Mosquito Control
I love everything about spring and the ability to finally get outside – early garden maintenance, seeing what is emerging, planning new projects. Recently on a warm day in late March, I was enjoying the front porch when I realized I was unwillingly providing dinner for a mosquito!
How did they find me?
Mosquitoes use a combination of cues to find a blood source, the most important being the production of carbon dioxide (CO2). On a very basic level, when we breathe humans take in oxygen and expel CO2, a waste product which must be removed from the body. Mosquitoes can sense CO2 from more than 30 feet away and follow the trail to its source. When it lands, the mosquito uses receptors to sense human odor, which can be distinguished from animal odor, and other receptors to “taste” our skin and find a place to bite. Turns out, I had essentially broadcast that the blood buffet was open for business just by existing and enjoying the fresh air.
MOSQUITO PHOTO
Mosquito Life Cycle
Because mosquito larvae must have water to develop, female mosquitoes lay eggs on the surface of water or in places that will later fill with water. Once in water, eggs hatch within 24 to 48 hours. The larvae that emerge feed on organic material in the water and mature into pupae in 7 to 10 days. Adult mosquitoes emerge 3 to 4 days later and initially feed on plant nectar. Mating occurs quickly after mosquitoes emerge and the female mosquitoes then begin to search for blood on which to feed. Blood is necessary to produce eggs. Male mosquitoes feed only on plant nectar.
PHOTO – LIFE CYCLE
Benefits of Mosquitoes
Considering the aggravation, itching, and spread of disease, it might be difficult to conceive that mosquitoes serve any beneficial purpose. The mosquito is actually an important pollinator of some plants such as Platanthera obtusata, the blunt-leaf orchid. Also, because male mosquitoes only feed on plant nectar, they are an incidental pollinator of many plants.
Mosquitoes are also part of the food chain for other pollinators and wildlife including dragonflies and frogs. Because 96% of backyard birds rely on insects as a vital food source for their young, mosquito populations help feed these babies. Even mosquito larvae serve as a food source for fish and other aquatic life.
“Live and let live” only goes so far
While they may be beneficial, the fact remains mosquitoes are responsible for the transmission of some diseases in humans and animals including West Nile virus, Zika, and many forms of encephalitis. They are also annoying, and bites are itchy and can become infected. And there are certain times when a swarm of hungry “nuisance only” mosquitoes (those not armed with disease) is undesirable or intolerable and reduction of mosquito populations around our homes is necessary.
Many options for mosquito control are available. Some are more effective than others and others may seriously impact beneficial insect populations like bees and butterflies. Following is some of the most common methods to control mosquitoes along with information on effectiveness and any associated risks.
Eliminate Breeding Sites
As with many things, the safest and most effective method of controlling mosquitos involves no chemicals or machines: eliminate mosquitoes’ ability to reproduce. Because mosquitoes require still, standing water to complete their life cycle, dumping collected water and reducing areas where water collects prevents eggs from hatching and larvae from developing into mature mosquitoes.
Boats, children’s pools and toys, buckets should be stored so they do not collect water. Because even a couple of ounces of water can host larvae, anything that can collect even a small amount of water should be monitored and emptied. Remember, also, that tarps used to protect outdoor items and plant saucers collect water and must be monitored.
Bird baths, decorative ponds, and water features without fish should be flushed at least twice weekly. Alternately, you might use a bubbler or pump to keep the water moving. When water cannot be eliminated, larvicides containing Bti, a naturally occurring bacteria available for home use in “dunks,” kill mosquito larvae for up to 30 days causing no harm to fish, birds, and other wildlife.
Gutters and downspouts should be kept clear to allow water to drain. Extended downspouts and rain barrels can be fitted with screens to prevent mosquitoes from entering to lay eggs. In your yard and garden, correct drainage problems and low-lying areas where water might collect. Dense vines such as English Ivy on trees provide habitat for breeding and food source for mosquitos.
Sprays and Insecticides
Spray chemicals, used by mosquito control companies and available for home use, rely on pyrethrins, derived by chrysanthemum flowers, or pyrethroids, synthetic chemicals that mimic pyrethrins. These products can be effective to control mosquitoes and may be advertised as “natural” or “organic.” They are chemicals which are regulated and approved for use by the Environmental Protection Agency.
The products are also non-selective and, therefore, highly toxic to pollinators and other insects. Always READ and use the products only according to the label directions. The EPA acknowledges the chemicals are toxic to bees on contact one or more days after treatment. The EPA requires that products containing certain chemicals display a Bee Advisory box on the label. The information alerts purchasers which products are potentially hazardous to bees and provides instructions on how to limit bee exposure.
Because mosquitoes reproduce quickly and travel from 100 yards to several miles (depending on the species) from their breeding site in search of blood, spray controls are less effective when used in a single yard.
If you choose to spray, do so at times other insects are less active, such as early or late in the day, with little or no wind to avoid drifting of chemicals. If you use a mosquito control company, insist they follow the above restrictions. Also, select a company licensed by the Virginia Department of Agriculture and Consumer Services and ask for information on the content of their product.
Repellents
In light of concerns about impact of repellants on bees, a Virginia Tech entomology professor tested the impact of Thermacell, a vapor-producing repellent device, on honeybees. The devices vaporize synthetic analogs of pyrethrins as a mosquito repellent. The research found no difference in tested bee behaviors (which included how often honeybees visited and communicated information to other bees) between feeders inside the treatment area and control feeders. I was excited to read about the research because I have found these devices to be effective if started about 10 minutes before going into an area.
Chemical repellents are applied to skin or clothes or released into the air and interfere with a mosquito’s ability to detect cues that lead to humans. The most commonly used contain, DEET, a synthetic chemical available in several concentrations; the length of protection increases as the concentration of deet increases. However, none are completely effective and some raise safety concerns. Guidelines for use should be followed carefully.
Plant derived chemicals such as citronella are reported to be as repellent as DEET, but not as long lasting. Geraniol-based products (Mosquito Safe) and products containing oil of lemon eucalyptus are reported to last as long as DEET. It should be noted that wristbands, candles, and coils containing the same chemicals were found to have little or no effectiveness. Use of a simple electric fan can also be very effective. Fans interrupt a mosquito’s ability to fly and may make it more difficult for them to follow human scent.
What Does Not Work
Devices designed to attract and kill insects, such as Bug Zappers, attract few mosquitoes but are highly detrimental to other insects, including beneficial pollinators. Additionally, there is no scientific support indicating that sonic or ultrasonic devices which emit a sound or mosquito repellant plants have any ability to repel mosquitos.
The Bottom Line
It is possible to enjoy the outdoors without swarms of feeding mosquitoes. Nuisance mosquito populations can be controlled with simple, proven strategies that do not harm pollinators and other beneficial insects. Elimination of standing water is a very effective solution for control without chemicals. Use of a fan or repellents, such as vapor-producing devices or those applied to skin or clothing, will keep away most that remain.
Sources
How Mosquitoes Tell the Difference Between Animal and Human Hosts (And Why It Matters), NIH MedlinePlus Magazine, Sept 26, 2022. https://magazine.medlineplus.gov/article/how-mosquitoes-tell-the-difference-between-animal-and-human-hosts-and-why-it-matters
Mosquito Control Around Homes and in Communities, NC State Extension
https://entomology.ces.ncsu.edu/mosquito-control-around-homes-and-in-communities/
Impacts of native and invasive plants on mosquito ecology and management. https://www.maine.gov/dacf/php/gotpests/bugs/documents/Impacts%20of%20native%20and%20invasive%20plants%20on%20mosquito%20ecology%20and%20management.pdf
Mosquitoes and their Control, Virginia Cooperative Extension Publication ENTO-202NP, https://www.pubs.ext.vt.edu/ENTO/ENTO-202/ENTO-202.html
Aedes communis: The Pollinating Mosquito, United States Department of Agriculture, https://www.fs.usda.gov/wildflowers/pollinators/pollinator-of-the-month/aedes_communis.shtml#:~:text=In%201913%2C%20it%20was%20first,that%20live%20in%20wetter%20environments
What You Need to Know Before Spraying for Mosquitoes, National Wildlife Federation Blog, https://blog.nwf.org/2020/09/what-you-need-to-know-before-spraying-for-mosquitoes/#:~:text=The%20most%20widely%20used%20residential,risk%20to%20pets%20and%20people
Mosquito Management, Colorado State University Extension, https://extension.colostate.edu/mosquito-management/
Honey Bees Unfazed by Vaporized Mosquito Repellent, Study Finds, Entomology Today, https://entomologytoday.org/2023/12/08/honey-bees-unfazed-vaporized-mosquito-repellent-thermacell/