either significantly increased or had no effect on the biting-pressure at short distances compared with the unprotected control.” So traps may even work to bring more mosquitoes to the area.
Keep the balance: We looked at products that had as little impact as possible on honeybees, moths, butterflies, and other positive or neutral insects. Many options, such as foggers, yard sprays, and bug zappers, offer proven effectiveness against bugs, but they kill indiscriminately. During our interview, Conlon told us this kind of wholesale insect destruction could have a ripple effect: Not only are “Many of these insects … beneficial predators on other insect pests,” but you’re “going to kill food that is generally reserved for birds and bats.” On the AMCA website, he even draws a link between the increased prevalence of bug zappers and the decrease of the songbird population in some affluent suburbs.
Along the same idea of keeping a balance, the introduction of new animal predators likely doesn’t yield significant results. Bats are the most commonly cited animal option for mosquito control. When we asked about them, Conlon told us, “Absolutely, they’ll eat mosquitoes. But can they survive on eating mosquitoes? Only if you’ve got an enormous mosquito population.” He added that they tended to eat moths and june beetles instead. “I’m not going to say that people shouldn’t use bats, but if they think that putting a bat house in your backyard is going to solve your problem if you’re living next to a salt marsh, you’re kidding yourself.”
Be practical: We decided that our recommendation needed to be easy to use, safe, and affordable. Price was far less important than finding the most effective option, but we still looked for something we could simply set out, turn on, and expect to do its job while we ignored it. Even as we came across mosquito traps that cost upward of a thousand dollars, we didn’t enforce a strict price cutoff, but we did hope that we could find a pick that could work effectively for an initial (and ongoing) cost we could actually see ourselves paying. Evaluating that cost for each option, we compared it against what we knew about the relative effectiveness of spray repellents and their costs, versus the value we’d place on a more convenient alternative.
Our criteria steered us toward a group of products known as “spatial repellents.” These devices are basically diffuser units that emit a repellent into the air, creating a bug-free zone that repels bugs (rather than killing them), and many of them happened to be affordable and widely available. To shop for spatial repellents, we checked the best sellers on the Amazon, Home Depot, and Walmart sites, as well as outdoor retailers like Bass Pro Shops, Cabela’s, and Dick’s Sporting Goods. Narrowing an initial field of more than 50 options using the above criteria, we got our hands on 12 products for testing. We looked at the Thermacell Radius Zone Mosquito Repellent, the Thermacell MR450 Armored Portable Mosquito Repeller, the Thermacell Patio Shield Mosquito Repeller, the Thermacell MR-BPR Backpacker, Off Clip-On Mosquito Repellent, Off Mosquito Coils, and Pic Mosquito Repellent Coils. In addition, we tested a pack of mosquito bracelets and downloaded a sonic repeller app. At Conlon’s suggestion, we also tested the efficacy of a Vornado 630 Medium Air Circulatorfan, Summit’s Mosquito Bits, and Philips 60-watt bug light bulbs.
How we tested
Given what our research showed about the variations in mosquitoes from location to location and species to species, we determined that there was no test we could perform that would produce consequential data regarding the effectiveness of a repellent; we relied on established studies for that. So our testing was more about getting a sense of what these products were like to use, as we took them out nightly for three weeks to a back patio in mosquito-ridden rural New Hampshire and on a three-day July camping trip in Maine. There, we simply lived with them, taking note of their ease of use, durability, and projected long-term costs, as well as factors such as how long they would stay on at a given time before needing a resupply of repellent or fuel, which ones burned themselves dry if you forgot about them, which ones were safest around kids and pets, plus other observations that anyone buying these items for the first time would want to know.
Our pick: Thermacell Radius Zone Mosquito Repellent Gen 2.0
The Thermacell Radius Zone Mosquito Repellent Gen 2.0 is the most convenient, easy-to-use spatial repellent we found, and it’s nearly as good at stopping mosquitoes from bothering you as a full application of a spray repellent. Compared with similar designs, the Radius is easier to refill and recharge, more efficient with its use of repellent, and more convenient to live with, and it doesn’t present the hazards that some other options do. It won’t stop every single mosquito from getting you, its coverage area is limited, and it loses efficacy in windy conditions—but all spatial repellents share those flaws. This is a new pick for 2019, replacing our previous pick, the original Thermacell Radius. The differences are that the interface is a little easier to use, the charging port is more discreet, and the battery lasts longer. The two are compatible with the same repellent cartridges.
The principle behind the Radius is simple: The device generates heat to vaporize a little vial of liquid repellent, which slowly disperses out of the unit, protecting an area from mosquitoes and other biting insects. In use the Radius is silent and odorless, and although a small amount of vapor is visible when exiting the top of the Radius, it visually dissipates quickly.
Other products (including many from Thermacell) do similar things, but what’s unique about the Radius is that its heat source runs on a rechargeable lithium-ion battery. The battery holds a charge for about six and a half hours and can operate while charging (with the included USB/outlet adapter cable). Currently the Radius is the only spatial repellent that uses a battery; every other Thermacell model (including our runner-up) vaporizes repellent using a butane cartridge or the fuel tank of a camp stove—that means you need to monitor the supply of both the repellent and the fuel source. With the Radius, as long as you’re near an outlet and you have a repellent cartridge, you’re all set.
According to Thermacell, the protected area of the Radius is about 110 square feet, roughly a 10½-foot square. During testing, we experienced protection beyond this range. We spoke to Lawrence Feller, senior consultant to Scientific Coordination (Thermacell’s regulatory consultant), and he said that the company’s own internal testing showed an effective area closer to 15 by 15 feet (225 square feet) and that the company is in the middle of more testing and is likely to start the process to change the marketing material for the Radius to indicate a larger coverage area. In a study done by the US Department of Defense (which Thermacell provided to us), a Thermacell unit showed some effectiveness at a range of 25 feet from the device.
This coverage area is comparable to that of Thermacell’s butane-based alternatives, which have an advertised coverage of 225 square feet. But the Radius has an edge on the Off Clip-On Mosquito Repellent, which uses a little fan rather than heat to disperse the repellent. The fan method doesn’t create as large of a protected area, and we found the fan to be a touch noisy—not obnoxious, but more noticeable than the silent Thermacell Radius.
The Radius also stands apart from other options due to its long-lasting repellent cartridges, which come in a 40-hour size or a 12-hour size. These last longer than competing models’, including those of the Off Clip-On, which has a 12-hour duration, and other Thermacell models, which use four-hour repellent pads. Another unusual element of the Radius is that its repellent cartridges are clear and the repellent is in liquid form, so you can easily gauge how much is left. With the other Thermacell models, such as the MR450, our runner-up, and the MR150, you need to watch the color fade from the repellent pad, which is tedious and inconclusive—we were never sure when the effectiveness started declining. The Off Clip-On was even worse in that regard, giving absolutely no indication of the remaining repellent. Unlike with those other options, you can simply set the Radius out and know that it’s working, so you can spend less time swapping out repellent, worrying if you’re going to run out, or wondering if you’re out already (as you get eaten alive by bugs). We compared the active ingredients of the repellent cartridges and pads, and you can read our findings in the section about the effectiveness and safety of Thermacell repellents.
In addition, the Radius has a timer setting that automatically shuts the unit down after 120 minutes. It’s easy to forget these things are on, but if that happens, the Radius does a better job conserving its repellent and power than, say, the butane-based Thermacell MR450, which will needlessly drain both the butane and the repellent if you leave it running. You set the timer by double-pressing the power button, and you can tell it’s active when the power light fades on and off. In the first generation of the Radius, the timer setting was on the bottom of the unit, which was a little more inconvenient. The current version also has a lock function that prohibits the Radius from accidentally turning on.
We also like the overall design of the Radius. It’s small and sleek, and it doesn’t draw much attention to itself when sitting on a picnic table. Overall, it’s not very durable, and if you’re looking for something more portable for outdoor activities, we recommend the Thermacell MR450, our runner-up pick. Compared with options such as mosquito coils, the Radius has a safety advantage around pets or small children, simply because it doesn’t put any exposed hot (or burning) parts within reach. But like any spatial diffuser, it is not recommended for use indoors.
Flaws but not dealbreakers
The biggest downside to the Thermacell Radius is that it loses its effectiveness in any sort of wind. However, all similar spatial repellents share this flaw, and mosquitoes struggle similarly in the wind.
The Radius’s performance in our tests was not perfect, as our sources predicted. Particularly when we were in the Maine woods, we found that even after 25 to 30 minutes of the Radius being active, an occasional mosquito would land on us and take a bite. The conditions were mostly still, but a very slight breeze did pass through from time to time. Whether the few mosquito bites were the results of the wind’s interference or just the general limitations of the Radius, it proved Joe Conlon’s point that there is no silver bullet when it comes to controlling mosquitoes.
The Radius is designed for mosquitoes, so you may not see a huge reduction in other flying pests. Thermacell told us that more robust bugs, such as horseflies, will be repelled by the Radius, but because they’re less susceptible to the small amount of chemical repellent in the air, they may be able to fly into the protected area and get a bite in before absorbing enough to be prompted to go away.
The usefulness of the Radius is more limited than that of some other options. Considering the way the cartridge sits loosely inside and the top stays on with magnets, it’s really a tabletop-only item. For any kind of outdoor activity—such as camping, fishing, hunting, or attending a sporting event—the more durable MR450, our runner-up, is a better option.
The Radius, like all spatial repellents, also needs time to start working. It typically takes around 10 to 15 minutes for the repellent to “saturate” an area. After we learned this, we got in the habit it putting it out on the patio a few minutes before going out there ourselves.
Finally, there are long-term costs to consider, as with most spatial repellents. In addition to making the initial investment, you’ll also need to purchase cartridge refills. If you used it roughly three days a week, two hours each time, and an additional five hours on weekends, you’d need a new 40-hour cartridge every month. These added costs are high, but not out of the range for effective spatial repellents. The butane-powered Thermacell models, which we think aren’t as convenient to use and don’t have added features like the timer, use 48-hour refill packs of butane and cartridges that usually cost around the same.
Runner-up: Thermacell MR450 Armored Portable Mosquito Repeller
The Thermacell MR450 Armored Portable Mosquito Repeller is as effective as the Radius, and with a slender, rugged design and a belt clip, it’s also more portable and durable. The downsides of the MR450 involve the repellent pads and the heat source. Instead of a rechargeable battery, this model uses a butane cartridge, which is less convenient and—because this model also lacks a timer setting—is easy to waste by accident. The pads are good for just four hours, a tenth of the Radius’s 40-hour cartridge, and, unlike with the Radius, on this model it’s difficult to gauge how much repellent remains. We like the MR450 model’s tough versatility, but there’s no reason to dismiss several similar butane-based options from Thermacell that may meet your needs better; all of them essentially work the same, and compared with the Radius, they all lack the conveniences of a rechargeable battery and a clear repellent cartridge.
The MR450 starts up with a few clicks of a button, and a little light goes on when the area is sufficiently saturated with repellent. We like the light because it allowed us to tell at a glance that the unit was on. Thermacell’s other portable units lack this feature, and its presence lessened the chances of our leaving the unit on accidentally—an easy mistake that can waste a repellent pad and drain a butane cartridge.
The MR450 is built like an oversize remote control, and we liked it for its easy portability and increased durability over the Radius. The rubber overmold looks designed to take a tumble, and the belt clip on the back is a nice touch, likely to be appreciated by anyone who hunts or fishes (remember, it’s for stationary activities only). We did notice while wearing the MR450 on a belt, seated, that it heats up enough to feel through a T-shirt—not enough to burn you, but pretty warm.
The repellent pads of the MR450 are good for only about four hours each, in contrast to the 12- and 40-hour cartridges of the Radius. The pads come out of the package bright blue, and as you use them, they slowly turn white. Once all of the color is gone, the pad is done. During use, it’s hard to gauge how quickly the pad is fading, which is especially important once the repellent gets very low; you’re basically guaranteed to either change out a pad before it’s truly expired or to use an expired one for too long. We much preferred the Radius’s clear liquid vial, which allowed us to quickly and easily determine how much repellent was left and when to reach for a new cartridge.
The heat for the MR450 comes from a small, replaceable butane cartridge, not a li-ion battery, and it has a 12-hour life. The timing does sync up with the four-hour repellent pads, and refill kits are available with three pads and one cartridge. It’s too easy to leave the unit heating once the repellent pad is expired, though, which throws that coordination off. And without a timer mode on the MR450 as on the Radius, it’s too easy to leave this model running by accident. The butane cartridge is another thing you need to have on hand in case you run out. Also, if you spend a good amount of time outdoors, you have to swap out repellent pads quite often, more than once a day even. The upside of the butane is that it’s more portable for camping and other outdoor activities in places where outlets to charge the Radius are scarce.
The MR450 typically costs a bit less than the Radius, and the long-term costs are slightly lower (but in the same ballpark). The price difference is not enough to make this model a better value than the Radius.
As for effectiveness, the MR450 is right on a par with the Radius. Like the Radius and all other spatial repellents, the MR450 has a hard time keeping an area protected in any kind of wind. It does use a different type of repellent, which we compare in detail in our section on the effectiveness and safety of pyrethroid repellents.
Budget pick: Pic Mosquito Repelling Coils
For similar mosquito-repelling effects at a far lower price, we like Pic Mosquito Repelling Coils. When ignited, these coaster-sized spirals slowly burn down like incense. This releases smoke containing a pyrethroid (the labeling on some Pic coil packaging says the active ingredient is “Pyrethrins,” while other Pic labeling names allethrin specifically) that creates an area protected from mosquitoes, similar to the Thermacell products. Like our pick, these coils offer proven effectiveness as a spatial repellent. They’re a fraction of the cost of any Thermacell offering, and they have no fuel or battery that needs monitoring. But there are some key differences between coils and our other picks: Some people find the smoke’s strong odor unpleasant or irritating, the burning ember at the tip can be a safety issue, the coils can drop ash as they burn, and they’re not as portable or durable as our picks.
The Pic coils are inexpensive and long lasting. In our testing, each one lasted about seven hours. In comparison, similar Off coils cost more and lasted only about five and a half hours. The higher cost of the Off coils is due in part to the fact that each comes with a small tray to catch bits of ash as the coil burns down. With the Pic coils, you need to put your own small plate underneath to catch the ash—a minor inconvenience we thought was worth tolerating for the Pic’s lower price and longer-lasting effects.
The coils’ smoke and odor were the main reasons we chose a smoke- and odor-free Thermacell product as our main recommendation. Although some owners say they like the smell of a mosquito coil’s smoke, others say they don’t, and we found it unpleasant (it can leave a taste in your mouth and irritate your throat too).
The fire hazard of the coil’s burning ember is a factor you don’t have to worry about with the Thermacell Radius or MR450, especially if you need to leave your repellent unattended for a bit. For some people, this isn’t an issue, but if you’re in a fire-prone area or if you have kids or pets around, it’s a drawback.
The ash, the smoke, and the weaker durability of coils relative to our pick together make the Pic repellent less portable and versatile than a Thermacell option. We chose Pic’s coils over several similar coils because they had a slight edge in price, and because they seemed less fragile than competitors, as some owners who have used multiple coil types claim. We have no reason to believe that one of these coils performs better than another coil with the same active ingredients while both are ignited.
The effectiveness and safety of pyrethroid repellents
Metofluthrin and allethrin, the active chemicals in the Thermacell Radius and MR450, respectively, are both pyrethroids, based on a compound found in the chrysanthemum flower. (Permethrin is also a pyrethroid.) Numerous studies have demonstrated their effectiveness at repelling mosquitoes when used in a spatial repellent, and both chemicals have undergone thorough vetting by the EPA and other regulatory agencies around the world and are deemed safe for this intended use.
First, the effectiveness:
The Radius uses metofluthrin, which the Journal of the American Mosquito Control Association found to be “highly effective at repelling mosquitoes.” In the Proceedings of the Fifth International Conference on Urban Pests (PDF), researchers write that their “findings further confirm the potential for metofluthrin passive emanators as a valuable and cost effective tool in providing protection from biting mosquitoes.”
Allethrin has received similar accolades.2 A study published in Acta Tropica, a journal of infectious diseases, compared a number of mosquito control methods and found that the three tested diffuser-style repellents, including a Thermacell model, “significantly reduced the biting-pressure … when positioned at short distances from a volunteer.” Of the three tested spatial repellents, the Thermacell was the “most effective.” Another study “showed highly significant protection provided by the TMR [Thermacell Mosquito Repellent]” against a variety of mosquitoes and sand flies.
Thermacell provided three other sets of test results to us.3 One, conducted in Costa Rica by the US Department of Defense, found that the tested Thermacell unit was “very effective in protecting persons up to 25 feet away from the unit from attack by phlebotomine sand flies, mosquitoes, culicoides outside in Costa Rica.” A second, done by the US Department of the Army, says that the tested Thermacell repellent was “very effective in preventing mosquitoes (primarily anopheles sinenis) from entering military bunkers.” The organization Scientific Coordination (on behalf of Thermacell) studied the Thermacell repellent’s effectiveness against black flies in accordance with EPA protocols and concluded that the Thermacell was “surprisingly good against the notoriously persistent attacks of black flies.”
Now, the safety:
Both chemicals, in their pure form at high, regularly administered doses, have shown toxicity to lab animals, but spatial repellents like our picks use a diluted version that then vaporizes into the air in an outdoor setting. Joe Conlon, writing about repellents and pesticides on the AMCA website, notes, “The dosages at which these products are legally dispensed are at least 100-fold less than the point at which public health and environmental safety merit consideration.”
The EPA, whose data requirements, Conlon writes, are “among the most stringent in the federal government,” has stated (PDF) that metofluthrin “is practically non-toxic to mammals and birds,” even though it is “highly to very highly toxic to aquatic animals and insects.” The EPA approves of its use in a spatial repellent, in spite of its risk to aquatic life, because in vaporized form it’s “not expected to have a high aquatic concentration.”
In the same fact sheet, the EPA classifies (PDF) metofluthrin as a neurotoxicant and potential carcinogen.4 This concern stems from studies showing tumors that appeared in the livers of rats, but only when researchers gave them extremely large doses of undiluted metofluthrin regularly over an extended period of time. Again, this kind of dosage has very little relationship to what you could potentially absorb while sitting near a Thermacell Radius. In fact, other researchers (PDF) have come out against the labeling of metofluthrin as a carcinogen, with one paper (PDF) stating that “it is reasonable to conclude that Metofluthrin will not have any hepatocarcinogenic [liver-damaging] activity in humans, at least at expected levels of exposure.”
Other effective ways to combat mosquitoes
Use a fan: Moving beyond chemical and spatial repellents, the ACMA’s Joe Conlon told us that a simple fan, such as our pick in our guide to the best fan (the Vornado 630 Medium Air Circulator), is an easy, low-tech way to keep mosquitoes away, due to the fact that they’re such weak flyers. Conlon told us, “There is no scientific data that I’m aware of that has ever tested that out to find out how many cubic feet per minute you need to keep mosquitoes at bay, but I think most people would agree that if you’re outside sitting on a porch and you’re in 15-mile-per-hour winds, you’re not getting bitten by mosquitoes.”
As for placement, Conlon recommends keeping the fan low, below table level, because the specific mosquitoes that spread Zika (of the species Aedes aegypti) “tend to prefer the lower extremities to bite” and “like to hide underneath outdoor furniture.” Obviously, using a fan is not compatible with using the Thermacell Radius, but there’s no reason you couldn’t combine fans with a personal application of an effective bug repellent on a breezy day, in a larger open space, or in other situations where the Radius won’t work for you.
Start at the source: If you have an obvious source of standing water near your home, such as a birdbath or a water feature, you can use Summit’s Mosquito Bits to kill the mosquito larvae. Conlon told us that the toxin involved is released only at the pH level found in a mosquito’s gut; it’s harmless to people, fish, and animals.
Prevent attraction: Last, Conlon recommended bug bulbs, which have a bright yellow hue. The color of the light doesn’t repel mosquitoes, but it doesn’t attract them either. We tested some, and although the color looks dramatic on the bulb, the actual light is only a little warmer than that of a regular bulb. Because they don’t repel mosquitoes, we had difficulty gauging their effectiveness.
Ineffective methods that aren’t worth your time
Citronella candles, like the Cutter Citro Guard, have no proven effectiveness. In fact, according to the AMCA, citronella candles “do not offer significantly more protection than other candles producing smoke.” A study in the Journal of Insect Science “found no indication that such candles repel Ae. aegyptifemales.”5
We don’t recommend foggers, like the Burgess 1443 Propane Insect Fogger, or bug zappers, like the Flowtron BK-15D Electronic Insect Killer, because of their indiscriminate killing of bugs, both positive and neutral. Bug zappers in particular are nearly useless when it comes to controlling mosquitoes. According to the AMCA, a Notre Dame study showed that after a season’s worth of bug zapping, only 4 to 6 percent of the bugs killed were mosquitoes.
Mosquito traps are another category that doesn’t live up to the marketing claims. The AMCA’s Joe Conlon told us that traps, whether propane-based like the MegaCatch Pro 900 and Mosquito Magnet Patriot Plus or UV-based like the Katchy Electric Insect Trap, “will capture mosquitoes, there’s no question about it, but they’re not as attractive as humans are.” A study published in Acta Tropica showed effectiveness only when four traps (the roughly $400 Blue Rhino SV3100) were set up in a perimeter fashion.6
A number of products rely on sound to repel mosquitos. The only problem is that there is zero evidence that they work. Conlon, writing for the AMCA, notes, “At least 10 studies in the past 15 years have unanimously denounced ultrasonic devices as having no repellency value whatsoever.” We asked him about this, and he told us, “I could send you pictures of sound producers that have got mosquitoes standing on them.” A Cochrane review from 2007 backs Conlon up on this assessment, finding “no evidence to support their promotion or use.”
Another popular item with minimal, if any, effectiveness is a bracelet that has been impregnated with a natural repellent. A study in the Journal of Insect Science states: “Although the active ingredients in some bracelets may be mosquito repellents, we hypothesize that the concentrations that are emitted by all of the bracelets that we tested were too low to have an effect.” In our interview, Conlon told us, “They appeal because you put a bracelet on and you’ll never have another bite forever. That sounds appealing, but it’s ridiculous.” He continued, “If you’ve got a bracelet that’s got mosquito repellent inculcated into it, you’re not going to have mosquitoes laying on the bracelet—but 3 inches away from the bracelet, you’ll have mosquitoes landing. That’s just the way it is.” There is no reason to believe that similar products, such as the Don’t Bite Me Patch, would work any better than a bracelet.
Thermacell’s first generation of the Radius (our previous pick) is very similar to the Gen 2.0. The differences are that its battery has less run time and the interface is clunkier, putting the lock function and the timer on the bottom of the unit (the Gen 2.0 adds them to the single-button interface). The two models are similar enough in price that we don’t see any compelling reason to recommend the first version over the second.
Thermacell has a number of other models, but none offer the convenience of the Radius’s lithium-ion heat source or the durability of the MR450. Handheld models like the MR150 are not as robust as the MR450 and don’t have the indicator light. Other tabletop units, such as the Thermacell Patio Shield Mosquito Repeller, use butane and are larger and more conspicuous than the Radius.
Thermacell also has designs that incorporate a battery-powered lantern. These models use repellent pads and butane cartridges, like our runner-up. It’s safe to assume they have the same mosquito-repelling qualities as our picks, but they also have the same downsides as the other butane-powered units—namely, the short-duration repellent pads and the potential for wasting fuel.
The Thermacell MR-BPR Backpacker does not use butane; instead it attaches to a camp-stove canister. This design sidesteps some of the hassle of the butane cartridge, and it would likely work well if you’re at a campsite, but outside of that environment a camp stove is not a convenient fuel source for most people.
Off Mosquito Coils demand a larger initial investment than Pic coils and don’t last as long. They come with a small metal dish to catch the dropping ash, but we preferred just using our own dish with the less expensive and longer-lasting Pic coils.
The idea behind Off Clip-On Mosquito Repellent is very similar to that of the Thermacell models except that this design uses a little fan, rather than a heat source, to disperse the repellent (metofluthrin). The downside, we found, was that it made a little whirring fan noise that sometimes chattered when we moved the unit. It offers some effectiveness in keeping mosquitoes at bay, but a study from the Journal of Medical Entomology showed that its effectiveness “was not sustained at distances greater than 0.3m from the device.” It typically costs just under $10, making it one of the least expensive options; the long-term costs are low as well, with refills lasting up to 12 hours (this Off model also takes two AA batteries, which you need to factor into the costs).
1. Conlon writes, “The process of a mosquito questing for a blood meal involves a complex, interconnected cascade of behaviors, each probably having its own cues, be they visual, thermal, or olfactory. The complexity of these questing behaviors may account for the bewildering variations in trapping efficiency noted for certain species of mosquitoes at different times, seasons and places. With 174 species of mosquitoes currently recognized in the United States, this is no small issue and will require many years before research can provide a clarification.” Jump back.
2. According to a 1951 article in the Journal of the American Chemical Society, allethrin was developed in the late 1940s and is considered a first-generation pyrethroid. Metofluthrin is much newer. The primary difference between the two is that metofluthrin vaporizes much more easily. Allethrin needs a butane heat source to vaporize, but metofluthrin can vaporize on its own. This is why metofluthrin works in conjunction with the lower temperature that the Thermacell Radius’s lithium-ion battery provides. Jump back.
3. These three studies were conducted on behalf of Schwabel, Thermacell’s parent company. Jump back.
4. Some people also believe that pyrethroids such as metofluthrin and allethrin may cause allergies, but the EPA looked into the matter in 2009 (PDF) and found “no clear and consistent pattern of effects reported to indicate conclusively whether there is an association between pyrethrins/pyrethroid exposure and asthma and allergies.” Jump back.
5. Female mosquitoes are the ones that bite. Also from the study: “The citronella candle combined with a human subject attracted slightly more mosquitoes that the human bait person alone; however, this difference was not statistically significant.” Jump back.
6. Conlon also refutes the claims that we found on many trap models: “The ones that purport to keep an entire acre mosquito free, that’s complete nonsense. Those are extrapolations from caged studies that are done in small tented areas where mosquitoes can’t escape.” Jump back.
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