What is a Larvicide?   A larvicide is a product used to control mosquitoes in their immature stages while they are still in water. These products, which may be biological or chemical, are applied directly to water sources that contain mosquito eggs, larvae, or pupae. By preventing these immature stages from developing into adults, larvicides help reduce the number of biting mosquitoes in the community.

What are the Benefits of Larvicides?  Using larvicides to target mosquitoes in their immature stages helps reduce the number of adult mosquitoes that emerge and bite people. By lowering adult mosquito populations, larvicides play an important role in reducing the risk of West Nile virus and other mosquito-borne diseases in the community.

How is WALS Used at the District as Part of the Integrated Mosquito Management Program?
The District uses Wide Area Larvicide Spraying (WALS) with a truck-mounted sprayer that produces a strong air stream combined with a fine mist of larvicide diluted in water. This method allows the larvicide to drift into small, hard-to-find breeding sites, making it an efficient way to treat a wide range of mosquito habitats and reduce mosquito populations. 

What Product Does the District Use for WALS?
For Wide Area Larvicide Spraying (WALS), the District uses VectoBac® WDG, an organic product approved by the Organic Materials Review Institute (OMRI). VectoBac contains a naturally occurring bacterium, Bacillus thuringiensis subspecies israelensis (Bti). When mosquito larvae ingest Bti, it releases protein crystals that damage the larvae’s gut lining, ultimately killing them.

Learn more about Bti from the U.S. Environmental Protection Agency: EPA – Bti Mosquito Control

Will This Approach Kill Adult Mosquitoes?
No. This method uses only a larvicide, which targets mosquitoes in their larval stage before they develop into biting adults. The District uses separate tools and strategies to control adult mosquito populations.

How Can I Find Out Where These Treatments Are Taking Place?
Residents can sign up for the District’s spray notification list to receive updates on treatment locations and schedules: Spray Notification Sign-Up

Will Spraying Affect Bees?
No. When Wide Area Larvicide Spraying (WALS) is conducted with VectoBac® WDG, it does not harm bees or other beneficial pollinators.

Will the Application Leave Any Residue?
The spray may leave behind tiny dried droplets that can sometimes appear as a fine dust on outdoor surfaces. These residues are harmless, easily washable, and will not damage your home, garden, outdoor furniture, or vehicles.

Is the Product Harmful to Humans or Pets?
No. When applied as directed, Bti is safe for people, pets, wildlife, aquatic life, beneficial insects, and honeybees.

Learn more here: CDC – Bti Fact Sheet

Do I Have to Go Indoors During Spraying?
No. It is not necessary to go indoors during the application. However, residents who prefer may choose to go inside for added comfort.

Learn more about the product here: bit.ly/VectoBac