West Nile Virus

Larvicides

What are larvicides?

Larvicides are chemicals or natural bacteria that can be used to kill mosquito larvae.

What are mosquito larvae?

Larva is one of the four stages in a mosquito's life cycle. Adult mosquitoes lay eggs, which hatch into larvae; larvae then become pupae, from which the adult mosquitoes emerge. Adult mosquitoes lay their eggs on surfaces of standing or slow-moving water and the larvae live and develop into pupae in the water.

In what form are larvicides used?

Larvicides come in the forms of liquid, granules or briquets.

Where are larvicides used to kill mosquitoes?

The New York City Department of Health and Mental Hygiene applies larvicides to standing water where mosquitoes can breed. DOHMH generally uses the briquet and granule forms of larvicides in catch basins (storm drains). The products will be placed into the storm drains by hand. For other types of standing water, granules or liquid products may be applied by hand, or sprayed from backpacks or trucks. For wetlands, swamps and marshes, where access may be difficult, larvicide may be applied from a helicopter.

What larvicides will be used to control the larval mosquito population?

DOHMH will use Bacillus sphaericus (Vectolex), and Bacillus thuringiensis israelensis (Aquabac, Mosquito Dunks, Bti Dunks or Vectobac) and/or Methoprene (Altosid). These products have been approved for mosquito control by the U. S. Environmental Protection Agency and the New York State Department of Environmental Conservation (NYSDEC). Altosid mimics an insect growth hormone and prevents the development of adult mosquitoes from pupae. Vectolex, Aquabac, Mosquito Dunks, Bti Dunks are Vectobac are bacterial pesticides that can damage the gut of the mosquito larvae that feed on them, causing the larvae to starve to death. All three have been found to be highly effective in larval mosquito control.

When will these larvicides be used for mosquito control?

Initial application of larvicide usually begins in early to mid-May wherever mosquito larvae are found. Follow-up applications take place periodically throughout the summer months.

If larvicides are used for larval mosquito control now, does that mean the use of pesticides for adult mosquitoes won't be needed later on?

The use of larvicides is part of our first line of defense against mosquitoes carrying the West Nile virus. This preventive approach also includes encouraging residents to eliminate standing water around residences where mosquitoes breed. If WNV poses a risk to human health, targeted application of pesticides to control the adult mosquito population will be performed.

Are larvicides available to the public for home use?

Some local hardware stores may carry a product called Mosquito Dunk® that contains a larvicide - Bacillus thuringiensis israelensis (BTI) - for use in areas of standing water around the home. The New York City Department of Health and Mental Hygiene recommends eliminating standing water around the home to reduce breeding sites for mosquitoes and warns that direct handling of larvicides may cause skin and eye irritation. Use these products only as directed by manufacturer. If these products are purchased for home use, we recommend careful reading of the hazards label, directions, and details regarding storage and handling.

Am I likely to be exposed to larvicides?

Larvicides are applied in storm drains, catch basins and other areas to which the general public does not have access. Larvicides are not applied in areas that drain into waters consumed by humans.

Are there negative health effects of exposure to larvicides?

Concentrated exposure to Altosid, as well as Vectolex and Aquabac/Vectobac, can cause mild eye and skin irritation.

What should I do if I am exposed to larvicides?

If you are exposed to a larvicide, rinse the eyes with tap water for 20 minutes and wash the skin thoroughly with soap and water. If the symptoms persist, contact your doctor or local emergency department. You may also contact the New York City Poison Control Center at (212) POISONS (764-7667).

For more information on West Nile virus, call 311 or visit nyc.gov/health/wnv.