Mosquitoes: Managing these Uninvited Guests

Mosquito on glass, credit Susannah Anderson

Summertime during a pandemic means spending more time at home in our yards or social distancing at parks or recreation areas. And while we should all be doing our best to gather only in small groups, you’ve probably had at least a few uninvited guests to your outdoor gatherings in the form of mosquitoes. Over 50 species of mosquitoes live in the Pacific Northwest, active on warm summer days when we’re trying to enjoy the outdoors.1 While male mosquitoes feed solely on flower nectar, most adult female mosquitoes feed on protein-rich blood from a variety of animals – including humans.1

Illness Transmission

During feeding, adult females may transmit West Nile virus (WNV), Zika virus or St. Louis encephalitis, among other pathogens.2 It’s important to remember that in the Pacific Northwest WNV presence is not common,3,4 and most people infected with WNV will have no symptoms.2 About one in five people who are infected will develop a fever with other symptoms.2 Less than 1% of infected people develop a serious illness.2 While illness as the result of a mosquito bite is very unlikely, most people would certainly like to avoid the nuisance of red, itchy welts.

Habitat & Breeding Prevention

Reducing mosquito habitat is the most effective way to manage mosquitoes and prevent getting bit. Immature mosquitoes (called larvae) are wingless filter feeders that live in standing water.1 Mosquito larvae can often be seen wriggling near the surface of mud puddles, ponds or other standing water sources. The larvae of some mosquito species thrive in sewer water, while others are found in as little as a bottle cap of water.1 Since adult mosquitoes can fly long distances, preventing mosquito breeding habitat and managing the wingless larval stage is most effective.1

Identify and eliminate sources of standing water around your home and neighborhood, including drip trays beneath potted plants, over-irrigated lawns, unused pools and old tires.6 Birdbaths should be emptied and cleaned every few days. 

So what do you do when you want to provide water trays for pollinators or have fish ponds or livestock troughs? Consider applying Bacillus thuriengiensis israelensis (Bti). This naturally occurring bacterium is harmless to people and animals, and it is approved for use in organic farming.7 Bti is toxic only to the larvae of mosquitoes, blackflies and fungus gnats, and mosquitoes have not shown a resistance to Bti even with greater use.7 Purchase doughnut shaped “dunks” of Bti at your local garden store or online. Mosquitofish (Gambusia affinis) may also be used in water troughs and backyard ponds, but care should be taken with this efficient predatory fish to keep it from entering local waterways.8

Safe Alternatives for Control

To avoid mosquito bites while outdoors – especially around dawn or dusk – wear long-sleeved shirts and pants.6 Broadcast spraying pesticides to kill adult mosquitoes, a practice referred to as “fogging,” is generally the last resort for managing mosquitoes.9 Many adult mosquitoes rest during the day in cool, protected areas, such as the underside of vegetation; this behavior limits contact with the fogging agents.1 Overuse of spraying can cause resistance to develop among target mosquito species, and there are certainly human health concerns with these chemicals.9 

Mosquito fogging, credit Don McCullough

Inviting bats to move in to your neighborhood is an option for controlling adult mosquitoes in many communities. According to BatBnB, a project promoting bat habitat and natural pest control, "a common bat can eat thousands of insects in a single night, making them the perfect substitute for nasty pesticides. By eating everything from beetles to mosquitoes, bats help keep your garden and your family safe."10 For tips on bat box placement and other factors to consider, see the BatFAQ from Bat Conservation International.11 

Natural Repellent Recipe

When avoiding mosquitoes isn't an option, try a natural repellent instead of chemicals. Here is one we like:

    • 2 tablespoons of witch hazel
    • 2 tablespoons of one or a combination of the following: grapeseed oil, jojoba oil, almond oil, olive oil, or neem oil (which contains natural insecticidal compounds)
    • 100-110 drops essential oils: lemon eucalyptus, rosemary and peppermint in a 6/3/1 ratio

Mix everything together in a small pump spray bottle. Shake before applying. Do not use on pets. Looking for essential oils? Our Business League supporter Mountain Rose Herbs has a bunch! 

To learn more about mosquito prevention options in your area, consult your vector control district and visit NCAP’s Mosquito Protection page.

  1. Snyder J. IPM in schools: mosquitoes [Internet]. Oregon State University Extension Service and Washington State University Extension: PWN Pest Press; Issue 12, Spring [cited 2020 Jul 14]. Available from:
  2. Centers for Disease Control and Prevention. Prevent Mosquito Bites [Internet]. U.S. Department of Health and Human Services; reviewed 2019 Apr 22 [cited 2020 Jul 14]. Available from:
  3. Oregon Health Authority. West Nile virus activity [Internet]. Public Health Division; undated [cited 2020 Jul 14]. Available from:
  4. Washington State Department of Health. West Nile virus [Internet]. Undated [cited 2020 Jul 14]. Available from:
  5. Centers for Disease Control and Prevention. Zika virus: Zika in the US [Internet]. U.S. Department of Health and Human Services; reviewed 2019 Nov 7 [cited 2020 Jul 14]. Available from:
  6. Centers for Disease Control and Prevention. West Nile virus: prevention [Internet]. U.S. Department of Health and Human Services; reviewed 2019 Oct 17 [cited 2020 Jul 14]. Available from:
  7. U.S. Environmental Protection Agency. Bti for mosquito control [Internet]. 2017 Aug 8 [cited 2020 Jul 14]. Available from:
  8. Nico L, Fuller P, Jacobs G, Cannister M, Larson J, Fusaro A, Makled TH, Neilson ME. Gambusia affinis (Baird and Girard, 1853) [Internet]. Gainesville (FL): U.S. Geological Survey, Nonindigenous Aquatic Species Database; 2016 Jan 25 [revised 2020 Apr 10; cited 2020 Jul 14]. Available from:
  9. Grodner MG, Criswell J, Sutherland C, Spradley P, Renchie DL, Merchant ME, Johnsen M, Sawlis S. The best way to control mosquitoes: integrated mosquito management explained. University of Arkansas Cooperative Extension Service; 2007 June [cited 2020 Jul 14]. Available from:
  10. BatBNB [Internet]. Louisville (KY); undated [cited 2020 Jul 14]. Available from:
  11. Bat Conservation International. BatFAQ: answers to questions about bat houses [Internet]. Austin (TX); undated [cited 2020 Jul 14]. Available from:

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  • Monica Chavez
    followed this page 2020-08-12 05:55:06 -0700
  • Ncap Staff
    published this page in BLOG 2020-07-29 12:08:23 -0700