Species Urophora quadrifasciata - Four-barred Knapweed Gall Fly

Urophora quadrifasciata (Meigen 1826)

2-3 mm

Native to Europe, introduced in NA in 1988 to control knapweeds (now across most of the US)

Introduced to control knapweed (Centaurea spp.)

Two generations a year. Overwintering generation emerges as adults from galls in the mature seedheads in the spring when new flower buds are beginning to form. Female fly uses her ovipositor to penetrate half grown flower buds it lays eggs among the developing stamens. May lay more than one egg per seedhead. Eggs hatch in three to four days and larvae chew down in a floret into the ovary causing the plant to start forming a gall about eight days after larvae hatched.

U. affinis has less extensive wing markings

Fact sheets: R.F. Lang(1) • M.B. Sacry(2)