After the virus itself, the main villain of the Zika outbreak has been the Aedes aegypti mosquito, its primary vector. These mosquitoes are sneaky, and resilient, as my colleague Adrienne LaFrance recently reported—able to breed in the smallest amounts of standing water, predisposed to bite people from behind when they’re not looking. You can imagine them swarming through packed cities, nipping people behind the knees, twirling their tiny mosquito-sized mustaches, and cackling as they fly away.
But another mosquito that’s been keeping its head down, lurking in Aedes aegypti’s shadow, not getting much attention, mentioned usually as an afterthought, can also carry the Zika virus. Its name is Aedes albopictus, and the Pan-American Health Organization recently reported that tests of the mosquito done in Mexico came back positive for Zika.
This is notable, but not necessarily surprising. It’s been suspected for a while that this mosquito could spread Zika, since it also spreads dengue, chikungunya, and yellow fever. In a 2013 study, Aedes albopictus, also known as the Asian tiger mosquito, was successfully infected with Zika virus in a lab in Singapore. Researchers also found Zika in Aedes albopictus collected in the wild in Gabon from 2007-2010.
But according to the PAHO report, “This is the first evidence of the presence of Zika virus in Aedes albopictus captured in the environment in Mexico and in the Americas.”
In terms of its potential impact on the current Zika outbreak, Aedes albopictus is better than Aedes aegypti in some ways and worse in others. On the one hand, Aedes aegypti’s favorite blood is people blood, while Aedes albopictus is less picky and will also nibble on animals. The one that bites only people is, logically, more likely to spread the virus. But on the other hand, Aedes albopictus has been called “the most invasive mosquito in the world” and has “relatively cold-hardy and long-lived eggs,” allowing it to survive in cooler temperatures than Aedes aegypti. In the United States, the Asian tiger mosquito has a wider potential range, which extends up deep into the Midwest and over much of the East Coast.
Estimated Range of Aedes aegypti and Aedes albopictus for 2016
Still, because of its feeding and breeding habits, the Asian tiger is expected to stay only a secondary vector for Zika. Aedes aegypti lives and breeds closer to humans than Aedes albopictus, which is “a little more rural,” says Stan Cope, the president of the American Mosquito Control Association and the director of entomology and regulatory services at Terminix. Plus, “If [an Aedes albopictus mosquito] happens to pick up Zika from a human, that mosquito is much more likely to then bite something other than a human and the virus will not survive in those other animals,” he says.
But these two Aedes species have an important similarity—they pose a serious difficulty for mosquito control. For one, they bite in the daytime, which, Cope says, makes them different from many other mosquito species in the United States. So fogging in the early evening, which is the typical time according to the Pesticide Research Institute, is not ideal for taking down Aedes mosquitoes.
They lay eggs right on the edge of the water, rather than directly on it, and the eggs are super resilient; they can survive a long time. “When we raise these in the lab, we would have them just lay their eggs on damp filter paper in a little glass dish,” Cope says. “And all you had to do was dry those pieces of paper, and you could put them in a Ziploc bag, and six months later you could drop them in water and within about a minute they hatch.”
So both Aedes aegypti, Zika’s Most Wanted, and Aedes albopictus, the sidekick, are seriously hard to fight. And Congress hasn’t funded that fight, which puts the U.S. at a disadvantage.
“Not only are they disease vectors but they’re horrible nuisances,” Cope adds. “I used to sit in my backyard in Maryland, and I’d get 100 bites in 10 minutes from these things. The Asian tiger mosquito is just a very, very aggressive feeder.” And in this Zika summer, when the appearance of a mosquito bite may cause worry as well as itchiness, that is a threat to people’s health and peace of mind.