Sunday, October 4, 2026

Vector District Sets Overnight Mosquito Treatments in Altadena This Week

The San Gabriel Valley Mosquito and Vector Control District will treat part of Altadena for mosquitoes between midnight and 5:30 a.m. Wednesday and Thursday, Oct. 7 and 8, citing a significant public health risk.

The Altadena treatment area lies between Glenrose Avenue and Marengo Avenue, south of East Mariposa Street and north of West Woodbury Road.

West Nile virus activity in the district’s mosquito samples had surpassed its five-year average as of early September, the district said. Los Angeles County had also documented more human infections than its five-year average for the same period, according to the county Department of Public Health.

Crews working from trucks will use ultra-low volume adulticide and low volume larvicide applications to target mosquitoes at multiple stages of their life cycle, according to the district.

In both Altadena and Monterey Park (where a treatment is also scheduled for the same days and hours), specialists will apply AquaDUET to target adult mosquitoes. The district said the product contains Sumithrin and Prallethrin, active ingredients formulated to mimic properties of chrysanthemum flowers.

Because it is suspended in water, the application will not harm the finishes on cars or homes, the district said.

In Altadena only, specialists will also apply VectoBac WDG, a biological larvicide containing Bacillus thuringiensis subsp. israelensis to water sources holding immature mosquitoes. The goal is to reduce the number that develop into biting adults, the district said. The district has described VectoBac WDG as specific for mosquitoes, with no known risk to humans and wildlife when applied according to the label.

Altadena recorded its first West Nile virus-positive mosquito sample of the year on July 23 and has had three, according to district data updated Sept. 28.

District-wide, 177 samples had tested positive as of that update. Each sample is a random collection of 10 to 50 mosquitoes from a trap. The virus spreads through the bite of an infected Culex mosquito, which is most active at dusk and dawn, and there is no human vaccine or cure, the district said.

“Although current WNV activity is higher than usual, our teams are purposely equipped to deal with this challenge,” Tristan Hallum, the district’s director of scientific programs, said Sept. 3. Los Angeles County had documented 100 human West Nile infections and five deaths as of Sept. 18, according to the county Department of Public Health.

The treatments may be postponed or delayed if weather conditions are not favorable or if there are operational delays, according to the district.

Area-wide pesticide treatments are reserved for severe conditions, including abnormal mosquito population spikes, abnormal virus activity and public health emergencies, the district has said. Most of its pesticide use is against mosquito larvae, using Bacillus thuringiensis var. israelensis, according to the district.

The district asks residents to eliminate standing water in clogged rain gutters, rain barrels, discarded tires, buckets and anything else that holds water for more than a week. It also asks them to change the water in pet dishes, birdbaths and other small containers weekly and to report neglected swimming pools. It recommends repellent containing DEET, picaridin, IR3535 or oil of lemon eucalyptus, along with light-colored, long-sleeved shirts and long pants.

NEED TO KNOW

Event: Mosquito control treatment by the San Gabriel Valley Mosquito and Vector Control District. When: Wednesday, Oct. 7, and Thursday, Oct. 8. Time: Midnight to 5:30 a.m. Where: Between Glenrose Avenue and Marengo Avenue, south of East Mariposa Street and north of West Woodbury Road, Altadena. For more, call (626) 814-9466 or visit https://www.sgvmosquito.org/2026-10-03-mosquito-control-treatments-scheduled-in-altadena-and-monterey-park