Illinois Natural History Survey - University of Illinois

Using Biological Control to Lose Loosestrife in Illinois

Late in the summer, many wetlands throughout northern Illinois and the upper half of the U.S. turn into seas of bright pink-purple. Although pretty from a distance, the beauty is deceiving. The sea of purple is due to the invasion and takeover of wetland habitats by an exotic weed--purple loosestrife.

Purple loose-strife is a European perennial that invaded the U.S. over a century ago. In Illinois, it has become a serious pest in the last two decades, crowding out native vegetation in once-pristine sedge meadows, bogs, and other high-quality wetlands. With few herbivores feeding on them, these large plants grow unchecked, producing millions of long-lived seeds and forming dense stands in which little else will grow.

In response to the problem in Illinois, a team from the Illinois Natural History Survey (INHS) is attacking purple loosestrife using biological control as part of a national program against the weed. Biological control of weeds uses herbivorous natural enemies that normally keep plants in check in their native habitats. Because loosestrife is an exotic perennial that is not closely related to agronomic or threatened native plants, the weed is a perfect candidate for biological control. In the early 1980s, U.S. Fish and Wildlife Service (USFWS) biologists and European biocontrol specialists identified the numerous insect species that feed on (and control) purple loosestrife in its native European habitats. Five beetle species that proved extremely host-specific were sent from Europe to the USFWS lab at Cornell University for further testing, rearing, and broader 
U. S. distribution.

Taking advantage of this national effort in 1994, Illinois Department of Natural Resources (DNR) biologists and land managers from several Illinois counties purchased beetles from the USFWS program. Seven thousand leaf-feeding chrysomelid beetles, Galer-ucella calmariensis and G. pusilla, (at $2 apiece) were released in seven sites in northern Illinois. In 1995, INHS biologists assumed leadership of the Illinois biological control project, in partnership with DNR and county land managers. In June 1995, another 3,000 adult leaf-feeding beetles were released, as well as several hundred eggs of another agent, the root-feeding weevil Hylobius transversovittatus.

Adult beetles, eggs, and larvae from the 1994 releases were found at all release sites, indicating successful overwintering. Because of that finding, the program expanded during the winter of 1995-1996, with plans for large-scale releases in 1996. State and county land managers selected 30 threatened, high-quality wetlands needing control measures as release sites. INHS entomologists conducted training sessions for land managers covering beetle biology, release strategies, and plans for monitoring releases. In preparation for mass rearing, approximately 10,000 beetles were cultured and refrigerated to simulate overwintering; after "overwintering," these beetles were caged on over 500 loosestrife plants in the greenhouse to produce the new generation of beetles for release.

Purple loosestrife running rampant in northern Illinois.

The goal was to release at least 2,000 beetles at each of these 30 sites, from mid-May through June when purple loosestrife was actively growing. Production from the refrigerated adults exceeded expectations, with over 170,000 adult Galerucella reared and released. Several high-quality sites, such as Brandenburg Bog and Wauconda Bog (both in Lake County), Weingart Road Sedge Meadow (McHenry County), and Ferson Creek Fen (Kane County), received large numbers of beetles. Also, over 600 Hylobius eggs were inoculated in plant stems at several of the sites.

Field observations made this spring have shown that beetle populations survived a second winter and are growing. Although the 1996 goal for numbers of beetles released was exceeded, the project is not finished. Successful biological control of purple loosestrife will require all of the available control agents, and it will take years for populations of these natural enemies to develop. Over the next few years, Survey entomologists and state and county cooperators hope to rear and release the available control agents at sites where purple loosestrife occurs throughout Illinois.

The total eradication of purple loosestrife in Illinois or anywhere else in North America is unlikely. However, the goal of our biological control program is to reduce the weed's population to a level low enough that the native plants can regain their competitive edge, and help restore valuable wetland communities in Illinois.

David Voegtlin, Center for Biodiversity, and Robert Wiedenmann, Center for Economic Entomology

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Subject: INHSPUB-00422
Last Modified 8/16/96

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