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Larval Mosquito Control

Mosquitoes can be controlled while in their larval developmental stage. Inspectors conduct daily inspections to find the mosquito larvae and take the necessary action to kill them. Small containers are emptied, while larger naturally occurring areas may require the use of an insecticide. This process is known as larviciding, and while time consuming and labor intensive, it prevents the larvae from becoming flying, biting mosquitoes.

  • Bti (Bacillus thuringiensis israelensis) is applied in either liquid or granular form to areas of standing water with mosquito breeding. Bti, is a naturally occurring soil bacterium. The bacterium produces proteins in a crystalline form. When the mosquito larvae eat these crystals, the proteins attack their gut wall, killing the larvae. Bti has a highly specific mode of action, and is of minimal environmental concern. Bti is quickly biodegraded and leaves no residue.
  • Bacillus sphaericus (Bs) is a common soil-inhabiting bacterium and is applied in either liquid or granular form to areas of standing water with mosquitoes breeding. The bacterium produces a protein toxin that may be used to control mosquito larvae. Bs is nontoxic to nontarget organisms.
  • Methoprene (Altosid) is an insect growth regulator that is applied in liquid, granules, pellets, or briquets to areas of standing water with mosquito breeding. This material prevents the mosquito larvae from emerging as viable adult mosquitoes.
  • Gambusia are species of mosquito-eating fish. These fish are used to stock unmaintained pools and will reproduce and continue to eat mosquito larvae.

Storm drain treatment program

In 2006, due to an increasing number of mosquito breeding complaints in storm drains, the County implemented the larvicide treatment of storm drains. Bacillus thuringiensis israelensis, Bacillus sphaericus and Methoprene are used to control larvae in storm drains.

Adult mosquito control

These are some of the insecticides used in the County's adult mosquito control program:

  • Bio-Mist 30+30 (Permethrin) is a synthetic version of Pyrethrin insecticide, derived from the Chrysanthemum. Rotating insecticides reduces the likelihood of insecticide resistance.
  • Naled (Dibrom Concentrate) is an oil-based organic phosphate insecticide used solely for aerial application. It is highly effective in controlling adult salt marsh mosquitoes. It is somewhat irritating if droplets get onto the skin or in the eye.

Effectiveness and safety of insecticides

The insecticides used are known as contact sprays. As the name implies, the insecticide must contact the mosquito in order to kill it. The insecticides do not prevent or repel mosquitoes from an area. Adult mosquitoes that migrate into an area after spraying are not killed, and it may sometimes appear that the spraying was ineffective.

The insecticides used to control mosquitoes are non-persistent. They last only a short period of time, and are biodegraded into harmless byproducts. All insecticides used are EPA approved, and used in strict accordance with label instructions.

Mosquito-related resources

Back to Top Page Last Edited: Wed Mar 26, 2014 4:56:06 PM

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