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Wisconsin Natural Resources magazine

Wisconsin Natural Resources magazine

August 1998

Purple loosestrife clogging a wetland. Can hungry beetles help clear waterways of this invading plant? © Brian Pruka.
Purple loosestrife clogging a wetland. Can hungry beetles help clear waterways of this invading plant?

© Brian Pruka.

An invasion beaten by eatin'?

Voracious beetles can't get enough of that purple stuff.

Brock Woods

How you can help the beetles win the battle

Though it's a beautiful summer bloomer, purple loosestrife is a persistent threat to Wisconsin wetlands. This aggressive European perennial with its spike of bright purple flowers was introduced into the state as a colorful garden flower after the turn of the century. Free from natural controls found in its European homeland, loosestrife has infiltrated more than 40,000 acres of wetlands in the state, mostly during the last 20 years, and continues to spread.

Uncontrolled in a wetland, purple loosestrife outcompetes and replaces native plants (even cattails), often forming thick, impenetrable stands. Waterfowl, muskrats and other animals decline significantly as the invading plant smothers good habitat.

Traditional control methods, such as cutting, pulling, flooding and treating with herbicides, often injures neighboring plants. Also, it's too costly and impractical to hand-treat loosestrife that has spread across a landscape. Perhaps the best long-term solution, and certainly the cheapest, is to enlist nature itself in the campaign to eradicate the plant.

Biological controls import some of the disease organisms, insects or other animals that naturally control invasive species in their native lands. The trick is to find agents that can control "pest" species without disrupting other natural cycles and becoming pests themselves.

In the 1980s and early 90s, the Department of Natural Resources worked with the U.S. Dept. of Agriculture to find, study and import "single-host" insects that only craved purple loosestrife. An ideal biocontrol agent would attack its chosen host and no other – a sort of botanical Fatal Attraction. The insects should find the plant, feed on loosestrife and either kill it or decrease its vigor, giving native plants a chance to reestablish.

Several species of beetles seemed like good candidates and in 1994 field trials, DNR researchers released 4,000 insects of some promising beetle species. Through 1997, researchers have released 90,000 foliage-eating beetles (two Galerucella species), 6,000 Hylobius beetles that mine loosestrife roots, and 500 flower-feeding beetles (Nanophyes) at 50 sites across the state. All four insect species thrive in our state.

Researchers monitor all the release sites, assisted by volunteers, and are conducting longer-term studies at a few places. Though the effects of Hylobius and Nanophyes on purple loosestrife are yet uncertain, the effects of Galerucella are often obvious and extremely encouraging.

The Galerucella beetle eats foliage quickly, stops the plant from flowering and badly weakens loosestrife plants on smaller sites in only two to three years! Larger sites may take much longer but results from tests elsewhere in the country show the beetle is very effective. The only limitation to date is that Galerucella does not seem to spread to new sites quickly, so it's necessary to start new colonies of Galerucella beetles in as many stands of purple loosestrife as possible to successfully control the plant.

Hungry beetle ready to chomp.
Hungry beetles devour loosestrife foliage and prevent the plant from flowering.

© Cornell University

Some citizen groups have already helped with this work, but more volunteers will be needed to control loosestrife statewide. DNR researchers are ready to help volunteers learn how to raise Galerucella in a beetle nursery, identify loosestrife stands, learn when to release beetles, and monitor progress. All tasks are easy and require little time. It's a great community project for wetland enthusiasts and for teachers who want to provide students with meaningful outdoor studies that provide a community service.

DNR researchers are working with other states to develop classroom materials to make it easier for teachers to consider such a project.

The Department of Natural Resources will supply directions, technical know-how and initial insect stocks as long as funds are available. Once a group rears beetles successfully, its program can continue DNR guidance. Last year three such groups raised and released beetles. Several more have already raised beetles this summer.

Join the program to control purple loosestrife!

If you're interested, please contact us soon: Beetles are be available this summer and fall while supplies last, but limited funding for this project makes future distributions uncertain.

608-221-6349 or 608-267-5066

Brock Woods

Purple Loosestrife Biocontrol Project
DNR Research Center
1350 Femrite Drive
Monona, WI 53716

Brock Woods is a research ecologist stationed at DNR's Research Center in Monona.