todd@beesafemosquitocontrol.com
Silver Spring, MD, USA
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A BEE-SAFE WAY TO BE SAFE FROM MOSQUITOS!

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Harms of Mosquito Spraying

The Harms of Traditional Mosquito Spraying

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The biggest mosquito control companies unfortunately still use the traditional “barrier spray” methods for mosquito control. Not only is this ineffective, but it is actively harmful to beneficial insects in your yard. These companies are largely spraying broad spectrum insecticides, mostly pyrethroids, that kill most insects in your yard. This includes the beneficial insects that pollinate your veggie garden, defend your perennials from pests, and feed the birds you’ve worked hard to attract to your yard. 


If your yard is smaller than an acre, a large portion of mosquitos you see in your yard are coming from neighboring yards. A barrier spray doesn’t have any impact on mosquitos outside your yard, they can just come right over. There is no “barrier.” Our baiting station system is the only product on the market we’re aware of that can actually impact breeding sites outside of your property, using the innovative auto-dissemination approach developed by In2Care. Additionally, because many of these companies don’t apply a larvicide, new mosquitos can emerge from within the yard mere days after the yard is sprayed.


One of the biggest issues with traditional mosquito control “barrier spray” treatments is the application method: spraying. Spraying inevitably results in spray drift, presents a risk of inhalation to humans and animals, and coats insects and surfaces insects will land on. This harms those insects whether they were targets of the spray or not. There are some pesticides that we would endorse as safe if used responsibly, and that we even use ourselves, that would be hugely detrimental if sprayed all over your yard. That is why Bee-Safe Mosquito Control is strictly no spray.


We’ve managed to get a list of pesticides used by two of the biggest mosquito control companies in the DMV. Below are the specific chemicals they use in yards in your neighborhood. We won’t name names, but they’re both national franchises with hundreds of locations throughout the US. The ecosystem is in crisis due to habitat loss, pesticide use, invasive species, and pollution. These companies are contributing to that problem, and we will use this space to show you exactly how they are damaging the ecosystem, regardless of what they may claim. We hope these companies will join Bee-Safe in going no-spray and adopting better practices.

Adulticides: The Worst Offenders

Fendona-CS (EPA Reg. #499-570)
Active Ingredient: Alpha-cypermethrin

Fendona-CS uses a broad spectrum pyrethroid insecticide to kill adult mosquitos. Unfortunately, it kills nearly every insect, arachnid, and possibly other invertebrates. You don’t have to look much further than the label for proof, but yet, these national mosquito control chains claim it is safe anyway. It literally says it kills bees on the label. These excerpts come directly from the label, which is linked above.

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Tempo SC (EPA Reg. #432-1363)
Active Ingredient: Beta-cyfluthrin

Tempo SC uses another pyrethroid insecticide, and it’s just as bad as the others. It too kills nearly all of the bugs in your yard, including pollinators. Again, we need go no further than the label for proof of this. It directly states that it kills bees, moths (and likely butterflies too), caterpillars, wasps, spiders, etc. This one apparently is harmful enough to humans that they had to list inhalation as a risk too.
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Bifenthrin PL (EPA Reg. #53883-124)
Active Ingredient: Bifenthrin

We have yet another pyrethroid insecticide, this time Bifenthrin. What’s a little bit more interesting about this one is that it is a granular product, rather than a spray. So for this particular product, you would spread the granules with a hand spreader and then water the area to “activate” the pesticide. Because it is granular, they aren’t required to list that Bifenthrin itself is “very highly toxic” to bees (source). What is even stranger is that this product doesn’t even list mosquitos as a target pest, which is actually legal (unfortunately). So the company using this is using it “off label.” 


But, that doesn’t change the fact that this will undoubtedly harm insects on the ground when the applicator waters it in and the granules dissolve Bifenthrin into the water, which spreads to cover the ground. According to the Xerces Society(source), approximately 70% of native bee species nest in the ground! Obviously, given the toxicity of Bifenthrin to bees, using this product would be hugely detrimental to native bees and probably most other insects and arachnids that live in or walk on the ground. 

Bifenthrin is also a PFAS chemical, also known as a forever chemical. It was designed to have longer residual impact, and they did that by fluorinating it. Bifenthrin is a known carcinogen.

Cyzmic CS (EPA Reg. # 53883-261)
Active Ingredient: Lambda-cyhalothrin

And we have yet another broad spectrum pyrethroid insecticide. It’s almost getting boring, except that these products are causing devastating harm in thousands of yards across the country. Straight from the label, this one confirms it’s just as bad as the rest. One interesting thing to note — the label lists the same application rate for both bees and mosquitos. Sometimes the big mosquito control firms claim that the rate of application is high enough to hurt mosquitos but low enough to not hurt bees. We think that claim is total rubbish, and this label seems to agree with us.
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DuraFlex (EPA Reg. #53883-426)
Active Ingredients: Bifenthrin, novaluron, pyriproxyfen

We’ve already talked about Bifenthrin in granular form, this time it’s in the form of a spray. This only makes it’s negative environmental impact worse. Bifenthrin is a PFAS chemical and a known carcinogen. The two new ingredients here, novaluron and pyriproxyfen, are actually not pyrethroids. Instead, they are larvicides. This addition would probably make this product more effective than those without a larvicide. We cover the larvicides in detail in the larvicides section. But again, as the label clearly notes this product is highly toxic to bees. 
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Stryker (EPA Reg. #53883-308)
Active Ingredients: Pyrethrins, piperonyl butoxide

There’s a lot to unpack with this one. First, Pyrethrins - the active ingredient here is actually a “natural” pesticide. It is derived from chrysanthemum flowers and is the model on which the pyrethroid synthetic chemicals are based. Which is the rest of the adulticides discussed here. So does this particular adulticide being “natural” change anything about the outcome? Not really. Still highly toxic to bees, fish, and invertebrates in general. Still listed on the label as being useful for killing caterpillars, spiders, wasps, etc. This is a prime example of why being “natural” does not necessarily equal safe. Sidebar — this pesticide label lists *skippers* as a “pest.” The small, enthusiastic butterflies that cover my ironweed and my phlox. Has anyone ever actually thought to themselves, “Hey, I’d really like to get rid of these butterflies?”

So, we’ve reached the end of the adulticides and we have all broad spectrum Pyrethroids and Pyrethrins. All of them from the same family of insecticides. Traditional mosquito control companies apparently have no originality, but more importantly, they apparently do not care at all about pesticide resistance. Mosquitos have already been documented to have developed resistance to this class of insecticides. Alarmingly, the prolific disease vector Aedes Aegypti seems particularly adept at developing pyrethroid resistance. The USDA conducted a study in Florida and found that 20 out of 20 Aedes Aegypti strains collected throughout the state were resistant (source). It is reckless for mosquito control companies to continuously apply the same class of insecticides to treat mosquitos, when it has been shown both in the US and around the world that mosquitos are developing resistance. So not only are the national franchise mosquito control companies killing beneficial insects, but their treatments are becoming less effective on mosquitos! This is yet another reason to target at the larval stage. Bee-Safe’s baiting stations use 2 active ingredients that are from completely different classes, so you won’t have to worry about pesticide resistance with our system. 

We do see a new active ingredient, piperonyl butoxide. It’s a synergist, meaning it isn’t intended to kill insects by itself, rather it improves the effectiveness of the adulticide. But, it’s still not going to prevent pesticide resistance. It’s often paired with Pyrethrins or Pyrethroids, and it’s definitely less harmful than both, so it’s not worth much discussion.

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Larvicides: Sounds Better…But Are They Safe?


We definitely want to clarify that we don’t oppose larvicides as a whole. But, we do oppose spraying them as the application method, and we can’t endorse using the wrong larvicide in the wrong place. One exception here is anything BTI based. There are BTI sprays that exist, and because BTI is so specific to mosquitos, the damage from spraying should be pretty much zero for beneficial insects. But, BTI is not always 100% effective against all larval stages of all species. So we still prefer to do the work of conducting a proper breeding site inspection and targeted larviciding by hand.

Altosid WXRG (EPA Reg. #89459-104) 
Active Ingredient: Methoprene

Methoprene is an insect growth regulator that’s mode of action is to prevent metamorphosis from progressing in insects. While Methoprene is widely regarded as safe for humans and other vertebrates, the same cannot be said for invertebrates. Thankfully, Methoprene is not considered toxic for bees, though that can’t be said definitively for bee larva. However, Methoprene has been shown to be toxic to several species of Lepidoptera (butterflies and moths) and is considered a broad spectrum insecticide (source). Used in a granular form applied directly to standing water that poses no risk of runoff, Methoprene is likely a safe larvicide to use. However, granules spread across an entire property or sprayed would likely cause death and other sub lethal effects on Lepidoptera populations, particularly the eggs and larva.

Tekko Pro (EPA Reg. #53883-335) 
Active Ingredients: Novaluron, Pyriproxyfen

Novaluron and Pyriproxyfen are both insect growth regulators and work by disrupting the growth of immature insects. They are both considered broad spectrum, which is problematic, given that this product is a spray.

Novaluron is a relatively new pesticide, so there have been relatively few studies on it. However, in at least one solitary bee species, the alfalfa leaf-cutting bee, it has been found to be toxic to the eggs and larva, and can also cause females to lay non-viable eggs (source). The methods of action that caused larval death (of greater than 85%) were diverse. Residue on foliage, contaminated pollen, and direct contact were all found to be capable of causing mortality. It is likely that similar effects would be seen in other bee species. It has also been found to be lethal to the caterpillars of at least one species of Lepidoptera(source). Therefore, we would not recommend spraying this in any area with foliage or flowers. Given that this product is also toxic to fish and aquatic life, we would not recommend spraying it anywhere it could run off, such as on hard surfaces. That pretty much eliminates any possible use case outside of standing water that isn’t likely to run off.

Pyriproxyfen is actually one of the active ingredients in our baiting stations. As a spray, it has many of the same issues as Novaluron. The key difference though is that it is only applied inside baiting stations in our system, and is not applied as a spray or to foliage, the ground, or anywhere else. Because it affects the larval stages, an adult bee that improbably comes into contact with it in the station would be unaffected. Since bee larva remain in the nest, and it is not applied to anything used as food for bee larva, they would not come into contact with it. Very few insects exist as larva in water, the most notable ones being mosquitos and dragonflies. Fortunately, dragonflies prefer larger bodies of water than our baiting stations, and they also prefer to be able to access the water surface easily by flying just over the top of the surface. Our baiting stations do not provide this, so it would be extremely unlikely that dragonflies would lay eggs in our baiting stations. One of the key aspects of our system is the auto dissemination of this larvicide by the female mosquitos to other breeding sites. Fortunately, mosquitos are far more susceptible to Pyriproxyfen than dragonflies, and mosquitos would be incapable of transferring enough Pyriproxyfen to a suitable dragonfly breeding habitat (a larger body of water) to harm the dragonfly nymphs. A dosage of 0.01 ppm of Pyriproxyfen has no effect on dragonfly nymphs, but kills 96-98% of mosquito larva (source). 

The “Green” Options: We Wish Natural Meant Safe

We might ruffle some feathers with our critiques of these products, but we are in the business of telling the truth and trusting the science. We appreciate the attempts the makers of these products have made to be more environmentally friendly, as well as the companies and customers that chose to use these products instead of the more damaging alternatives. However, the safety and efficacy of these products still matter.

Ecovia G (Label) 
Active Ingredients: Thyme Oil, Clove Oil, Lemongrass Oil, Rosemary Oil

Ecovia MT (Label) 
Active Ingredients: Soybean Oil, Clove Oil, Citronella Oil, 2-phenylethel propionate, Lemongrass Oil 

Stop The Bites (Label) 
Active Ingredients: Castor Oil, Lemongrass Oil, Geraniol, Cedarwood Oil, Sodium Laurel Sulfate, Corn Oil


All 3 of these products claim to actually kill (rather than just repel) mosquitos and other pests. Since they have lots of ingredients in common, we will go ingredient by ingredient and assess the safety and efficacy. One important difference is Ecovia G is a granular product rather than a spray, which generally does make it less damaging to beneficial insects. Many gardeners will be familiar with horticultural oil, neem oil, etc. Spraying oils on insects can have the effect of preventing them from breathing, which is how those products work for gardening purposes. This is why spraying oils all over your yard, natural or otherwise, can be inherently damaging. Remember, natural does not always equal safe! Some well known substances derived from plants that most people wouldn’t consider safe: cocaine, opiates, ricin, cyanide…


Lemongrass Oil

Lemongrass oil is found in all 3 products above, and is considered a broad spectrum insecticide and repellent. Unfortunately there isn’t a ton of research on its toxicity to various insects. But, we do know that it is effective as an insecticide against at least one Coleoptera (beetle) species(source), as well as at least one Lepidoptera(butterfly/moth) species(source). We also know that for honeybees it can serve as an attractant(source), while for at least 2 species of wasps, it serves as a repellant (source). Depending on your goals, repelling wasps may be a pro or a con for you. However, it is likely that lemongrass oil is able to cause mortality in other Coleoptera and Lepidoptera species, probably including important pollinators. So for that reason, we wouldn’t recommend spraying a large portion of your yard with lemongrass oil.

Clove Oil

There is very very little research on the impact of clove oil on most groups of insects. The little research that has been done would seem to suggest that bees and Lepidoptera would not be harmed by it. The research does seem to show that it acts as a repellent for seemingly all insects. There are some insects that have been shown to be susceptible to it. While clove oil has performed well as a repellent of mosquitos compared to other essential oils, its performance is unfortunately measured in hours rather than days or weeks (source). In our opinion, clove oil has not shown enough effectiveness to justify covering a yard in it without more data on the impact it has on a variety of insect species. It is perhaps best used as a topical repellent.

Castor Oil

Like many other active ingredients in this category, there just isn’t enough research. There is evidence that castor oil is effective at killing mosquito larva and adults (source). The issue is, there is also evidence that castor oil is effective against the larval stage of at least one Lepidoptera species (source). It is not clear if there have been any studies on toxicity for bees. Due to the potential effect on beneficial Lepidoptera (butterfly/moth) species, we cannot recommend using castor oil in a spray, as caterpillars would likely be present in the same areas that would be sprayed for mosquitos.

Cedarwood Oil

Again, not a lot of research. No definitive research on bees could be found but it is believed to be safe for bees. It was found to cause mortality in 2 Coleoptera (beetle) species and 1 Lepidoptera (butterfly/moth) species (source). It is likely that it would then be toxic to other species within those groups as well, potentially including beneficial pollinators. Cedarwood Oil was also found to be ineffective at repelling mosquitos (source). Therefore, we would not recommend using it as a spray. 

Corn Oil

Corn oil’s mode of action is similar to that of horticultural oil products used commonly in gardening. It essentially smothers and suffocates the insect by blocking air exchange. Because this mode of action suggests effectiveness against a wide range of insects, we would consider it a broad spectrum insecticide. It has been shown to cause mortality in at least one Coleoptera (beetle) species(source) and is thus likely to affect others, potentially including beneficial pollinators. It has also been shown to cause mortality in at least one Lepidoptera (butterfly/moth) species (source). There does not appear to be any research on the effect on bees, though it is likely that any bee hit directly by the spray would be impacted. Because of the potential risks to beneficial Coleoptera and Lepidoptera, we would not recommend using corn oil as a spray.

Citronella Oil and Geraniol

These are grouped together because geraniol is a major component of citronella oil, which is an essential oil derived from the Java citronella plant, a close relative of the lemongrass plant. At high concentrations it can be effective at repelling mosquitos, primarily by masking the scents mosquitos use to target you. This effect, however, is short lived, on the scale of hours rather than weeks. At high concentrations and application rates, citronella oil has been found to be effective at killing mosquitos. However to be an effective method of control, it would have to be much longer acting than it is, since it is targeting the adult stage. It is likely that citronella oil at this high of a concentration and application rate would be damaging to non-target insects since it is applied as a spray and is an oil. There has not been much study on what this impact would be. Given that the impact in repelling or killing mosquitos is so short, and given the potential risk to non-target insects, spraying citronella oil widely across a yard is not recommended. Citronella candles generally do not produce enough of a repellent effect to have a significant effect (source).

2-Phenylethel Propionate

There has been very little study on this chemical. However, it is primarily used as an insect attractant for baited traps, specifically for beetles. It is not clear why this would be included in a mosquito spray product. It is not believed to be effective at killing insects and is usually combined with another insecticide (source).

Sodium Lauryl Sulfate

You likely recognize this one from your bottle of shampoo. It is used extensively in commercial products, and thus is likely safe for humans. It is a surfactant, and its use as a pesticide is typically in flea and tick shampoos. There is very little research on its effectiveness against other insects, including adult mosquitos and all of the many beneficial insects. Applied directly to mosquito breeding habitat, its behavior as a surfactant can cause larval mosquito mortality. (source). It’s likely used in a low enough concentration in a spray formulation that it effectively does nothing to adult mosquitos, but, if it were at a high enough concentration to kill adult mosquitos, given that it also kills fleas and ticks, it is likely it would be very broad spectrum and detrimental to beneficial insects if used in a spray formulation.

Soybean Oil

Soybean Oil has not been shown to be effective as a mosquito repellent at all, despite its presence in mosquito repellant products (source).  It is yet another plant derived oil that’s only plausible mode of action, like the horticultural oil you may use on spider mites, is to suffocate the insect. This is by its very nature broad spectrum when applied as a spray to large portions of a yard.

Rosemary Oil

Rosemary oil has been found to be an effective repellent in high concentrations. However, its effectiveness is measured in just hours, approximately 8 hours (source).  I couldn’t locate any studies showing it would actually kill mosquitos, but it would be the same mode of action as other oils, as mentioned many times on this page. I wouldn’t recommend using rosemary oil, just as I wouldn’t recommend any of the other essential oils on this list. 

Thyme Oil

Yet another essential oil. Thyme oil is regarded as one of the most effective essential oils for repelling mosquitos, but again, it is effective for mere hours rather than days or weeks. It has shown some insecticidal activity, especially against mites (source). Given that it was effective against mites and not against honeybees, it is likely the mode of action was smothering/suffocation, just like a horticultural oil used on aphids and spider mites. Given this, it is either unlikely to kill adult mosquitos because of too small of a concentration or too fine of a droplet size, or it is likely to kill a wide diversity of insects without being very specific to mosquitos.