GENEALOGY
Original sources for
U.S. release was Austria, Greece, Hungary, and Romania. First U.S.
releases made in 1988. Now established in Colorado, Montana,
Oregon, and Washington. There are populations established in
Stevens County.
LIFE CYCLE
In Stevens county,
overwintered adults emerge from the knapweed roots mid to late
July and into September. Mature adults are up to 20 mm long. They
feed on younger leaves if available, leaves, and tissue from the
stems. Females place a single egg in a chewed out hole on the root
crown just below soil level. She may produce more than 100 eggs in
her lifetime. Adults die before winter. When the eggs hatch the
larvae begin tunneling into the knapweed roots. The larva
overwinters in the root.
EFFECT
The larval root
tunneling severely damages the weed. Adults eat above ground plant
parts.
REDISTRIBUTION
This agent does not fly
and spreads slowly if not manually redistributed. Not easy to spot
in the field due to it’s mottled color and habit of sitting
perfectly still. When disturbed they often drop to the ground.
Best chance to see and collect them is in the heat of the day. To
collect, quickly bend the entire plant over into a collection net
or pan. It is harder to hand pick them. They have a powerful grip
but do not bite. For making a new release 50 adults is considered
a workable number. A new colony stands the best chance of survival
and establishment at new sites which are dominated by Diffuse
Knapweed, spaced enough (1-2 feet) to allow the soil to become hot
and dry. South facing slopes and/or large open fields of knapweed
are best. A site free of disturbance (including development,
traffic, herbicides, and regular grazing) increases the chances of
establishment.
COMMENTS
The year 2000 marked
the beginning of an effort to distribute this agent in Stevens
County. Although Cyphocleonus achates is an excellent agent once
established, it’s inability to fly to new weed patches is a
drawback. Therefore, the seed head weevil Larinus minutus (a
strong flyer) has proven to be a more valuable natural enemy
against Diffuse and Spotted Knapweed.
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Cyphocleonus achates
Cyphocleonus achates
Root damage |
