Bangasternus orientalis 
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Common Name
Yellow starthistle bud weevil
Weed Impacted
This beetle attacks yellow starthistle. Larval feeding within the seed heads reduces seed production.
Insect Description
Adults are mottled brown weevils, 4-6 mm (approx. 3/16 to 1/4 in) long, with a short, blunt snout. Larvae are whitish grubs found within the seed heads; however, in the field these larvae may be virtually indistinguishable from the larvae of other seed head beetles.
Life Cycle
Overwintering adults appear on plants in the spring through early summer. Eggs are laid on young leaves under developing flower heads. Larvae hatch, tunnel into the stem, and ultimately into the flower head, where they feed on young seeds. Pupation occurs within the seed heads. New adults then exit the plant to overwinter.
Field Identification
Several insects have been released for control of yellow starthistle. B. orientalis can be distinguished from the other seed head beetles, Eustenopus villosus and Larinus curtus, by its much shorter and blunt snout. B. orientalis also has much shorter body hairs than E. villosus.
Availability
This beetle is readily available wherever yellow starthistle is found. Adults can be collected from spring through early summer. However, because its impacts are usually secondary relative to E. villosus, and because it is likely already present at most starthistle sites, redistribution may be unnecessary.
Comments
B. orientalis was one of the first biocontrol agents introduced for yellow starthistle, and it was abundant in the field after its initial release (1985). Since then it has been displaced at most sites by E. villosus, and now only occurs in relatively low numbers.
Using the Agent: Integrated Weed Management (IWM)
New releases of B. orientalis should only be made where other seed head agents (E. villosus, Chaetorellia australis) have not established. Releases should be made at sites where yellow starthistle 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
Bangasternus orientalis adult - Charles Turner, USDA Agricultural Research Service, bugwood.org http://www.insectimages.org/images/768x512/0022051.jpg
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