Frequently Asked Questions about Aquatic Weeds in Lakes
1. How Were Weevils Discovered?
2. Would we be infesting our lake with an exotic species if we introduce weevils?
3. If I already have weevils, why do I need to add more?
4. Will the weevils become a nuisance? Specifically, do they bite or swarm homes in the fall?
5. How many weevils are needed per acre of milfoil?
6. What is defined as long-term control of milfoil?
7. How long will it take to achieve lake-wide milfoil control?
8. What time of year is best for stocking?
10. Does fish predation affect weevils?
12. Does someone need to come out to visit the lake before the stocking?
13. Are there any permits necessary for stocking weevils?
1. How were weevils discovered? Dr. Sallie Sheldon of Middlebury College in Vermont discovered that this little aquatic beetle was responsible for milfoil control in one of the university ponds. After 10 years of research, a program for the biological control was developed and proved very effective in extensive field trials. Since 1998, EnviroScience has continued large-scale stocking projects and has achieved success in nearly 200 lakes across the United States and Canada. In addition, EnviroScience supports university research at institutions in both the U.S. and Canada.
2. Would we be infesting our lake with an exotic species if we introduce weevils? No. The weevils are native to the United States and Canada. In fact, our biologists find indigenous populations of weevils in most lakes, so there is a high possibility that weevils are already living in your water body on the milfoil. The weevil’s original host plant is a native species called Northern watermilfoil; however, once Eurasian watermilfoil was introduced in the 1940s, weevils switched preference to the exotic species over its original host plant.
3. If I already have weevils, why do I need to add more? Native populations usually too small or too scattered to keep up with the rapidly growing milfoil- the milfoil can grow up to an inch a day! By stocking relatively large numbers of weevils all the same age in close proximity, the adult weevils more easily find each other and the population is able to reproduce faster. By jump starting the natural populations in this way the weevils are able to achieve higher numbers more quickly and gain lake-wide control of the milfoil.
4. Will the weevils become a nuisance? Specifically, do they bite or swarm homes in the fall? No, the weevils remain on the plants in the water until some adults go to shore in late fall to hibernate in the winter very close to the shoreline. The weevils not only rely exclusively on milfoil for their food, but also for completion of their entire life stages. Without the plant, the weevil cannot survive. Thus, there is zero chance of the weevil leaving the shoreline to swarm around homes or live on your pets.
5. How many weevils are needed per acre of milfoil? The goal for all Milfoil Solution® programs is to establish a self-sustaining weevil population that keeps milfoil below nuisance levels. Each ecosystem responds differently, so weevils are not stocked on a per acre basis. Instead, weevils are stocked based on the size of the infestation, and to some extent how rapidly control is desired. 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 strategy.
6. What is defined as long-term control of milfoil? Milfoil can never be eradicated from a water body once introduced, not even with herbicides or harvesting. However, as the natural predator of milfoil, the weevil will return every spring and spread around the lake in search of more food (milfoil). Visible signs of long-term control is a vast decrease in abundance of milfoil, maintenance of any remaining stems below the lake surface at a non-nuisance level and the increase in native plant species where milfoil once-dominated.
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 two to five years.
8. What time of the year is best for stocking? Mid-May through early August is best. Stocking weevils by midsummer allows several generations to establish a good healthy population before overwintering on the shoreline. In addition, each generation will cause significant damage to the plant, effectively reducing the plant’s ability to grow.
9. When the levels of the Eurasian watermilfoil weed collapse because of predation by the weevils, what will the weevils eat then? As a predator/prey relationship, the weevil population in the lake will decrease naturally as the quantity of its food (milfoil) decreases. As mentioned, the weevil is also restricted to certain types of milfoils (Eurasian watermilfoil, Northern watermilfoil and a hybrid of the two) because it relies on the plant for food and completion of its life stages. The weevil will sustain its population in balance with the milfoil. Moreover, the weevil will begin to rebuild its population to control any resurgence of milfoil for years after stocking.
10. Does fish predation affect weevils? No. They are not a preferred food choice and only incidentally found in the stomachs of bluegills. In 2006 EnviroScience did a large study in New York and an independent consultant did a similar study in 2007 where the gut contents of sunfish in weevil stocking areas were examined. In both studies, very few weevils were found in the guts of these fish, indicating that predation levels are very low. In addition, sunfish are common components of the fish community in virtually all of our project lakes.
11. I heard that weevils don’t work in lakes with many seawalls, developed shoreline and with high boat-traffic. Is that true? No. EnviroScience has stocked weevils in a variety of lakes most of which have heavily developed shoreline and high boat traffic and have experienced great success. Weevils are resilient insects that do not need specific types shoreline to overwinter. We recommend informing the community about weevils and suggest marking stocking areas with a buoys during the first seson to minimize prop damage in the immediate area for a few weeks after stocking while the weevils are getting established
12. Does someone need to come out to visit the lake before the stocking? No. We only need to positively identify that you indeed have Eurasian watermilfoil (see Identify Milfoil) and that there are dense milfoil areas for stocking weevils. Our biologists will determine stocking locations with your input when they bring the weevils. However, if you have a recent vegetation survey map, it will help us design a more precise proposal.
13. Are there any permits necessary for stocking weevils? The permits for stocking weevils are not the same for herbicides. EnviroScience applies and maintains all the permits necessary for each state at no cost to the client. For Canadian clients, there is no permit necessary, but regional approval from any local conservation groups or Parks Canada if part of the waterway is government-owned may be necessary.
