THEGREENGROK    The Chemical Marketplace

The Chemicals That Promise Summer Without Mosquitoes

by Bill Chameides | April 24th, 2014
posted by Wendy Graber (Researcher)

Permalink | 3 comments


What would you do to avoid the bite of a mosquito? (Lukas Hofstetter)

More than 80,000 chemicals are produced, used
and present in the United States. These
are some of their stories.

What else are you getting with services that offer mosquito-free yards?

Growing up in New York in the ‘50s, mosquitoes were a summertime nuisance — a source of lots of scratching but not much more than that. Today, with the appearance of West Nile virus and Dengue fever, each bite poses a potential (albeit remote) health threat. These days controlling mosquitoes is not only serious business, but fodder for big business.

The Mosquito Eradication Business: Looking to Take a Bite Out of Your Wallet

A message urging to “Safeguard Your Yard” may have appeared in your inbox. Other offers abound on the Web promising “No bugs. No bites. No kidding,” or simply joyfully announcing that  “Outside is Fun Again.

The hook might vary, but they are all selling the same service: to wipe out the mosquitoes in your yard through (1) barrier spraying your yard “to coat trees, shrubs, and foliage” with an insecticide and/or repellent every three weeks or so; or (2) a misting system — think something akin to a installed sprinkler system — that would spray your yard with chemicals at set intervals (typically multiple times per day).

Are you tempted? It’s understandable. Who wouldn’t want to “send mosquitoes packing before they can ruin the fun”? Unfortunately there is a catch: getting rid of the pesky, buzzing biters requires zapping them with a chemical solution that may pose health risks to you and your family.

Now you won’t be surprised to learn that all of the companies we looked into claimed to be using chemicals that are safe and “approved by the U.S. Environmental Protection Agency.”1  But as the savvy buyer in the chemical marketplace knows full well, such claims should be taken with a grain of salt, even if they claim that the chemicals are derived from natural products.2  For example, some companies tout the safety of their chemicals by noting that they are derived from chrysanthemum flowers. Others note that they use synthetic versions of those same flower-derived chemicals. Despite the emphasis on natural, the issue is that these chemicals may have some nasty properties for you and me. So as always in the chemical marketplace: caveat emptor.

mosquito pupa

Mosquito pupa. (Alberto Garcia)

Case Study – Company A

Here’s what we learned from a few phone calls and a little digging into one company that shall remain nameless. The company uses bifenthrin for barrier spraying and permethrin and piperonyl butoxide (PBO) for misting.  Bifenthrin and permethrin are broad spectrum pyrethroid insecticides, PBO is a synergist that makes insecticides more potent.

Like so many of the tens of thousands of chemicals in the marketplace, there is limited data available to assess the risks of these chemicals. Because they are pesticides they are regulated under the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA). Under the act, EPA is given authority to license a pesticide but only if it can ascertain that it does not pose any  “unreasonable adverse effects.” In doing so, EPA must balance the risks to people and the environment against the benefit of its use “taking into account the economic, social, and environmental costs and benefits of the use of any pesticide.”

So here’s an important point: preventing an “unreasonable adverse effect” from a chemical is not the same as assuring that it is safe. So a company trying to sell you a mosquito spraying system may tell you that the chemicals they use are EPA approved; that’s great, but that does not mean they are risk free.3


The local franchise of the company TheGreenGrok talked to stressed that bifenthrin (as used) is milder than DEET (the preferred topical insect repellent for many), similar to the toxicity of a hair lice treatment, and has EPA’s lowest caution ranking.  All that is well taken, but it is also worth noting that, according to the National Pesticide Information Center, bifenthrin is highly toxic to fish and small aquatic organisms, very highly toxic to bees, and classified by the U.S. EPA as a possible human carcinogen based on research on mice. Rat studies, on the other hand, did not show carcinogenic effects.

EPA reports than bifenthrin is “relatively persistent in the environment…[and] has the potential to bioaccumulate.” Other more recent work (based on animal models and human cell lines rather than studies of actual people) hints that bifenthrin may have additional toxic effects (including endocrine disruption, DNA damage, fertility issues, and increased risk for inflammatory responses). When fed high doses, both rats and rabbits developed tremors.

People and pets are advised to avoid areas recently sprayed for a minimum of 20 to 30 minutes until the solution dries to avoid acute effects, which according to the National Pesticide Information Center can include numbness and itching with contact. Breathing in bifenthrin can be an irritant and eating it is a no-no. So if you have a toddler running around your backyard, pulling grass and leaves, and putting them in his or her mouth, it’s probable that they are ingesting some pesticide. Spray drift can be an issue and water body contamination is to be avoided. Pets can experience acute effects as well, including vomiting, reduced activity, and partial paralysis. (Read more here. See video of spraying here.)

Bifenthrin does not exactly sound benign to me.


As we’ve written before — permethrin is classified by EPA as “likely to be carcinogenic to humans” based on animal studies. Animal studies also point to permethrin as an endocrine disruptor. Even so, EPA concluded in 2009 [pdf] that, given their knowledge at that time, permethrin was below their level of concern. On the other hand, the National Pesticide Information Center’s factsheet [pdf] for permethrin shows it has a similar profile to bifenthrin for its acute effects on people and pets, and its toxicity to bees and aquatic life.


PBO is also considered a possible human carcinogen [pdf] and has been linked to delayed cognitive development in toddlers similar to problems posed by other prenatal neurotoxicants such as lead. (More here.)

Are They Safe?

If by safe you mean without any risk, the answer is certainly “No.” No system that uses insecticides is risk free. The level of risk will depend upon the specific chemical being used, the caution you take in hightailing it away from your yard when the spraying or misting occurs, and the frequency and amount of spraying that occurs. Whether or not one of these systems is for you depends on how much risk from chemical exposure you are willing to take vs. how much you want to rid your yard of mosquitoes.

And remember:
1. Just because you are told that EPA has approved the chemical does not mean it is safe.  It just means that is doesn’t have an “unreasonable adverse effect.” According to the agency: “no pesticide is 100% risk free.
2. Even a chemical linked to a natural product such as chrysanthemum flowers may still be toxic and carcinogenic.


There are about 200 species of mosquitoes in the U.S. A mosquito can lay its eggs in as little as a teaspoon of water and it takes about a week for the adults to emerge.


What About Good Neighbors?

I recently received an e-mail inquiry from a reader of TheGreenGrok asking if his family is being put at risk from the “pyrethrin” in a neighbor’s misting system. So far we’ve been talking about pyrethroids — the synthetic versions of pyrethrins.

Pyrethrins are generally considered less toxic and less persistent than their synthetic cousins and generally less effective, which is why synthetic versions were developed in the first place. For example, pyrethrins are allowed on organic foods, but are still highly toxic to aquatic organisms, toxic to bees and other beneficials, and can cause acute effects like skin irritation and coughing in people [pdf]. Taking data from animal studies, EPA has wavered on whether pyrethrins are carcinogenic and currently finds that they are unlikely to cause cancer in people [pdf]. However, pyrethrins are often used with other chemicals like PBO to make them more effective.

So the answer to the emailer’s question is that if enough of the insecticide wafts over to his yard, he and his family may be at some risk. I suspect that the risk is probably small, but it ultimately depends upon many, many factors: whether other chemicals are present, the size of the two yards, where the misting nozzles are located, the size of the droplets being misted, the wind conditions when they spray, and the sensitivity of the family members to the chemicals.

If the concern about a neighbor’s misting or barrier spraying system is significant, one recourse it to find an environmental chemist to look for traces of insecticide in your yard and perhaps even in your blood or urine samples. I am not a lawyer, but it is possible that positive findings might provide grounds for a cease and desist order. Negative results should provide some peace of mind.

Bottom Line

If you are contemplating using a barrier spray or misting system, I would advise you to find out what chemicals the company plans to use and carefully check the health effects data on those chemicals.

And before going forward, bear in mind that EPA reports that these systems

“have not yet been studied sufficiently to document their effectiveness in controlling mosquitoes or other yard and garden pests, nor have they been scientifically proven to control or prevent the spread of West Nile Virus or other diseases.”

The American Mosquito Control Association also has several concerns about misting systems.   And don’t forget the time-tested low tech approaches for dealing with mosquitoes: eliminate standing water, sit outside with a fan to blow those buggers away, and, when all else fails, become a sultan of swat.


End Notes

1 EPA registers pesticides for certain uses. As the toxicity of the chemical increases, its use becomes more restricted and more directed. EPA’s approval assumes use of a chemical is as directed.

2 TheGreenGrok did not identify all the chemicals in all the products used by companies linked to in this post. Some companies report using all natural repellents or garlic as the active ingredient in sprays. No chemicals—natural or otherwise—were reviewed other than the ones discussed in the post.

3 In the case of bifenthrin, EPA has begun a review of its safety and expects to complete its study sometime in 2016.

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  1. Lowelda
    May 4, 2014

    I am surprised that you did not delve into DEET which is highly toxic, has a long FDA warning label, and is aggressively marketed to unwitting consumers.

  2. Solar Landscape Lights
    Apr 28, 2014

    Great article and advice.

    Thank you

  3. Philip Haddad
    Apr 25, 2014

    Good timely advice. In particular the pointing out of the threat to bees, without which, pollination becomes inefficient and crop loss becomes expensive.


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