Most Wanted: Aedes aegypti

Although it infests only a portion of the United States, the Aedes aegypti mosquito poses a significant threat to the health and well-being of millions of Americans who may come in contact with this global pest control scourge.

It is most recognized currently for its transmission of the Zika virus, however it also can carry and transmit chikungunya, dengue and yellow fever. (In fact, it is often called the yellow fever mosquito.) 

Why does the Aedes aegypti pose so many problems around the globe, and how can PMPs properly identify and best address this menacing mosquito?

Identifying the Aedes aegypti Mosquito. Like other mosquitoes, the Aedes aegypti is active just before sunset; unlike most others, it also is active and bites during daylight hours.
• Adults. At about 4-7 mm in length, the adult Aedes aegypti is dark brown to black with white scales on the top of its thorax similar to the shape of a violin. The hind-leg tarsal segments appear striped with white bands; the abdomen may be solid in color or have white scales, and the tip is pointed. The adult female is larger than the male and has mouthparts adapted for blood feeding.
• Larvae. Because these larvae breathe oxygen through a siphon in their posterior, they will hang vertically in the water with the siphon held above it. The siphon of these larvae is also shorter than that of other mosquitoes. The larvae often are found around homes, usually in artificial containers that hold water, such as bird baths, tires, tree holes, tin cans, water-holding storage drums, etc.
• Eggs. The Aedes' black, oval eggs are laid singly on moist soil or debris just above the water level of their breeding areas. They hatch when the temperature is warm and the eggs get wet – from rain, rising water, etc.

The Proliferation of Aedes aegypti. The primary reason that the Aedes aegypti mosquito is such a problem is because it is so highly adapted to living with humans, according to Stan Cope, president of the American Mosquito Control Association and director of entomology and regulatory services for Terminix. “It feeds almost exclusively on humans,” he said. This is a problem because the diseases it spreads, such as Zika, are human-only viruses as well. So, if this were a mosquito that did some of its feeding on other animals that could not be infected with the virus – i.e., “dead-end hosts” – the virus would be more likely to burn out. But because it feeds only on humans, there is the potential of transmission every time it feeds. 

Other reasons for the success of this insect are:
• It breeds in standing water, which people in underdeveloped areas are likely to drink or use for other necessities such as washing. After 24 years as an entomologist in the Navy, Cope said he learned, “You can't just tell people, who don’t understand, that you will put something in their drinking water to kill the mosquito larvae.”
• The Aedes aegypti mosquito is a “very secretive biter,” Cope added. It tends to bite from the knees down, particularly favoring smelly feet that put off a lot of CO₂. So most people don't feel the bite, and one mosquito can theoretically continue to fly around and bite everyone in the group – infecting all if it is infected.
• Once the female has a blood meal, she can lay about 250 eggs. Unlike the Culex which “puts all her eggs in one basket" on the water to hatch in a couple days, the Aedes female lays her eggs in small groups – flying around an area putting a few eggs in various moist spots, increasing their chances of survival. Once moistened, the eggs can dry out and survive for a year, then hatch once wet again. 
• Although there is not a lot known about this mosquito’s resistance to insecticides, Cope said, mosquitoes have a generational turnover every few weeks, making them prime candidates for resistance issues.
• The Aedes mosquito tends to harbor very close to and inside homes (e.g., in closets, under beds, etc.) during the times that other mosquitoes are flying (sunset to dawn) – that is, the time that the mosquito trucks are spraying. This means sometimes state or local control efforts often have little effect on this mosquito as the fog doesn’t penetrate the areas in which they harbor. 

Mosquito Control. Because of this, “the primary things we preach are source reduction and personal protection,” Cope said. This means not only repellents and loose, long-sleeved clothing when possible, but ensuring screens and doors are tight fitting to keep mosquitoes out of the home, eliminating conducive conditions, and educating customers.

The CDC also recommends that source reduction and larvicide treatments be begun prior to mosquito season. Then, particularly if any imported or locally acquired Zika cases occur, any standing water that cannot be eliminated should be treated with long-lasting larvicide and larval habitats eliminated within 200 yards of the home. 

For adult mosquitoes, an outdoor adulticide treatment should be made up to 200 yards from the home and outdoor residual and spatial insecticide treatments applied, repeating as needed to reduce mosquito presence.