Hitting Mosquitoes Where It Hurts

Early in the morning of June 4, two twin-engine Beechcrafts lifted into the air on the Eastern Shore of Maryland.

Their goal: to head off swarms of Eastern Salt Marsh mosquitoes before they hatch. Their target: 200 acres of wetlands and salt marshes flooded by high tide and heavy rains. Their plan: to spray the area with a new larvicide, a pesticide targeted at the larval stage of insects, in hopes of reducing the potential population of adults, which bite fiercely and can carry diseasesincluding West Nile virusup to 20 miles away.

"These marshes in the Fishing Bay area are very productive," said Michael Cantwell, chief of mosquito control for Maryland's Department of Agriculture.

Fishing Bay is a small bay to the south and east of the Chesapeake. This year it produced what the department's chief entomologist was calling "a monster brood," with as many as a hundred larvae in a pint of water.

Once the floodwater recedes, larvae are left in isolated depressions that retain enough water to allow them to transform into adult mosquitoes over 7 to 14 daysdepending on the temperatureand swarm out of the marshes looking for a blood meal. That's the cycle Maryland mosquito control hoped to interrupt by using a very specific natural larvicide that has virtually no impact on other species.

Perennial Pests

Yes, it's that time of year again when whining mosquitoes zigzag and follow your breath until an annoying ritual takes place: They land, you swat, they die or fly away to lay eggs, you swell and itch.

Mosquito-control officials and other experts say it's almost impossible to forecast how good or bad a year will be in terms of mosquitoes. Too much depends on weather and timing.

While Maryland was targeting its monster brood, for instance, Texas mosquitoes have been mostly no-shows. Both are coastal states, which provide rich mosquito habitatTexas has the most varieties of any statethough the worst infested areas in the United States are the Florida Everglades and the Arctic National Wildlife Refuge in Alaska.

"We really haven't found very much this season," said Richard Duhrkopf, a biologist and mosquito researcher at Baylor University in Waco. "We had a very cold and very, very dry winter, so there were fewer adults around to get the population up and running. In Texas we're about a month behind."

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Hitting Mosquitoes Where It Hurts