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Larviciding

Fact Sheet   Adobe Portable Document Format (PDF) 60KB

Larvicides are a type of pesticide that kill insect larvae before they develop into adult insects. To reduce the risk of West Nile virus, larvicides are used to control specific species of mosquitoes.

Larvicide applications in Halton:

In Halton, larvicide is being used in areas where monitoring information shows that mosquito larvae are present. Larvicide is only applied when other measures for the reduction and control of breeding sites do not work to minimize the risk of West Nile virus.

This web page contains information about sites in Halton where larvicide has been applied as well as general information about the use of larvicide to treat standing water sites and catch basins.

What larvicides are being used in Halton?

The two larvicides being used in Halton are methoprene and Bti (Bacillus thuringiensis israelensis).

  • In catch basins - Methoprene is used. Methoprene is a synthetically produced mosquito hormone or growth regulator that interferes with the mosquito life cycle. It prevents the mosquito larva from reaching maturity and reproduction. Methoprene is used in catch basins if larvae are identified. This product is applied in a pellet or briquet form.

Catch basins collect water, dirt and other debris. Water in a catch basin rises to a certain level inside the basin, then drains into an outflow pipe, which is a storm sewer.

  • In standing/stagnant water - Bacillus thuringiensis israelensis , know as Bti , is used. This is a bacterium, which contains protein crystals that rupture digestive cells in mosquito larvae when ingested and is applied in a granular form. This agent is used to control mosquito larvae in temporary stagnant water. This product is applied in a granular form.

Stagnant water is water that remains in an area for more than 1 week (7 days or more) and is not flowing or subject to wind or wave action. Standing water can collect on the ground, a roof, pool covers, and in containers such as tires and eaves.

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Are there any risks to using these products (methoprene and Bti)?

  • Both larvicides are of very low risk to people, nature and the environment.
  • In mammals, methoprene is quickly and completely broken down and excreted mostly in urine and feces. It does not irritate eyes or the skin.
  • Methoprene can be slightly toxic to some aquatic life but the product does not persist in the environment.
  • Bacillus thuringiensis israelensis (Bti) has no short or long term health effects on humans or on wildlife, including aquatic organisms.
  • Bti is only used on temporary stagnant water (ditches, etc.) and on temporary or permanent non-flowing water sites. It represents a very low risk to other non-target insect species.

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How is the larvicide program carried out?

The Halton Region Health Department’s West Nile virus program focuses on four areas: public education; monitoring and surveillance; eliminating potential mosquito breeding sites, and; larviciding.

  • If stagnant water can be removed to eliminate the potential mosquito breeding site, this is done. In this case, larviciding is not necessary.
  • If the stagnant water cannot be removed, (as in catch basins, ditches, ponds, etc.) these areas are monitored for the presence of mosquito larvae. Larvicide is applied only when mosquito larvae are found.
  • The larvicides used in Halton Region are granular (Bti) and in pellet or briquet form (methoprene). Larvicide is not sprayed into the air or onto surrounding land.

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How does the Health Department investigate possible breeding sites?

 The definition used for stagnant water is water that persists for 7 days or more.

  • If the site meets the definition for stagnant water, the site will be investigated.
  • The investigation includes dipping of the water to determine if mosquito larvae are present.

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Will the Region apply larvicide on private property?

  • No, the Region will not apply larvicide on private property.
  • The permits held by the Region do not allow larvicide to be applied on private lands.

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What larvicide can I use on my property?

  • There is a larvicide product containing Bti that received federal approval this year and is available at local stores.
  • This larvicide product can only be used for the treatment of standing water sites on your own property. The product is available at many hardware stores.

Please Note - The manufacturer’s instructions for use must be strictly followed at all times. This larvicide cannot be applied to catch basins or other waters that can drain off your property.

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Do I need a permit to apply larvicide on my own property?

  • You do not need a permit to treat standing or stagnant water as long as the water does not drain off of your property.
  • However, a permit is required to treat catch basins on private property.
  • The manufacturer’s instructions for use must be strictly followed at all times.

Please Note - Do not put larvicides into a catch basin. It is illegal and can only be done by a licensed pest control operator with a permit from the Ministry of Environment.

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What can I do about the municipal catch basin in my backyard?

  • You can place window screening over the grate to prevent the mosquito from entering/exiting the catch basin. This can be purchased at a hardware store.
  • Remove the netting during a heavy rainfall to prevent flooding and replace the netting once the water has drained.

Please Note - Do not put larvicides into a catch basin. It is illegal and can only be done by a licensed pest control operator with a permit from the Ministry of Environment.

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Are there any other ways to control mosquitoes that don’t include the use of pesticides?

There are several ways to control mosquitoes other than by the use of pesticides.

  • You can remove all potential places where mosquitoes might breed.
  • This includes items around the yard such as old tires and containers where water might collect.
  • Also, fill in low areas and ditches that can collect water.
  • Elimination of mosquito breeding sites is an effective measure of control although it may not be feasible in all cases.
  • In addition, mechanical controls such as light and chemical traps using carbon dioxide can be used to control mosquitoes.
  • Other methods of adult mosquito control include reliance on natural enemies such as dragonflies, bats and birds.
  • The use of natural enemies to the mosquito and mechanical means of controls are viewed by experts as having limited success. They would not lead to a significant control of adult mosquitoes. In addition, bats are known carriers of rabies , a disease that is always fatal. Therefore, attracting and housing bats to control mosquitoes is not recommended.

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What are storm water retention ponds?

  • Storm water retention ponds are ponds that are designed to handle water overflow from rainfall, snowmelt, and runoff caused by activities such as watering lawns and washing cars.
  • There are two types of ponds:
    • Wet ponds always have some water present.
    • Dry ponds fill and empty throughout the season.
  • Both types of ponds may support animal life including birds, fish, reptiles and insects. However, the main intent of the storm water retention ponds is to maintain the health of streams, lakes and aquatic life by reducing the effects of human uses of water and urban development.

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Are storm water ponds good mosquito breeding sites?

  • Storm water retention ponds are not usually considered good mosquito breeding sites.
  • Changes in water level and exposure to wind are some of the factors that help deter mosquitoes from laying their eggs along the surface of the water. However, rock formations, vegetation, and debris can create pockets of standing water that may allow mosquitoes to breed at the site.

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Is the Health Department planning on treating storm water retention ponds with pesticides?

  • All storm water retention ponds in Halton region are monitored by larval dipping throughout the WNV season to determine if they are a mosquito breeding site.
  • Larviciding if deemed necessary.

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