Frequently asked question about weevils

This is a list of question that Rebecca of EnviroScience has answered about the weevils. She invites anyone to call or email her at the numbers listed below if you have question. We are doing this now as it is the only thing we can do with limited moneys and all the complicated permits that chemical call for and of course it is safe. Be assured we are working hard to get grants and raise money to fight this weed. Thank you for you help to all those that have sent donations. We want to keep moving froward. Don’t forget you can send your donation by PayPal now.
To keep informed about the milfoil make sure to go to our website and click at the right under the milfoil news. Scroll down after the donation button. Any of the headlines will take you to articles to read. We keep adding more all the time.

Frequently Asked Questions About
Controlling Eurasian Watermilfoil with Milfoil Weevils
1. How was the relationship between milfoil weevils and Eurasian watermilfoil
Dr. Sallie Sheldon of Middlebury College, Vermont, found the milfoil weevil,
Euhrychiopsis lecontei, associated with the collapse of Eurasian watermilfoil
(Myriophyllum spicatum) infestations in some of her study lakes. After 10 years of
research, biological control field trials proved effective in reducing the milfoil. Marty
Hilovsky of EnviroScience worked with Dr. Sheldon and Middlebury College to
establish the commercial application of milfoil weevils. Since 1998, EnviroScience has
continued large-scale stocking projects and has achieved success in lakes across the
United States and Canada. In addition, EnviroScience supports university research at
institutions in both countries.
2. Are weevils an exotic species?
No. The milfoil weevil is native and widespread across the northern United States and
Canada. Its original host plant is the native Northern watermilfoil (Myriophyllum
sibiricum); however, once Eurasian watermilfoil was introduced, weevils switched
preference to the exotic species over the original host plant.
3. If weevils already occur in a lake, why do more need to be added?
Native populations are typically sparse and unable to keep up with the rapidly growing
milfoil. By stocking large numbers of weevils all the same age in close proximity, the
newly emerged adults will easily find each other to mate. Those adults can lay egg
for the next generation or two, which will hatch and begin damaging nearby healthy
milfoil. This enables more rapid lake wide expansion of the weevil population.
4. Will the weevils become a nuisance?
No, the weevils are specialists on Eurasian and Northern watermilfoils and the hybrid
cross of the two. The weevils not only rely exclusively on milfoil for their food, but also
for completion of their life cycle. The last generation of adults goes to shore in late fall
to hibernate for the winter.
5. How many weevils are needed per acre of milfoil?
Weevils are not stocked on a per acre basis but rather on the size of the milfoil
infestation, and to some extent how rapidly control is desired. Each water body is
different, but once a self-sustaining population is achieved, management costs drop
significantly and only occasional monitoring of the weevil and milfoil levels should be
necessary. Long-term monitoring is an important component for any milfoil
management program and should be considered when deciding on a management
6. What is defined as long-term control of milfoil?
Visible signs of long-term control are a vast decrease in milfoil density and
abundance, maintenance of any remaining stems below the lake surface at a nonnuisance
level, and the increase in native plant species where milfoil once dominated.
Milfoil can never be entirely eradicated from a water body, only managed. However,
as the natural predator of milfoil, the weevil will return every spring and continue to
damage and eliminate milfoil.
7. How long will it take to achieve lake-wide milfoil control?
Many factors play a role in determining the time needed for control, including lake
size, quantity and density of the milfoil, and the number of weevils stocked. However,
in most stocked lakes, lake-wide control (not eradication) has been achieved in three
to five years.
8. What time of the year is best for stocking?
June through early August is best. Stocking weevils by midsummer allows for
production of an additional one to three generations before the weevils move to shore
for overwintering.
9. When the levels of the Eurasian watermilfoil weed collapse because of
predation by the weevils, what will the weevils eat?
Just like all predator/prey relationships, the weevil population in the lake will decrease
naturally as the quantity of its food (milfoil) decreases. A low population of weevils will
remain on scattered stems. If environmental factors favor milfoil resurgence, the
weevil population increases and regains control within one to two seasons.
10. Are any permits required for stocking weevils?
EnviroScience maintains USDA APHIS permits for all states that allow the use of
biological control of exotic weeds. Some state environmental agencies prefer to be
notified of any projects in advance. This is a blanket, state-wide permit that is no cost
to the client.
11. Does fish predation affect weevils?
No. Studies in New York and Michigan in the last five years found that milfoil weevils
are not a preferred food choice and only incidentally found in the stomachs of
bluegills. One recent project, a three-year study of pan fish gut analysis from five
reservoirs, with high weevil densities in northern Michigan, confirmed that less than
five percent of blue gills contained a milfoil weevil.
12. Do weevils work in lakes with developed shoreline or high recreational
Yes. EnviroScience has augmented successful long-term control programs in a variety
of lakes with heavily developed shoreline and recreational traffic. Prior to installing
weevils, it is recommended that the community be informed and educated about the
use of weevils. EnviroScience marks the stocking areas with buoys during the first
season to minimize propeller damage in the immediate area for a few weeks after
stocking while the weevils become established. In addition, there are ways to
encourage weevil populations through cultivating a more natural shoreline buffer zone.
13. What can I do to help keep the milfoil from further spreading?
Regardless of the management strategy, boaters can help to prevent further spread of
the milfoil by avoiding very dense milfoil that is at the surface of the water. Milfoil
fragments created by propellers will re-root themselves to grow healthy mature plants
causing a larger infestation. Additionally, lakefront owners who harvest the milfoil on
their property should be careful to pick up as many fragments as possible. Milfoil is
rich in nitrogen, so use it as compost for your garden.
14. Does someone need to visit the lake before the stocking?
No. The most important first step is to have a positive identification that the problem
plants are Eurasian watermilfoil. Secondly, there needs to be dense milfoil areas for
stocking the weevils. Any recent vegetation survey map is useful when designing a
plan and choosing stocking areas. However, through discussion with an interested
lake resident, sufficient information can be usually obtained to develop a project plan.
It is sometimes possible for one of the Lake Management Division staff to visit the lake
when traveling in the area.
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Best regards,


Rebecca McMenamin
Lake Management Milfoil SolutionĀ®
EnviroScience, Inc
3781 Darrow Rd.
Stow, OH 44224
Cell: (330) 507-2451
P: (800) 940-4025
F: (330) 688-3858
[email protected]

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