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The rain is gone; now brace for the bite


First, it was the rain that wouldn't stop. Soon it will be the mosquitoes.

Last week's downpours and overflowing streams filled roadside ditches, woodland pools, dips in soybean fields and every bucket and discarded tire in the region.

And that has created vast new breeding opportunities for the annoying and potentially dangerous insects.

"I think we're going to have a pretty spectacular season," said Mike Raupp, an entomologist at the University of Maryland, College Park.

More mosquitoes won't just mean more bothersome bites, but also more potential cases of West Nile virus and encephalitis in people and horses, along with heartworm in dogs.

"With the deluge, there will be an awful lot of [breeding] habitat. And if the trend of thundershowers continues, and maintains these habitats, we'll see a bumper crop by the second or third week of July," Raupp said.

Cy Lesser, the chief of the Mosquito Control Section of the state Department of Agriculture, agrees. His crews are already treating all the breeding pools they can reach before the larvae mature and fly off in search of blood.

"We've been larviciding all week," he said. "Unfortunately, the scope of the area that's flooded is well beyond our means ... so we're doing the areas we think are closest to the [human] population."

Homeowners are already calling for help. But "the bulk of our complaint calls certainly are going to begin [this] week when the adult mosquitoes are on the wing and biting," Lesser said.

That's when spraying for the adults will ramp up, too - but only in communities that already participate in the state's control program. Lesser's $3 million budget has been flat for years, he said, with no money to expand.

"It's one of those years that could potentially be a budget-buster just this summer, not even worrying about next spring," he said. The state's fiscal year runs from July through June.

Mosquitoes begin their lives when a female lays tens or hundreds of eggs in stagnant water or damp soil. If it's dry, many mosquito species' eggs can remain dormant for years until the rains resume.

The eggs hatch into wriggling larvae that stay in the water but breathe through tiny snorkels that break the surface. They grow into pupae that later transform into adults.

After mating, the males buzz off harmlessly to feed on nectar and die. The females - the only ones that bite - fly in search of blood, which provides the proteins they need to produce eggs. They might lay two or more batches of eggs in their five-week lifetimes.

Some species fly less than a kilometer in search of blood, but salt marsh mosquitoes will fly up to 30 miles.

The recent rain and flooding have made breeding possible nearly anywhere. Worried callers are telling mosquito control officials that their yards - where normally a few low spots fill up after a thunderstorm - are "almost completely flooded now, and they have been since last Saturday," Lesser said.

They have good reason to worry. "It's gonna be pretty itchy around here," Raupp said.

The mosquito expert maintains a variety of containers around his home as "mosquito meters." They include old Frisbees, 5-gallon pails and wheelbarrows that allow him to monitor breeding trends.

"It was going to be a pretty dull mosquito year here about a month ago, around Memorial Day," Raupp said. At that point, weather conditions were "droughty," and his containers were dry. May had brought just 1.6 inches of rain to Baltimore, and rainfall for the year was running 5 to 7 inches below normal.

Then the rain returned, and thundershowers filled his containers. They were quickly infested with larvae as the neighborhood's adult mosquitoes leaped at the summer's first good breeding opportunity.

Their young wrigglers are now grown, and after six days of heavy rain across most of Maryland, the new generation is busy generating another, much bigger brood.

The bugs "have just been waiting for this event to happen," he said. "They'll be feeding and dumping their eggs into what is a spectacular habitat for the larvae."

Hot weather now will keep the adult females active, mating, seeking blood meals and laying their eggs. More summer thunderstorms, if they occur, will keep the breeding pools viable.

"This is exactly what these guys need to really ramp it up," Raupp said. "It ought to be spectacular."

That's what his skeeter meter says, anyway.

"My wheelbarrow was teeming with mosquito larvae, as were my Frisbees," he said. A swale in his front yard, which is dry four years out of five, now holds 5 inches of water, and "there are literally tens of thousands of larvae in that thing."

"We are rockin'," he said, enthusiastic as only an entomologist could be about it.

New England has already seen the same response to heavy rains that fell there in mid-May. Raupp visited and got a preview. "I went into the woods, and I was eaten alive," he said.

Lesser said the adult mosquitoes that emerge from the breeding pools in coming weeks will include members of types such as Aedes and Psorophora, which develop in flooded ditches, woodland pools and flooded fields.

"We're finding them in large numbers," Lesser said.

Among their number are Aedes vexans, which he said had been "almost nonexistent" this year because of the drought. Not anymore. Also, "the Aedes atlanticus, a woodland pool mosquito ... will be quite numerous [this] week."

Aedes albopictus, the imported Asian tiger mosquito that has become an urban pest in Maryland in recent years, might actually have been flooded out of its favorite flower pots and clogged gutters, Lesser said. But it's likely to bounce back in the water that remains, emerging as a big problem in two more weeks.

Culex species - the primary vectors for West Nile virus - are breeding now in stagnant waters and will become a bigger problem when the adults emerge in large numbers in about two weeks.

Most people infected by the West Nile virus have few symptoms or none at all. But those with immune systems weakened by age or illness can become seriously ill. The virus has been blamed for 758 deaths in the United States since it first appeared in 1999. More than 19,000 people have become seriously ill.

The number of Marylanders infected by the West Nile virus has been dropping in recent years after peaking in 2003 with 73 illnesses and eight deaths. Last year, the virus made just five people sick, and none died.

"We don't know if there will be an increase in West Nile activity, but certainly the ecological factors for it are going to be present," Lesser said.

Culex salinarius mosquitoes seek blood meals from birds and people, potentially carrying the virus between them. Culex restuans chiefly feeds on birds, helping to spread and maintain the reservoir of the virus in the bird population.

Culex pipiens feeds mostly on birds but will bite people later in the summer, spreading the virus to humans.

Scientists aren't sure why West Nile case counts rise and fall the way they do. But they say precautions that people now take might help explain the recent declines.

Experts are urging Marylanders to reduce the bugs' breeding territory by dumping all the water-filled containers they can find in their yards and neighborhoods. Mosquitoes can breed in items as small as bottle caps.

They also urge avoiding exposure to bites by staying indoors when mosquitos are biting. If outside, wear light-colored clothing, long pants and long sleeves.

Adults can use mosquito repellants containing DEET on their exposed skin, but it's not recommended for children. A new alternative repellant, Raupp said, is called Picaridin, which is advertised as being formulated for the whole family.

There are also new lines of clothing called BUZZ OFF, using material impregnated with a repellant called permethrin - a man-made version of a substance derived from chrysanthemums.

And don't forget the animals. Unvaccinated horses are vulnerable to the West Nile virus and to the lethal mosquito-borne eastern equine encephalitis virus. Dogs can contract heartworm from mosquito bites.

"We are urging everybody ... to make sure their dog's up-to-date on their heartworm medication," Lesser said. Horse owners, too, should consult with their veterinarians.


Tips on preventing breeding sites

Clean out rain gutters.

Get rid of old tires and drill drainage holes in those used for swings.

Turn wading pools upside down or move them inside.

Dump the water at the bottom of plant holders twice a week; store empty clay and plastic pots upside down.

Throw away trash that can collect water, such as empty cans.

Check canvas and plastic tarps for trapped water.

Pump out bilges in boats; store canoes, kayaks and small boats upside down.

Empty and refill bird baths at least twice a week.

Take pets' food dishes indoors after feeding, and clean and flush water dishes regularly.

Keep garbage cans dry and don't leave lids upside down.

Repair leaking outdoor faucets.

Check the sites of home improvement projects for proper drainage, and be sure equipment such as wheelbarrows is not collecting water.

Inspect ornamental ponds, tree holes and other low, marshy areas for mosquito larvae. If larvae seem to be present, call the nearest Mosquito Control Office: Eastern Maryland: 410-543-6626; Southern Maryland: 301-373-4263; Central and Western Maryland: 301-927-8357; Annapolis Headquarters: 410-841-5870

Report ditches that have been full of stagnant water for a week or more to a Mosquito Control Office. Do not attempt to clear the ditches; they might be protected by wetlands regulations.

[Maryland Department of Agriculture's Mosquito Control Section]

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