Skip to main content

WALS - Wide Area Larvicide Spraying

May contain: truck, transportation, vehicle, and machine


Along with asking residents to do their part in keeping their backyard free from potential mosquito breeding sources, the Delano Mosquito Abatement District will be evaluating a program known as Wide Area Larvicide Spray (WALS). WALS will be conducted during the mosquito season (March – November) to try to combat and suppress urban container breeding mosquitoes, primarily the Aedes aegypti (Yellow Fever) mosquito.

Often, the majority of these urban container breeding mosquitoes reproduce in cryptic and hidden sources in residential backyards. It is just not possible for the District Mosquito Technicians to inspect thousands of households in our jurisdiction and treat all the possible habitats for urban container breeding mosquitoes.

WALS is an approach to larvae control using natural occurring bacterium to kill the mosquito larvae in water sources. This treatment targets the larval stage of the mosquito and will not reduce adult numbers initially. Control of mosquitoes in their larval stages is the backbone of most mosquito control programs. WALS treatments are carried out using low volume spray equipment mounted on a truck. The equipment allows us to direct the mist to target areas where mosquitoes breed and hide. The District will monitor areas of WALS treatment for population numbers of these container mosquitoes.

Where Will the Spraying Take Place

The spraying will take place in areas of concern -- determined by the district’s mosquito and disease surveillance programs. Our technicians use a variety of surveillance techniques and treatment criteria to ensure effective mosquito control with the least amount of risk to residents and the environment.

What Will Be Sprayed

The District plans to use Vectobac WDG, a biological larvicide, during the WALS operation. VectoBac Biological Larvicide is a mosquito larvicide that contains the time-proven, naturally occurring and environmentally compatible bacteria, Bacillus thuringiensis subsp. israelensis (Bti). Bti is very target-specific and its toxicity is limited to mosquitoes and related flies. This product has no impact on bees and will not harm people, pets, nor wildlife including other aquatic life or other insects. There may be very small dried droplets or fine dust residue on some outside surfaces following treatment. The dried droplets are washable and will not affect your home, garden, outdoor furniture or vehicle. You can learn more about Bti here.

When Will Spraying Take Place

WALS will be conducted during the night (11PM-4AM) when people are indoors, to limit accidental exposure, even though bti is non-toxic to humans, birds, pets, fish, etc.

VectoBac WDG Label and SDS

Vectobac WDG LABEL.pdfVectobac WDG SDS.pdf