Folder Milfoil Weevil (Euhrychiopsis lecontei) Research for EWM Management


Eurasian Watermilfoil Strategic Biological Control Program 2011-2013: Final Technical Report 

Authors: Mark Clymer

Author Affiliation: LCWC

Journal: EPA/GLRI Invasive Species Grant: No. GL-00E00809; March 31, 2014

Abstract:  This project supports the Great Lakes Restoration Initiative and the Great Lakes Water Quality Agreement, pursuant to Public Law 112-10. The grant will support the Les Cheneaux Watershed Council’s work to stock 65,000 milfoil weevils in approximately 16 locations in three bays in the Les Cheneaux Islands region of northern Lake Huron, Michigan to control the invasive Eurasian watermilfoil and restore important perch spawning grounds. The project includes monitoring to assess the long-term effectiveness of this biological control strategy for watermilfoil.

pdf 2_Les Cheneaux Conceptual Proposal 8/17/2011

Conceptual Project Outline: Biological Control of Eurasian Watermilfoil with theMilfoil Weevil, Euhrychiopsis lecontei in Bays of Lake Huron

Authors: Rebecca McMenamin

Author Affiliation: EnviroScience, Inc.

Journal: Prepared for the Les Cheneaux Watershed Council, August 2011

Abstract:  Demonstrate the potential for milfoil weevils to provide sustainable and low maintenance control of EWM in three bays of Lake Huron. This objective will be accomplished by stocking a total of 65,000 milfoil weevils in approximately 16 locations over a two-year period beginning in July of 2011. In 2013, a follow-up monitoring survey of all program sites will be completed to document the extent to which the weevils have controlled the EWM in the project areas. It is expected that Eurasian watermilfoil will transition from a dominant species to a relatively small part of the overall plant community.

pdf W1 aqbva993

Euhrychiopsis lecontei (Dietz) as a Potential Biocontrol Agent of Eurasian Watermilfoil (Myriophyllum picatum L.)

Authors: Alfred F. Cofrancesco, Holly

Author Affiliation: US Army Corps of Engineers

Journal: Aquatic Plant Control Research Program Vol A-99-3 August 1999

Abstract: Crosson Euhrychiopsis lecontei (Dietz) is a small native weevil that feeds on various species of watermilfoil. Its natural host is northern watermilfoil (Myriophyllum sibiricum Komarov); however, it has been shown to feed extensively on Eurasian watermilfoil (Myriophyllum spicatum L.). The ability of this insect to feed on and damage Eurasian watermilfoil has led to its use in the management of this nonindigenous plant.

pdf W2 Jun2001ProgRep

Factors Influencing the Control of Eurasian Watermilfoil With Native Or Naturalized Insects


Authors: Raymond M. Newman1, David W. Ragsdale2 & David D. Biesboer3

Author Affiliation: 1Department of Fisheries & Wildlife; 2Department of Entomology; 3Department of Plant Biology University of Minnesota St. Paul, MN 55108

Journal: Minnesota Department of Natural Resources, Fourth Status Report for 1999-2001

Abstract: Although declines of milfoil in several lakes have been related to the occurrence of E. lecontei, it is clear that at many sites in Minnesota, weevil densities do not get high enough to effect control. Fish predation may be one factor limiting populations in some lakes.
The aim of this project is to monitor a set of milfoil populations for potential declines, determine factors that may be limiting control agent densities and their effectiveness in the field, determine the effects of fish on weevil augmentations and determine if chronic effects such as sediment quality or competition with native plants is responsible for declines of milfoil associated with herbivores. This report summarizes our methods and collection efforts in 2000 and presents preliminary results of our research through 2000.

pdf W3 LCMR2001May04 FinalRepFinal r

Biological Control of Eurasian Watermilfoil Completion Report for 2001-2004


Authors: Raymond M. Newman

Author Affiliation: Department of Fisheries, Wildlife and Conservation Biology, University of Minnesota


Abstract: The aim of this project is to attempt to detect milfoil declines and assess milfoil weevil populations, identify and manipulate factors that may be limiting control agent densities and identify and manipulate factors that may limit the effectiveness of milfoil control agents (plant community response). This report presents our results from 2001-2003 and summarizes our overall results during the past 10 years and provides some final conclusions and recommendations.

pdf W4 weevilpubs

Publications About Euhrychiopsis lecontei, the Watermilfoil Weevil updated January 2000


Authors: various

Author Affiliation:


Abstract: Bibliography of Publications About Weevils

pdf W5 Mazzei et al 1999

Developmental Rates of the Native Milfoil Weevil, Euhrychiopsis lecontei, and Damage to Eurasian Watermilfoil at Constant Temperatures


Authors: Kristine C. Mazzei, Raymond M. Newman, Alyson Loos, and David W. Ragsdale

Author Affiliation: Department of Fisheries and Wildlife and †Department of Entomology, University of Minnesota, St. Paul, Minnesota 55108

Journal: Biological Control 16, 139–143 (1999)

Abstract: The native aquatic weevil Euhrychiopsis lecontei (Dietz) is a potential biological control agent of Eurasian watermilfoil (Myriophyllum spicatum L.). The weevil reduces the viability of milfoil by mining plant stems. We determined the influence of temperature on the developmental rates of the weevil and damage to Eurasian watermilfoil stems. Single E. lecontei eggs were laid on rooted plants in individual tubes filled with water and 16 such tubes were randomly assigned to each of eight environmental chambers set at constant temperatures of 15, 19, 21, 23, 25, 27, 29, and 31°C with a 16-h day length. Weevils and plants were monitored daily and development times were recorded for the egg, larval, and pupal stages. Length of watermilfoil stem damaged (cm) was estimated at 21, 25, and 29°C. Developmental rate was linearly related to temperature, up to 29°C; the developmental maximum appeared to be between 29 and 31°C.Average egg hatch occurred in 12.0 days at 15°C and in 4.2 days at 31°C. Average larval development time took 20 days at 15°Cand 6.1 days at 31°C. Complete egg to adult development ranged from 16.6 days at 29°C to 61.7 days at 15°C. The lower developmental threshold was between 8.2 and 10.5°C, and egg to adult development required 309 6 27.6 (2 SE) degree-days above 9.8°C. Daily stem damage increased with temperature but total damage (by larvae) was equal across temperatures and averaged 15.1 6 1.9 cm. Field temperature data indicated that up to five generations could be completed in a typical summer in Minnesota lakes.

pdf W6 v38p78

The Weevil-Watermilfoil Interaction at Different Spatial Scales: What We Know and What We Need To Know


Authors: Robert P. Creed, Jr.

Author Affiliation: Department of Biology, Appalachian State University, Boone, NC 28608.

Journal: J. Aquatic. Plant Manage. 38: 2000.

Abstract: The North American weevil (Euhrychiopsis lecontei (Dietz)) is being considered as a biological control agent for Eurasian watermilfoil (Myriophyllum spicatum L.). This native insect damages watermilfoil plants and is frequently associated with declining watermilfoil populations. Weevils and watermilfoil interact over at least four different spatial scales—1) the level of the individual plant, 2) the level of beds within lakes, 3) lakes within geographic regions and 4) geographic regions—and we still have much to learn about the interaction at these different scales. For example, at the level of the individual plant, we have a good idea of how weevil herbivory influences plant growth but we still need to determine whether or not weevils can cause plant death. At the level of beds, we do not know how long it takes a weevil population to reach a density that will result in a significant reduction in watermilfoil biomass. Finally, at the level of lakes within geographic regions, we do not know if differences in lake productivity influence the weevil-watermilfoil interaction. It is my hope that addressing these questions and filling in the gaps in our knowledge will lead to a better understanding of the interactions between these two species and to more efficient use of the insect in watermilfoil control projects.

pdf W7 v38p88

Euhrychiopsis lecontei Distribution, Abundance, and Experimental Augmentations for Eurasian Watermilfoil Control in Wisconsin Lakes


Authors: Laura L. Jester1, Michael A. Bozek1, Daniel R. Helsel2, & Sallie P. Sheldon3

Author Affiliation:
1Wisconsin Cooperative Fishery Research Unit 4, College of Natural Resources, UW—Stevens Point, Stevens Point, WI 54481.
2Wisconsin Department of Natural Resources, 101 S. Webster St., Madison, WI 53703.
3Middlebury College, Department of Biology, Middlebury, VT 05753.

Journal: J. Aquat. Plant Manage. 38: 2000.

Abstract: The specialist aquatic herbivore Euhrychiopsis lecontei (Dietz) is currently being researched as a potential biological control agent for Eurasian watermilfoil (Myriophyllum spicatum L.). Our research in Wisconsin focused on 1) determining milfoil weevil distribution across lakes, 2) assessing limnological characteristics associated with their abundance, and 3) evaluating milfoil weevil augmentation as a practical management tool for controlling Eurasian watermilfoil. The geographic distribution of the milfoil weevil is widespread with 49 new records of the weevil among Wisconsin lakes containing Eurasian watermilfoil. Among 31 of the Wisconsin lakes that contained the milfoil weevil, their abundance varied from non-detectable to 2.5 weevils per stem of Eurasian watermilfoil. No whole-lake characteristics and only some milfoil bed characteristics such as the percentage of natural shoreline, the depth and distance of the Eurasian watermilfoil bed from shore, the number of apical tips and the percentage of broken apical tips per stem of Eurasian watermilfoil, were significantly correlated with milfoil weevil abundance. Twelve Wisconsin lakes augmented with one of three different treatment levels of weevils (1, 2 or 4 weevils per Eurasian watermilfoil stem) showed some significant damage to the Eurasian watermilfoil in small study plots at the end of the first treatment season. Additional sampling to assess long-term effects of this augmentation is ongoing.

pdf W8 v38p98

Temporal and Spatial Changes in Milfoil Distribution and Biomass Associated with Weevils in Fish Lake, WI


Authors: Richard A. Lillie

Author Affiliation: Wisconsin Department of Natural Resources, Bureau of Integrated Science Services, Ecological Inventory and Monitoring Section, 1350 Femrite Drive, Monona, WI 53716.

Journal: J. Aquatic Plant Manage. 38: 2000.

Abstract: During the course of an eight year monitoring effort, the Wisconsin Department of Natural Resources documented a significant decline in milfoil biomass and distribution in Fish Lake, Wisconsin. Average milfoil biomass declined by 40- 50% from 374-524 g dw m -2 during 1991-93 to 265 g dw m -2 during both 1994 and 1995. Milfoil recovered fully in 1996- 98 to 446- 564 g dw m -2 . The size of the milfoil bed, as discerned from aerial photographs, shrank from a maximum coverage of 40 ha in 1991 to less than 20 ha during 1995. During the “crash” of 1994-95, milfoil plants exhibited typical signs of weevil-induced damage, including darkened, brittle, hollowed-out growing tips, and the arching and collapse of stems associated with loss of buoyancy. Monitoring of weevils and stem damage during 1995-98 showed highest densities and heaviest damage occurred near shore and subsequently fanned out into deeper water from core infestation sites each spring. The extent of milfoil stem damage was positively correlated with weevil densities (monthly sampling). However, weevil densities and stem damage were lower during 1995 (when milfoil biomass was in decline) than during 1996-98 (when milfoil biomass was fully recovered).

pdf W9 v39p63

Overwinter Habitat and the Relationship of Overwinter to In-lake Densities of the Milfoil Weevil, Euhrychiopsis lecontei , a Eurasian Watermilfoil Biological Control Agent


Authors: Raymond M. Newman1, David W. Ragsdale2, Alyson Milles2 & Cary Oien2

Author Affiliation:
1 Department of Fisheries, Wildlife, and Conservation Biology, University of Minnesota, 1980 Folwell Ave. St. Paul, MN 55108.
2 Department of Entomology, University of Minnesota, St. Paul, MN 55108.

Journal: J. Aquat. Plant Manage. 39: 2001.

Abstract: The native weevil Euhrychiopsis lecontei has been associated with declines of Eurasian watermilfoil (Myriophyllum spicatum). The weevil spends all summer on submersed plants, producing 3 to 6 generations. In September to November adult weevils move to shore where they overwinter in leaf litter at drier sites near the shoreline. Mean November shoreline densities from 1992-1998 at Lake Auburn (mean = 43 N/m2) and Smith’s Bay of Lake Minnetonka, (mean = 125 N/m2) have ranged from zero to over 200 N/m2. Overwinter mortality is not severe (survival was typically >60%). Adults collected from terrestrial habitat have developed flight muscles and limited flight has been observed in the spring but submersed adults in summer do not have developed flight muscles. Adults return to the water in spring and females begin to develop and lay eggs after the water temperature reaches 10-15C. Spring (May-June) and Fall (September) inlake densities in these two lakes have ranged from zero to 40 N/m2 and Lake Auburn typically had higher in-lake weevil densities (mean of 15 N/m2 compared to 4 N/m2 at Smith’s Bay). There was no relationship between in-lake and shoreline densities at Lake Auburn, but Smith’s Bay spring in-lake densities were correlated with spring shoreline densities. Inlake densities were not correlated between the two lakes but shoreline densities were correlated over time, suggesting that regional climatic factors may influence shoreline densities. Weevils disappeared from Lake Auburn in-lake samples in July 1998; no weevils were found there in shoreline or in-lake samples in 1999. In-lake factors such as fish predation may be more limiting than overwinter conditions.