HAYWARD, CA July 22, 2026 - On July 20th, the invasive mosquito Aedes aegypti was detected for the first time in Castro Valley. In response, Alameda County Mosquito Abatement District staff have increased mosquito monitoring and control efforts in the area and will conduct a truck-mounted larval treatment during nighttime hours on July 23 to prevent additional adult mosquitoes from emerging. 

Application details: 

• Insecticide: VectoBac® WDG 
• Active ingredient: Bacillus thuringiensis subspecies israelensis (Bti) 
• Bti is a naturally occurring soil bacterium that produces proteins that specifically target and kill mosquito larvae, as well as the larvae of black flies and midges. It is non-toxic and non-pathogenic to humans, birds, fish, mammals and beneficial insects, including pollinators. 

• Method: Truck-mounted ultra-low volume sprayer 
• Date & Time: July 23 (weather permitting), 11:00 p.m. - 1:00 a.m. 
• Residents are encouraged to stay indoors during these hours. 
• Location: The treatment area is between Norbridge Ave/Forest Ave and Sapphire St, bounded by David St and the 580 Hwy (see map below). 
• Additional details: The treatment may leave a light residue on outdoor surfaces. The residue will wash away with water and it is safe to drain into the sewer. 

Aedes aegypti is an invasive mosquito that can transmit diseases such as dengue, chikungunya, Zika, and yellow fever. Like all mosquitoes, Aedes aegypti requires standing water to complete its life cycle but can develop in as little as a bottle cap of water. Eliminating standing water is the most effective way to prevent mosquitoes. Covering or treating water with mosquito-specific larvicides is a good option for water that cannot be dumped or drained. 

Operations Director Erick Gaona said, “We detected this mosquito in back-to-back traps in the area, indicating that Aedes aegypti has found standing water sites to reproduce. To help control the spread of this invasive mosquito, we will conduct a wide-area larval control treatment. Our goal is to deliver the treatment into cryptic water sources that are difficult for our staff to access.”

Community cooperation is essential for effective mosquito control. Residents are encouraged to:

• Report mosquito activity in your neighborhood to the District. 
• Eliminate standing water where mosquitoes breed, including outdoor containers, plants, unmaintained swimming pools, and other hidden sources. 
• Protect yourself from mosquito bites by wearing long, loose-fitting clothing, using EPA-registered insect repellent, and ensuring window and door screens are in good repair. 

The District remains committed to protecting public health through ongoing mosquito surveillance, larval control, and community education throughout Alameda County.

 

The area between Norbridge Ave/Forest Ave and Sapphire St, bounded by David St and Interstate 580 in purple is the treatment zone.

 

Media Contact

Erika Castillo

Regulatory & Public Affairs Director

510-755-3384

erika@mosquitoes.org