Stop The Spray

Mosquitoes.

They plague our summers and ruin outdoor fun.

The worst pests are Asian tiger mosquitoes: they bite morning, noon, and night, and can breed in a thimbleful of water.

Understandably we want to rid ourselves of this awful pest.

So: What to do about mosquitoes?

Some neighbors turn to commercial mosquito fogging, persuaded by claims that the product is effective and “safe.”

But mosquito fogging is an expensive approach that is neither effective nor safe for the environment.  It harms native bees, butterflies, fireflies, moths, and other beneficial insects and organisms. It contaminates streams, such as Little Hunting Creek.

How effective and harmless is mosquito spraying?

How effective can it be when the chemicals in the product only target adult mosquitos within direct range of the fog?

By some estimates, no more than 20-30% of adult mosquitos are killed in one treatment. Meanwhile all mosquito larvae, which are laid and hatched in standing water, are unaffected. They continue to grow, unaffected by the spraying until they emerge as adults. As a result, the adult population of mosquitos is quickly replenished while nearly every other insect the fog touches is indiscriminately killed.

Mosquito spray producers point to EPA statements that the chemicals are safe for bees when used according to label instructions. But there are severe limitations to the EPA’s testing method. The agency only tests on honeybees and only measures the chemical toxicity resulting from surface exposure, not oral ingestion.

This is problematic. Honeybees are only one species of bees and are non-native to boot. That leaves 400 species of native bees in Virginia, along with all butterflies, moths, dragonflies, ladybugs, fireflies, and numerous other beneficial insects that are not tested. Those insects have entirely different life cycles, foraging methods, and ways of protecting and feeding their larvae which render them tragically vulnerable. It is a folly to extrapolate EPA’s honeybee-focused test results to other insect species.

When EPA approves use of a pesticide, it balances environmental risks against 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 causes. The limits EPA imposes appear on the product label and have the force of law.

When a pesticide is registered for use by the EPA, that does not mean 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 are also known risks.

How does mosquito fogging harm the ecosystem?

Mosquito fogging kills pollinators and other insects.

Pyrethroids are the main chemicals in the sprays that mosquito services use to kill mosquitoes in residential yards.  Pyrethrin is found in nature, so mosquito services advertise the insecticide as “natural.”  But pyrethroids are acutely toxic to terrestrial invertebrates, including pollinators such as bees and butterflies.

One spray of mosquito fog leaves a persistent residue on the surface of everything it touches. Repeating the applications every 10-30 days, as many commercial services recommend, just compounds the problem. The EPA says it considers how long the chemical residue persists in the environment and its effect on honeybee colonies. However, honeybees can forage up to 5 miles away from their hives if necessary, far away from the fogged area and the residue. Our native mason bees, on the other hand, forage no further than 300 feet from their nests. They are wholly dependent on the health of their immediate surroundings to eat and reproduce. Adults have no way to avoid exposure.

Neither do their larvae. Leaf cutter bees and mason bees, for example, produce dough balls that are left in hollow stems for their developing larvae to eat. The balls are composed of pollen and nectar from the flowers in their immediate foraging range. As the larvae hatch and eat the dough balls, they ingest concentrated levels of the pesticides and die. For our native bees, there is no honeybee equivalent of the hive to ensure their survival. They live their lives alone. As their larvae die, all subsequent lines of offspring from affected individuals are gone for good.

Mosquito sprays kill insects and destroy the food web.

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. Amphibians, reptiles, and mammals also depend on insects to survive.

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 streams—such as Little Hunting Creek—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 (ULV) 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 risk is much greater for aquatic invertebrates, who 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.

Control Methods at a Glance

Here are easy, inexpensive and responsible ways to manage mosquitoes:

• Eliminate the source: Standing water – even just a thimble full – means mosquitoes can breed. Get rid of it!
• Larvicides: Let them lay their eggs, but kill the larvae before they become adults to control the adult (biting) population.
• Water Wigglers: If you have water, such as in a bird bath, keep it in motion so mosquitoes can’t lay their eggs.
• Adult Mosquito Traps: Lure adults in, but don’t let them out.
• Personal Protection: Pants, long sleeves and bug spray can help protect your skin.
• Fans: Weak fliers like mosquitoes can’t get close enough to bit if the air is moving.
• Community Efforts: Spread the word and get your neighbors to join you in pesticide-free mosquito control.

More detailed information on these measure below!

How can mosquitoes be controlled without spraying?

Here are some safe and effective approaches to manage their habitat and control the immature stages before the mosquitoes emerge as adults. 

Eliminate the source:  First, you must minimize standing water in and near your yard. This practice kills mosquito larvae before they become biting adults. (Mosquitoes do not breed in flowing water, such as Little Hunting Creek.) Common mosquito larval habitats include corrugated extension pipes coming off downspouts, rain barrels and landscape features such as ponds without fish, bird baths, toys, garden and sports equipment, covers over lawn furniture or tarps covering woodpiles—anything that holds even a small amount of water for at least 7 days. Regularly inspect your property for containers or areas that hold water, then remove or empty them. Change the water frequently in places where you want it – like birdbaths – so the larvae have no time to grow and emerge. Maintain your gutters and downspouts so the water flows. Keep swimming pools and hot tubs clean and properly chlorinated.

Larvicides: To effectively manage mosquitoes, they must be killed before they become adults. Bacillus thuringiensis israelensis (BTI) is an effective biological control, widely available in a product called Mosquito Dunks™ at lawn and garden stores.  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, lay their eggs on the surface, and when they hatch, the larvae are killed by the BTI. Learn how to make your own mosquito larvae traps here.

Water Wigglers: Water wigglers are devices you can purchase to keep water moving in birdbaths. They were designed to attract birds to the sight and sound of running water but also stop female mosquitos from laying eggs. That’s because female mosquitoes want to lay their eggs in funky, standing water, not moving water.

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 (GAT) can eliminate female mosquitoes and significantly reduce populations. GAT traps can be purchased or inexpensively constructed. (Note that dumping all sources of water weekly helps ensure maximum draw of egg-laying female mosquitoes to the trap.

Personal protection. By wearing long sleeves, long pants, and applying insect repellent (such as DEET or picaridin or OLE) to exposed skin, you can protect yourself from mosquito bites while spending time outdoors.

Deck Fans: Mosquitos are weak fliers. Turn on a fan while you enjoy your deck and make it harder for mosquitoes to reach you.

Community Efforts: Mosquito control is very successful when several neighbors in a larger community participate. Talk to your neighbors or give them a brochure developed by the Northern Virginia Bird Alliance about source removal, mosquito larva traps, fans, and water wigglers. Show them your homemade mosquito bucket and encourage them to do the same. Some studies tout this approach above all others, suggesting that mosquito populations can be reduced by 85% when the whole street or block works together.