They travel far for blood

RODERWOLDE, Netherlands - How far does a mosquito fly? Harry Boerema wants to know.

Boerema lives near a drainage project, where Dutch authorities are dredging a huge 3-foot basin in the northern rural landscape to head off flood waters and protect towns and villages from disaster.

The project threatens to inflict hordes of mosquitoes on people living around the water retention area, so scientists set out to calculate how to keep the boundaries of the ditch far enough from human habitation to protect residents from pest infestation.

The question they needed to find out: How far does a common European human-biting mosquito fly?

What they found surprised them: A hungry female looking for a "host" will fly at least 150 yards, three times farther than previously thought, said Piet Verdonschot, who conducted the research.

The 4,200-acre basin, begun in 2003, is designed to collect heavy rainwater that will slowly be channeled to the North Sea. But frequent wet-dry cycles will be perfect breeding grounds for mosquitoes.

Buzzing pests are nothing new for Boerema, a retired professor of architectural history who has lived for 36 years in his quiet cottage set amid dairy farms.

"I don't mind them to a certain extent. But not in surplus," he says. "I'm a nature lover, and mosquitoes are part of nature - although not the most likable ones."

Not everyone took the prospect of living on water's edge with such equanimity, and local complaints led authorities to commission the mosquito research, said project manager John Tukker.

At the outset, Verdonschot believed mosquitoes stay within about 50 yards of their breeding ground. The biggest nuisance for humans often originates in flower pots, buckets of collected rainwater or any kind of water left stagnant in the back garden or barnyard.

"The assumption in the literature is that people who suffer bites have bred their own specimens in their own gardens," he said.

Hundreds of mosquito species exist around the world - 36 in the Netherlands alone - but Verdonschot concentrated on the two species most common in the Dutch climate: the culex pipiens, which prefers birds to people but will still keep you awake at night during the summer, and the Culiseta annulata, larger, more aggressive insects active year-round. Neither normally carries dangerous diseases.

Verdonschot, an aquatic ecologist working for the private environmental research institute Alterra, hatched 40,000 mosquitoes in large tents in a grassy field.

The tents were surrounded by concentric circles of traps set at 50 yards, 100 yards and 150 yards. Around the edges of the field were ditches with tall reeds and wild grasses on the banks.

The traps drew mosquitoes into smoke from dry ice then instantly froze them. At the end of each day researchers collected the corpses and counted them one-by-one, using tweezers under a microscope.

Verdonschot expected most mosquitoes to be caught in the closest traps. Instead, about 80 percent were found in the farthest, meaning most flew at least 150 yards from the tent where they were hatched.