Weevils - Eurasian Watermilfoil

From the Lakeland -Times.

Since we have EWM on berry Lake I thought this article was interesting.

"9/26/2008 9:01:00 AM
Weevils could be the answer
To the Editor:

How many of us like the thought of using chemical herbicides in our lakes to control Eurasian watermilfoil for the next 20 years?

Your lakes board certainly doesn't! We have been using 2, 4D for the last four years and the results leaving something to be desired. This year good results were found in Kennedy Bay (by the town hall) but results in other treated areas are not good enough.

We are confident that we have found a biological solution that can do a better job than herbicides. The solution is a very small weevil (scientific name-Euhrychiopsis lecontei) that occurs naturally in both lakes.

In fact, on July 15, biologists from EnviroScience of Stow, Ohio, the only vendor of weevils, did an assessment of our lakes and found we have a healthy population already at work on the EWM.

All we need to do is to stock more so that they can dominate the existing stands of the weed. We are now in a race with the milfoil; we must accelerate the population of weevils to the point where they consume the weed faster than it grows.

The weevils are very small averaging from 2-3 mm in length; their color is dark and they spend their lives in the top meter of the milfoil plant (it would take approximately 10 lined up nose to tail to equal one inch).

Let's look at the life cycle of these little critters. They winter on shore hidden in debris, so let us start with them waking up in the spring.

Once awake, they go through an extensive stretching and calisthenics program to get themselves ready to go to work. They then fly to the water where they seek out patches of EWM. They dive into the water and begin to feed on the milfoil. Their feeding on the weed (leaves and stem tissue) is not the destructive part of their role. If they can find a breeding partner(s), they lay two eggs per day (once the adult weevils emerging from the shore have bred and laid eggs, they die.)

These eggs are laid in the buds of the plant. Soon the eggs hatch each producing a larva. These larva are the destructive force because they burrow into the stem of the plant and eat their way down the inside of the stem.

Not only does this destroy the plant's ability to transport food, it punches holes in the stem and lake bacteria attack the plant as well. Soon the plant stem falls over and the plant is severely wounded but not dead.

They emerge from the stem as mature weevils with the process from eggs to adults taking somewhere between 20-30 days. As adults, they quickly begin the breeding process all over again. Come fall the surviving insects emerge from the lake and fly to shore where they hide in the debris until they awaken in the spring.

According to the vendor, 5,000 weevils stocked in June can reproduce into tens of thousands flying to the shore in the fall - all prepared to attack the milfoil next spring.

We all have stores of biological controls that have run amok.

For example, the Asian lady bugs brought in to control aphids. They swarm into our homes in the fall and become a nuisance. This is not the case with weevils. They are grown in their nursery eating EWM and this sets their food preference for this particular weed. We have been told by lakes that have used weevils for years that a cyclical pattern will evolve.

The milfoil will flourish providing food for the weevil population which will begin to grow because of the abundant food. Because this population growth must accelerate even more rapidly, the weevils are usually stocked to speed things up. When the population of the insects is large enough, the weevils will "knock down" the milfoil destroying their own food source.

Once the EWM is gone, the weevils are dramatically diminished. The milfoil will again begin to flourish (recall it didn't die) and the weevils now have their food source back so they will begin to proliferate again. In most cases stocking is again required to accelerate their numbers.

In 2009, we plan to stock approximately 30,000 weevils at a cost of $40,000 (They cost $1.20 each plus the cost to tie the nursery stems to the existing plants).

These funds will come from our treasury since the DNR does not yet provide grants for such experiments. We say "experiment" because in a biological system strange things can happen. Weed patches have already been selected in both lakes for this trial. We will need to be patient since seeing results can vary from months to several years.

We will continue to treat selected areas with herbicides until we better understand the potential of the weevils. In addition we have selected an area in Lake Minocqua and have hired a diver to pull all EWM within this area. We will be evaluating this test next spring to determine the effectiveness of this control method.

After talking with lake officials in Michigan and New York we are extremely confident that the weevil route is the approach to take.

One lake official relayed the story of how a dog walked out onto the milfoil and fell through. They went to a great deal of trouble to make their rescue. Let's hope we never see conditions like these.

Richard W. Garrett

for the board of the Minocqua-Kawaguesaga Lakes Protection

Association

Minocqua" Weevils could be the answer