Aedes Mosquito: The Day Biter

by Christian Shepherd
photography by Claudia Ceja

In a quaint neighborhood near the western border of La Verne above Baseline Road, where residents can still be spotted grabbing the local newspaper from their driveways, Los Encinos Park has been wilted by the enduring California summer. Unbeknownst to the residents, the quiet park hosts an ideal habitat for a special breed of mosquitoes, contemned most for their aggressive biting behavior and potential to carry a variety of pestilent tropical viruses and diseases.

The park’s entrance, littered with the remnants of a wood chip path, leads down two flights of wooden stairs that are riddled with thick, hollow nails protruding out of their fixtures; a hazard for visitors, but far from the most concerning issue. The walk is pathed with flattened dead grass and packaging from convenience store refreshments. Polar Pops seem to be the local favorite.

Follow that path another 10 yards, and you will find another local favorite: a green, muddy pool full of stagnant drain water, home to hundreds of Aedes mosquitoes and their developing larvae and pupae. The surrounding air is thick with the smell of rot, but the musk quickly fades into the background after a few minutes as swarms of mosquitoes bzzzz past, like a train’s engine crescendoing as it bellows toward your ear and then fading as it passes by.

The Aedes mosquito is not native to the Southern California area. It is an invasive species that derives from Africa, but can now be found in tropical, subtropical and temperate regions throughout the world. The Aedes is most known for its affinity for aggressive biting during daytime, often through layers of clothing, a behavior many residents are unaccustomed to.
Hendricks Peña, a vector control specialist for the San Gabriel Valley Mosquito and Vector Control District, frequents this location. It is a hot spot for Aedes breeding and, despite his consistent treatment of the area, he has been unable to remove the mosquito population. The street drainage provides a water source that regularly enough washes away pesticides, but allows the mosquitoes to complete a breeding cycle—typically around seven days.

Peña holds onto a long, thin pole connected to a plastic white container, stained and speckled different shades of green and brown, and dips it into the water, fishing out different stages of Aedes metamorphosis.

The first dip reveals a group of larvae, barely noticeable among the decayed greenery and murky water. The second, a single pupa, has a noticeably thicker, browner shell and even thicker head. He only needs the one dip to know that he would once again have to bombard the infestation with treatments.

His boots, battered from more than a few of these treks, are exactly 12 inches long—a perfect tool for measuring the width and length of stagnant bodies of water. This one was roughly 10 steps, toe to heel, which he then uses to calculate a specific amount of pesticide and oil to treat the mosquito habitat. On this visit, he will be opting for water dissolvable packs of pesticides deemed safe by government regulation, along with CocoBear, an oil that is sprayed over the surface of the water. The mosquito larvae, about a centimeter wide, use their trumpets to penetrate the surface of the water to breathe. Their snorkels are not strong enough to penetrate the applied oil, effectively suffocating and killing the larvae before they finish their metamorphosis.

The Aedes mosquito is one of a few species of mosquito that can carry Zika, a virus that can have devastating effects on a newborn child. If a mother is afflicted with Zika during her pregnancy, the child can develop a plethora of brain defects, including microcephaly, a condition where the head of the child is significantly smaller in proportion to other children their age. In 2016, there were 5,168 Zika virus cases reported in the United States, according to the Center for Disease Control and Prevention. Predictively, 4,897 of those cases involved travelers returning from affected areas. Concernedly, 224 cases were transmitted through presumed mosquito-borne transmission. California, Texas, Florida and New York have the highest confirmed rate of Zika. That number dropped significantly the following year in 2017, when the CDC reported only 425 total cases of Zika, 427 from returning travelers and seven from mosquito transmission. As of September 2018, only 41 total cases have been reported, all of which are from returning travelers.

The Aedes mosquito presents a unique challenge for Peña and other vector control specialists working on cutting the population of mosquitoes in the San Gabriel Valley area. Unlike other species, the female Aedes mosquito needs significantly less water to plant her eggs—all 250 of them. “The whole life cycle could take place in something as small as a water bottle’s lid, which makes it much more difficult to fight since any standing water has the potential of reproducing them,” explains Bob Neher, an emeritus University of La Verne biology professor and ex-vice president of the San Gabriel Valley Mosquito and Control District. He served as an elected member of the La Verne City Council when La Verne was converting its historic orange groves to housing. “The single eggs can then dry, and the egg forms a little capsule around it so it doesn’t totally dry out. These eggs then can live for over a year and, when they are rehydrated, they can hatch out and reinfest in an area where you thought you had them under control.”

Bob is an older man, dressed in loose khakis and a patterned cotton button-down. His hands are sunken, exposing thick purple veins under a thin layer of skin—an invitation to a blood eating mosquito. His office, found inside one of the oldest buildings at the University, is covered with small vials, droppers and both a stapler and tape dispenser so outdated it is now an alluring retro piece. There are two microscopes on the same desk, a newer model dark in color and covered in plastic and an older gray machine left exposed to the elements. He has a young mind when it comes to the subject of mosquitoes. Directly above the microscope is a photograph of a peculiar looking beetle with long antennae and a framed collection of butterflies from the Philippines. Bob completed his Ph.D. in plant systematics, but his natural inclination for insects led him to foster his curiosity through his work at the Vector Control District.

Bob has passionately worked alongside vector control to help keep the—as he pronounces it— “mosquit-uh” population under control, but recent efforts from the department have not been enough to mitigate the Aedes outbreak. “There have always been mosquitoes, but the control district has pretty well kept them down in number, until this year when the Aedes outbreak got reintroduced.” Bob and other vector control employees know that one of the most concerning attributes of the Aedes is that they are not picky about where they do their nesting.

“I did an inspection on this property that recently held a party,” remembers Levy Sun, public information officer for the San Gabriel Valley Mosquito and Vector Control District, who can identify the Aedes mosquitoes in the park from their flight paths. “We did a thorough check, from the front yard to backyard, and almost nothing held water until, finally, I got to the recyclables. The bottle caps were off the bottles, and beer cans were opened. I took a look at one of the beer cans with my flashlight and saw that it was mixed with beer and water. I was thinking, ‘There is no way anything survives with that.’ Upon closer inspection, mosquito larvae were just swimming around in there, clearly having a good time with the beer, but it shows how resilient these mosquitoes are.”

The Aedes mosquito goes through four stages of growth, from egg to larvae, to pupae, to an adult mosquito. As an egg, larvae and pupae, all the mosquito needs to survive is a small water source and access to oxygen. The process takes less than a week. The adults live for anywhere between two weeks and a month depending on environmental conditions. “I popped open the lid of one of these oil wells. Part of the well was filled with oil, the other, water. The portion with the water had mosquito larvae swimming inside. They will take advantage of anything we give them. We give an inch, they take a foot and rear their young and start a new generation,” says Levy.

Bob explains the anatomy of the Aedes mosquito is particularly resistant to traditional methods of treatment and that when vector control first started tackling the Aedes problem, there was concern in the department. “The sentiment was worry, because we knew that this was a tricky mosquito to work with. It’s past the ability for us to control it. We can knock them down and knock them down, but they are always going to come back,” Bob explains. “Even if you fumigated cargo, because the eggs can be encapsulated and dried, your fumigant might not get them all. Even if you had only a half of dozen that hatched out, it could be very serious.”

Unfortunately for his line of work, Levy is highly allergic to the saliva of the Aedes mosquito, so when he is out doing fieldwork with his colleagues, he makes sure to spray a few extra pumps of insect repellent on his extremities, neck and facial areas. While his body has had a chance to grow accustomed to the native Culex mosquito, it is still not used to the saliva of the Aedes species, since it has only been sighted in the area since 2011. Levy, who came to the site alongside his colleague Peña, brought examples of both the Culex and Aedes mosquitoes in two small plastic boxes. The mosquitoes are only a quarter of an inch long, so a magnifying glass is strategically placed on the box to reveal their mostly black bodies, speckled with white spots on most of their joints. However, unlike the native Culex mosquito, which gets its blood meal from one bite on one target, the Aedes mosquito takes several bites from numerous targets, making it a particular contender when it comes to starting an epidemic. That, coupled with the increasing regulations on legal pesticides and methods of combating them, has Levy concerned. “It has us worried that if there is ever a major outbreak, we wouldn’t be able to respond,” Levy says, also citing the importance of responsibly using pesticide control. This is part of the reason that vector control specialists adopt an Integrated Post Management System that utilizes all safe and effective methods of combating mosquito populations without relying solely on pesticides. The methods of treatment, in addition to the surface oil treatment and pesticides, include the release of mosquito fish, a two-to-three-inch-long surface feeder that targets mosquitoes during the early stages of metamorphosis, and the administration of a bacteria that sterilizes male mosquitoes, preventing females from rearing viable offspring.

An outbreak an ecosystem as densely populated and strongly hydrated as the San Gabriel Valley could mean an epidemic, spreading not only Zika but also diseases like Yellow Fever, Malaria, Dengue Fever and a more obscure virus called Chikungunya, which causes the victim to experience severe joint pain and fever for up to a week. Left from this list is the West Nile virus, which is carried by the native Culex variety. In a sample size of 165 mosquitoes, vector control positively identified one infected West Nile Virus mosquito, which is carried during the month of July primarily by the Culex variety.

“We’ve got more new house development and things around. Each time you add another area where people are living, you have that much more potential for breeding mosquitoes,” Bob worries. “I am really concerned about this infestation; it has the potential to be really serious. We are really fortunate that we haven’t had any diseases.” The environments that we create for them—recyclables, plant saucers, vases of water, bird feeders, dog bowls, patio furniture, and the worst offender, swimming pools, are their preferred habitats. A non-functioning swimming pool left without mosquito pesticides or other treatments can produce a staggering 3 million mosquitoes a month. Unfortunately, even if every resident of the San Gabriel Valley were to make a concerted effort to prevent mosquito reproduction, eliminating them entirely is not a possibility. “We used to talk about elimination of a species of mosquito. First of all, its impractical, second of all, it’s impossible. Once they are there, and they become kind of naturalized, you’re going to have mosquitoes; you have to learn to live with them and to keep the numbers down,” Bob explains.

While Levy says that there have not been any reports of major disease incidents in the San Gabriel Valley yet, that does not mean that it will never happen. All it takes is one bite on one resident returning from a foreign country who was bitten by a disease-carrying Aedes to start an epidemic. “Mosquitoes are the carriers of diseases that kill more people in the world than any other thing. Humanity faces a real challenge when it comes to the diseases that they carry. It is the No. 1 killer,” Bob warns. ■