St. Johnswort Beetle
Insect: Beetle (Coleoptera: Chrysomelidae)
Photo By: Stevens County Noxious Weed Control Board, WA.
Origin: Northern and central Europe and western Asia. (1)
Over the wintering stages: Chrysolina hyperici could be an egg, larva, or at times an adult. (1)
Egg stage: In the fall the eggs are laid on leaves of the St. Johnswort weed. This only happens in their native country Europe, and were they were released in California and Oregon. The eggs are laid in the spring in the other parts of north western United States. The females deposit hundreds of eggs either one at a time or in a cluster. The eggs don't hatch for six or seven days. The eggs are long and orangish in color. (1)
Larval stage: After hatching the larvae eat the leaf buds. They eat all the leaves off, and then move to another plant before they mature. Larvae dig down into the soil, make cells, and then finally pupate when they are mature. They are fat and C-shaped. They become a grayish-pink. They can resemble larvae of the C. quadrigemina species. (1)
Pupil stage: They are pupils for about 12 days in the late spring. (1)
Adult stage: The adults feed for weeks in the spring. Then the go back into the soil to rest in the summer. When it starts to rain in the fall season the beetles emerge, mate, and lay eggs. If it doesn't rain then they will mate and lay eggs in the spring. They can be about five millimeters long and they are metallic colors. (1)
Type of Damage to Host: Larvae: They eat the roots of the weed. This destroys the growth of the weed almost completely in the spring.
Adult: They eat the buds, which also destroys the weed.
Plant Species: St. Johnswort
Location: Buds and roots. (2)
Host Impact: In the fall the adults dig a whole and stay there until the fall or spring rains. They then mate and lay their eggs on the leaves of the St. Johnswort. Once they hatch the larvae start to eat the leaves. They usually eat in the fall on the lower roots. If they feed in the spring the weed can outgrow the damage that the insects did to it. (1)
Release Habitats: The beetles like moist or dry regions. They don't like shaded, rocky areas, or bare lands. (1,2)
Collecting, Transporting, and Releasing: You collect the adult beetles by using a sweep net. (3) They can be kept for several weeks in a cool place such as a refrigerator for two weeks. They can be transported over several days (in a cooler with an ice pack) with out any effect on them. (1)
Redistribution: You should release the adults in groups of 250 or more to one infested area. (3)
Purchasing: If you would like to purchase Chrysolina hyperici you can contact your local extension office. You can also go to one of these web sites: Bio-control, Integrated Weed Control.
Remarks: Chrysolina hyperici likes the more moisture places. Feeding in the fall and winter makes the plant incapable to survive the heat of the hot summer. (1)
1. Rees, Norman, et. al., Ed., Biological Control of Weeds in the West, Western Society of Weed Science, in Cooperation with USDA ARS, MT Dept. of Ag, and MT State Univ., Color Printers, Bozeman, MT, Feb., 1996.
2. Syrett, P., Hort Research, [website], Available: http://www.hortnet.co.nz/publications/hortfacts/hf401050.htm, 1998
3. Harris, P., Lethbridge Research Center, [website], Available: http://res2.agr.ca/lethbridge/weedbio/agents/achryhyp.htm, Last updated: 12/28/2000
By: Heidi Uptmor 2/26/02
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