Meet the new Aedes mosquito spreading misery around a wide swath of Southern California

While no serious illnesses have been detected yet, these transplanted mosquitoes can transmit the viruses that cause Zika, dengue, chikungunya, and yellow fever.  Meet your new neighbors: tiny but aggressive mosquitoes in the Aedes genus.  Also known as the “ankle biter” in vector control circles, these tropical and subtropical mosquitoes have invaded Southern California and are reproducing at an alarming rate.  

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Desperate and miserable, Luz Flores of San Pedro took to social media for advice on the evening of Monday, August 20.

“Is anyone else getting these bites in their legs and arms? These are extremely itchy, swollen, hot and hurting … any help is much appreciated. Tried cooling, alcohol, warm spoon, peroxide and nothing helps the itching!”

Flores, 46, soon found out she wasn’t alone, after 200-plus responses quickly piled onto the Facebook thread.

“Me too, I have mosquitos all over!!!!!” one commenter wrote.

“Horrible! Those mosquitos are vicious!” posted another.

Meet your new neighbors: tiny but aggressive mosquitoes in the Aedes genus.  Also known as the “ankle biter” in vector control circles, these tropical and subtropical mosquitoes have invaded Southern California and are reproducing at an alarming rate.

The recent Golden State arrivals are so far spreading human misery mainly in the form of itchy, painful bites across Los Angeles and Orange counties and even into San Bernardino, Riverside and San Diego counties.

“We are getting absolutely overwhelmed with calls,” said Kelly Middleton, director of Community Affairs for the Greater Los Angeles Vector Control District. “They’ve continued to spread out.

“We typically find communities where the first-year levels are kind of low and some people report a problem. By the second or third year, a lot of people are dealing with these mosquitoes.”

In time, the mosquitoes could possibly wind up spreading some very nasty diseases.

And that notion is keeping vector control officers hopping.

Diseases

While no serious illnesses have been detected yet, these transplanted mosquitoes can transmit the viruses that cause Zika, dengue, chikungunya, and yellow fever.

For now, “it’s more the possibility of disease,” said Lora Young, director of communications for the Orange County Mosquito and Vector Control District. “We haven’t seen any Zika or dengue or chikungunya, but there is now a possibility of those because we have the mosquito that can spread them.”

The expansion of the tiny black-and-white mosquitoes in Orange County has been rapid, Young said.

“From 2016 to 2017 we’ve seen it almost double,” she said. “This year, 25 (out of 34) cities have infestations.”

The other cities, she said, have wide areas of infestations within their boundaries.

“Northern Orange County has the most activity but we’re finding it in south Orange County as well,” Young said. “They’re spreading rapidly.”

Three species

For the past seven years, three species of Aedes mosquitoes from Asia, Mexico/Central America, Australia  and southern states of Texas, Louisiana and Florida — Aedes albopictus(the Asian tiger mosquito, 2011), Aedes aegypti (the yellow fever mosquito, 2014) and Aedes notoscriptus (2017) — have been making their new home in Southern California, Middleton said.

Not native, they still find comfortable surroundings in people’s backyards and patios, according to the GLAVCD website.

They don’t fly very far, so much of their spread has been facilitated by the transportation of their eggs in everything from flower pots to cars.

“These are really backyard breeders,” Young said.

Unlike California’s more native and nocturnal mosquitoes, which can also be dangerous with their spread of the West Nile Virus, these new species are known to bite during the day.

They’re not shy and they are so tiny that often people never see what bit them, leading to speculation about everything from spiders to bed bugs to sand flies or fleas.

Aedes bites, often inflicted on ankles and legs below the knees, look like clustered pinpoint marks. They quickly become inflamed and expand into big red welts and rashes with scratching.

“They look like chigger bites, and they itch really bad too,” reads one comment on the San Pedro group Facebook page.

“We react to them worse” than we do to bites from California’s regular mosquitoes, Middleton said. “Our immune system is not used to them.”

While over-the-counter creams help with the bites, some residents are so desperate for relief that they head for the doctor and urgent care clinics.

Flores, who works in Long Beach, estimates she’s gotten bit more than 20 times this summer.

She decided to seek help from urgent care Tuesday evening, saying she had paid for so many over-the-counter remedies that she might as well spring for a prescription medicine.

“I’m tired of spending money on all these over-the-counter medications that don’t work,” Flores said.

What to do

Vector control officials stress that neighbors need to work together to prevent the spread of the mosquitoes.

Residents should make sure window screens are well-fitted, and do weekly checks around their properties for standing water.  Saucers under flower pots, drainage areas, fountains and pet water bowls are likely breeding grounds.

“With these three species, they lay eggs on the sides of barrels (and other containers),” Middleton said. “So you can dump out the water but they can still remain alive in people’s yards for years.”

Always apply EPA-approved insect repellents that have DEET, Picaridian or oil of lemon eucalyptus, Middleton said.

“A lot of the botanicals don’t work” with these mosquitoes, she said.

Finally, be prepared for a few more months of this, Middleton said.  Because of the increasingly humid summers Southern California has been seeing, the mosquitoes may be here to stay.

“This may become our new normal,” she said.

Excerpt from Wikipedia

The Centers for Disease Control and Prevention traveler's page on preventing dengue fever suggests using mosquito repellents that contain DEET (N, N-diethylmetatoluamide, 20% to 30%). It also suggests:

  1. Although Aedes aegypti mosquitoes most commonly feed at dusk and dawn, indoors, in shady areas, or when the weather is cloudy, "they can bite and spread infection all year long and at any time of day."[7][8]
  2. Once a week, scrub off eggs sticking to wet containers, seal and/or discard them. The mosquitoes prefer to breed in areas of stagnant water, such as flower vases, uncovered barrels, buckets, and discarded tires, but the most dangerous areas are wet shower floors and toilet tanks, as they allow the mosquitos to breed in the residence. Research has shown that certain chemicals emanating from bacteria in water containers stimulate the female mosquitoes to lay their eggs. They are particularly motivated to lay eggs in water containers that have the correct amounts of specific fatty acids associated with bacteria involved in the degradation of leaves and other organic matter in water. The chemicals associated with the microbial stew are far more stimulating to discerning female mosquitoes than plain or filtered water in which the bacteria once lived.[9]
  3. Wear long-sleeved clothing and long trousers when outdoors during the day and evening.
  4. Use mosquito netting over the bed if the bedroom is not air conditioned or screened, and for additional protection, treat the mosquito netting with the insecticide permethrin.

Insect repellants containing DEET (particularly concentrated products) or p-menthane-3,8-diol (from lemon eucalyptus) were effective in repelling Ae. aegypti mosquitoes, while others were less effective or ineffective in a scientific study.[10] The Centers for Disease Control and Prevention article on "Protection against Mosquitoes, Ticks, & Other Arthropods" notes that "Studies suggest that concentrations of DEET above approximately 50% do not offer a marked increase in protection time against mosquitoes; DEET efficacy tends to plateau at a concentration of approximately 50%".[11]

Mosquito control is currently the best method for disease prevention. This primarily includes source reduction, pesticide spraying for larval control and "fogging" for adult control, or the use of mosquito traps like the lethal ovitrap.

Although the lifespan of an adult Ae. aegypti is two to four weeks depending on conditions,[12] the eggs can be viable for over a year in a dry state, which allows the mosquito to re-emerge after a cold winter or dry spell.[13]