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Use of Aquatic Weevils to Control a
Nuisance Weed in Lake Bomoseen, Vermont
United States
Environmental Protection
Agency |
Office of Water
(4503F) |
EPA 841-F-97-002
October 1997
Number 3 |
|
Watershed Protection:
Clean Lakes Case Study
Use of Aquatic Weevils to Control a
Nuisance Weed in Lake Bomoseen, Vermont
|
Key
Feature: |
Use of a biological
control for a nuisance macrophyte |
Project Name: |
Lake Bomoseen |
Location: |
Rutland County, VT
USEPA Region 1 |
Scope/Size: |
Watershed area 10,025 hectares (24,470 acres)
Lake area 960 hectares (2,370 acres) |
Land Type: |
Ecoregion #60, Northern Appalachian Plateau
and Uplands |
Stressor: |
Eurasian watermilfoil (Myriophyllum
spicatum) |
Stressor Source: |
Accidental introduction |
Data Sources: |
State |
Data Mechanisms: |
Plant and invertebrate sampling |
Monitoring Plan: |
Yes |
Control Measures: |
Aquatic weevil (Euhrychiopsis
lecontei) |
SUMMARY
Lake Bomoseen, located in western Vermont (Figure 1), has had a long
history of weed problems. By the early 1980s, Eurasian watermilfoil
(Myriophyllum spicatum) was the dominant weed species in the lake.
Eurasian watermilfoil is an introduced species that is difficult to
control due to its ability to survive in various environmental
conditions. At one point the watermilfoil covered 240 hectares of the
lake, impairing its recreational and commercial uses. In addition to
Lake Bomoseen, the macrophyte has been documented to exist in
approximately 42 other Vermont lakes. One of those is Brownington Pond
(located in northeastern Vermont), which experienced a decline in its
watermilfoil population in 1989. Following the discovery of this natural
decline, the Vermont Department of Environmental Conservation (VTDEC) was
awarded a U.S. Environmental Protection Agency (USEPA) grant to
investigate the decline and its causes. It was hoped that the
investigation would benefit other lakes with Eurasian watermilfoil
problems.
Researchers from Middlebury College, working under contract for VTDEC,
documented fluctuations in the Brownington Pond Eurasian watermilfoil
population and then investigated possible causes, including the role of
herbivores. The researchers concluded that a native aquatic weevil,
Euhrychiopsis lecontei, was largely responsible. They proceeded to
examine the specific effects of the weevil on the Eurasian watermilfoil
and native plant species to determine the feasibility of the weevil as a
biological control. The weevil was deemed appropriate and potentially
effective as a control for the Eurasian watermilfoil and the weevil
population in Lake Bomoseen was augmented (i.e., added to) in 1993 and
1994. Although an overall reduction in the Eurasian watermilfoil
population dramatic enough to be noticeable to lakeshore owners has not
yet occurred, the technique has shown promise in controlling the growth
of the weed. Results from the monitoring of introduction sites have
shown that over the last 4 years weevil survival has been good and that
the plants have suffered extensive weevil-induced damage. These initial
results indicate that, over time, the weevil might be able to reduce
nuisance growth in Lake Bomoseen and could potentially be used in other
lakes with similar problems.
Contact: | Betty Hutchinson, Vermont
Department of Environmental Conservation, 103 South Main Street, Building
10 North, Waterbury, VT 05671-0408, phone (802) 241-3777. |
BACKGROUND
Lake Bomoseen is located in western Vermont in the towns of Castleton and
Hubbardton in Rutland County (Figure 1). It is the largest lake that
lies entirely within the state's boundaries, with a surface area of
approximately 960 hectares (2,370 acres). The lake is mesotrophic and has
an average and maximum depth of 8.2 m (26.8 feet) and 19.8 m (65 feet),
respectively. It drains a 10,025-hectare (24,470-acre) watershed, has
five major inlets, and empties to the Castleton River.
A portion of the lake's shoreline is contained within Bomoseen State
Park. Most of the remaining area around the lake is privately owned.
The lake has such recreational accommodations as a public beach, marinas,
and public boat launches, in addition to the state park. There are
approximately 1,000 residences around the lake, as well as restaurants
and other commercial facilities (Holly Crosson, VTDEC, personal
communication, 1997).
CHARACTERIZING THE
PROBLEM
Dense aquatic weed growth has been a consistent
problem in Lake Bomoseen since the early 1940s. In 1977 the town of
Castleton began to harvest the dominant exotic weed species in the lake,
curly leaf pondweed (Potamogeton crispus). The weed harvesting was
funded under section 314 of the Clean Water Act from 1977 to 1979. The
harvesting then continued with state and local funds and was successful
in the control of the pondweed until the early 1980s, when Eurasian
watermilfoil (Myriophyllum spicatum, hereafter referred to as EWM)
replaced P. crispus as the dominant species in the lake. Mechanical
harvesting has remained the primary method for the control of EWM on Lake
Bomoseen.
Since its accidental introduction in the mid-1900s, EWM has spread to at
least 40 states and 3 Canadian provinces, making it one of the most
widespread nuisance macrophytes in North America (Sheldon and Creed,
1995). Once introduced, EWM frequently becomes the dominant species in a
lake. The widespread distribution of EWM can be explained by its ability
to live in various environmental conditions; it can withstand a broad
range of aquatic environments, from oligotrophic to eutrophic waters, and
it grows in water depths from as shallow as 0.5 meter to as deep as 8
meters (26 feet). It also can grow in substrates ranging from poor,
sandy sediment to highly organic soils and can survive in wide ranges of
salinity, pH, and temperature conditions (Aiken et al, 1979; Nichols and
Shaw, 1986; Smith and Barko, 1990, as cited in Sheldon and Creed,
1995).
EWM beds are groups of plants of similar height and leaf form (Figure 2).
The plants grow quickly and, when they reach the water surface, grow
laterally to form a canopy. In contrast to many other macrophytes that
grow to variable heights and leaf shapes, EWM grows as thick walls of
uniform height and leaf forms. Because of this, the dense EWM beds
usually support a lower abundance and diversity of invertebrates than do
native aquatic plant beds (Sheldon, 1995; Sheldon and Creed, 1995). In
addition to its effects on aquatic life, EWM hinders the use of waters for
recreational boating, swimming and, fishing.
IDENTIFYING POSSIBLE
CONTROLS
In 1989, biologists with the Vermont Department of
Environmental Conservation (VTDEC) noticed a natural decline in the
population of EWM in Brownington Pond in the northeastern region of the
state. In 1990, VTDEC was awarded a $575,000 grant from the USEPA under
section 314 of the Clean Water Act. The purpose of this grant was to
examine the possibility of using aquatic herbivores found in Brownington
Pond as a biological control for other EWM populations. This Clean Lakes
Demonstration Program grant was awarded for the purpose of highlighting
new and unique techniques for lake restoration.
Working under contract for VTDEC, researchers from Middlebury College
mapped and studied the decreases and increases in EWM in Brownington Pond
from 1990 through 1995. The study investigated a variety of factors
(e.g., herbivores, water chemistry, and sediment chemistry) that could
have influenced the fluctuations. The results of the plant and
invertebrate sampling suggested that herbivorous insects played a primary
role in the EWM declines observed in 1989 and 1992. The researchers were
able to eliminate other factors as reasons for the declines, and the
focus turned toward the herbivore populations in the pond.
The two main EWM herbivores present in Brownington Pond were an aquatic
weevil native to North America, Euhrychiopsis lecontei (Figure 3,
illustration courtesy of Susan Warren, VT DEC), and the caterpillar
Acentria ephemerella. In examining the herbivores, the researchers
noticed variations in the abundance of the aquatic weevil between 1990
and 1994 and compared the variations to those of the EWM. They noticed
that the fluctuations in the weevil populations compared to the EWM
populations were similar to those exhibited by predator-prey or
host-parasitoid models (Creed and Sheldon, 1995). The evidence suggested
that the naturally occurring weevil populations might have played a role
in the decline of the Brownington Pond EWM population.
The Middlebury College researchers conducted laboratory and field
experiments to further examine the relationship between EWM and the
weevils, as well as their relationships to other herbivores and
macrophytes. It was discovered that Phytobius leucogaster, another
species of aquatic weevil, did feed on the EWM but had no significant
negative effect on its growth (Sheldon, 1995). It was also discovered
that the Acentria larvae reduced EWM growth in laboratory experiments
(due to stem-cutting during feeding and retreat construction (Creed and
Sheldon, 1994)). However, extensive caterpillar damage was not observed
in Brownington Pond (Creed and Sheldon, 1994).
By researching the feeding behaviors of the weevil, the researchers were
able to determine that all of its life stages can cause damage to the
plant. The first instar larvae cause extensive destruction to the
growing tip of the plant, thus preventing new stem growth. The late
instar larvae hollow out the stem by feeding on its vascular tissue, thus
reducing the plant's ability to transport the nutrients necessary for
growth. The late instar larvae also destroy the lacunal system of the
EWM, which serves as a gas reservoir for respired carbon dioxide (Nichols
and Shaw, 1986, as cited in Creed and Sheldon, 1994) and also permits gas
exchange between the plant roots and shoots (Grace and Wetzel, 1978,
Nichols and Shaw, 1986, as cited in Creed and Sheldon, 1994). The adult
weevils can damage the plant by feeding on its upper leaves, which can
affect the plant's energy balance by transferring photosynthesis
responsibilities to deeper leaves (Creed et al., 1992). The feeding may
also make the plant more susceptible to infections by bacteria and fungi
(Sheldon and Creed, 1995; Creed et al., 1992).
In addition to these direct effects, larval tunneling can also cause the
plant to lose buoyancy and collapse into deeper waters, where it is
subject to conditions different from those at the surface. This indirect
effect of loss of buoyancy could in fact be more significant than the
direct loss of leaf and stem tissue discussed above (Creed and Sheldon,
1995; Creed et al., 1992). It can cause the plants to sink out of
well-lit surface water, possibly to depths with insufficient light for
photosynthesis (Creed et al., 1992). Plants that lose buoyancy due to
weevil feeding could also entangle and sink other, undamaged plants.
The Middlebury College researchers conducted laboratory feeding trials to
quantitatively assess the effects of the weevils on the EWM. The plants
were collected and cleaned of all invertebrates, eggs, and other
material. Data were collected concerning the plants' appearance, weight,
and length. The plants were then placed in clear cylinders and either
zero, two, or four adult weevils were added to each cylinder. The
results of the laboratory experiments showed that the wet weight of the
EWM averaged 50 percent less in the two-weevil containers than in the
no-weevil containers and 130 percent less in the four-weevil containers
(Sheldon, 1995). In addition, the final plant shoot lengths were an
average of 25 percent shorter in the two-weevil containers and 60 percent
shorter in the four-weevil containers (Sheldon, 1995).
In field experiments, weevils were added to 30.5-centimeter-diameter,
2-meter-tall cylindrical enclosures in two lakes in which weevils were
not present. Forty days after the addition of the weevils, the EWM
plants in the three experimental weevil enclosures were compared to those
in the three control enclosures. Plant weights were lower for the plants
with weevils. In addition, the macrophyte formed canopies in the control
enclosures and the surrounding areas, but in the weevil enclosures there
were no plants at the water surface (Sheldon and Creed, 1995). The
plants had collapsed, and most were at least 1 meter below the surface
(Sheldon and Creed, 1995).
In addition to the effects on EWM, the Middlebury College researchers
also investigated the effects of the weevils on other aquatic
macrophytes, including several native watermilfoil species. They found
that the weevils had no significant negative effects on the native,
non-watermilfoil species, with no evidence of weevil feeding or egg-laying
(Sheldon and Creed, 1995). Although the weevils did feed and lay eggs on
portions of the native watermilfoil M. sibricum, the resulting damage was
not considered significant (Sheldon and Creed, 1995; Sheldon, 1995).
Based on the results from the Middlebury College laboratory and field
experiments, the weevil was deemed acceptable by VTDEC as an experimental
biological control because of the possibility that it might be able to
control EWM and the low risk it posed to non-target native aquatic plants.
INTRODUCTION OF A BIOLOGICAL CONTROL
AGENT
In the summer of 1993, VTDEC issued a Biological Control Permit under the
state's Aquatic Nuisance Control Permit Program allowing the release of
weevils into two Vermont lakes, including Lake Bomoseen (Sheldon, 1995).
Rearing of the weevils took place at VTDEC's environmental laboratory in
Waterbury and at Middlebury College.
In the summer of 1993, more than 5,000 weevils were added to three
unharvested sites in Lake Bomoseen— Cedar Mountain, Neshobe Island, and
Eckley Point (Figure 4). In the summer of 1994, approximately 15,000
additional weevils were introduced to the same three sites by both VTDEC
and Middlebury College. The distribution of the weevils released in 1994
was 9 percent eggs, 77 percent larvae, 13 percent adults, and 1 percent
pupae (Hanson et al., 1995).
Weevils were added to the three unharvested sites in Lake Bomoseen at
least once a week throughout the summers of 1993 and 1994. Data were
collected concerning the numbers and life stages of weevils released at
each location, and any notable weevil damage was recorded at each site on
each release date. Each augmentation area was paired with a site that
acted as the control "no-weevil" site for later comparison during the
monitoring efforts.
RESULTS
Monitoring was conducted through 1995 at the augmentation sites.
Monitoring consisted of collecting stem samples for weevil counts during
the summers and quantitative plant and invertebrate samples at the end of
each summer. The stem samples were examined, and all weevil eggs,
larvae, pupae, and adults were counted and removed. Three random plant
samples were collected at the end of the summers from each of the six
unharvested areas for examination of plant health and growth. Weevils
were counted and, along with other invertebrates, removed. The plants
were then dried and weighed. In addition to collection of samples,
visual observations were made of the sites to assess the effects of the
weevils. Throughout the sampling periods, apparent weevil damage was
noted at all sites in Lake Bomoseen.
The results of the quantitative analysis of the collected samples suggest
that the weevil is successfully established in the Lake Bomoseen sites.
Since the initial release on June 30, 1993, over 20,000 weevils have been
placed in Lake Bomoseen. Data collected in 1993 and 1994 show that the
total number of weevils collected at the augmentation sites was greater
than in the "no-weevil" sites and greatly increased from one year to the
next (Table 1). These findings indicate that the weevil is surviving and
thriving in the environment. Table 2 shows that the EWM biomass at the
Cedar location was substantially less in the augmentation area as
compared to the "no-weevil" control area (although a similar result was
not observed at the Neshobe location). There was less EWM in both
augmentation sites at the end of 1994 compared to 1993 (Table 3).
Table 1 A comparison of
overall total number of weevils collected on stem transects in Lake
Bomoseen at augmentation and control sites between 1993 and
1994. |
|
Augmentation sites |
No-weevil control sites |
Location |
1993 |
1994 |
1993 |
1994 |
Cedar |
34 |
73 |
25 |
32 |
Neshobe |
28 |
80 |
23 |
54 |
Source: Sheldon, 1995. |
Table 2 Results of 1994
quantitative invertebrate and plant sampling in Lake Bomoseen (means ± 1
S.E.) after 2 years of augmentation. |
|
Augmentation sites |
No-weevil control sites |
Location |
dry wt (g)¹ |
# weevils² |
dry wt (g) |
# weevils |
Cedar |
21.32 (1.96) |
0.67 (0.44) |
30.22 (2.88) |
2.33 (0.44) |
Neshobe |
34.59 (7.94) |
1.33 (0.44) |
27.96 (6.46) |
1.00 (1.33) |
¹ Weights are total dry weight of
Myriophyllum spicatum.
² Number of weevils per sample plant.
Source: Sheldon, 1995. |
Table 3 Comparison of 1993
and 1994 EWM biomass at weevil augmentation sites in Lake
Bomoseen. |
Location |
1993 dry weight (g)¹ |
1994 dry weight (g)¹ |
Cedar |
27.38 (5.76) |
21.32 (1.96) |
Neshobe |
62.50 (10.60) |
34.59 (7.94) |
¹ Values are mean (± 1 S.E.) total dry
weight.
Source: Sheldon, 1995. |
CONCLUSIONS
Although the conclusions drawn from the Lake Bomoseen results are
preliminary, the increased weevil populations and the decreased EWM
biomass at the weevil introduction sites in Lake Bomoseen suggest that
the weevil may be able to limit the nuisance plant over time. Laboratory
and field experiments have documented the correlation between weevil
populations and negative effects on EWM and have illustrated the weevil's
apparent specificity in feeding on EWM as opposed to other native aquatic
plants (Creed and Sheldon, 1993, 1994, 1995; Creed et al., 1992; Newman et
al., 1996a; Sheldon, 1995; Sheldon and Creed, 1995). These preliminary
results suggest that Euhryhchiopsis lecontei could potentially act as a
biological control for the introduced macrophyte EWM and could provide a
unique management opportunity for lakes with problems similar to those
experienced by Lake Bomoseen.
OTHER EXAMPLES OF WEEVIL-ASSOCIATED
EURASIAN WATERMILFOIL DECLINES
Fish Lake, Wisconsin
At least three lakes in Wisconsin have experienced EWM crashes that are
believed to be associated with the aquatic weevil Euhrychiopsis
lecontei—Devil's Lake in Sauk County, Lake Wingra in Dane County, and
Fish Lake in Dane County (Lillie and Helsel, 1997). Of the three, Fish
Lake is the best documented case of an EWM crash.
Fish Lake, a 100-hectare (247-acre) seepage lake located in the northwest
corner of Dane County, was the subject of an extensive fish
research-management study conducted by the Wisconsin Department of
Natural Resources (WDNR). The study included monitoring of EWM beds from
1991 to 1995.
During the early years of the study, EWM covered approximately 40
hectares (100 acres) or nearly 40 percent of the total lake bottom
(Lillie, 1996). In 1991, EWM represented 93 percent of the total plant
biomass in the lake; that percentage decreased to 77 percent by 1994
(Lillie, 1996). EWM biomass in all vegetated sites of the lake decreased
from 532 g/m2 in 1991 to 268 g/m2 in 1994 (Lillie, 1996). These
substantial declines in biomass and its relative dominance indicated that
the population in Fish Lake was in the process of crashing by 1994. These
declines continued in 1995.
During the study, a large population of weevils was documented to exist
in Fish Lake. Given the occurrence of the weevil in the lake and
documented feeding habits of the weevil (Creed and Sheldon, 1993, 1994;
Creed et al, 1992; Newman et al, 1996a), it is possible that the weevil
is largely responsible for the continual decline of EWM populations in
Fish Lake. |
McCullom Lake, Illinois
McCullom Lake is a 99-hectare (244-acre) glacial lake in the City of
McHenry in northeastern Illinois. A Phase I Diagnostic/Feasibility Study
was conducted for McCullom Lake from 1989-1992 under a grant from U.S.
EPA's Clean Lakes Program. This study identified many factors affecting
the lake's ecology and recreation, including colonization of the lake by
EWM.
In 1993, the City of McHenry received a Phase II
Restoration/Implementation grant from the Clean Lakes Program, thereby
enabling it to implement the restoration and protection strategies
identified in the Phase I study. An important part of the Phase II
project was to re-establish a balanced community of aquatic plants since
EWM had spread to about 70 percent of the lake by the summer of 1994 and
was choking out many of the native plant species.
Because of the lake's small watershed (249 hectares [616 acres]) and
limited motorized watercraft access, the potential for EWM re-infestation
was deemed comparatively small—but only if the existing EWM growth could
be completely eliminated (or close to it). Consequently, a "one-time"
herbicide application was planned to selectively remove the existing EWM
plants. Future re-infestations would be controlled at an early stage
through hand pulling and other non-herbicide control strategies.
However, just prior to the herbicide application in early spring 1995,
almost no trace of EWM could be found. Soon after, the aquatic weevil
Euhrychiopsis lecontei was identified on a few floating fragments of EWM.
These fragments (and the isolated EWM beds that later emerged) exhibited
extensive damage characteristic of weevil activity.
The EWM has remained suppressed well below nuisance levels through 1996
and 1997. The McCullom Lake Clean Lakes Program grant recently has been
extended for an additional year to continue monitoring the EWM and weevil
communities and to document their interactions.
(Source: Robert Kirschner, personal
communication) |
Cenaiko Lake, Minnesota
Ongoing research supported by the Minnesota Department of Natural
Resources (MNDNR) and conducted by researchers at the University of
Minnesota is examining the possibilities of the weevil Euryhchiopsis
lecontei as a biological control agent for EWM. Researchers have
examined nine lakes (eight in Minnesota and one in Wisconsin) that had
existing EWM and weevil populations.
Of the nine sites, the most pronounced weevil infestation was found in
Cenaiko Lake in Anoka County, Minnesota. Weevils caused severe damage to
the EWM plants in Cenaiko Lake, most likely resulting in the plants'
decreased abundance. EWM biomass (wet weight) at Cenaiko Lake declined
from 974 g/m2 in July 1996 to 239 g/m2 in September 1996 (Newman et al.,
1996b). Researchers estimate that the biomass in June 1996 (before
sampling) was close to 2,000 g/m2 (Newman et al., 1996b). In July
1996, EWM was approximately 50 percent of the total plant biomass in the
lake; by September 1996, this value had decreased to 14 percent.
Monitoring of Cenaiko Lake did not begin until June 1996 when a dense
population of weevils was discovered during reconnaissance studies for
introduction sites (Newman et al., 1996b). Cenaiko Lake was then added
to the list of regular sampling sites. Plant samples collected at
Cenaiko Lake, as well as at other sites, were processed for
invertebrates, plant biomass, and stem damage.
Because monitoring is still ongoing, sampling and data are limited for
this study. However, the preliminary results indicate the weevils in
Cenaiko Lake may be responsible for the natural decline of
EWM. |
REFERENCES
Aiken, S. G., P.R. Newroth, and I. Wile. 1979. The biology of Canadian
weeds. 34. Myriophyllum spicatum L. Canadian Journal of Plant Science.
59:201-215. Cited in Sheldon and Creed, 1995.
Creed, R.P., Jr., S.P. Sheldon, and D.M. Cheek. 1992. The effect of
Herbivore Feeding on the Buoyancy of Eurasian Watermilfoil. Journal of
Aquatic Plant Management 30:75-76.
Creed, R.P., Jr., and S.P. Sheldon. 1993. The effect of feeding by a
North American weevil, Euhrychiopsis lecontei, on Eurasian watermilfoil
(Myriophyllum spicatum). Aquatic Botany 45:245-256.
Creed, R.P., Jr., and S.P. Sheldon. 1994. The effect of two herbivorous
insect larvae on Eurasian watermilfoil. Journal of Aquatic Plant
Management 32:21-26.
Creed, R.P., Jr., and S.P. Sheldon. 1995. Weevils and watermilfoil: Did
a North American herbivore cause the decline of an exotic weed?
Ecological Applications 5(4): 1113-1121.
Grace, J.B., and R.G. Wetzel. 1978. The production biology of Eurasian
watermilfoil: a review. Journal of Aquatic Plant Management 16:1-11.
Cited in Creed and Sheldon, 1994.
Hanson, T., C. Eliopoulos, and A. Walker. 1995. Field Collection,
Laboratory Rearing and In-lake Introductions of the Herbivorous Aquatic
Weevil, Euhrychiopsis lecontei, in Vermont. Vermont Department of Environmental
Conservation, Waterbury, VT.
Kirschner, R. 1997. Personal communication. Natural Resources
Department, Northeastern Illinois Planning Commission, Chicago, IL. July
16, 1997.
Lillie, R.A. 1996. A quantitative survey of the floating-leafed and
submersed macrophytes of Fish Lake, Dane County, Wisconsin. Transactions
of the Wisconsin Academy of Arts and Sciences 84:111-125.
Lillie, R.A., and D. Helsel. 1997. A native weevil attacks Eurasian
watermilfoil. Wisconsin Department of Natural Resources Research
Management Findings 40(March): 1-4.
Nichols, S.A., and B.H. Shaw. 1986. Ecological life histories of the
three aquatic nuisance plants, Myriophyllum spicatum, Potamogeton
crispus, and Elodea canadensis. Hydrobiologia 131:3-21. Cited in Creed
and Sheldon, 1994.
Newman, R.M., K.L. Holmberg, D.D. Biesboer, and B.G. Penner. 1996a.
Effects of a potential biocontrol agent, Euhrychiopsis lecontei, on
Eurasian watermilfoil in experimental tanks. Aquatic Botany 53:131-150.
Newman, R.M., D.W. Ragsdale, and D.D. Biesboer. 1996b. Can Eurasian
Watermilfoil Be Managed in Minnesota by Biological Control With Native or
Naturalized Insects? Third progress report to the Minnesota Department
of Natural Resources, Ecological Services, St. Paul, MN.
Sheldon, S. 1995. The Potential for Biological Control of Eurasian
Watermilfoil (Myriophyllum spicatum) 1990-1995. Final report.
Department of Biology, Middlebury College, Middlebury, VT.
Sheldon, S.P., and R.P. Creed, Jr. 1995. Use of a native insect as a
biological control for an introduced weed. Ecological Applications
5(4):1122-1132.
Smith, C.M., and J.W. Barko. 1990. Ecology of Eurasian watermilfoil.
Journal of Aquatic Plant Management 28:55-64.
This case study was prepared by Tetra
Tech, Inc., Fairfax, VA, under the direction of Anne Weinberg in EPA's
Office of Wetlands, Oceans and Watersheds, Watershed Branch. The authors
extend their appreciation to those who helped to review the case study,
especially Robert Creed at Appalachian State University and Holly Crosson
of the Vermont Department of Environmental Conservation. To obtain
copies of this case study, contact your EPA Regional Clean Lakes
Coordinator, or request a copy from:
National Center for Environmental Publications and Information (NCEPI)
11029 Kenwood Road, Building 5
Cincinnati, OH 45424
FAX (513) 489-8695
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