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Winter 2013

Urban Jungle

The changing natural world at our doorsteps | Illustration and text by Patterson Clark      

February 5, 2013

Mosquitoes: Winter slumber of the micro-vampires


When temperatures slip below freezing and the ground heaves with frost, some of us dream of a black fate for any lingering mosquitoes poised for the gush of spring.

But only harsh cold for sustained periods will knock back the invasive advance of the Asian tiger mosquito, Aedes albopictus — and the Washington area is too far south for that. The geographical limit for the insect appears to be about 200 miles to the north, where average winter temperatures are a few degrees below freezing.

New England and Upstate New York may suffer occasional summer outbreaks of the mosquito, which sometimes arrives at recycling plants in old tires sent from New York City and New Jersey, but the frigid winter climate there is too much for the tiger.

In D.C., the aggressive black-and-white bloodsucker keeps itself in play for next season by depositing drought-resistant, cold-hardy eggs that lie in wait for extended daylight, warmer temperatures and standing water.

If the micro-habitat is right, adults can survive the winter, too.

The northern house mosquito, Culex pipiens, uses a hibernation strategy known as diapause. After mating in autumn, females sip nectar (instead of blood) to build up fat reserves that will sustain them through the cold months. They seek out basements, storm sewers, stables, hollow logs or animal burrows in which to hide from the freeze.

Another Washington biter, the common malaria mosquito, Anopheles quadrimaculatus, can do that, too, but it is most effective at surviving the winter as submerged larvae, which practice their own form of diapause.

All three species can carry diseases:

Mosquito-borne diseases of the Mid-Atlantic

People can use winter to deliver a blow to summer's mosquitoes:

♦ Empty standing water collecting in tarps, pots, machinery, toys, tires, bird baths and gutters.

♦ As weather warms, add mosquito dunks to ponds. These round cakes of bacteria dissolve and kill mosquito larvae.

♦ Flush out ponds and drainage pipes. Make sure that streams are flowing freely.

♦ Getting rid of adults in diapause is trickier. Even natural pesticides, such as pyrethrum, can be toxic or deadly to the amphibians, fish, mammals and beneficial spiders and insects sharing the space.

Sources: Maryland Department of Agriculture, Centers for Disease Control and Prevention, University of Florida, Rutgers University, Journal of Medical Entomology, Central Massachusetts Mosquito Control Project, National Pesticide Information Center, Proceedings of the Royal Society B: Biological Sciences, Vector Borne Zoonotic Diseases, Journal of the American Mosquito Control Association

Asian tiger mosquito, Aedes albopictus

Aedes albopictus

Aedes Culex Anopheles

Encephalitis
Eastern equine
St. Louis
LaCrosse
West Nile virus
Dengue fever
Malaria
Dog heartworm