GLIN==> News Release - Weevil Attractants Identified for Invasive Plant

["Marie E. Zhuikov" <mzhuikov@d.umn.edu>]

                           MN SEA GRANT
                           NEWS RELEASE
4/18/06
Contact: Marie Zhuikov, mzhuikov@umn.edu or (218) 726-7677

       Chemical Attractants Draw Weevil to Invasive Aquatic Plant

Scientists at the University of Minnesota have discovered, for the 
first time, at least two chemical insect attractants released by an 
aquatic plant. Professors Ray Newman and Florence Gleason, and their 
graduate student, Michelle Marko, identified the chemicals as glycerol 
and uracil. These compounds are produced by Eurasian watermilfoil, an 
invasive plant, and lure a native species of weevil (Euhrychiopsis 
lecontei) to eat, mate, and lay their eggs on the plants.

Both glycerol and uracil are produced by other plants, but are released 
at higher concentrations by Eurasian watermilfoil. This is bad news for 
the milfoil because the weevils are a natural biocontrol measure for 
this exotic plant that has plagued North American waters since the late 
1940s. Eurasian watermilfoil can form dense mats of vegetation and 
crowd out native aquatic plants, clog boat propellers, and make water 
recreation difficult. It has spread to 177 lakes, rivers and streams in 
Minnesota.

"If you look at terrestrial systems," said Newman, a professor with the 
department of fisheries, wildlife, and conservation biology, "there are 
many insects that specialize by feeding on certain plants -- cabbages, 
for instance, and the attractants are well-known. This is the first 
time a chemical attractant for an insect has been found for an aquatic 
plant."

The researchers gathered milfoil from lakes across Minnesota and then 
grew the plants in lab tanks for several days before extracting 
chemicals the milfoil released into the water. They tested the extracts 
on the weevils to determine their preference.

To pinpoint the attractants, the researchers used techniques as 
complicated as mass spectrometry and nuclear magnetic resonance 
spectroscopy, and as simple as a salad spinner.

Glycerol is a sweet-tasting thick liquid used in many products humans 
eat, such as candy, cakes, food coloring, and flavorings like vanilla. 
Uracil is a more complicated chemical with derivatives that are 
important to cell metabolism, particularly carbohydrate metabolism.

The weevil's attraction to these compounds increases as concentrations 
increase. "Although other aquatic plants also release glycerol and 
uracil, the higher concentrations released from Eurasian watermilfoil 
as it grows make it more obvious to the weevils," said Gleason, a 
professor with the department of plant biology.

Weevils used in the experiment were collected from the same lakes as 
the milfoil used by the researchers. The tiny weevils were placed in a 
"Y-tube" that had attractant materials in one side of the top of the Y 
and control materials placed in the other side. Weevils usually made 
their preference for the attractant materials clear within five 
minutes. The research team's results were published in the December 
2005 issue of the Journal of Chemical Ecology.

"These findings would be useful for sampling or collecting adult 
weevils," said Newman. "The attractants could be used to lure weevils 
living in a lake into a trap so that they could be released elsewhere 
or used for research purposes, or the attractants could be used to get 
an idea of how many weevils live in an area."

What's the other mystery attractant? "There's a third compound we're 
aware of, but can't identify," said Newman. "Results are clear that 
glycerol and uracil are attractive to the insects, but there seems to 
be at least one more."

Reprints of the article, "Chemically Mediated Host-Plant Selection by 
the Milfoil Weevil: A Freshwater Insect-Plant Interaction," are 
available free by contacting Minnesota Sea Grant at seagr@d.umn.edu or 
(218) 726-6191. Ask for JR 511.

Minnesota Sea Grant is part of a network of 30 Sea Grant College 
Programs spanning coastal states throughout the United States and 
Puerto Rico.

                                 -30-


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