Do Mosquito Yard Sprays Work? What the Research Shows

Yes, for some mosquitoes and for a limited time. In a University of Kentucky field trial, yards sprayed by a pest management professional had 85% to 90% fewer bites from the Asian tiger mosquito than untreated yards, and leaves from sprayed plants still killed mosquitoes in lab tests up to six weeks later. The same sprays did not reduce Culex mosquitoes, the group CDC ties to West Nile virus.

What a barrier treatment is

A barrier treatment is a residual adulticide: an insecticide sprayed onto vegetation and building surfaces that dries there and keeps killing mosquitoes that land on it. CDC describes residual sprays as targeting the places where mosquitoes land and rest, and notes that mosquitoes rest in dark, humid spots such as under patio furniture, in a carport or in a garage.

Both field trials described below used pyrethroids, synthetic insecticides that act like the pyrethrins extracted from chrysanthemum flowers. EPA states that pyrethroids are toxic to fish and to bees, and that product labels can include buffer zones near water and language to protect pollinators. CDC’s adulticide guidance says not to apply adulticides to plants in bloom or to plants that bees, butterflies and other pollinators visit.

Both agencies tie safety to the label. CDC says EPA-registered adulticides have been studied for effectiveness and safety when used according to label instructions, and EPA says pyrethroids can be used in public health mosquito control programs without unreasonable risks to human health when applied according to the label, while noting that high exposures from accidents or spills can affect the nervous system.

Yard sprays versus area-wide spraying

The spray a homeowner hires and the spray a public mosquito control program releases over a neighborhood are different operations. CDC lists three chemical classes used as adulticides: organophosphates such as malathion and naled, natural pyrethrins, and synthetic pyrethroids such as permethrin, sumithrin and deltamethrin. EPA describes how public mosquito control programs apply pyrethroids: as an ultra-low-volume spray of fine droplets that kills adult mosquitoes on contact, at rates below 4 fluid ounces per acre. A yard barrier treatment, by contrast, leaves a residue on leaves and surfaces that mosquitoes touch when they land.

What the field trials found

Two published trials on suburban properties found fewer Asian tiger mosquitoes on sprayed yards for weeks, and the one that measured Culex found no effect on it.

University of Kentucky, 2007. A pest management professional sprayed bifenthrin or lambda-cyhalothrin, at the maximum concentrations on their labels, as barrier treatments on residential properties, with water-sprayed properties for comparison: 24 properties in all. Researchers measured mosquitoes weekly for 2 weeks before and 8 weeks after treatment, using five methods, including carbon dioxide-baited traps, egg traps and counts of mosquitoes landing on people. Treated yards had 85.1% (bifenthrin) and 89.5% (lambda-cyhalothrin) fewer Asian tiger mosquito bites than the controls, and leaves from treated plants still killed mosquitoes in lab tests up to 6 weeks later. Culex mosquitoes were not reduced by either product. The authors concluded that sprays on low vegetation miss the daytime resting sites of Culex.

North Carolina State University, 2020. Researchers worked with 16 pairs of neighboring yards. One yard in each pair received a bifenthrin barrier spray, larval habitat management (removing or treating standing water), or both, and mosquitoes were monitored in both yards for 33 days. Barrier sprays, alone or combined with habitat management, significantly reduced Asian tiger mosquitoes, with no loss of effect 25 days after treatment. Treatments that included habitat management were significantly more effective. The untreated neighboring yards also had fewer mosquitoes, but those differences were rarely significant.

Why the species matters

A barrier spray reaches mosquitoes that rest in low vegetation near homes and misses those that rest elsewhere. The Asian tiger mosquito, which the NC State researchers describe as a container-breeding mosquito that lives around houses, fits that pattern.

Culex does not. CDC says West Nile virus cycles between mosquitoes, especially Culex species, and birds, and the Kentucky trial found no reduction in Culex. A provider who identifies which mosquitoes are biting in a yard can say whether a barrier spray fits the problem.

Standing water still sets the limit

Sprays kill adults; standing water produces the next generation. CDC recommends that once a week, items that hold water be emptied and scrubbed, turned over, covered or thrown out, naming tires, buckets, planters, toys, pools, birdbaths, flowerpot saucers and trash containers. For large bodies of water that cannot be dumped or covered and will not be used for drinking, CDC lists larvicides.

The NC State trial backs the combination: treatments that included habitat management were significantly more effective.

Misting systems and “natural” sprays

CDC does not recommend automatic misting systems for homes, and EPA generally does not review products sold under the minimum risk exemption. Misting systems spray insecticide on a timer, and CDC’s position covers homeowners and residential areas alike. CDC notes that there are no data on their effectiveness, that they can harm bees, butterflies and other pollinators because they spray while those insects are active, that they may run when no mosquitoes are present, and that users cannot monitor mosquitoes for insecticide resistance.

Some products marketed as natural are minimum risk pesticides, which are exempt from federal registration. EPA says it also does not provide a label review for these products, so what their labels claim has not been checked by the agency.

When to call a professional, and what to ask

CDC’s page on mosquito control at home lists an outdoor adulticide, applied where mosquitoes rest, among the steps outside the home, and its adulticide page names licensed mosquito control professionals among those who apply these products. A company can look for breeding sites, treat water that cannot be removed, and apply residual sprays according to the label. Questions worth asking:

• Which mosquitoes are you targeting, and how did you identify them?
• Which active ingredient will you apply, and on which parts of the property?
• How will you keep the spray off blooming plants and away from ponds, streams and drains?
• How often will you reapply, and how will you check that the treatment is still working?
• Will you find and deal with standing water, or only spray?
• Is your license current for this type of application in this state?