Knapweed Insects (continued)
Knapweed Gall Flies
Urophora affinis (left) &
U. quadrifasciata (right)
Seed Head Gall Flies, Urophora affinis and U. quadrifasciata, attack the flowerheads of diffuse and spotted knapweeds. The
formation of seed head galls directs nutrients away from seed
production in attacked heads as well as in unattacked heads on
the same plant. Both flies are capable of developing in the same
plant, exerting a greater stress to these weeds. Because of the
widespread distribution of these two flies throughout the knapweed
infested areas of the U.S., we do not recommend further releases.
The Knapweed Flowerhead Weevils (on the previous page) would be a better choice.
Agriculture Canada released two seed head flies and a root boring
beetle in British Columbia against diffuse knapweed. Seed production
in field research plots declined approximately 97% from 1976 to
Knapweed Flower Moth
Metzneria paucipunctella, the Knapweed Flower Moth, lays eggs on developing knapweed
flowerheads. The larvae feed on the receptacle tissues of the
flower, eliminating seed production in the attacked head. The
larvae overwinter in the seed head and emerge the following summer
as adults. Because of high winter mortality of this moth in the
U.S., we do not recommend further releases. The Knapweed Flowerhead
Weevils would be a better choice. They are cold hardy and very effective.
Back to Knapweed Insects (main page).
Biological Control of Weeds, Inc.
1418 Maple Drive Bozeman, MT 59715