GENEALOGY
Original source for U.S.
release was Australia. First U.S. release occurred in California in 1946.
In 1949 Chrysolina was brought to Stevens County, and was the first
BioControl agent ever released in the county. Established in California,
Idaho, Montana, Oregon, and Washington. Widespread in Stevens County,
these agents are everywhere they are going to be.
LIFE CYCLE
These agents have a somewhat
confusing life cycle. Females may lay eggs in fall or spring. It’s
possible to find eggs, larvae, or adults year round. Any of the three
stages may overwinter. Sunlight kills the larva, but the adults avoid
shade. Adults enter the soil and become dormant during summer. Fall and
Spring rain is thought to stimulate them to emerge, mate, and lay eggs.
Eggs are deposited singly or in clusters of 2-4 on the underside of leaves
in the fall or spring. A female can lay hundreds of eggs in her lifetime.
Eggs are oval in shape, and orange in color. When the eggs hatch the
larvae start feeding on younger leaves. Larvae hide from the sun during
the day under leaves or in the soil. When the larvae are mature they
construct cells in the soil and change into adults. Adult beetles are
metallic green, blue, bronze, or black in color, and about 5 to 7 mm long.
EFFECT
Both adult and larvae consume
the leaves of St. Johnswort. Larvae feed nocturnally, adults feed during
the day.
REDISTRIBUTION
Shake adults off into a sweep
net, pan, or funnel assembly. You can collect adults from St. Johnswort
blooms in June. Sometimes dozens of adults can be collected from a single
plant. Their presence from year to year is variable.
COMMENTS
These agents devastated St.
Johnswort in areas that had a favorable weather and rain pattern. Parts of
California and western Oregon are examples. Chrysolina did so well in
California that a monument was erected in it’s honor. Unfortunately, the
agents life cycle is often out of synchronization with the weather
patterns of the inland northwest, and this serves to disrupt the impact of
the agents from year to year . Overall, these agents have reduced St.
Johnswort in Stevens county, but expect their effect and population to
vary from year to year.
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