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Rainy Weather’s a Summer Treat for Mosquitoes

July 08, 2009 - BANGOR -- The record-breaking rainfall for June has turned Maine into a breeding ground for tiny creatures with a huge thirst for blood.

Get out your bug dope, entomologists say.

“I think we’re going to have a tremendous summer mosquito crop,” said Frank Drummond, professor of insect ecology and insect pest management at the University of Maine in Orono.

River beds, drainage ditches, swamps, marshes and streams are all breeding sites for biting bugs; the sustained high water levels in these areas give certain species of mosquitoes ample time to hatch and grow.

Kim Foss, a mosquito surveillance coordinator for Municipal Pest Management in Kittery, said mosquitoes such as the Aedes vexans — primarily floodwater mosquitoes — are found “pretty much everywhere in Maine,” and will hatch if water stays on the ground for seven to 14 days.

“Eggs are in the soil, so when you get re-flooding of those areas, those eggs hatch,” she said. “Some of them could develop in five to nine days because their metabolism speeds up,” she added.

Foss said there are between 45 and 48 different kinds of mosquitoes in Maine and New Hampshire.

“Different species come out at different times of the season. The snow melt mosquitoes — they’ve already emerged. For some species, the swamps are fuller. They could benefit from all this rain,” State Entomologist David Struble said.

According to the National Weather Service, June set a record of 8.12 inches of rain in Bangor while Acadia National Park recorded 10.64 inches. NWS hasn’t been measuring rainfall in Acadia long enough to know if that constitutes record-setting rainfall.

If this wet weather continues, we could be dealing with mosquitoes well into October, Drummond said.

Drummond also expects black fly, deer tick and horse fly populations to swell next year due to higher water levels in rivers that provide highly oxygenated water to the eggs. These insects hatch once a season for the most part, though there are certain species of black flies that hatch during summer and fall months.

“[For black flies] much of the population is one generation a year,” he said. “There are some species that keep coming out all season up on the Penobscot and Piscataquis [rivers]. They may benefit some from the high water.”

While many people may think that higher mosquito populations can increase the risk of contracting West Nile Virus, the opposite may be true.

“You may have a concentration of disease in a drought year,” said Foss. “If you have limited water supplies, you have birds and mosquitoes looking for that supply.” According to Dr. Dora Anne Mills, state epidemiologist and director of the Maine Center for Disease Control, Maine has never detected West Nile Virus in a human, but the virus has been found in mosquitoes in Maine and humans in New Hampshire, Massachusetts and Canada. “We had detected West Nile Virus in some mosquito pools and birds over the years. We’re no longer testing frequently because the funding dried up several years ago,” she said.

The CDC continues to test humans for West Nile virus. Mills said testing the state’s mosquito and bird populations is no longer necessary, because they already have been determined as the carriers of the virus in Maine.

One mosquito-borne virus that actually resulted in a fatality in Maine is eastern equine encephalitis, or Triple E. Last year, a York County resident died from the virus, which can be contracted by humans, horses and birds.

The Culex genus of mosquitoes, the primary disease carrier — or vector — of the West Nile Virus and Triple E, thrives in standing water. Several entomologists and the CDC recommend removing pools of standing water to prevent the Culex mosquito eggs from hatching.

“The best thing to do is to clean gutters, dump any standing water,” Foss said. Pet dishes, toys, tarps, buckets and old tires can all be breeding grounds for mosquitoes.

Mills recommends wearing appropriate clothing and using insect repellent to reduce the risk of contracting Triple E or West Nile viruses. These precautions also prevent tick bites, which are a larger problem in Maine, she said. Last year, there were approximately 900 cases of Lyme disease reported in the state.

By Dan MacLeod
Bangor Daily News Staff
July 2, 2009


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