An interview with experts: Are backyard mosquito sprays safe and effective?

Person spraying pesticides in air
July 20, 2020

We get a lot of questions and concerns about backyard mosquito sprays. We interviewed two experts to learn more about the risks.

Each year, more yards are being sprayed for mosquitos. Did you know you could be poisoning your yard but mosquito populations are not being reduced?

Before deciding to spray your yard, know the facts. Spraying can harm you, your kids, pets and your neighbors. The chemicals can also harm birds and insects that help eat mosquitos and pollinate your yard.

To learn more about the problems with mosquito spraying, we interviewed Deborah Landau, an entomologist and conservation scientist at The Nature Conservancy, and Mary Travaglini, a certified organic land care professional and organic landscape manager at the Montgomery County, MD Department of Environmental Protection. These experts agree: Mosquito treatments, including the alleged “all natural” variety can harm you and your environment, while not actually reducing mosquito populations.

Person spraying pesticides in air

How effective are mosquito sprays?

MT: Published and peer-reviewed research by Professor David Pimentel shows that only 0.1% of the pesticides on average reached the target pests. [Pimentel, Cornell University 1995]. When Pimentel looked specifically at flying insects in the study, like mosquitos, the average was less than 0.0001%, or only one in a million. This is because the droplet size of a pesticide must be small and must float in the air.  The droplet size of a mosquito spray must be so small that the chemicals must float in the air, but they also easily drift out of the target area, killing other insects or mingling into the air we breathe.

DL: Sprays can only kill mosquitos that are in your yard at the time of spraying. Mosquitos typically fly 1-3 miles, so they can quickly re-populate your yard. A commercial mosquito treatment will be more likely to kill butterflies, bees and ladybugs in your yard at the time of application than the mosquitoes you’re trying to get rid of. Mosquitos are most active at dawn and dusk, but mosquito spray companies often come during the day when most pollinators are active.  If the treatments target standing water, beneficial insects that eat mosquitos, like dragonfly larvae, will also be killed. If the spray is focused on wet areas, such as piles of wet leaves, chances are they’re killing far more fireflies than mosquitos. Sadly, birds will often pick up insects killed by insecticides, and eat them or feed them to their young.

Dead bee in a flower

What am I getting for my 300 dollars’ worth of a pesticide spray?

MT: If we turn the .0001% effectiveness into dollars and cents, a millionth of $300 dollars’ worth of spraying is .0003, which is not even a third of a penny. In fact, we’d have to spend $10,000 before we even got once cent worth of value! Spend your time and money cleaning gutters, removing standing water, and getting together with the neighbors to do this throughout the neighborhood.

DL: Over time, mosquitos become resistant to pyrethroids (the active ingredients most mosquito treatments) through gene mutation in mosquito populations. Mutations in just this one single gene are enough to make mosquitos in one area resistant to the pesticides very quickly. Companies that spray on a regular schedule will make your mosquito population become resistant even faster. So essentially, you’ll be left with a yard and neighborhood full of super skeeters.

Mosquito staying dry under a wet leaf

Is there anything I can do to control mosquitos in my yard besides spraying?

DL: If you want more bang for your buck, purchase BTI mosquito dunks; they’re cheap, effective, and easy to use (you just place them in areas that hold water). And these are a bacteria that will only kill mosquito larvae. You should always remove standing water from your yard, including under flowerpots, inside wheelbarrows, and pretty much on anything plastic. Don’t forget to clean out your gutters even in summer (you’ll be rewarded with a dry basement in addition to fewer mosquitos)!

MT: There’s a reason why Disneyland, in a part of Florida with lots of mosquitos doesn’t use pesticides to control mosquitos. They take an approach that neighborhoods, HOAs, and businesses can all use right here—they ensure water doesn’t stay standing long enough for a mosquito to lay its egg and hatch into an adult—which is about 7 days.

Cleaning gutters reduces mosquitos

I still hear about West Nile virus? Is this a concern?

MT: The CDC reported 6 cases of West Nile in Maryland in 2019, and no deaths. In 2018, there were 245 cases of all types of mosquito borne illnesses in Maryland, although it cannot be attributed to whether those were carried in the bodies of visitors or spread by mosquitos in the State. I looked up estimated cancer diagnoses for the first half of 2020, and we’re already at nearly 35,000 cancer cases. I’ll choose long sleeves and clearing standing water instead of spraying chemicals that won’t actually be effective but are a risk to my health.

DL: Prevent mosquito bites by wearing long sleeves and using non-toxic repellents that use oil of lemon eucalyptus (OLE). Data shows OLE-based repellants are just as effective as the synthetic DEET formulations. DEET can be toxic at high levels and can damage synthetic clothing. A fan on your deck can be surprisingly effective – mosquitos are weak fliers, and the breeze from a fan will not only cool you off but will keep them away from the area.

What about the “all natural” alternatives that a company has told me about?

MT: Companies might describe that the chemicals used are derived from chrysanthemum flowers, but they are not from plant extracts. Commercial pyrethroids are synthetically produced to mimic the same properties of the pyrethrins in chrysanthemum flowers. Both chemicals paralyze the nervous system of many insects, but synthetic pyrethroids and the undisclosed chemicals they are mixed with are designed to be more lethal. Pyrethroids are neuropoisons in humans, and can cause rashes, respiratory distress, allergic reactions, headache, nausea, convulsions, and more. The additives can cause a host of other reactions. Pyrethroids are also very toxic to fish and other aquatic life, and spread easily on the wind to neighboring properties and into streams. The chemicals can persist on surfaces for days, further killing insects that come into contact.

MT: I looked up the data from the national poison control centers – over 27,000 calls were placed to poison control in 2018 for pyrethrins and pyrethroids, accounting for over 33% of the pesticide calls to poison control alone! Imagine how many more exposures are unknown.

Child sitting in the grass

Here’s another tip: If you’re looking for a way to reduce the entire population, consider these simple devices called OviTraps—used by the military around the world effectively to reduce mosquito populations. Don’t forget to keep removing standing water from your yard all summer long and remind your neighbors to do the same. Your neighbors, pets, birds, pollinators, fireflies and skin will thank you!


2 comments on "An interview with experts: Are backyard mosquito sprays safe and effective?"

  1. Scott Gordon says:

    In Montgomery County a major pest mosquito is the Asian tiger mosquito, an aggressive day biting invasive species. This species often remains in the immediate environment, flying only a few hundred yards, especially when the location provides all of its essential living requirements: a bloodmeal source for reproduction, sugar/nectar for energy, adequate resting sites and available egg laying sites. I agree that there are alternatives to backyard pesticide spraying such as using environmentally friendly alternatives like Bti, but I would not recommend ovitraps for general use. While they are frequently used by scientists as a mosquito surveillance and research tool, they can become a problem if not properly maintained. Ovitraps are small soup-size cans, painted black, partially filled with water and provided with a substrate (wooden paddle or paper lining) on which mosquitoes will lay their eggs. Ovitraps must be inspected and maintained on a weekly basis which includes replacing the egg substrate, dumping out the water and replacing it with new water). Failure to do this maintenance can result the ovitrap becoming a mosquito producer. Any eggs laid on the substrate will hatch when it rains and the new breeding site will attract more tiger mosquitoes. Since ovitraps are often put out in large numbers, a portion often go missing, either through the action of animals or just failure to relocate a trap. Another drawback to ovitraps is that they do not trap and kill the egg laying female mosquito. Since container breeding mosquitoes often practice “skip oviposition” where they lay only a portion of their eggs in any one container, by not trapping the egg laying female the ovitrap at best collects only a small portion of her eggs and she can move on to other sites. A better alternative is the gravid Aedes trap (GAT) which traps the egg laying female on a sheet of sticky paper inside the trap before she can lay her eggs thereby preventing both the next generation of eggs from hatching and removing egg laying females from the population. These traps require no power, use no toxic chemicals, are relatively inexpensive and require very little maintenance. Several neighborhoods in Montgomery County are encouraging residents to join in large scale tiger mosquito control programs using GAT traps. A paper published in Nature in 2018 by Brian Johnson and others “Neighbors help neighbors control urban mosquitoes” describes the results of first 2 years of a control program using GATs in University Park, MD. The paper is open access and available at

  2. Richard Kramer says:

    Keep in mind that the Ovitraps are effective for some aedes species as Scott mentions. The problem is with other genera such as culex that have a greater flight range.

    Disney isn’t a good model for residential mosquito management. They control 10s of thousands of acres so they can larvacide and use other methods to prevent larval development – manage the breeding sites ( water) and you control mosquitoes. You can not control your neighbors yards and their breeding sites.

Leave a Reply

Your email address will not be published. Required fields are marked *