Two insect species that act as natural enemies of musk thistle in
Europe have been imported to the United States. These weevils are
reared and released into areas infested with musk thistle. Once
established, these biological control agents can provide long-term
control of the weed because they reproduce and spread on their own.
The thistle head weevil (Rhinocyllus conicus) feeds on the
base of the flower heads, reducing the ability of musk thistle to
produce seeds. This insect can reduce musk thistle stands by up
to 95%. However, this weevil also feeds on native thistles and there
is some concern that it can decrease populations of rare species.
The rosette weevil (Trichosirocalus horridus) burrows into
the thistle rosette and feeds on its growth tissue. This insect
can kill first-year rosettes and stop the growth of older plants.
It is also effective in controlling plumeless thistle.
Introduction
Two insect species that act as natural enemies of musk thistle in
Europe have been imported to the United States. These weevils are
reared and released into areas infested with musk thistle. Once
established, these biological control agents can provide long-term
control of the weed because they reproduce and spread on their own.