By Leslie A. Cameron, Extension Master Gardener
Mosquitos in Northern Virginia can make our gardens uncomfortable places. How can we eradicate these pests without damaging the environment?
Why Spraying for Mosquitoes Might Not Be Your Best Option
Hiring a mosquito control company can be costly. Treatments typically occur every three or four weeks at an estimated cost of $40-$70 each, which can run $500 to $800 or $900 for a three-month season, depending on the size of the property and frequency of treatments. In addition, although insecticides used today are safer, no insecticide is 100 percent safe. The active ingredients in the most commonly used mosquito sprays are pyrethroids and organophosphates. Organophosphates are toxic to many species of birds and to animals, and pyrethroids are highly toxic to honeybees, fish, and aquatic invertebrates (not just mosquitoes), and even though they have low toxicity to humans, birds, and animals, mosquito control companies typically recommend that children and pets stay indoors during spraying and for 30 minutes to an hour after.
Insects are declining dramatically in number and diversity. Researchers Sánchez-Bayo and Wyckhuys (2019) reviewed more than 70 historical reports of insect decline from around the world. Among their findings:
- A German study documented a 76 percent decrease in flying insects over just three decades.
- A study in Belgium reported that 19 of 64 species of butterfly had gone extinct since 1834, and 69 percent of remaining species were steadily declining.
- The Illinois Natural History Survey reported that half of 16 bumblebee species surveyed had declined in numbers from 1900 to 2007, and 4 species had become extinct.
- A study in the Netherlands, Belgium, Luxembourg, and Denmark found that 34 percent of 419 species of ground beetle declined between 1950 and 1980.
Sánchez-Bayo and Wyckhuys estimated that roughly 41 percent of insect species are in decline and that a third of all species are threatened with extinction in the countries included in the studies, and they believe we are in the midst of the largest extinction event on Earth since the late Permian (248 million years ago) and Cretaceous periods (over 65 million years ago).
In a Puerto Rican rain forest, researchers Lister and Garcia (2018) also found declines in lizards, frogs, and birds, which rely on arthropods for food. They concluded that the decline in the abundance of arthropods is “indirectly precipitating a bottom-up trophic cascade and consequent collapse of the forest food web” (Lister & Garcia, 2018, p. E10397). North America has nearly three billion fewer birds than were here 50 years ago. The decline in availability of insect food supply is considered a critical factor.
The widespread use of pesticides is one of several factors thought to be driving these staggering declines. For more information on what is happening to insects, see “Insects Make My Food And… Other Reasons We Should Worry About the Decline in Bug Populations.”
We need insects to pollinate food crops, to aid in decomposition of dead plants and animals and returning nutrients to the environment, and to keep pest insects in check.
In the words of entomologist Doug Tallamy: “The reason we need to stop hating [insects] is because we won’t exist on this planet without them… If we succeed in our war of eliminating insects, we’re actually killing ourselves.”
What We Can Do to Protect Ourselves and Our Families Instead of Spraying Pesticides
It helps to understand mosquitoes and their lifecycles. Mosquitoes can live up to three months, and overwintering adult mosquitoes can live up to eight months. Hibernating females become active in late spring when temperatures reach 50 degrees, and they always lay eggs in standing water. The eggs hatch within 2-3 days, and adults appear 7-10 days later. Only females bite. They need a blood meal to lay eggs, which they then lay in water, and the cycle starts again. They track down humans and animals to bite by smelling exhaled carbon dioxide, by seeing us (they can see in shades or black and white and they can see movement), or by body heat.
Of the 30 species of mosquito common in Virginia, the two most commonly encountered in our area are Culex pipiens (Culex) and Aedes albopictus (Asian tiger). The small brown Culex mosquitoes (which can transmit West Nile) are most active and more likely to bite at dawn or dusk. Their range is a half mile to two miles. The Asian tiger mosquitoes (which can transmit West Nile, yellow fever, and other diseases) are most active and more likely to bite during the day. Their range is around 600 yards.
Controlling mosquito populations at the larval stage is the most effective strategy. This means getting rid of temporary standing water, even very small amounts. (Permanent pools attract predators that eat mosquito larvae.) In our yards and landscapes, temporary water sources include ditches, holes in trees, bird baths, saucers under potted plants, leaky hoses, wagons and other toys, kiddie pools, clogged rain gutters, drains at the ends of downspouts (especially corrugated), open trash bins, upturned lids, wheelbarrows—any place where even a tablespoon of water stands for more than seven days. Empty these containers at least every seven days. Where it is difficult to empty the water, use BTi (Bacillus thuringiensis israelensis, the active ingredient in Mosquito Dunks and Bits), which is selective and kills mosquito larvae without harming birds, beneficial insects, or other wildlife.
When outside at times mosquitoes are active, wear repellent (25%-30% DEET, 20% Picaridin, oil of Eucalyptus, or IR-3535[Merck 3535]), make sure screens don’t have holes, and wear long sleeves and pants. Use oscillating fans when sitting outside—mosquitoes are weak flyers.
Property managers can make sure gutters, downspouts, and drain pipes drain freely, and water doesn’t accumulate on flat roofs. Rain barrels and cisterns should be securely screened or sealed.
Mosquitoes can rest and breed during the day under dense ground covers that provide a moist, shady environment. Consider replacing dense ground covers like English ivy (which is nonnative and quite invasive) with native, less dense ground covers, like Pachysandra procumbens (Allegheny spurge), Eurybia divaricata (white wood aster), or other native ground covers.
Pesticide sprays have only minimal and short-term effectiveness. These pesticides kill the adult mosquitoes that come into contact with the spray. Given their rapid lifecycle, mosquitoes will repopulate quickly. Common ingredients like pyrethroids (including Permethrin, Resmethrin, Sumithrin) and Organophosphates (Malathion, Naled) used in these sprays are toxic to other insects and in some cases animals. These pyrethroids, which are synthetic versions of naturally occurring pyrethrins, were engineered to be more stable in sunlight and to last longer in the environment, increasing the length of time pollinators and other beneficial insects may be exposed. If you must use a pesticide applicator, ask if they are licensed by the Virginia Department of Agriculture and Consumer Services (VDACS), whether they use integrated pest management strategies and not just adulticides, and whether their staff is trained on proper application. Pesticides should not be applied when pollinators are active, on food crops, on flowering plants that pollinators visit, on windy days, in the hottest part of the day, or before rain. If you suspect misuse of a pesticide, contact the Virginia Department of Agriculture and Consumer Services, Office of Pesticide Services at 804-371-6560.
The following tactics do not work: bug zappers, spraying Listerine, wearing dryer sheets, VapoRub or vanilla; wristbands, ultrasonic devices, plants marketed as mosquito-repellent, propane driven CO2 emitters, bats or purple martins (mosquitoes make up just 1%-3% of their diets), or eating garlic.
More information on controlling mosquitoes (and ticks) is available from the Master Gardeners of Northern Virginia, Arlington Regional Master Naturalists, or the Extension Master Gardener Help Desk in the Virginia Cooperative Extension Office in Arlington.
- Lister, B.C., & Garcia, A. (2018). Climate-driven declines in arthropod abundance restructure a rainforest food web. Proceedings of the National Academy of Sciences, 115(4), E10397-E10406. Available from https://www.pnas.org/content/115/44/E10397
- “Mosquito and Tick Control.” (2020). Master Gardeners of Northern Virginia. Available from https://mgnv.org/reading-room/mosquito-and-tick-control/.
- Sánchez-Bayo, F., & Wyckhuys, K.A.G. (2019). Worldwide decline of the entomofauna: A review of its drivers. Biological Conservation, 232, 8-27. Available from https://mahb.stanford.edu/wp-content/uploads/2019/02/2019_Sanchez-Bayo-Collapse-of-insect-fauna.pdf