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Urophora cardui

Common names:   Thistle stem gall fly
Size:   5 to 8 mm long
Plant species:   Canada Thistle
Life stages:   Egg: Between 1 and 30 eggs are laid in the shoots at any time during the host's warm, active growing season
    Larva: Larvae tunnel into stems and form galls. Multiple larvae are found in one gall. Overwintering occurs in this stage.
    Pupa: Pupation occurs in the galls in the early spring, and lasts 24 to 35 days at 64 to 68 degrees F.
    Adult: Adults emerge in the late spring and early summer.
Site of attack:   Stem.
Impact on host:   Gall acts as a metabolic sink, reducing host's vigor, making it less able to compete with favorable vegetation. Increased vulnerablility to pathogens and other biocontrol insects. Stems above the galls are retarded and may be unable to produce seed heads.
Habitat:   Disturbed, high-density areas, close to moisture (either high relative humidity or available surface water). Shade preferred. Areas that are flooded, grazed, mowed or treated with herbicide are not conducive to fly survival. Areas which experience very cold winters and dry, hot summers are not conducive to species survival.
Redistribution:   Collect galls in the fall, winter or early spring. Store in paper sacks or cardboard boxes at 39 to 46 degrees F. Galls must remain moist during storage.
Source: Biological Control of Weeds in the West, N.E. Nees,


Harney County Weed Control
450 N Buena Vista Ave.
Burns, OR 97720
Phone: (541) 573-2506
Fax: (541) 573-8387

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