Urophora sirunaseva
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Common Name
Yellow starthistle gall fly
Weed Impacted
This fly attacks yellow starthistle. Larvae are associated with galls formed within seed heads. Galls are abnormal tissue growth that displace seeds and steal vital nutrients and energy away from normal plant growth and reproduction.
Insect Description
Adults are small, black flies, 3-6 mm (approx. 1/8 to 1/4 in) long, with dark wing bands and a yellow spot on the back. Larvae are maggot-like and found in galls within seed heads.
Life Cycle
U. sirunaseva completes two generations per year. Adults begin emerging from galls in the spring. Eggs are laid in the developing flowers of intermediate-stage, closed flower heads. A woody gall is formed around each larva, and the larvae feed within the gall on gall tissue. Multiple galls may be formed within a single seed head. Mature larvae overwinter and pupate within the galls.
Field Identification
The presence of U. sirunaseva in the field can be indicated by galls within the seed heads. U. sirunaseva is easily distinguished from the yellow starthistle peacock fly, Chaetorellia australis, by its much darker body color.
Availability
This agent is readily available in Washington, Idaho, Oregon, and California. Adults can be collected from May through August; infested seed heads can be harvested and moved to new sites in late winter. However, its redistribution may be unnecessary because of the superior impact by E. villosus.
Comments
U. sirunaseva is not abundant in the field, likely due to the success of other seed head insects like Eustenopus villosus. The potential of this fly to significantly impact yellow starthistle is apparently limited.
Using the Agent: Integrated Weed Management (IWM)
New releases of U. sirunaseva should only be made where other seed head agents (e.g. Eustenopus villosus) 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 Credits
Urophora sirunaseva adult - Eric Coombs, Oregon Department of Agriculture, bugwood.org http://www.insectimages.org/images/768x512/0022065.jpg
Urophora sirunaseva larva/gall - Charles Turner, USDA Agricultural Research Service, bugwood.org http://www.insectimages.org/images/768x512/0022064.jpg
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