Chaetorellia acrolophi 
<<back to spotted knapweed
Common Name
Knapweed peacock fly
Weeds Impacted
This fly prefers spotted knapweed, but can also attack diffuse knapweed, squarrose knapweed, purple starthistle, and two other species of Centaurea (both non-native). Larvae reduce seed production by feeding on seeds.
Insect Description
Adults are amber-colored flies, 4-5 mm (approx. 3/16 in) long, with green eyes and light-brown banded wings. Larvae are whitish or yellow-colored and found within the seed heads.
Life Cycle
In its native range (Europe), C. acrolophi completes two generations per year. Adults usually appear in the field in May, and females lay eggs about one week after emergence. Eggs are deposited under the bracts of closed knapweed buds and hatch after four days. Young larvae burrow into and begin feeding within flower heads. Older larvae feed on developing seeds and other structures, often completely destroying the contents of the flower head. Complete larval development takes 10 to 15 days. Larvae overwinter in seed heads and pupate within them the following spring.
Field Identification
C. acrolophi adults are similar in appearance to several other knapweed flies, including Terellia virens and two species of Urophora (U. affinis and U. quadrifasciata). Generally, C. acrolophi is lighter in color than either Urophora species, both of which are dark brown or blackish (also, Urophora larvae form galls on flower heads instead of feeding within them). The presence of wing bands distinguishes C. acrolophi from T. virens , which has clear wings. Urophora spp. are typically much more common in the field than either C.acrolophi or T. virens. Contact a professional entomologist or trained biological control practitioner for positive identification.
Availability
This fly has established in Washington, Oregon, Wyoming, and Colorado, but its availability for redistribution is currently limited. Infested seed heads are harvested in the fall or early spring. To inquire about availability and to request this biocontrol agent, please download, complete and submit this form.
Comments
This agent is most effective on cool, wet sites. C. acrolophi has a difficult time establishing where other seed head agents (i.e. seed head weevils and moths) are present.
Using the Agent: Integrated Weed Management (IWM)
Several insects have been released for biological control of knapweed. C. acrolophi should only be released where other seed head agents have not established. Releases should be made where knapweed infestations are large and immediate eradication is not the primary objective.
Smaller, satellite knapweed populations can either be hand-pulled or sprayed. Consult with your county weed office, Extension office or an IWM practitioner to determine which herbicide treatments are safe and appropriate. Chemical applications on larger infestations should only be made after insect agents have definitively established, and then should be timed according to the life cycles of both the plant and the insect.
Mowing will not control knapweed, and mowing while plants are flowering interferes with the maintenance of strong agent populations. Prescribed burning may destroy aboveground parts, promote germination of existing seeds, and facilitate earlier treatment of developing plants. However, burning also increases the susceptibility of sites to new invasions by knapweed or other weeds.
Any management of knapweed should involve revegetation with native or other desirable plants, especially grasses. Revegetation promotes competition between plants, which 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.
Waldo, A. J. 2003. Identification and Control of Knapweed Species in Central and Eastern Oregon. Oregon State Univ. Extension Publication EC 1559. URL http://extension.oregonstate.edu/catalog/html/ec/ec1559/
Photo Credit
Chaetorellia acrolophi adult - CABI Biosciences archive photo, bugwood.org (insectimages.org), http://www.insectimages.org/images/768x512/0886056.jpg
Secondary content using h2 tag. Column 2
Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.
Heading using the h3tag
Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.