If you’ve noticed all the lawn signs for mosquito treatments, you may be wondering if mosquito yard sprays harm other insects. If so, you’re not alone. As an Extension entomologist, this is a common question that I get from the public every year. To get to the bottom of this question, it helps to understand the different types of mosquito spraying that’s done.
One approach (Ultra Low Volume or ULV) is sometimes used by municipalities or abatement districts to control mosquitoes. These ULV applications generally involve using specialized equipment mounted on trucks or aircraft to apply extremely tiny droplets which kill adult mosquitoes by direct contact as the droplets float in the air. Such applications use very small volumes of insecticides either undiluted or with minimal dilution and are often applied after dark when mosquitoes are most active. The microscopic droplets from ULV treatments disperse relatively quickly and have little residual activity—think of them like a “one time strike” to knock down mosquito numbers.
The vast majority of research on mosquito sprays and non-target organisms has looked at these ULV-type treatments. Some good news is that these studies suggest that impacts to non-target insects are relatively small and short-lived. It turns out that the ULV treatments are most effective on insects with very small body mass, so insects larger than mosquitoes tend to be spared. A good summary of the impacts of ULV treatments on non-target organisms can be found in a 2012 review paper by J.A.S. Bonds in Medical and Veterinary Entomology.
Case closed, right?—Not quite. Here in Wisconsin, we don’t really use ULV treatments a whole lot for mosquitoes. The common yard treatments are what we’d call “perimeter”, “barrier”, or “residual” treatments. Such treatments are applied via a backpack sprayer to create a coating or “barrier” on treated surfaces which affects mosquitoes that land on it. These treatments involve applying a residual insecticide (usually from the pyrethroid group) to vegetation in yards and around structures. The pyrethroid products are broad-spectrum and often last for a few weeks or longer depending on the formulation. These same ingredients (and sometimes the exact same products) can also be used to control a wide range of yard, garden, and structural pests (e.g., Japanese beetles, garden pests, household ants, etc.).
While the pyrethroids are very common and widely used for a range of purposes, there’s a knowledge gap when it comes to the impacts of mosquito “barrier” treatments on other insects. While this knowledge gap exists, a few studies raise concerns. One study by Dr. Karen Oberhauser and colleagues found that monarch caterpillars could be harmed or killed even 3 weeks after spraying. A more recent (2022) study by Qualls et al. found that honey bees were harmed 28 days after “barrier” treatments were applied. Thus, if a yard is being sprayed for mosquitoes monthly during the warm season, there are reasons for concern. More research is needed to help understand the effects of these “barrier” yard treatments on insects that often land on vegetation in yards, such as moths, butterflies, fireflies and other beetles, true flies, bees, wasps and other pollinators.
- Bonds, J.A.S. 2012. Ultra-low-volume space sprays in mosquito control: a critical review. Medical and Veterinary Entomology. 26: 121-130.
- Oberhauser, K.S., Brinda, S.J., Weaver, S., Moon, R.D., Manweiler, S.A., and N. Read. 2006. Growth and Survival of Monarch Butterflies (Lepidoptera: Danaidae) After Exposure to Permethrin Barrier Treatments. Environ. Entomol. 35(6): 1626-1634.
- Qualls, W.A., Moser, B.A., Periera, R.M., Xue, R-D, and P.G. Koehler. 2022. Impacts Of Barrier Insecticide Mixtures On Mosquito, Aedes Aegypti And Non-Target Honey Bee, Apis Mellifera. Journal of the Florida Mosquito Control Association 69: 34-42.