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Importance of Reducing Mosquito Breeding Sites

Adult mosquitoes emerge from stagnant water after completing development.

Adult mosquitoes emerge from stagnant water after completing development.
LayLa Burgess, ©2018 HGIC, Clemson Extension

Background

South Carolina is home to over 50 different species of mosquitos, providing a food source for birds, fishes, frogs, bats, and other animals. Mosquitoes are close relatives of flies in the gnat and no-see-um taxa. The term mosquito means “little fly”, indicating that they are a midge-like, two-winged insect. Mosquitoes complete their life cycle in four stages: egg, larva, pupa, and adult. Availability of standing water is integral to these life stages and highly influential on the overall number of mosquitoes produced. Water allowed to “stand” for five days or more can become a potential mosquito-breeding site.

Adult female mosquitoes produce eggs that are deposited in stagnant water to develop. Capture and retention of water in an area or location can be unlimited, allowing mosquitoes the advantage of high reproductive success. Large populations of mosquitoes rapidly become a nuisance, earning them the moniker “pest insect”. Mosquitoes are most noted for the itchy bite they inflict upon contact, but are also known to be potential vectors of disease.

South Carolina’s Department of Health and Environmental Control (DHEC) lists West Nile, Eastern Equine Encephalitis, La Crosse encephalitis, St. Louis encephalitis virus, and dog/cat worm as common diseases potentially carried by mosquitoes. Zika virus has been a recent addition of concern by DHEC, though “South Carolina has not had any confirmed Zika cases reported in 2018.” Zika virus spreads primarily from the infected bite of two mosquito species, Aedes aegypti and Aedes albopictus (Asian Tiger Mosquito). For more information on Aedes albopictus, see HGIC 2471, Asian Tiger Mosquito.

The almost endless availability of standing water for mosquito reproduction, combined with the ability to vector potentially harmful disease, drives the importance to limit breeding sites. Reducing breeding sites is simple, start by identifying potential locations of water retention and eliminate them. Unfortunately, there is a catch. Many places where water pools and becomes stagnant are overlooked. Effective local community level mosquito management centers on identifying common and uncommon locations that retain water around homes, landscapes, or properties. This, followed by appropriate action, altering individual habits, and changing the surrounding habitat can help dry up the situation.

Mosquito Biology and the Role of Water

The mosquito life cycle consists of four developmental stages: egg, larva (referred to as the wriggler), pupa (referred to as the tumbler), and the adult. The life cycle, from egg to adult, takes approximately 8-10 days.

Depiction of the mosquito life cycle.
Art Cushman, USDA Systematics Entomology Laboratory, Bugwood.org

Mature female mosquitoes generally require a blood meal prior to egg production and can lay masses of 50 to 200 eggs at a time in or on a water source. There are two mosquito egg types: floodwater eggs (laid in water, but require a drying period to become viable) and permanent water eggs (require standing water to hatch). For the majority of permanent water mosquito species, the egg, larva, and pupa stages require water for development.

Permanent water eggs hatch in 2-3 days once laid in or on exposed water. After hatching, a series of larval phases (referred to as instars) will occur indicated by molting and an increase in size. For approximately one week, the wrigglers (larvae) will feed on small pieces of settled organic matter in stagnant water. They periodically “wriggle” to the surface of the water to breath air at this time. After reaching their final instar and feeding stops, the wriggler will begin to take on the comma-shaped appearance of the pupae (tumblers). The tumbler stage lasts approximately two days, but can extend up to a week. The adult mosquito emerges, crawls out of the water, and flies once its body parts have hardened. At this time, the adult mosquito is ready to begin mating. Female and male mosquitoes use flower nectar as a carbohydrate (sugar) source for energy. Only female mosquitoes bite, as they require protein from a blood meal prior to producing new eggs.

Identifying Potential Water Retention Locations

Water only needs to remain stagnant for a minimum of 5 days to become a potential breeding site for mosquitoes. Some types of mosquitoes only need a tablespoon of water to develop in. One tablespoon of water is the approximate fill size of a bottle cap. Taking the time to identify and eliminate areas of water retention will help lower mosquito numbers.

Unfortunately, it is common for people to leave items, usually larger than a bottle cap, lying around outside homes or properties. An important first step to reducing areas that retain water is simply not to create them. Proper storage of items in and around the home or property reduces the initial potential for water collection. Turning items over so that water drains rather than fills can become a simple practice.

Perform routine checks for common items or places that hold water.

Suggestions include:

  • flower pots and collection saucers
  • cans, cups, and bottles
  • coolers
  • pet bowls
  • animal troughs
  • buckets, barrels, and drums
  • watering cans
  • old tires and hubcaps
  • wheel barrow
  • birdbaths and fountains
  • children’s toys
  • wagons
  • trash cans
  • unmaintained swimming or kiddie pools
  • low lying areas that create puddles
  • tire ruts
  • woodpile

When left outside, items such as buckets, used candles, cups, and lids become a significant source of water capture and retention.

When left outside, items such as buckets, used candles, cups, and lids become a significant source of water capture and retention.

When left outside, items such as buckets, used candles, cups, and lids become a significant source of water capture and retention.

When left outside, items such as buckets, used candles, cups, and lids become a significant source of water capture and retention.

When left outside, items such as buckets, used candles, cups, and lids become a significant source of water capture and retention.
LayLa Burgess, ©2019 HGIC, Clemson Extension

Practice thinking outside the box regarding uncommon sources of water retention. Suggestions include:

  • caps and lids
  • outdoor vases (cemeteries)
  • plant cuttings rooting in water
  • leaf axils and blades of plants of over grown shrubs
  • wading pools
  • garden ponds
  • rain barrels
  • clogged gutters and downspouts
  • boats, canoes, and kayaks (especially if uncovered)
  • junk vehicles
  • discarded appliances
  • unsecured plastic sheeting and tarps
  • improperly fastened pool covers
  • tree or stump holes
  • leaf piles
  • cut open-ended bamboo used in landscaping
  • fire and barbeque pits
  • bricks or cement blocks with holes
  • unused pipes
  • dysfunctional drain ditches, basins, or cisterns
  • leaky pipes that pool water
  • nonfunctioning storm drains
  • air conditioner drain areas
  • flat roofs in the shade
  • old shoes or boots left outside
  • garden tools

Foliage can capture water. Excessive overgrown foliage can retain lots of moisture, allowing humidity to build and providing excellent conditions for insect reproduction.

Foliage can capture water. Excessive overgrown foliage can retain lots of moisture, allowing humidity to build and providing excellent conditions for insect reproduction.
LayLa Burgess, ©2019 HGIC, Clemson Extension

Water collects easily in a motorized vehicle for children, if left exposed outside.

Water collects easily in a motorized vehicle for children, if left exposed outside.
LayLa Burgess, ©2019 HGIC, Clemson Extension

Toys are no exception to the ability to hold water.

Toys are no exception to the ability to hold water.
LayLa Burgess, ©2019 HGIC, Clemson Extension

The Take Home Message

It is commonplace to hear: “It’s hard to enjoy the outdoors because there are so many mosquitoes.” Prior to seeking chemical control options to solve the dilemma, spend time outside reducing areas and items that retain water. This worthwhile activity aids in reducing the numbers of mosquitoes along with potential problems and helps create positive habits as stewards of the environment.

Water often funnels, collects, and becomes stagnant in low grades or “bottoms” areas. This can easily lead to creating potential mosquito breeding sites that need attention.

Water often funnels, collects, and becomes stagnant in low grades or “bottoms” areas. This can easily lead to creating potential mosquito breeding sites that need attention.
LayLa Burgess, ©2019 HGIC, Clemson Extension

The combined knowledge of the mosquito life cycle, the role that water plays in it and the ease with which water can be collected in the environment promotes the need for efficient identification of water capture and retention. Whenever possible, manage, reduce, or eliminate locations or items holding water. Avoid water fill or pooling by promoting water drainage. Properly store, remove, or dispose of unwanted items rather than leaving them outside. Secure coverings tightly and use sand, dirt, or cement to fill voids in the landscape or foundations. Mosquito dunks or pellets, containing Bti (Bacillus thuringiensis var. israelensis), are a form of biological control used to kill mosquito larvae in fountains, ponds, or birdbaths that need to hold water. For more information on Bti, see HGIC 2770, Less Toxic Insecticides.

Resources:

  1. South Carolina Department of Health and Environmental Control- Protect Your Home Against Mosquitoes
  2. English: https://www.scdhec.gov/sites/default/files/Library/CR-011740.pdf
  3. Spanish: https://www.scdhec.gov/sites/default/files/Library/CR-010304.pdf

If this document didn’t answer your questions, please contact HGIC at hgic@clemson.edu or 1-888-656-9988.

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