Weevil Shows Potential To Control Eurasian Watermilfoil

October 24, 1996

DULUTH, MN. University of Minnesota Sea Grant researchers report that a tiny freshwater weevil (Euhrychiopsis lecontei) shows promise as a possible control for Eurasian watermilfoil, an exotic plant that has infested North American waters since the late 1940s.

Susan Solarz and Ray Newman conducted experiments at the University of Minnesota with a native weevil that normally eats northern watermilfoil, an usually benign native relative of the Eurasian type. Solarz and Newman found that weevils introduced to Eurasian watermilfoil in a lab setting prefer to lay eggs on the Eurasian variety over native varieties. The weevil lays its eggs on the tips of the milfoil plant. Once they hatch, the young burrow down the stem, eating their way through the plant, which slows down the growth of milfoil. Under the right environmental conditions, this could provide a chemical-free control method.

Eurasian watermilfoil continues to slowly spread throughout North American freshwater lake and river systems, usually due to transport by boaters. It currently is found in 40 states and three Canadian provinces. It can form dense mats of vegetation and crowd out native aquatic plants, clog boat propellers and make water transport and recreation difficult.

Currently milfoil is controlled through harvesting and chemical treatments, both labor intensive and costly. Estimates are that chemical treatments can run between $200-$300 per acre of water treated, while combinations of harvesting and chemicals can run considerably more.

A frequently cited example of the high control costs is Lake Minnetonka, a large multi-bay lake just west of Minneapolis that is a popular boating and fishing lake for Twin Cities residents. Control costs there have run as high as $250,000 a year. In Minnesota the plant currently impacts 75 lakes, primarily in the Twin Cities area, and four rivers or streams. Nationally the U.S. Army Corps of Engineers estimates millions of dollars are spent annually to control Eurasian watermilfoil infestations.

"Their results show that the weevils are definitely worth looking into as a control method and that additional research is necessary," said Chip Welling, coordinator of the Minnesota Department of Natural Resources' Eurasian watermilfoil program.

Newman and colleagues are currently monitoring experimental use of the weevil in Minnesota to seek answers as to where and where not it will work and what are the optimum conditions for its successful impact. Other researchers in Wisconsin, Vermont and Washington state are also investigating the use of the weevil.

"Finding a natural way to inhibit Eurasian watermilfoil is important," said Newman. "Although it is unlikely the weevils will eradicate Eurasian watermilfoil infestations, under certain conditions, which we are still investigating, they can reduce the amount of the plant that spreads across the water's surface, which can provide major benefits, especially for boaters."

"While chemical control may still play a role in specific settings -- such as near crowded lake accesses, and to clear navigational channels -- natural controls have advantages," said Newman. "First, these weevils are already here; there isn't the danger of adding a new exotic pest. The weevil specifically targets Eurasian watermilfoil, reducing the risk that native plants will be harmed in the process. Second, effective biological controls may result in long-term declines at a relatively low cost. This reduces the need for repeated treatments usually required with chemical and mechanical controls."

Solarz and Newman also discovered that once weevils are reared on the exotic plant in the lab, they will spend more time looking for it if the Eurasian variety is removed, instead of simply switching to the native species. They can eventually switch, but the weevils have long coexisted with the native variety.

Solarz and Newman's results were recently published in the international peer-review journal, Oecologia.

Contact for More Information:

Ray Newman, Minnesota Sea Grant Researcher 612-625-5704, E-Mail: rmn@fw.umn.edu

Marie Sales, Minnesota Sea Grant Communications Director 218-726-7677, E-Mail: msales@d.umn.edu

Note: an image of the Euhrychiopsis lecontei weevil is available on Minnesota Sea Grant's web site: http://www.d.umn.edu/~seagr/news.html.

National Sea Grant College Program

Related Plant Articles from Brightsurf:

More plant diversity, less pesticides
Increasing plant diversity enhances the natural control of insect herbivory in grasslands.

Plant pathogens reorder physical structures of effectors to escape plant recognition
Phytophthora infestans is an oomycete, or water mold, that causes the devastating potato disease known as late blight or potato blight and was responsible for the famous Irish Famine of the 1840s.

Plant living with only one leaf reveals fundamental genetics of plant growth
Clinging to the walls of tropical caves is a type of plant with a single leaf that continues to grow larger for as long as the plant survives.

Statistical analyses of plant metabolites allow solid testing of plant defense theories
High-throughput analyses of small substances in Nicotiana attenuata reveal that plants re-organize their metabolism to produce highly-specific defense metabolites after insect attack.

Plant detectives develop new way to trace global spread of major plant disease
A team led by Oregon State University scientists has developed a way to potentially thwart the spread of a disease-causing bacterium that harms more than hundred plant species worldwide, an advance that could save the nursery industry billions of dollars a year.

A hormone -- plant style
Researchers from the Faculties of Chemistry and Biology at Bielefeld University have now found a method that might make the production of a biologically significant precursor of jasmonic acid more efficient and cheaper.

How three genes rule plant symbioses
A study published in Nature Plants, led by scientists from the John Innes Centre in the UK and the University of Toulouse/CNRS in France, describes the discovery of a common genetic basis for plant symbioses

Getting to the root of plant survival
In a first-of-its-kind study, researchers have been able to identify hormones and proteins that interact to regulate root emergence.

Ants fight plant diseases
New research from Aarhus University shows that ants inhibit at least 14 different plant diseases.

How a protein connecting calcium and plant hormone regulates plant growth
A new Tel Aviv University study finds that a unique mechanism involving calcium, the plant hormone auxin and a calcium-binding protein is responsible for regulating plant growth.

Read More: Plant News and Plant Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.