Larinus curtus
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Common Name
Yellow starthistle flower weevil
Weed Impacted
This beetle attacks yellow starthistle. Larvae feed on developing seeds and can reduce seed production by up to 100%.
Insect Description
Adults are dark brown or black weevils, 5 to 6 mm or approximately 1/4 in long (not including the snout), and are often speckled with pollen.
Life Cycle
Adults are active from June to early August, feeding on yellow starthistle flowers and pollen. Females lay eggs at the base of flowers in heads with open flowers. Eggs hatch after about four days, and larvae begin feeding on developing seeds. Larvae complete development in two to three weeks. Pupation occurs in chambers formed within seed heads, and the pupal stage lasts about five days. New adults emerge from seed heads, feed, then overwinter under plant litter near the host plant.
Field Identification
L. curtus is one of three weevils that have been approved for control of yellow starthistle. In the field, it can be distinguished from both Bangasternus orientalis and Eustenopus villosus by its darker color (may also occasionally appear yellow when it is completely covered with pollen). It is also has much shorter hairs than E. villosus.
Availability
This biocontrol agent is no longer being distributed in Washington.
Comments
This beetle has done best in the Columbia Gorge and Snake River areas of Washington and Oregon, but has failed to build strong populations elsewhere.
Using the Agent: Integrated Weed Management
L. curtus should only be released where other seed head beetles (E. villosus , B. orientalis) have not established. Releases should be made at sites where yellow starthistle infestations are large and immediate eradication of the weed is not the primary goal.
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
Larinus curtus adult - G. R. Johnson, USDA Agricultural Research Service, bugwood.org (insectimages.org), http://www.insectimages.org/images/768x512/0022061.jpg
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