What is a larvicide?

A larvicide is a chemical that is used to kill mosquitoes when they are in the larval, or immature, stage of the life cycle. Mosquito larvae are immature mosquitoes that live in water before maturing into flying adults. Their growth rate depends largely on water temperature and can be as little as 7-10 days in warm weather.

Where do I use larvicides?

Larviciding involves the application of approved pesticides to aquatic habitats where mosquito larvae thrive:

  • Ornamental ponds (with no fish)
  • Non-chlorinated swimming pools
  • Pool covers that collect water
  • Low lying areas that maintain stagnant water for more than one week
  • Marshy areas fully within homeowners' property lines
  • Rainwater cisterns
  • Catch basins
  • Roadside ditches

When do I use larvicides?

Larvicides should be used when mosquitoes are breeding. Since mosquitoes don't breed in the winter in the Northern Virginia area, larvicides should be used from the spring (April - May) through the fall (October).

What kind of larvicides can I use around my home?

Bacillus thuringiensis var. israelensis (Bti) is a biological pesticide that is a naturally occurring bacteria found in soil throughout the world. Bti is used for mosquito larval control in a broad range of freshwater and salt marsh habitats. No special licensing or certification by the DEP is needed if these products are used on a homeowner's own property.

There are only a few Bti products available to homeowners through hardware stores or nursery and garden centers. Bti is specific for aquatic flies (such as mosquitoes) and is less harmful to the environment than most insecticides and larvicides.

Methoprene is an insect growth regulator that interferes with the normal life cycle of an insect and prevents it from reaching maturity and reproducing by mimicking an insect growth hormone. Therefore, methoprene prevents the development of adult mosquitoes from larvae. Methoprene is used in aquatic areas to control mosquitoes and several types of flies, moths, beetles, and fleas. Methoprene is sold in retail and specialty pet stores.

Are larvicides safe to use?

Biological pesticides such as Bti are very specific to mosquito, black fly and midge larvae and are not known to affect human health. Due to the very low toxicity of methoprene and low potential for human exposure methoprene does not present a health threat.

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