Eustenopus villosus
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Common Name
Yellow starthistle hairy weevil
Weeds Impacted
This weevil attacks yellow starthistle and a few other non-native species of the genus Centaurea. Both larvae and adults suppress the spread of new plants by interfering with seed production. Adults feed on and destroy young seedheads; larvae feed inside the flower heads and can reduce seed production by up to 100% in the infested heads.
Insect Description
Adults are hairy, brown weevils with white-colored stripes running the length of their backs. Not including their long, slender snouts, they are 4-6 mm (approx. 1/8 to 1/4 in) long.
Life Cycle
Adults are active from May through August. Females lay eggs early to mid-summer by chewing holes in mature seed head buds, depositing single eggs inside, and then covering the hole with sticky, chewed plant material. Eggs hatch in three days, and larvae begin feeding within the flower head on developing seeds. New adults emerge in three to four weeks and then overwinter under plant litter near the host plants.
Field Identification
The presence of E. villosus on yellow starthistle can be determined by holes in seed head buds where eggs have been laid, or by deformed, crook-shaped buds (caused by chewing/egg laying). Adults are easily recognized by their long hairs and whitish stripes.
Availability
This beetle is readily available. Adults are typically collected from early to mid-summer. To inquire about availability and to request this biocontrol agent, please download, complete and submit this form.
Comments
E. villosus has readily established and built up strong populations at most release sites, and thus has excellent potential to serve as an effective biological control agent. Some collection sites in Washington and Oregon are no longer available due to declining yellowstar thistle populations.
Using the Agent: Integrated Weed Management (IWM)
New releases of E. villosus should only be made where weed infestations are large and immediate eradication is not a primary objective.
Individual plants and smaller, satellite populations can either be hand-pulled or sprayed, although studies have shown that yellow starthistle can develop resistance to some herbicides. Consult with your county weed office, Extension office or an IWM practitioner to determine which herbicide treatments are safe and appropriate.
Any management of yellow starthistle should involve revegetation with native or other desirable plants, especially grasses. Competition between plants stresses weeds and can allow 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.
Gibbs, L.A., M.W. Murray, T.M. Sterling, and N.K. Lownds. 1995. Comparison of picloram-resistant and -susceptible yellow starthistle in a replacement series. Proceedings, Western Society of Weed Science 48:26.
Sterling, T.M., N. K. Lownds, E.P. Fuerst, T.S. Prather, and R.H. Callihan. 1991. Potential mechanism of picloram resistance in yellow starthistle (Centaurea solstitalis L.). Weed Science Society of America Abstracts 31:80.
Photo Credit
Eustenopus villosus adult - J. Andreas, WSU Extension
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