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Terellia virens
Biological agent type
Seed head fly.
 
Plant species attacked
spotted knapweed (Centaurea stoebe)
 
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Terellia virens adult
Terellia virens adult
Images by Eric Coombs, Oregon Department of Agriculture.
Terellia virens larvae
If images are downloaded and used from the ODA web site please be sure to credit the photographer.
Site of attack
Seed.
 
Mode of attack
The larvae feed on seeds in the flower head.
 
Destructive stage
Larval-internal.
 
Collection and release information
The flies are collectible in Lane County at the Cougar Reservoir site.  Collection can be done with a sweep net during adult stage in June-July. Consult with ODA for availability for your area.
 
History in Oregon
The seed head fly Terellia virens was released in Hood River, Lane, and Deschutes Counties in 1993. Adults were recovered at all sites.  The fly also attacks diffuse knapweed. The mobile larvae feed on the developing seeds and are less vulnerable to predation by Metzneria larvae than the Urophora larvae.
 
Release status in Oregon
 
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distribution map