| Biological
control of purple loosestrife using leaf- feeding beetles |
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Quick
facts
Natural
enemy: Galerucella
calmariensis and Galerucella pusilla
Common names: Black-Margined
Loosestrife Beetle, Golden Loosestrife Beetle
Class:,
Order:, Family:
Insecta, Coleoptera: Chrysomelidae
Pest:
Purple Loosestrife (Lythrum salicaria) an exotic invasive
plant species infesting wetlands, wet meadows, ditches, and shallow
margins of ponds and lakes.
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Description
Both
loosestrife beetles are similar in appearance and range from 3-6 mm
(1/8-1/4 inch) in length. They are about half as wide as they are
long. Coloration is light brown or tan. The black-margined loosestrife
beetle (G. calmariensis) typically has a dark stripe on each
side of the body when viewed from the top. The golden loosestrife
beetle (G. pusilla) is usually uniform in coloration. Because of variable
color characteristics it is difficult to differentiate between the
two species in the field. |
Above,
Galerucella adult and below, larvae
Photos by Kurt Stepnitz, MSU
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| Biocontrol
significance |
In
the spring, adult loosestrife beetles chew holes in purple loosestrife leaves
but do little real damage to the plant. However, young larvae feed on shoot
tips (apical meristems) of the purple loosestrife plant stunting its growth.
Older larvae can cause 100% defoliation of leaf and stem tissues, causing
desiccation and severe plant stress. Large numbers of newly emerged adults
can cause further defoliation. Localized reductions in plant height and
flowering may occur as early as the season following release. Typically
it takes three to five years for populations of loosestrife beetles to build
to levels that kill plants. In the first one to two years following release,
adult beetles tend to move less than 100 m from the initial site of release.
As the population increases, beetles may move larger distances (up to a
few miles). As beetles begin to stunt loosestrife plants, other previously
suppressed wetland plants can grow. Over time, when loosestrife plants are
killed outright, additional plants can sprout from seeds, tubers etc. |
| Life
history |
In
spring (late April to early June) overwintering adults emerge from soil
and litter, feed for several days on purple loosestrife foliage and reproduce.
In MN the beetles have been observed to occur about the time that French
lilac blooms. After mating, females lay eggs in small masses, which may
be on leaves or stems. The egg-laying period lasts from mid-May to mid-July
with the peak three to four weeks after initial emergence. An average female
may lay 300 to 500 eggs during this period. Larvae emerge from eggs in 7-10
days and feed on tissues of developing shoots and leaves. Larvae feed for
three to four weeks, going through three instars before moving down into
the soil or plant litter to pupate. Upon emergence the new adults feed for
several days to weeks before moving into the litter or soil below to overwinter.
This period of emergence occurs typically from July to September. The total
maturation time from egg to adult is approximately 40-60 days. A second
generation has been observed in some years and locations. |
Recommendations
for use |
For sites with fewer than 100 plants, hand removal or
spot treatment with registered herbicides is recommended. For larger infestations,
release of loosestrife beetles is recommended. Releases are typically
of pupae and adult beetles. The larger the numbers released, the better
the chance for establishment. A minimum of 2,000 to 3,000 beetles per
site are recommended. Releases in successive years will improve the chance
for establishment. Larger sites (greater than 5 acres) will benefit from
multiple releases of 2,000 to 3,000 beetles at various locations within
the site.
Beetles may be released at any time after purple loosestrife
emerges in the spring until late August. Beetles released prior to the
summer solstice (June 21) may reproduce and show significant increase
in the year of release. Beetles released after the summer solstice are
likely to feed and overwinter without reproducing. These same beetles
will reappear the following spring to restart the cycle.
Place release containers at the base of purple loosestrife
plants and allow beetles to emerge naturally onto the foliage. Concentrating
beetles on a few plants is recommended. Place 1,000 to 3,000 beetles on
or near an individual plant and allow them to redistribute naturally.
Releases of adults made during cooler times of the day help to discourage
rapid long-distance flights.
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| Suggestions
for enhancing impacts |
Do
not attempt to establish loosestrife beetles in sites where insecticides
are used, i.e. mosquito adult sprays. Insecticide for larval mosquito control
are unlikely to harm loosestrife beetles Success has been seen at both wet
and dry sites. Establishing beetles into mixed stands containing desirable
vegetation will likely encourage more rapid habitat restoration. Further
restoration efforts may be needed where loosestrife has existed as the predominant
plant or where other exotic invasive species occur. |
| Sources
of natural enemies |
Loosestrife
beetles are not commercially available at present. Field insectaries have
been established in many states. Contact your state Department of Natural
Resources or Agriculture to determine availability in your area. |
| More
information and selected references |
Illinois Natural
History Survey http://www.inhs.uiuc.edu/cbd/loosestrife/bcpl.html
Biological Control
of Purple Loosestrife: A Guide for Rearing of Leaf-Feeding Beetles. 1998.
A. Loos and D. Ragsdale. http://www.extension.umn.edu/distribution/horticulture/DG7080.html
The Purple Loosestrife
Project Cooperators Handbook. 2000. Michigan State University Extension
Bulletin E-2690 sections 1-5. MSU Extension Bulletin Office, E. Lansing
MI, 48824. (517) 355-0240.
http://www.msue.msu.edu/seagrant/pp/
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| Prepared
by |
David
Ragsdale, Robert Wiedenmann and Doug Landis. Copyright
and reprint information. (Last update September 1, 2000) |
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