Researchers Hope Weevils Can Stop Spread Of Aquatic Plant

Wisconsin researchers are hoping that a weevil can help control the spread of Eurasian watermilfiol, an aquatic plant that has become a problem on many Wisconsin lakes.

Many lakes are clogged with the watermilfoil, which can reach more than ten feet in length and can cover the surface with a thick mat of vegetation. University of Wisconsin research scientist Susan Knight said it is particularly a problem in southern Wisconsin.

“Instead of being clear water – to swim over, or to fish or to boat over – you’re going through weeds that are right up there at the surface,” said Knight. “It’s a real problem. It really interferes with recreation especially.”

Knight is in the third year of an experiment involving a tiny native insect, the watermilfoil weevil.

“A weevil is about an eighth of an inch,” said Knight. “The eggs are very tiny. You need strong glasses on, or good young eyes.”

The weevil larvae feast on milfoil. Knight said it could be an alternative to the commonly used herbicide 24D, which has been approved by the U.S. Environmental Protection Agency, but which can also kill other plants in a lake’s ecosystem.

“There are so many unknowns with a chemical,” she said. “We don’t know if there are some organisms that are being affected that aren’t actually being tested for. And we don’t know what the long term effects are, and some of these lakes are being treated year after year after year.”

She added: “The biological control, especially this one, is native, so it’s hard to imagine anything actually going wrong.“

Some lakefront homeowners have started to raise their own weevils in the hope that they can help control the milfoil. Tests so far are inconclusive.