Attack of the weevils: tiny insects safely control the pesky aquatic weed milfoil

MIDDLEBURY, Vt. - On Saturday, Aug. 27, Middlebury College Professor of Biology Sallie Sheldon pulled on her wetsuit and dove into the waters of Fairfield Pond in Fairfield as part of an effort to control the pond’s infestation of Eurasian watermilfoil. Her weapons: aquatic weevils, tiny beetles that feast on the invasive plant.

Sheldon and two student researchers, Middlebury College sophomore Julie Erickson and Lincoln resident Jess Lueders-Dumont, who will attend Colby College this fall, spent part of their summer growing the bugs-a milfoil weevil, Euhrychiopsis leconteia, native to North American waters-in tanks in the greenhouse attached to Middlebury’s Warner Hall. To introduce the bugs to Fairfield Pond, Sheldon collected milfoil plants from the pond and brought them to Middlebury, where they were placed in the tanks, and weevils were given the chance to deposit their eggs. “Our weevils are egg-laying machines,” says Sheldon.

Now covered with weevil eggs, the plants were placed back in the bed of milfoil in Fairfield Pond from whence they came. This technique-harvesting the plants from a specific lake or pond and then putting them back into the same pond-helps insure that no non-native species will make their way into the water. The expectation is that the eggs will soon hatch into weevils-Sheldon says the eggs have a remarkable hatch rate of nearly 90 percent-and that this will begin a cycle that will create enough weevils in the pond to begin controlling the Eurasian watermilfoil invasion.

Professor of Biology Sallie Sheldon places weevils on milfoil in Fairfield Pond. (Sally Ann Collopy)

Sheldon’s work in Fairfield has been strongly encouraged by the members of the Fairfield Pond Recreation Association, in particular the husband and wife team of Bruce and Sally Ann Collopy.  The Collopys have been at the forefront of the association’s long battle with Eurasian watermilfoil, which in the past has involved everything from hand-to-hand combat-divers manually pulling the weeds out of the bottom-to the construction of bottom barriers to prevent weed growth.

Sheldon expects that she will need to apply more eggs to Fairfield Pond in the spring, but that once established, the weevils will be able to make a serious dent in the weed beds that have bedeviled the users of Fairfield Pond and many other lakes since Eurasian watermilfoil arrived, uninvited, possibly via water from a fish tank, many years ago.