Pesticide Information

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

Article written by, and reprinted (with slight modifications) and permission of, the Department of Environmental Protection, Montgomery County, MD

Each year, more yards are being sprayed for mosquitoes. Did you know you could be poisoning your yard and, at the same time, 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 mosquitoes and pollinate your yard.

To learn more about the problems with mosquito spraying, we interviewed Deborah Landau (DL), an entomologist and conservation scientist at The Nature Conservancy, and Mary Travaglini (MT), 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.

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 mosquitoes, 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 mosquitoes that are in your yard at the time of spraying. Mosquitoes 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. Mosquitoes 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 mosquitoes, 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 mosquitoes. Sadly, birds will often pick up insects killed by insecticides, and eat them or feed them to their young.

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 one 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, mosquitoes become resistant to pyrethroids (the active ingredients in most mosquito treatments) through gene mutation in mosquito populations. Mutations in just this one single gene are enough to make mosquitoes 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.

Is there anything I can do to control mosquitoes 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 mosquitoes)!

MT: There’s a reason why Disneyland, in a part of Florida with lots of mosquitoes, doesn’t use pesticides to control mosquitoes. 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.

DL: Prevent mosquito bites by wearing long sleeves and using non-toxic repellents that use oil of lemon eucalyptus (OLE). Data shows OLE-based repellents 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 – mosquitoes 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.

Here’s another tip: If you’re looking for a way to reduce mosquitoes, 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!

Resources

A plan titled, "Pesticide Education Plan for North Oaks Residents: Working to Change the Way People View the Use of Pesticides" was approved by City Council on February 11, 2021. The plan was written by a committee consisting of city residents and several North Oaks Natural Resources Commission members, as well as representatives from NOHOA, the North Oaks Golf Club, and the North Oaks Company.

This is Phase 1 of the plan, which specifically addresses mosquito and tick control. In the future, a plan to address the use of other insecticides, herbicides, and fungicides will be drafted. This plan dovetails nicely with the City's Pollinator Resolution that was passed in July of 2019.

• Pesticide Education Plan
• What you Don't Know Can Hurt You
• Tips for Reducing Mosquito Bites
• Backyard landscape best practices for pollinators
• Natural Wildlife Magazine article on Backyard Mosquito Spraying
• Conservation guide; pollinators, plants, pesticides
• Pretty Plants with Deadly Consequences: Beware Neonicotinoids