- Leafy Spurge
- Knapweeds
- St. Johnswort
- Yellow Starthistle
- Musk Thistle
- Canada Thistle
- Tansy Ragwort
- Toadflax
- Poison Hemlock
- Purple Loosestrife
- Educational Materials
(insect photographs)
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.

Knapweed Flower Moth
Metzneria paucipunctella
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 1988.

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
Phone 406-586-5111

Email: bugs@bio-control.com