A mosquito draws blood from a person's arm — a reminder of the health risks posed by rising mosquito populations and the importance of prevention.
Los Angeles, California – As summer intensifies and California’s mosquito season reaches its peak, public health officials are facing twin realities: a sharp rise in dengue fever cases across the state and a modest but promising breakthrough in mosquito control that may slow the spread of the disease.
The Aedes aegypti mosquito — the primary vector for dengue — has now established itself in at least 25 California counties and over 400 communities, many of them in Southern California and the Central Valley. Just ten years ago, the species was virtually unknown in the region. But climate change, urban development, and travel-related infections have allowed this invasive mosquito to flourish. In 2024, California saw 725 reported dengue cases, up from 250 the year before. Eighteen of those were acquired locally — a troubling sign that the virus is beginning to circulate independently of travel.
Most dengue cases are mild, but the disease can cause severe symptoms and, in rare cases, death. And while effective treatments are limited and vaccines remain unavailable in the U.S., efforts to control the mosquito population may offer the best hope of slowing transmission.
For the first time in a decade, scientists have reported a year-over-year decline in the population of Aedes aegypti mosquitoes in some of California’s hardest-hit areas. A pilot program using sterilized male mosquitoes appears to be working. These males, raised in labs and sterilized using X-ray machines, are released into the environment where they mate with females — who then lay eggs that never hatch.
The program has led to substantial reductions in mosquito populations in targeted zones. In parts of San Bernardino County, populations dropped by 44%. In the Sunland-Tujunga area of Los Angeles, the reduction reached 82%. In other areas like Rancho Cucamonga, officials introduced mosquito-eating fish into standing water, leading to a 65% decrease in populations.
The promise of the sterilized mosquito program has attracted interest from vector control agencies across the state. However, scaling the method to larger regions presents logistical and financial hurdles. Los Angeles County officials estimate a broader rollout would cost homeowners roughly $20 per person annually — a relatively modest figure, but one that still requires funding, staffing, and infrastructure to sustain long-term.
Meanwhile, public health officials remain concerned about broader dengue trends. A lack of rapid testing, insufficient vaccine options, and cuts to federal research — including climate-related disease tracking — leave California vulnerable. While mosquito control offers hope, the continued spread of dengue suggests the fight is just beginning.
