GENEALOGY
Original source for
U.S. release was Greece. First U.S. releases were made in 1991.
Now established in Montana, Oregon, and Washington. In Stevens
County, starting in 2000, this has been the most heavily collected
and redistributed agent of all time. It is now well established
throughout the county, and needs little assistance.
LIFE CYCLE
Overwintered adults
emerge from the ground litter in late May or June and begin
feeding. Females lay clusters of eggs in open flowers. When the
eggs hatch the larvae start feeding on flower parts and immature
seeds. The larvae are aggressive and kill one another and other
species within the seed head. The surviving larvae feed and go
through numerous changes. Pupation into an adult takes place
inside a cocoon made of chewed seed and flower parts and is
attached to the flower receptacle. The new adults emerge from
their cocoon in July and August. These adults feed before going
into the ground litter to hibernate.
EFFECT
Both adult and larvae
are destructive to Diffuse and Spotted Knapweed. Adults feed on
young leaves in spring, and leaves and flowers later on. A larva
often destroys all the seeds in it’s seedhead.
REDISTRIBUTION
June and early July are the best times to collect this agent. The
females have more egg laying ability at these times. A good
collection method is to bend the entire plant over into a sweep
net or container and shake the agents off. Place bugs in a paper
sack with a little food (knapweed) and some water (a clean
moistened sponge) for the trip to the new release site. Keep the
bugs cool during their captivity. New release sites should closely
resemble the environment from which the insects were collected.
Generally this will be open, sunny knapweed patches, where plants
are spaced enough for the ground between to be hot and dry.
Release about 250-500 adults for each new site.
COMMENTS
The year 2000 marked
the beginning of an effort to widely establish this agent
throughout Stevens County. Over the years they have proven to be
the best available BioAgent for Diffuse and Spotted Knapweed in
our area. The insects are probably now established everywhere they
are going to establish in Stevens County. Their impact is visible
throughout numerous areas. They need little further assistance. As
their populations increase over the coming years their impact
should become significant throughout the county.
MSdoc
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Larinus minutus
Larinus minutus
Larinus minutu
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on Diffuse Knapweed
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