Can a Beetle Stamp Out Lake Minnetonka's Milfoil?

Lake Minnetonka is about to enter uncharted territory.

In an effort to curb the spread of invasive milfoil, dense populations of  weevils—a type of beetle that grows to about the size of a grain of rice—will be introduced into a pair of isolated areas of Lake Minnetonka this season.

Steve McComas, known as the “lake detective” and owner of St. Paul-based Blue Water Science, is consulting on the project and says this is the first time in state history that a biological attack will be used on a commercial scale to combat an aquatic invasive species.

“This is the first time we’ll see a weevil project like this,” McComas said. “There have been some experiments in the past, but they were not for a specific management project. This is really new territory.”

The type of weevils that will be introduced to Lake Minnetonka this summer are native to Minnesota and can presently be found in Lake Minnetonka—easing a major concern expressed by the Department of Natural Resources (DNR) during the experiment’s planning stages.

“The DNR in the past has had some concerns and considerations about bringing in weevils from other states, and we wanted to make sure we’d be using weevils native to Minnesota,” McComas said. “Lake Minnetonka currently has weevils in it, but their populations are very low density.”

The weevils will be introduced sometime early this summer into Veteran’s Cove, along the south side of Big Island, and  just south of Grays Bay. EnviroScience, Inc.—a private firm headquartered in Ohio—has been hired by the Minnehaha Creek Watershed District to carry out the weevil project and received its state permit to conduct operations last week. The company will harvest weevils currently living in Lake Minnetonka for large-scale breeding and eventual re-introduction. EnviroScience has conducted similar projects in both the U.S. and Canada—specifically Michigan, where milfoil is prevalent—with mixed results.

But McComas says he anticipates weevils will produce a noticeable decrease in Lake Minnetonka's milfoil groves.

“They will reduce the heavy growth of milfoil, and the canopies (dense patches) will be eliminated,” he said.

McComas went on to add that regeneration of the weevil population will need to take place for at least two years in order to realize sustained results. Designed as a three-year program, the Minnehaha Creek Watershed District has only committed to funding the study for 2012. Typical weevil projects span at least three years, at which time McComas says the population could become self-sustainable.

While the exact number of new weevils that will be calling Lake Minnetonka home is tough to pin down, McComas estimates there will be about one weevil for every three stems of milfoil in the targeted areas.

McComas went on to stress that boaters and other water recreationalists won’t even notice the creatures. Additionally, McComas said it has only been recently discovered that weevils actually prefer to feed on non-native Eurasian milfoil over the milfoil that naturally grows in Lake Minnetonka, but the bugs will feed on both while completely bypassing other native plants.

Eurasian watermilfoil is a submersed invasive aquatic plant that was inadvertently introduced to Minnesota, according to the DNR. Milfoil was first discovered in Lake Minnetonka during the fall of 1987, and Eurasian milfoil limits recreational activities on water bodies by forming mats on the water surface and can alter aquatic ecosystems by displacing native plants.

Craig Dawson, the Minnehaha Creek Watershed District’s new invasive species director, said the watershed district will also be introducing weevils into Christmas Lake in Shorewood this summer and study how effective the weevils are in different settings—including how fish such as blue gills impact the new weevil populations.

Dawson said Libbs Lake typically sees low-speed boat traffic during the summer months, while Christmas Lake sees moderate-speeds and the open water near Big Island has the highest traffic speeds of the three.

“A lot of what the watershed district does is basically applied science, and they are science-based in the projects they take on," Dawson said.

EnviroScience will be looking to locally hire part-time staff to train, although exactly how many is unclear.