Agrilus hyperici 
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Common Name
St. Johnswort root borer
Weed Impacted
Larvae feed within the roots of St. Johnswort (Klamath weed, goatweed) and may completely consume the root. Most plants infested with these larvae die. A. hyperici attacks one native St. Johnswort (Hypericum concinuum) in California, but no long-term impacts have been reported.
Insect Description/Field Identification
Adults are dark, metallic bronze beetles, about 5 mm (approx. 3/16 in) long, elongate and somewhat flattened. Larvae are small white grubs found within the roots.
Life Cycle
Adults emerge in July and are active through early August in the warmest hours of the day. Females lay eggs in July and August on stems between soil level and 20 cm (approx. 8 in) above. Larvae then feed in roots from July until May or June of the following year, when they pupate within the damaged roots. Pupation lasts from 9 to 15 days.
Availability
These beetles have established in Washington, Idaho, Oregon, Montana, and California, but availability is currently limited. Adults are collected in July and August. To inquire about availability and to request this biocontrol agent, please download, complete and submit this form.
Comments
A. hyperici will attack plants growing in the shade, which are normally not attacked by Chrysolina spp.
Using the Agent: Integrated Weed Management (IWM)
A. hyperici should only be released at sites where St. Johnswort infestations are large and immediate eradication of the weed is not the primary objective. These beetles can be used with other St. Johnswort insects and can be especially effective where St. Johnswort plants grow in the shade.
Smaller populations of the weed can either be hand-pulled or sprayed, provided that chemicals will not leach or runoff into water resources. Consult with your county weed office, Extension office or an IWM practitioner to determine which herbicide treatments are safe and appropriate.
Mowing before the plants go to seed can help reduce spread of the weed; burning is not recommended as it can actually increase plant growth. Any treatment, whether biological, chemical, or otherwise, should include revegetation with native or other desirable plant species in order to promote plant competition. Competition stresses weeds, allowing for more effective treatment. For more information about revegetation, click here.
References
Coombs, E. M., J. K. Clark, G. L. Piper, and A. F. Cofrancesco, Jr. 2004. Biological Control of Invasive Plants in the United States. Western Society of Weed Science, Oregon State Univ. Press, Corvallis.
Photo Credits
Agrilus hyperici adult - Norman Rees, USDA Agricultural Research Service, bugwood.org (insectimages.org), http://www.insectimages.org/images/768x512/0025019.jpg
Agrilus hyperici larva - Norman Rees, USDA Agricultural Research Service, bugwood.org (insectimages.org), http://www.insectimages.org/images/768x512/0023015.jpg
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