Delta Mosquito and Vector Control District (DMVCD) has scheduled an adult mosquito treatment in southwest Visalia and Dinuba because of elevated West Nile virus (WNV) activity in mosquitoes. The treatments will take place between 2:00 AM and 6:00 AM on August 19, 2021, weather permitting. The District uses adult mosquito treatments to reduce the public health risk of WNV and St. Louis Encephalitis virus to District residents. The decision to treat certain areas is based on many factors including resources, vector abundance, environmental conditions, and arbovirus activity in mosquitoes and dead birds.

Maps of treatment areas in Visalia and Dinuba

Areas in southwest Visalia (left) and Dinuba (right) where adult mosquito treatments will take place between 2:00 AM and 6:00 AM on August 19, 2021.

DMVCD uses ground ULV to reduce WNV risk

DMVCD applies adult mosquito treatments with ultra-low volume (ULV) equipment that is mounted on a truck. This is referred to as ground ULV. Usually, ground ULV takes place in urban areas to control adult mosquitoes. The adulticides are applied at very low dosages. The low dosages, plus natural degradation by UV light and water, ensure minimal risk. The District uses U.S. Environmental Protection Agency (EPA) registered pyrethroid-based products for ground ULV adulticiding. Pyrethroids are synthetic insecticides, modeled after a botanical insecticide produced primarily from the flowers of Tancetum cinerariifolium, which is a species in the Chrysanthemum plant family. These botanical compounds act as the plant’s own insecticide to keep insects away. The District recommends that people who want to avoid exposure stay inside or away from the application area during, and for 30 minutes after, the application.

Adult female mosquito standing on a finger

A female Culex quinquefasciatus mosquito lands on a finger to take a blood meal. She needs the protein from blood to make eggs. Photo Credit: CDC James Gathany


Residents can reduce sources of standing water

Residents can help reduce mosquito abundance and disease risk. 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 into biting adults. Neglected swimming pools, fountains, potted plant trays, and pet water bowls are all common household sources of standing water. Additionally, DMVCD 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 resources page.