Gardening Guru: Mosquito Trouble

By Pam Wallace

UCCE Master Gardener

Last year, we published an article on the Aedes aegypti mosquito. This year, as I sit here struggling to not scratch the itchy welts on my ankles and elbows, and after hearing from numerous friends and neighbors about how they are unable to enjoy their backyards as much as they want, I thought we could all use a reminder about this pest, and what to do about it. One thing to remember is that while a broad spectrum insecticide will kill these pests, it will not affect the eggs they have already laid, and it will also kill any beneficial insects you have in your yard—like bees and butterflies! So please be cautious about spraying!

There’s a new(ish) pesky critter in town, and while it doesn’t directly affect our garden plants, it does affect our gardens, and more importantly, our gardeners!

Have you been bothered by multiple large, itchy welts, especially around your lower legs? Did you think the culprit was a gnat? Have you curtailed your backyard activities in order to avoid these bites? If you’ve answered yes to any of these questions, then it’s time to find out if you are unknowingly harboring the Aedes aegypti mosquito and allowing it to breed in your yard.

Basic Facts: The Aedes aegypti is a different mosquito species from the native California mosquitoes that most of us in the Valley are used to. It is much smaller, measuring only 1⁄8 to ¼ inches. Although this mosquito will bite at night and target any available area of your body, it does prefer to bite the lower legs during the daytime hours. It is so small, most people don’t feel it bite. What I find the most annoying about these bites is their excessive itch that no amount of anti-itch cream seems to alleviate.

Aedes aegypti is commonly known as the Yellow Fever mosquito. It can also transmit dengue, Zika, and chikungunya viruses, although it is important to note that none of these diseases are currently found in California. Although this mosquito can also transmit West Nile virus, it is not considered a significant source of infection. Invasive mosquitoes must acquire the virus from an infected human in order to transmit it.

Life Cycle: Only the female Aedes aegypti bites—it needs a protein found only in blood in order to produce its eggs. Although they can acquire this blood from any mammal, they prefer to feed on humans. About three days after feeding, the mosquito lays her eggs along the sides of a container holding as little as a teaspoon of water, or on a moist surface that is likely to later be flooded by water. The eggs will remain dormant until flooding occurs, which can be months or even years later. After hatching, the larvae, or wigglers, live in stagnant or nearly still water until they pupate into the adult stage. In summer the entire life cycle, from egg to adult, can be completed in a week or less. As each female can lay hundreds of eggs, you can imagine how many new adults are hatching every month. The winter months will slow this mosquito down, but unfortunately, they will still be around and ready to feast!.

Habitat: Residential backyards, where they are close to their food source, are the ideal habitat for the Aedes aegypti mosquito and its larvae. They will lay their eggs in artificial or natural water containers such as: water storage containers, flower pots, discarded tires, plates under potted plants, cemetery vases, buckets, tin cans, clogged rain gutters, ornamental fountains, water bowls for pets, birdbaths, etc. This species has also been found in underground collections of water such as open or unsealed septic tanks, storm drains, wells, and water meters. These mosquitoes can use natural locations or habitats (for example treeholes and plant axils).

Mosquito Control: Removing stagnant water and eliminating sources that can hold water is the most effective and pesticide-free way to prevent mosquitoes in your yard and home. It’s important to note that Aedes aegypti thrive with very small amounts of fresh water, unlike our regular mosquito visitors. Use the following methods, as described in the UCANR Zika virus publication: ipm.ucanr.edu/PDF/MISC/Zika_Pest_Alert_February_2016.pdf

Dispose of any refuse that can hold water, such as tin cans, containers, and in particular, used tires.

Drill holes in the bottoms of recycling containers and check uncovered junk piles.

Clean clogged roof gutters every year, and check storm drains, leaky outdoor faucets, and window wells.

Prevent the accumulation of standing water and empty water from wheelbarrows, boats, cargo trailers, pet dishes, toys, saucers underneath flower pots, and ceramic pots. If possible, turn these items over when not in use.

Do not allow water to stagnate in birdbaths, ornamental pools, water gardens, and swimming pools or their covers. Ornamental pools can be aerated or stocked with fish. Swimming pools should be cleaned and chlorinated when not in use.

Alter the landscape of your property to eliminate standing water. Keep in mind that during warm weather, mosquitoes can develop in any puddle of water. Larvicides are highly effective in controlling immature mosquitoes and should be considered when standing water cannot be eliminated. Some of those sold include the trade names Mosquito Bits, Mosquito Dunks, Mosquito Beater WSP, and Smartpond Mosquito Treatment, among others.

Also, consider talking with your neighbors—mosquito control is a shared responsibility.

Eliminating water sources will not provide immediate results; adult mosquitoes die off in approximately 10 days, but eliminating water sources reduces the number of larvae and pupae that will eventually emerge into biting adults. Scrub outdoor containers that have held water with hot, soapy water (or even better, a solution containing 10% bleach) to kill mosquito eggs. Store in a dry place.

Protect Yourself from Bites:
  • Make sure window and door screens are “bug tight.” Window screening is made to keep out mosquitoes, so repair any holes or tears.
  • Install weather-stripping to keep mosquitoes from entering around loose fitting doors and windows.
  • Use the proper type of light outside: incandescent lights attract mosquitoes, whereas fluorescent lights neither attract nor repel mosquitoes.
  • Use an insect repellent containing DEET. The higher the concentration, the more effective the repellent will be. Insect repellents deter mosquitoes from biting. Spray thin clothing with repellent because mosquitoes can bite through it. Be sure to follow all directions on product labels.
  • And most importantly, educate yourself! Since this mosquito is not native to California, it is important that we eradicate this pest. California has more than 60 mosquito and vector control districts. For more information, contact your local mosquito control district. They will come out and inspect your property (free of charge) and help you identify and eliminate sources of mosquito habitat.

For more information, contact Delta Vector Control District, deltavcd.com, 559-732-8606; or Tulare Mosquito Abatement District, tularemosquito.com, 559-686-6628.

Due to the shelter-at-home guidelines, the Master Gardeners have canceled all public events for the time being, but their phone lines are still open: 559-684-3325, Tuesdays and Thursdays between 9:30 and 11:30 a.m.

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