Delta Mosquito and Vector Control District (DMVCD) has scheduled Wide Area Larviciding System (WALS) treatments in southeastern Visalia between Walnut Ave and Tulare Ave, and Lovers Lane and McAuliff St. WALS treatments began on August 5, 2021. These treatments are scheduled to take place weekly for four weeks and then every other week for an additional four to eight weeks depending on conditions. Treatments will likely take place between midnight and 3:00 AM on Thursdays if conditions are appropriate.

DMVCD is evaluating WALS treatments in a neighborhood setting as an Integrated Vector Management tool to control Aedes aegypti in the district. The decision to treat this area was based on Aedes aegypti abundance data and environmental conditions. Current WALS protocol recommends multiple treatments to the same area over two to three months in order to be effective. At this time, the trial is only taking place in the area between Walnut Ave and Tulare Ave, and Lovers Lane and McAuliff St in southeastern Visalia.

WALS treatments are applied with low volume equipment that is mounted on a truck. DMVCD is using Vectobac WDG for the WALS applications. Vectobac WDG is Environmental Protection Agency (EPA)-registered as well as OMRI Listed. This product uses a type of naturally occurring bacteria, Bacillus thuringiensis subspecies israelensis (Bti). When eaten by mosquito larvae, Bti produces a protein crystal that destroys the larvae’s intestinal lining in the gut. You can learn more about Bti here. 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.

Mosquito Larvae

Aedes aegypti mosquito larvae live in small sources of standing water as they develop into biting adults. Photo Credit: CDC 1976

This treatment targets the larval stage of the mosquito and will not  reduce adult numbers initially. Instead, WALS treatments control the larval stage of the mosquito ant prevent them from developing into biting adults. WALS treatment targets the invasive Aedes aegypti mosquito, whose adult form is highly resistant to adulticide control methods.

Mosquitoes need standing water to lay their eggs and develop into adults. Mosquito larvae can take as little as 5-7 days to develop into adult mosquitoes. Dumping any water that lasts for more than 3 days will get rid of mosquito larvae before they can develop and emerge as biting adults. Fountains, potted plant trays, and pet water bowls are all common household sources of standing water. The DMVCD also offers free mosquitofish for larger water sources such as backyard ponds, water features, and animal water troughs. More information about preventing mosquitoes can be found on the DMVCD prevention page. District residents can reduce mosquito bites by using an EPA-registered insect repellent. More information about EPA-registered insect repellents can be found here. Insect repellent brochures are also available for download on the DMVCD Self-Help page.