Agapeta zoegana
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Common Names
Sulfur knapweed moth, yellow-winged knapweed root moth
Weeds Impacted
This moth attacks spotted and diffuse knapweed. Larvae feed within the roots (root mining), robbing the plant of nutrients and energy reserves, resulting in decreased plant biomass and density. Larval feeding can cause death in small plants and in plants infested with multiple larvae.
Insect Description
Adult moths are 11 mm (7/16 inch) long, yellow and distinctively marked with brown markings. Larvae are cream-colored caterpillars with brown head capsules and are found within knapweed roots.
Life Cycle
Adults emerge over a 12-week period from mid June to early September. Females mate within 24 hours of emergence and lay eggs one day later. Eggs are laid on the stems and leaves of knapweed and hatch in 7 to 10 days. Larvae migrate to the root crown area and begin mining the root, where they overwinter and pupate in the spring.
Field Identification
Agapeta zoegana larvae may occur with the larvae of two other knapweed root-feeding insects, the root borer Sphenoptera jugoslavica and the root weevil Cyphocleonus achates. Agapeta zoegana larvae have a distinct, brown head capsule, and are straight and elongate, rather than widened toward the head (S. jugoslavica) or C-shaped (C. achates). They are also generally much smaller than C. achates larvae.
Availability
Although, A. zoegana is becoming widespread, few sites have populations abundant enough for collection, making availability limited. Adults are collected in early August. To inquire about availability and to request this biocontrol agent, please download, complete and submit this form.
Comments
This moth has reduced knapweed biomass and density in western Montana. It does best in dry, well-drained, open sites with scattered vegetation.
Using the Agent: Integrated Weed Management (IWM)
Agapeta zoegana should be only be released at sites where knapweed infestations are large and immediate eradication of the weed is not the primary objective. Moths can be used with other knapweed insects. Most treatments are not directly compatible with the use of this biocontrol agent. Any control methods that directly kill the plant will reduce or eliminate biocontrol populations. Biocontrol agents can be used within large patches and satellite patches (which lead to increased spread) can be controlled using other management tools.
Small or satellite knapweed populations can be either hand-pulled or sprayed. A selective herbicide should be used to avoid diminishing the effects of strong grass competition. Consult with your county weed office, Extension office or an IWM practitioner to determine which herbicide treatments are safe and appropriate.
Any treatment regime, whether biological, chemical, or otherwise, should include revegetation with native or other desirable plants to promote plant competition. Competition stresses weeds and allows for more effective treatment. To learn more about revegetation and IWM, 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
Agapeta zoegana adult - Dimitri Geystor, http://www.galerie-insecte.org/galerie/image/dos12/big/agapeta1.jpg
Agapeta zoegana larva - USDA archive photo, uwadmnweb.uwyo.edu, http://uwadmnweb.uwyo.edu/capsweb/wyo_bio/WYO_BIO_PICS/agapeta_zoegana_larva.jpg
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