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Larvicide: Bacillus sphaericus 

Bacillus sphaericus is a naturally occurring soil bacterium that can effectively kill mosquito larvae present in water. B. sphaericus has the unique property of being able to control mosquito larvae in water that is rich in organic matter. B. sphaericus is effective against Culex spp. but is less effective against some other mosquito species. Commercially available formulations of B. sphaericus are sold under the trade name Vectolex^β. When community mosquito control is needed to reduce mosquito-borne disease, the Department of Health favors use of larvicide applications targeted to the breeding source of mosquitoes. Larvicides are more effective and less toxic than adult mosquito sprays, and the applications are unlikely to result in human exposure.

How does Bacillus sphaericus work?

B. sphaericus spores that are eaten by mosquito larvae release toxins into the mosquito's gut, causing the larvae to stop eating and die. B. sphaericus is only effective against actively feeding larvae, and does not affect mosquito pupae or adults. More information on the mosquito life cycle may be found on USEPA's Larvicides for Mosquito Control Web page. Granular formulations of B. sphaericus can be applied directly to water where mosquitoes breed or may be mixed with water and other substances and sprayed from the air or ground. Depending on the formulation and environmental conditions, B. sphaericus is generally effective from 1-4 weeks after application (3).

Where is Bacillus sphaericus applied?

B. sphaericus is typically applied to water with high organic content where mosquito larvae live. Areas where B. sphaericus is often the preferred choice for mosquito control include waste lagoons (where animal wastes are treated) and storm water catch basins.  Application of B. sphaericus is not permitted in reservoirs that contain drinking water (3). B. sphaericus formulations must be applied by licensed pesticide applicators.

Can I apply Bacillus sphaericus to my property?

B. sphaericus formulations may only be applied by a licensed pesticide applicators. Under most circumstances, to treat water that is connected or has the potential to reach surface waters of the state, property owners or a licensed pesticide control company must obtain a NPDES permit from either the Department of Health or the Department of Ecology. More information about the permit process for aquatic mosquito control in Washington is available on the Department of Health 's West Nile Virus, Aquatic Mosquito Control General Permit Web page.

Is B. sphaericus harmful to humans or pets?

No measurable health effects were seen in laboratory animals that were exposed to large concentrations of B. sphaericus by multiple routes of exposure. Cases involving human health effects following exposure to B. sphaericus are extremely rare. Mild eye and skin irritation may occur in humans following contact with B. sphaericus, based on effects seen for other Bacillus strains (2). No cases involving B. sphaericus have been reported in Washington during the past 10 years. Pets are unlikely to experience health effects from exposure to B. sphaericus based on the results from numerous studies involving laboratory animals.

Is B. sphaericus harmful to the environment?

B. sphaericus has very few environmental risks associated with its use. B. sphaericus is both non-toxic and non-pathogenic for a variety of species tested (3). Environmental persistence of B. sphaericus varies depending on the formulation used and environmental conditions. Breakdown of B. sphaericus usually takes several weeks but residual levels have been shown to persist in some waters for up to nine months. Recycling of B. sphaericus from mosquito corpses can increase its persistence (1). When used according to label rates, B. sphaericus does not appear to harm mammals, birds, fish, or most non-target invertebrates (insects and worms). Since B. sphaericus is primarily used in contained waters, the potential for contact among certain terrestrial and aquatic species is further limited. 

What precautions can I take to reduce my exposure to B. sphaericus?

B. sphaericus is generally applied to areas that are inaccessible to the public, so exposure is unlikely. Common sense steps, such as avoiding targeted areas during scheduled larvicide applications, will further reduce the chances for exposure. If irritation to eyes or skin occurs as a result of direct contact with B. sphaericus, rinse eyes with tap water and wash skin thoroughly with soap and water for 20 minutes. If symptoms persist, seek medical attention and report the incident to the Washington Poison Center at 1-800-222-1222 or the Washington State Department of Health, Pesticide Program at 1-888-586-9427.

Should I be concerned about other ingredients in B. sphaericus formulations?

Secondary or “inert” ingredients in pesticide formulations do not have to undergo the same stringent testing as active ingredients. It is possible that some individuals may be sensitive to other ingredients. For this reason, the Department of Health recommends that people minimize direct exposure to any pesticide as prudent public health practice. The USEPA's Inert Ingredients in Pesticide Products Web page has more information on inert ingredients in pesticides.

Need More Information?

Contacts:

Your Local Health Department

Washington State Department of Health, Pesticide Program at 1-888-586-9427

Web Resources:

Washington State Department of Health, West Nile Virus

·        United States Environmental Protection Agency, Larvicides for Mosquito Control  

References:

1.  Lacey, LA, 1990. Persistence and Formulation of Bacillus Sphaericus in Bacterial Control of Mosquitoes and Black Flies: Biochemistry, Genetics and Applications of Bacillus thuringiensis israelensis and Bacillus sphaericus, pp 284-294. Editors: Barjac and Sutherland. New Brunswick: Rutgers University Press.

2.  Siegel, JP and JA Shadduck, 1990. Mammalian Safety of Bacillus sphaericus in Bacterial Control of Mosquitoes and Black Flies: Biochemistry, Genetics and Applications of Bacillus thuringiensis israelensis and Bacillus sphaericus, pp 202-217. Editors: Barjac and Sutherland. New Brunswick: Rutgers University Press.

3.  Washington Department of Ecology. Aquatic Mosquito Control, National Pollution Discharge Elimination System, Waste Discharge General Permit. Permit no: WAG – 992000. Effective Date: May 10, 2002. 

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Last Update : 02/08/2008 11:26 AM
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