Bio-control of Purple Loosestrife
Purple Loosestrife has proven itself to be an extremely invasive exotic
species, capable of crowding out native plant species from wetland habitats.
In many cases, these species are important to the survival of native fish
and wildlife species. Purple Loosestrife has just started to gain a foot
hold in the Rondeau Bay marshes. The densest growth occurs in McGeachy
Pond which drains directly into the provincially significant wetlands along
Rondeau Bay's northwest shore.
Acting
on concerns voiced by Rondeau Bay's sportsman community, the Rondeau
Bay Watershed Rehabilitation Program moved to curtail the spread of
this exotic. The RBWRP agreed to assist Jim Corrigan, a researcher
from University of Guelph's Environmental Biology Department, in determining
the effectiveness of Galerucella beetles in the bio-control of Purple
Loosestrife. On June 28th, 1994, 300 pairs of the beetle Galerucella
pusilla were released at McGeachy Pond. The beetles, still feeding
on Purple Loosestrife plant material that they were raised on in the lab,
were placed on Purple Loosestrife plants adjacent to a large, shallow,
"drainage-style" ditch. Unlike some experiments conducted elsewhere,
these beetles were not caged on the plants prior to release.
Monitoring
of the site during 1995 only revealed "windowing" and "shothole"
feeding damage which was attributed to the likely presence of the beetles.
Monitoring occurred again on July 4 and August 2, 1996. During the first
visit, a single larvae was found following a half hour search. During the
second visit, a single egg mass was located following 20 minutes of searching.
These results confirm that the beetles have successfully over-wintered
for two years at the site, a measure denoting successful establishment
at the site. Results to date, however, suggest that only a trace beetle
population exists at the site. Similar results have been noted at most
other southwestern Ontario sites despite tremendous successes observed
at other sites throughout the province. At this time, based on province-wide
observations, little growth of this population is expected and impact of
the beetles on the Purple Loosestrife at the site may be minimal. Continued
observations through the summer of 1997 will help to quantify the ability
of these beetles to successfully control the spread of Purple Loosestrife
in this locale.
On
August 13th, 1997, the RBWRP released approximately 2000 Galerucella
larvae of both leaf-eating species (pusilla and calmariensis)
adjacent to Rondeau Bay Estates at the north end of Rondeau Bay. These
beetles were harvested on loosestrife stalks clipped from the tremendously
successful Dixie Road site in Mississauga. This second release is expected
to be more successful than the first as the Dixie Road beetles have become
accustomed to Ontario’s climate and the larvae released will pupate in
the immediate vicinity of the release site ensuring that adults will be
able to locate other adults in order to produce offspring. Monitoring will
be conducted by volunteers.
More Web sites on Purple Loosestrife
More information on Purple Loosestrife Awareness
in the Rondeau Bay watershed
This page was developed by Donna Wonnacott, Stan Sowinski &
Vicki McKay
Last revised July 3, 1998