State untroubled by national bug report Officials say few mosquitoes breed in stormwater ditches

Maine officials this week downplayed national reports about the danger of man-made stormwater ditches and ponds as mosquito breeding grounds during this summer of West Nile virus worry.

From tiny woodland puddles in skidder tracks to hundreds of lakes, the state has such an abundance of natural mosquito breeding areas that the artificial pools, built to catch runoff around large developments, don’t have much of an impact, said Dave Struble, of the Department of Conservation.

“We have no lack of spots where mosquitoes breed,” the entomologist said Tuesday.

Mosquitoes are of particular concern this summer because several species of the winged pests carry the West Nile virus, which can trigger illness and even death in people with weak immune systems. No one in Maine has contracted the disease, although the virus has been found in wildlife.

In urban areas, where much of the landscape is paved, stormwater holding areas are among the major mosquito breeding areas.

The ditches and ponds are built adjacent to large parking areas to control the water, often contaminated with small amounts of oil or gasoline. Water is diverted into the retention pond, where it can evaporate and return to the environment without contaminating nearby surface water.

The strategy has been used for many years and greatly reduces the environmental impact of “big-box” developments with large parking lots. Maine does not track exactly how many stormwater drainage ponds have been built, but the number is significant, said Lisa-Kaye Keen, an environmental specialist with the Maine Department of Environmental protection.

A federal report published this spring in Stormwater magazine found that 86 percent of stormwater basins sampled in 28 states harbored breeding mosquitoes. In the suburbs surrounding Washington, D.C., the issue has become controversial with public heath officials facing off against landscape planners over whether the basins cause more benefit than harm.

The species of mosquitoes known to carry West Nile prefers to breed in pools of stagnant water. In cities, drainage ponds are one of the few habitats available.

“It drives us crazy,” said Cyrus Lesser, chief of the mosquito control section of the Maryland Department of Agriculture. The ponds “are everywhere, and they give us fits. The worst part is that they are being installed adjacent to business and residential areas, right next to where people live.”

But little of Maine resembles urban Maryland and Virginia. Here, Department of Environmental Protection studies indicate that few mosquitoes breed in the stormwater, preferring natural habitats with more vegetation.

“We’ve actually gone out and sampled, and never found any larvae,” Keen said.

As a result, state officials have not concentrated on stormwater pools in their mosquito control efforts. Instead, educational materials have targeted homeowners, who are encouraged to empty birdbaths, wading pools and other pools of standing water in residential areas.

The Associated Press contributed to this story.