SciTech

America’s most dangerous mosquitoes

Aedes aegypti: The yellow fever mosquito.
Aedes aegypti: The yellow fever mosquito. Department of Entomology/Smithsonian Institution via The New York Times

With the spread of the Zika virus, the threat posed by the tiny mosquito has been magnified into shark-sized proportions.

But among the more than 3,000 species of the insect worldwide, only two in the Americas are actually known carriers of the virus: the yellow fever mosquito (Aedes aegypti) and the Asian tiger mosquito (Aedes albopictus).

Maps showing where the species might survive, notably, exempt the Northwest, the Mountain West and northern parts of the Midwest.

But Zika is not the only disease that mosquitoes can carry. Other threats include West Nile virus, dengue fever and various types of encephalitis.

In all, there are about 174 species of mosquitoes in the United States, said Joseph M. Conlon, a retired Navy entomologist who is a technical adviser to the nonprofit American Mosquito Control Association. Texas has the most species with about 85, and West Virginia has the least, with roughly 24.

A vast majority of these species in the United States, Conlon said, do not transmit any disease. And only female mosquitoes bite.

Here are six of the most common disease-spreading offenders endemic to the United States.

Aedes aegypti: Yellow Fever Mosquito: An intensely black mosquito, distinguishable by its pointed abdomen and two white stripes in the shape of a lyre on its back (the dorsal thorax), and white bands on its legs.

They primarily bite humans, rather than other animals, and they like to feed indoors. The combination makes them particularly dangerous when it comes to spreading disease.

Most cases of Zika, which can cause debilitating birth defects including microcephaly, have been transmitted through this aggressive insect. It can also carry the viruses that cause dengue fever, chikungunya and yellow fever.

The species rarely flies more than a block in its lifetime. It is mostly found in the South and the Southwest.

Aedes albopictus: Asian Tiger Mosquito: The insect is usually larger and more intensely black than A. aegypti, but with the same pointed abdomen. It has striking white stripes, including one white stripe down the middle of its back.

They have a nasty habit of feeding on the lower extremities, so they can be difficult to spot. And their bites are barely perceptible.

They are most likely to come out during the day. And they feed on pets and wild animals as well as humans.

They lay eggs in potted plants, buckets, tires, tin cans or wherever there’s a small pool of standing water.

The Asian tiger mosquito is known for spreading dengue and chikungunya viruses. It has also tested positive for Zika, West Nile, Eastern equine encephalitis and Japanese encephalitis. But it is not clear how efficiently it transmits the Zika virus.

It has been sighted in about 30 states, including Hawaii.

Culex pipiens: Northern House Mosquito: A nondescript brownish insect, with a rounded abdomen.

This is usually the one you’ll hear buzzing in your ear at night. It will overwinter in your attic if it can. It feeds on humans, other mammals and many types of birds, which are the main carriers of West Nile virus. The mosquitoes typically lay their eggs in dirty water, in ditches and shallow ruts.

Dozens of species have been known to carry West Nile, but the Culex pipiens is the primary culprit.

Most healthy people don’t even know they have been infected. But West Nile can cause flulike symptoms and, in rare cases, permanent neurological damage or death.

The species is found in urban areas across the country.

Culex tarsalis: Distinguishable by its rounded abdomen and light-colored band around its proboscis.

In Western states, this species is the primary carrier in rural areas for West Nile virus. They have also been associated with Western equine encephalitis, St. Louis encephalitis and California encephalitis.

The species is abundant in California, Utah and the western half of North America.

Anopheles quadrimaculatus: Common Malaria Mosquito: The dark brown insects feed on humans and other mammals, usually in the evening. They prefer to lay eggs in freshwater ponds, streams and lakes.

Only the Anopheles genus carries malaria.

The common malaria mosquito is found in large numbers in the Southeastern states, but it inhabits a wide swath of the East, from Mexico to southern Canada.

Anopheles freeborni: These straw-color insects are noted for the way their abdomens lift into the air when they sit. Their wings are dotted with dark spots. The female’s clear belly will turn red and swell when full of blood.

Females usually come out at dusk and fly farther than other species. They’ll travel from rural areas into homes or barnyards to feed. They prefer to lay eggs in leafy, sunlit pools and drains, rice fields and ponds.

They were once the primary carriers of malaria in agricultural areas on the West Coast, especially California. While malaria is gone, health officials worry that local mosquitoes could pick it up again from an infected human and trigger an outbreak.

What can be done about prevention?

Conlon recommends using repellents registered with the Environmental Protection Agency, ones that contain DEET, picaridin, IR3535, and oil of lemon eucalyptus and para-menthane-diol.

“Don’t listen to your Aunt Ethel who puts toad pee on her arm,” he said.

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