Invasive Mosquito Populations Have Spread in California
The Aedes aegypti mosquito has established a presence in 28 California counties, health officials reported.
Updated on Sept. 25, 2026 in Diseases — General
Live Poll
Do you regularly eliminate standing water in your yard to help prevent invasive mosquito populations?
Invasive Aedes aegypti mosquitoes have established permanent populations across 28 California counties, according to the California Department of Public Health. These mosquitoes are known for biting during the daytime and have been spreading across the state since their initial detection in 2020.
Why it matters
The presence of these mosquitoes increases the risk of local disease transmission because they thrive near humans and breed in small containers that standard pest control programs cannot easily treat. They are known to carry viruses including dengue, Zika, chikungunya, and yellow fever.
State officials have confirmed established Aedes aegypti populations in 28 California counties. While Shasta County mosquitoes have not tested positive for viruses this year, the species is capable of transmitting yellow fever, Zika, and heartworm to animals.
The players
California Department of Public Health
This state agency is responsible for monitoring infectious diseases and coordinating public health responses throughout California.
The details
The Aedes aegypti species persists by laying eggs in small amounts of standing water found in common household items like plant saucers, bottle caps, and buckets. They primarily travel to new areas by hitching rides in vehicles, outdoor equipment, and containers.
Timeline
The Aedes aegypti mosquito was first identified in Shasta County in 2020.
State health officials confirmed the infestation reached 28 counties by 2026.
The current mosquito season is expected to continue through fall 2026.
Health Landscape
The rapid expansion of Aedes aegypti populations reflects significant challenges for the California Department of Public Health's vector-borne disease surveillance program. This trend highlights the difficulty of managing invasive species that have integrated into suburban residential environments.
Residents should inspect their outdoor spaces weekly to empty standing water from plant saucers and buckets to prevent the mosquitoes from breeding near homes. Because these insects bite during the day, individuals are advised to use EPA-registered insect repellents when spending time outdoors.
The takeaway
The invasive mosquito's preference for breeding in small household containers means that individual property maintenance is the most effective way to curb population growth. Remaining vigilant about standing water is essential as the mosquito season is expected to last well into the autumn months.
Further reading
For more information on managing vectors and preventing bites, visit the California Diseases — General section.
More information
Find additional resources on public safety and mosquito control at the California Department of Public Health portal.
Live Poll
Do you regularly eliminate standing water in your yard to help prevent invasive mosquito populations?
