Drought drives mosquito numbers high

By Sharon Omahen
University of Georgia

Georgia's rainfall deficit has caused a mosquito population explosion that has led to a rise in the number of West Nile virus cases reported in the state.

The virus is carried by the southern house mosquito, which breeds in storm drains and thrives in polluted water, said Elmer Gray, an entomologist with the University of Georgia College of Agricultural and Environmental Sciences.

Mosquitoes are vectors of WNV, but birds are carriers. The mosquitoes become infected when they feed on infected birds. Infected mosquitoes then transmit the virus to humans through their bites.

WNV cases up in Georgia

Last year, nine cases of West Nile virus were reported in Georgia, he said. So far, 24 cases have been confirmed this year. And Gray is confident this number will keep rising.

"We haven't had much heavy rain this summer to flush out the storm drains (and wash away the mosquito larvae)," Gray said. "If we'd been hit by hurricanes and heavy rains, the storm drains would be flushed out, but buckets and tires would be full for the Asian tiger mosquitoes to breed in."

Only biters

Asian tiger mosquitoes are what Gray refers to as "nuisance" mosquitoes, but they are not vectors of WNV. They show up at backyard picnics and other social gatherings. This mosquito breeds in standing water found in old tires, buckets or anything that will hold rainwater.

"These mosquitoes are found in urban areas such as Atlanta and Athens," he said. "If you live on the coast or your property backs up to a swamp, you could have one of several species."

Man-made habitats

Gray's colleague Nancy Hinkle, also a UGA entomologist, says homeowners have actually helped Asian tiger mosquitoes overcome the lack of rainfall.

"Because people have irrigated their lawns more, water-holding vessels such as flowerpots, buckets and cans around homes have been regularly collecting water," Hinkle said. "People recognize the value of every drop of rain, and more and more people have fashioned rain-collection devices."

Storing rainwater to use to irrigate outdoor plants is wise. But it creates perfect backyard mosquito habitats, she said.

"Unfortunately, rain-collecting containers tend to support large populations of some of our most pestiferous mosquito species," Hinkle said. "In fact, the southern house mosquito is also known as the rain-barrel mosquito."

If he had a choice, Gray would choose to see heavy rainfall and high populations of Asian tiger mosquitoes.

"I'll take a few bites over an illness any day," he said. "Mosquito-vectored diseases can be a really serious health problem for you and your family."

Ticks and fleas constant

Ticks and fleas don't seem to mind droughts.

"Ticks are hardy, and their leathery skin and water-conserving behaviors protect them from the ill effects of drought," Hinkle said. "And because fleas are so well-adapted and so dependent on their host, they aren't usually affected, either."

Sharon Omahen is a news editor with the University of Georgia College of Agricultural and Environmental Sciences.