Hungry weevils may help state lakes

Andrew Tellijohn

As soon as weevils hatch, they find breakfast.
These tiny beetles with big appetites lay eggs on the tips of Eurasian watermilfoil, an exotic plant that forms dense mats of vegetation in lakes.
Soon after birth, the young weevils burrow down the plants’ stems and start chomping.
Some University watermilfoil researchers said this tiny weevil, which measures about the size of a pinhead, could be a natural eliminator of Eurasian watermilfoil.
The watermilfoil is a problem for many Minnesota lakes because it clogs boat propellers, crowds out native aquatic plants and hinders water navigation. If even a small piece is transported by a boat to an uninfected lake, the weed can spread to the entire lake. The exotic watermilfoil is present in more than 40 states.
University researchers have studied the plant since 1992 and said that the beetles may prove important to controlling the deadly plant.
“The key is to have a large enough number, a high enough density in the field,” said Ray Newman, associate professor of fisheries and wildlife. “If you have one or two per plant, they’ll probably have a pretty good effect.”
Chip Welling, coordinator of the University of Minnesota Department of Natural Resources’ Eurasian Watermilfoil program, said it is unusual for beetles to live in an aquatic environment.
“When I think of beetles, I certainly don’t think of water creatures,” said Welling. “(The weevil is) aquatic during the open water season.”
Although no one knows why the weevils prey on the Eurasian plant, University researchers said the beetles can be used as a natural way to eradicate it.
The weevils are safer to use than chemicals, which can affect plant and animal life in the water, Welling said.
“Part of the appeal of a biological control agent would be the hope they’d reproduce of their own accord,” he said.
The weevils normally feed on native Northern watermilfoil, a plant which does not grow as densely as the Eurasian plant. But, Newman said, the beetles will prefer feeding on the Eurasian plant if they are introduced to it.
“The weevil seems to be quite specific in its preference for plants in which it can develop,” Welling said.
Newman said researchers want to control watermilfoil, not eliminate it, because eradicating the weed might harm other aquatic species.
“If we could eliminate Eurasian watermilfoil without causing problems to other native vegetation, we’d eliminate it,” Welling said.