MiddFoiling with pond Weevils

Author: Brett Cluff

When Professor of Biology Sallie Sheldon came to Vermont nearly 20 years ago, she faced a serious problem. Intent on studying relationships between fish and certain aquatic plants, she was frustrated to find that a single plant species had come to dominate many bodies of water here in our state. The culprit: Eurasian water milfoil.

Ever since its artificial migration from Europe more than 50 years ago - probably via water from a fish tank - Myriophyllum spicatum, as the plant is known, has wreaked havoc on ecosystems throughout much of the United States and Canada. The plant forms dense mats of leaves on the surface of bodies of water that can crowd out native aquatic flora and fauna. It can interfere with recreational activities such as swimming and boating, provide fertile breeding grounds for mosquitoes, and can even hamper municipal water systems by clogging intakes. In as little as two years, water milfoil can overrun a body of water.

In looking for a natural solution to the problems posed by such overgrowth, "I decided to find out what ate the milfoil," said Sheldon. After testing several types of beetles, she settled on North American milfoil weevils as the best weapon. Milfoil weevils combat the invasive plants in two main ways. Adults chew on the leaves near the surface of the water, but it is their offspring that do the most damage. When the weevil eggs hatch, the larvae burrow into the stem of the plant and eat their way downward, destroying the plant's ability to transport nutrients from its roots to the leaves. Pupae form lower in the stem and crawl back up to repeat the process, but by then the damage is done. The weevils - unlike the milfoil itself - are native to North America, which means that they are not affected by the plant's natural defenses. Compounds in Eurasian milfoil protect it from attacks by hungry Eurasian weevils, but their counterparts here in the northeast are not susceptible.

Middlebury College sophomore Julie Erickson was one of Sheldon's assistant researchers this summer. While many students spend their free time over summer break in wetsuits, Erickson wore hers to work. One of her main responsibilities was to collect adult milfoil weevils from area lakes for breeding back in the lab. Such a task was easier said than done - the weevils are about half the size of a grain of rice.

"Factors such as temperature, light, and concentration of dissolved oxygen affected how many weevils we could catch," said Erickson. But she also said that the team became quite good at spotting beetle-laden milfoil by the end of the summer. "By breaking off the tips of the plants that had the most insects, we could collect about 50 weevils an hour on a good day," she said.

Once gathered, the milfoil stems and weevils were then transported to the greenhouse adjacent to Middlebury College's Warner Hall and separated into tanks. Milfoil weevils are prodigious reproducers: the 60 or so specimens in each tank produced so many eggs that they were usually ready to be re-transplanted in three to five days. Sheldon described them as "egg-laying machines." With a hatch rate of nearly 90 percent, Sheldon's team was assured of producing a viable population of larvae when the egg-laden milfoil plants were returned to their lakes. To guarantee that no non-native species had a chance to disrupt the ecosystem, the plants were only reintroduced to the bodies of water from which they came.

Sheldon's work has been so convincing that it caught the attention of EnviroScience Incorporated, which describes itself as a provider of "non-traditional and creative solutions to environmental problems." "I am a scientist, not a farmer," said Sheldon. She and the College licensed the weevil breeding and distribution process to EnviroScience in 1997 under the moniker "MiddFoil," and the program has since been put into place in more than sixty lakes throughout the U.S. and Canada.

In Vermont, Sheldon has been working with three separate lake associations to protect their bodies of water. This summer's research was focused on Glenn Lake near Fair Haven, but the Vermont Agency of Natural Resources has granted permits for MiddFoiling at Fairfield Pond, Eligo Lake in Craftsbury, and Lake Morey in Fairlee. Sheldon expects to introduce eggs into all three this autumn.

Ironically, past efforts to combat Eurasian milfoil are largely to blame for the species' successful expansion. Herbicides have been a major weapon for those trying to control its spread, but such chemicals kill many weevils along with the targeted plants. Sheldon and Erickson both stressed that cutting back on herbicide use could be the most effective approach in the long run. While it might result in a few years of especially heavy blooms, "the weevil populations would quickly rebound to the point where they could limit milfoil growth," predicted Erickson.

Although it is still too early to tell how successful the program will be for the three lakes in Vermont, Sheldon expects to see results next spring. She will be ready to transplant more weevils to the affected lakes if necessary. Thanks to the ingenuity of Sheldon's students, she is confident that progress will be made against the spread of Eurasian water milfoil. "Every student had their eyes and ears open constantly," she said. "Because Middlebury students are so creative in their approaches to these problems, it was astonishing how fast we were able to get things done."