Photo: Carolina Chickadee, Randy Streufert/Audubon Photography Awards
Elizabeth Train, Elizabeth Martin, Sarah Mayhew, and Barbara Tuset
Northern Virginia Bird Alliance’s Wildlife Sanctuary Program certifies yards and other properties as Wildlife Sanctuaries when property owners take steps to improve habitat and create a healthy yard that supports wildlife, and then observe 10 Sanctuary Species nesting, foraging, sheltering, or otherwise using the property. To qualify their yards, property owners are must adopt the Healthy Yard Pledge, including pledges to “Reduce pesticide and fertilizer use – No broad-spectrum spraying for mosquitoes” and to “Conserve water and protect water quality.”
Recently, we were confronted by the question of whether a yard where the homeowner has taken many steps to improve habitat can be certified as a Wildlife Sanctuary when the homeowner also employs a regular mosquito spraying service.
We reviewed the evidence and decided that the answer is no: broadcast spraying for mosquitoes is not consistent with creating a functioning wildlife sanctuary in one’s yard.
To qualify as a wildlife sanctuary, a residential yard should benefit wildlife species living in or visiting it at all stages of their lifecycles. Because insects are so critical to a healthy ecosystem and such a vital foundation for the food web, they should be protected along with other wildlife. Birds (as well as amphibians, reptiles, mammals, and virtually all native wildlife) depend on insects as prey. Nesting birds require an ample supply of caterpillars and other insects to support their nestlings.
A functioning wildlife sanctuary also should benefit the larger environment. Residential yards significantly affect water quality and aquatic ecosystems via streams that run through or adjacent to them, or stormwater runoff that is transported to streams by storm drains.
We conclude that the effects of mosquito spraying on insects and on the larger environment are too harmful to be approved in a Wildlife Sanctuary. Therefore, we will not certify a property as a Wildlife Sanctuary if the owner is spraying for mosquitoes.
Below we summarize our major concerns with mosquito spraying; our more detailed and fully documented discussion is in a longer paper available here.
Mosquito sprays kill pollinators and other insects essential to a functioning wildlife sanctuary.
Pyrethroids, the main chemicals that mosquito services use to kill mosquitoes in residential yards, are a class of broad-spectrum insecticides that are acutely toxic to terrestrial invertebrates, including pollinators such as bees and butterflies. Mosquito sprays kill all insects, including the caterpillars that birds rely on to feed their young throughout the breeding season. Nearly all terrestrial birds (96%), even seed eaters, feed their nestlings insects.
Pyrethroids used in mosquito sprays contaminate surface waters and kill aquatic organisms.
Spray drift can carry the chemicals directly to water, or residue can be carried to a stream through storm drains. Applying the chemicals to impervious surfaces, such as sidewalks and driveways, increases runoff into streams. If an applicator uses ultra-low volume spraying, which sprays fine or very fine droplets, the risk of drifting spray is greater, because droplets remain airborne longer.
Pyrethroids do not volatilize, are not soluble in water, and bind tightly to soil. They build up in sediments and affect benthic (sediment-dwelling) communities. There is some risk to fish, but the risks are much greater for aquatic invertebrates, because they live in the sediment where pyrethroids accumulate.
EPA reports that pyrethroid detections are widespread in surface waters across the United States, including effluent from sewage treatment plants, urban streams, and downstream of agricultural areas. Insecticide contamination is greater after storm events and near sites where the chemicals have been applied.
Following pesticide label instructions does not prevent harm to non-target species and the larger environment.
Following label instructions reduces but does not eliminate harms. When EPA approves use of a pesticide, it balances its environmental risks against its benefits. For example, pesticide use may control disease-carrying insects that pose a public health threat or control insects that threaten crops or structures, such as termites. In striking that balance, EPA attempts to impose limits on use and application that reduce the harm the chemical can cause. The limits EPA imposes appear on the product label and have the force of law.
When a pesticide is registered by the EPA for use in agriculture or horticulture, that does not mean that it is safe for non-target insects or aquatic organisms, even when applied according to label instructions. It means that there is an economic benefit to using it even though there also are known risks.
You can control mosquitoes without spraying.
The most effective, least harmful mosquito control strategy relies on habitat management and controlling the immature stages before the mosquitoes emerge as adults.
The first imperative is to minimize standing water. Common mosquito larval habitats include corrugated extension pipes coming off downspouts, rain barrels and landscape features such as ponds without fish, containers, bird baths, toys, garden and sports equipment, folds on tarps—anything that holds even a small amount of water for at least 7 days.
Larvicides
Effective mosquito management relies on killing them before they become adults. Bacillus thuringiensis israelensis (BTI) is an effective biological control, widely available at lawn and garden stores in a product called Mosquito Dunks™. The dunks are safe for birdbaths, rain barrels, ponds, ditches, tree holes, roof gutters, and anywhere water collects. One way to manage mosquitoes is to entice them to breed in a bucket filled with water, some straw, and a BTI dunk. The females are attracted to the scent of the straw and water and lay their eggs on the surface. When the larvae hatch, the BTI kills them. See how to set up a mosquito larva trap.
Lethal adult mosquito traps
Once larval habitats have been eliminated by removing or treating all sources of standing water, using a lethal trap that mimics a good oviposition site (larval habitat) such as the Gravid Aedes Trap can eliminate female mosquitoes and significantly reduce populations. GAT traps can be purchased or inexpensively constructed. Dumping all sources of water weekly helps ensure maximum draw of egg-laying female mosquitoes to the trap.
Personal protection
People can protect themselves directly by wearing long sleeves and long pants, applying insect repellent (such as DEET or picaridin or OLE) to exposed skin, and, when seated outside, deploying a fan to discourage mosquitoes.
So, while taking steps to protect our families from mosquitoes, let’s do all we can to protect all the creatures who share our environment!