Los Angeles has a thriving and growing mosquito population, and the situation has gotten considerably worse over the past decade. The city has long been home to native Culex mosquitoes, but since the early 2010s, aggressive invasive species from the tropics have established permanent footholds across LA County, bringing with them the potential for diseases that were previously unheard of in Southern California. In 2024, LA recorded its first cluster of locally acquired dengue fever cases, a disease more commonly associated with Southeast Asia and Latin America. What follows is what you need to know about LA’s mosquito landscape and, more practically, what actually works to protect yourself.
Which Mosquitoes Live in LA
The most common mosquito in the LA metro area has historically been Culex quinquefasciatus, sometimes called the southern house mosquito. Surveys in residential neighborhoods of Los Angeles and Orange Counties found it was the most abundant species collected, both as adults and larvae, followed by Culiseta incidens and Culex tarsalis.1Journal of Medical Entomology. Mosquito Abundance and Bionomics in Residential Communities in Orange and Los Angeles Counties, California These Culex mosquitoes are classic nighttime biters. They breed in standing water, feed primarily after dusk, and are the main carriers of West Nile virus in the region.
But it is the newer arrivals that have fundamentally changed the picture. Aedes aegypti (the yellow fever mosquito) and Aedes albopictus (the Asian tiger mosquito) are tropical species that bite aggressively during the day, can breed in absurdly small amounts of water, and are capable of transmitting dengue, Zika, and chikungunya. Before 2011, neither species was considered established in California. That changed when Ae. albopictus was found persisting in El Monte, within LA County, likely a surviving remnant of a population that arrived with imported “lucky bamboo” plants from China back in 2001.2PubMed Central. Public Health Response to Aedes aegypti and Ae. albopictus Mosquitoes Invading California, USA Genetic analysis confirmed those mosquitoes had survived an eradication campaign and quietly persisted in residential neighborhoods for nearly a decade.3PLoS ONE. Genetic Analysis of Invasive Aedes albopictus Populations in Los Angeles County, California and Its Potential Public Health Impact Since then, Ae. albopictus has spread to over a dozen cities in the county, and Ae. aegypti was detected in LA County by 2014.
More recently, yet another invader has shown up: Aedes notoscriptus, an Australian species first collected in LA after a resident called in a complaint about aggressive day-biting mosquitoes. That service request in the city of Montebello led to the identification of a species never previously recorded in the Western Hemisphere.4Journal of Medical Entomology. Detection and Establishment of Aedes notoscriptus (Diptera: Culicidae) Mosquitoes in Southern California, United States It has since been found across a wide swath of urban LA, from downtown to foothill communities more than 35 kilometers inland.
Why the Invasive Species Are So Hard to Control
If you have lived in LA for a while and feel like mosquitoes have gotten worse, the invasive Aedes species are the main reason. They behave differently from the native Culex mosquitoes in ways that make them much harder to manage. Day-biting mosquitoes like Aedes aegypti tend to take shorter, more frequent blood meals compared to nighttime feeders that gorge once on a sleeping host.5The Journal of Basic and Applied Zoology. Role of circadian rhythms in the host seeking initiation and feeding behaviour of day and night biting mosquitos-a brief review That means they bite more people over the course of a day, which also makes them more efficient at spreading disease.
Their breeding habits are the bigger headache. Aedes aegypti and albopictus lay eggs in tiny containers of water: a bottle cap, a saucer under a plant pot, a forgotten dog bowl. Studies of where Ae. aegypti larvae actually turn up in Southern California found that about 80% of positive habitats were containers, with another 14% being water features like birdbaths and fountains.6Scientific Reports. Impact of underground storm drain systems on larval ecology of Culex and Aedes species in urban environments of Southern California Underground storm drains, by contrast, were not major Aedes breeding sites; the water chemistry in LA’s storm drain system actually inhibited their larval development, though native Culex mosquitoes managed to develop there.7PubMed Central. Impact of underground storm drain systems on larval ecology of Culex and Aedes species in urban environments of Southern California This means the invasive species are breeding in private yards, on porches, and in backyards where vector control agencies cannot easily reach without homeowner cooperation.
The Diseases They Carry
West Nile virus has been the primary mosquito-borne disease concern in LA since it arrived in the early 2000s. The virus was first detected in dead birds and mosquito pools in the LA Basin and Riverside area and then spread rapidly through bird populations along riparian corridors from the San Fernando Valley to Long Beach.8PubMed Central. West Nile virus in California Culex quinquefasciatus turned out to be the primary vector, cycling the virus between itself and local bird populations in a pattern of emergence, amplification, subsidence, and occasional resurgence that has continued for over two decades.9PubMed Central. West Nile virus emergence and persistence in Los Angeles, California, 2003-2008 Warmer temperatures accelerate the cycle; research tracking sentinel chickens in the greater LA area showed that warming degree-days were associated with increased risk of the virus jumping from birds to people.10PubMed Central. Sentinel chicken seroconversions track tangential transmission of West Nile virus to humans in the greater Los Angeles area of California Most people who contract West Nile never develop symptoms, but a small percentage develop severe neurological illness, and there is no vaccine or specific treatment.
The bigger shift in recent years has been the arrival of dengue. In the summer and fall of 2024, LA County identified 14 locally acquired dengue cases, meaning people who had never left the area caught the virus from local mosquitoes. Epidemiologic investigation pointed to short transmission chains sparked by infected travelers returning home, with evidence of sustained transmission for up to seven weeks in at least one neighborhood.11PubMed Central. Investigation of and Response to Autochthonous Dengue, Los Angeles County, California, USA, August-November 2024 Fourteen cases may sound small, but the significance is in the precedent: local dengue transmission requires established populations of Aedes aegypti, warm enough temperatures for the virus to replicate inside the mosquito, and enough human-mosquito contact to keep chains going. LA now checks all three boxes during its warm months.
Climate Change Is Making It Worse
LA’s semi-arid climate was historically not ideal for tropical mosquitoes, but warming temperatures are shifting the math. Modeling work has suggested that a 3°C increase in temperature could roughly double the risk of a dengue outbreak in Los Angeles, because temperatures between 25°C and 30°C create the sweet spot where Aedes aegypti lives long enough and the virus replicates inside the mosquito fast enough for efficient transmission.12PLOS Climate. Changing temperature profiles and the risk of dengue outbreaks Interestingly, that same research found that already-hot cities like Miami and Phoenix could actually see reduced dengue risk at higher temperatures because extreme heat kills mosquitoes and shortens their lifespan. LA sits in a transitional zone where more warming pushes conditions toward the optimum for transmission rather than past it.
The drought-and-rain cycles common to Southern California also play a role. During droughts, residents store water in buckets, barrels, and improvised containers. Research in a comparable climate found that garden pots, plant propagation buckets, birdbaths, and water storage containers accounted for over half of all immature mosquitoes collected, and these container types became more common during drought conditions.13International Health. Increased container-breeding mosquito risk owing to drought-induced changes in water harvesting and storage in Brisbane, Australia When water storage compliance drops, mosquito populations can spike substantially.14PubMed Central. Simulating an invasion: unsealed water storage (rainwater tanks) and urban block design facilitate the spread of the dengue fever mosquito, Aedes aegypti, in Brisbane, Australia For LA, where rain barrels and water conservation are encouraged for sustainability reasons, proper screening and sealing of stored water is not just a good idea but an increasingly important public health practice.
What Actually Works for Personal Protection
The repellent landscape is well studied, and the evidence strongly favors a short list of active ingredients. DEET remains the most proven option, with protection times exceeding six hours at concentrations around 20%. Picaridin is a strong second choice, with a systematic review finding it had the best supporting evidence after DEET across Aedes aegypti, Aedes albopictus, and Culex species.15PubMed. EPA-Registered Repellents for Mosquitoes Transmitting Emerging Viral Disease At a 20% concentration, picaridin provided protection for roughly 410 minutes against Aedes aegypti, comparable to DEET at the same concentration.16Infectious Diseases in Clinical Practice. Efficacy of the DEET, IR3535, and Picaridin Topical Use Against Aedes Aegypti IR3535, the active ingredient in some “gentle” formulations marketed for children, provided solid protection in the range of 350 to 360 minutes. Oil of lemon eucalyptus is a reasonably effective plant-based option, though its protection time is shorter.
What about the products many people reach for first? Citronella candles and wristbands offer limited protection at best. The same systematic review noted that citronella provides only modest, short-duration protection.15PubMed. EPA-Registered Repellents for Mosquitoes Transmitting Emerging Viral Disease And some popular “solutions” are flatly ineffective: ultrasonic mosquito-repelling devices, outdoor bug zappers, and bat houses have been evaluated and found not to work against mosquitoes.17PubMed. Mosquitoes and mosquito repellents: a clinician’s guide Bug zappers are particularly misleading because they do kill insects, just not mosquitoes in meaningful numbers. The ultraviolet light attracts beetles, moths, and other harmless species far more than it attracts blood-seeking mosquitoes, which locate hosts primarily by carbon dioxide and body odor.
Reducing Mosquitoes Around Your Home
Because the invasive Aedes species breed in containers rather than ponds or marshes, individual homeowners have an outsized role in mosquito control. The principle is source reduction: eliminating the standing water where mosquitoes lay eggs. Given what the larval habitat surveys show for Southern California, the target list is straightforward.
- Plant saucers: These are consistently among the top breeding sites. Dump them weekly, or better yet, fill them with sand so water wicks up to the pot but does not pool.
- Birdbaths and pet bowls: Refresh the water at least twice a week. Aedes eggs can hatch in as little as a few days.
- Rain barrels and stored water: Screen all openings with fine mesh. Unsealed water storage containers are ideal mosquito habitat, providing food, temperature, humidity, and proximity to human hosts.
- Yard debris: Old tires, tarps, buckets, and anything that catches rainwater or irrigation runoff. Even a crumpled fast-food cup can hold enough water.
- Drains and gutters: Clogged roof gutters hold standing water after every rain or watering cycle. French drains and catch basins can also accumulate water.
Source reduction works because Aedes mosquitoes have a limited flight range, often staying within a few hundred meters of where they emerged. If you and your immediate neighbors eliminate breeding sites, you can substantially reduce the local population. The challenge is that one neglected property on a block can sustain enough mosquitoes to affect the entire neighborhood.
What LA’s Vector Control Agencies Are Doing
Los Angeles County is served by several vector control districts that conduct surveillance, larviciding, and adult mosquito spraying. For the invasive Aedes species, conventional spraying has had limited success because these mosquitoes rest in dense vegetation close to the ground and breed in spots that spray trucks and even backpack foggers cannot easily reach.
That limitation has pushed agencies toward newer approaches. One promising strategy is the sterile insect technique, in which male mosquitoes are sterilized using low-dose X-ray irradiation and released into the wild, where they mate with females but produce no viable offspring. A two-year program in southern California’s West Valley region released irradiated male Ae. aegypti every two weeks from April through November. In high-density areas, mosquito populations dropped by 59 to 78% in the first year and up to 88% in the second, compared to baseline levels.18Scientific Reports. Targeted, density-dependent sterile male releases to enhance Aedes aegypti population suppression in southern California When the sterile male releases were combined with In2Care mosquito stations, which use a slow-acting larvicide that female mosquitoes spread to other breeding sites, the reduction reached about 65%.19PubMed Central. Reduction in Aedes aegypti Population After a Year-Long Application of Targeted Sterile Insect Releases in the West Valley Region of Southern California Over 99.6% of eggs from females that mated with the irradiated males failed to hatch.
Surveillance itself has become more sophisticated. Agencies use a mix of trap types: BG Sentinel traps have proven the most sensitive for detecting Ae. aegypti spread into new locations, while autocidal gravid ovitraps placed at fixed sites and serviced weekly provide reliable monitoring of abundance within known infestation zones. Long-term, high-density placement of these traps also shows promise as a chemical-free trap-and-kill strategy.20PubMed Central. Surveillance, insecticide resistance and control of an invasive Aedes aegypti (Diptera: Culicidae) population in California Residents can support these efforts by reporting unusual daytime biting activity; the discovery of Ae. notoscriptus in Montebello literally began with a homeowner filing a service request.
Why Some People Get Bitten More Than Others
If you live with someone who never seems to get bitten while you are covered in welts, the difference is real and at least partially genetic. Variability in human attractiveness to mosquitoes is driven by differences in the composition and intensity of the chemical signals your skin releases. Your skin’s bacterial community plays a central role, as does your genetic makeup, particularly a class of immune-related genes called HLA alleles, which influence what volatile compounds your skin produces.21PubMed Central. Variability in human attractiveness to mosquitoes Carbon dioxide output, body heat, and certain metabolic byproducts also contribute. People who produce more lactic acid or certain fatty acids on their skin tend to be more attractive to mosquitoes.
There is no reliable way to change your baseline attractiveness. Some internet advice suggests eating garlic, taking B vitamins, or wearing certain colors, but none of these have held up under controlled testing. The practical takeaway is simpler: if you know you are a mosquito magnet, be more diligent with repellent and source reduction than the average person.
Mosquitoes and Your Pets
Mosquitoes in LA are not just a human health concern. Dog heartworm, a parasitic disease transmitted by mosquito bites, has historically had low transmission rates in southern California, but the establishment of new mosquito species is changing the risk calculus. Research on heartworm transmission ecology in California found that Ae. albopictus was significantly associated with heartworm cases in Southern California, while Ae. aegypti was linked to cases in the Central Valley.22PubMed Central. Ecological drivers of dog heartworm transmission in California The newly arrived Ae. notoscriptus is considered the most important domestic vector of dog heartworm in its native Australia because of how efficiently it transmits the parasite and how readily it feeds on dogs.4Journal of Medical Entomology. Detection and Establishment of Aedes notoscriptus (Diptera: Culicidae) Mosquitoes in Southern California, United States Whether its arrival will drive an uptick in heartworm in LA remains to be seen, but veterinarians in the area have increasingly recommended year-round heartworm prevention for dogs rather than the seasonal approach common in colder climates.