Euhrychiopsis lecontei Weevil
University of Minnesota Sea Grant researchers think a tiny freshwater
weevil(Euhrychiopsis lecontei) shows promise as a possible control
Eurasian watermilfoil. Watermilfoil continues to slowly spread in Minnesota,
usually due to accidental transport by boaters.
Susan Solarz and Ray Newman conducted experiments at the University of
Minnesota with a native weevil that normally eats northern
usually benign native relative of the Eurasian type. Solarz and Newman
found that weevils introduced to Eurasian watermilfoil in a lab setting
to lay eggs on the Eurasian variety over native varieties. The weevil
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.
"Their results show that the weevils are definitely worth looking into as
a control method and that additional research is necessary," said Chip
coordinator of the Minnesota Department of Natural Resources' Eurasian
"Finding a natural way to inhibit Eurasian watermilfoil is important,"
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
water's surface, which can provide major benefits, especially for
"While chemical control may still play a role in specific settings --
near crowded lake accesses, and to clear navigational channels -- natural
controls have advantages," said Newman. "First, these weevils are
here; there isn't the danger of adding a new exotic pest. The weevil
specifically targets Eurasian watermilfoil, reducing the risk that native
will be harmed in the process. Second, effective biological controls may
in long-term declines at a relatively low cost. This reduces the need
for repeated treatments usually required with chemical and mechanical
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
variety is removed, instead of simply switching to the native species.
can eventually switch, but the weevils have long coexisted with the
Eurasian watermilfoil is an exotic plant that has infested North American
waters since the late 1940s. If can form dense mats of vegetation and
out native aquatic plants, clog boat propellers and make water recreation
difficult. Eurasian watermilfoil has spread to 75 lakes, primarily in
Cities area, and four rivers or streams. The most recent finding was in
Lake (the northwest Metro area) this summer.
Solarz and Newman's results were recently published in Oecologia. A
of this journal article, "Oviposition Specificity and Behavior of the
Watermilfoil Specialist, Euhrychiopsis lecontei," is available from
by calling 218.726.6191.