Urophora quadrifasciata
seed head gall fly
Diptera: Tephritidae

Biological Control Links     Photos: [spotted knapweed]
[larva/galls]     [galls/knapweed seeds]     [Urophora  affinis]

Photo by: Bob Richard, USDA-APHIS-PPQ.

Origin: Native of Europe. (10)

Life Cycle: In summer the adult, female gall fly lays her eggs upon the knapweed flower buds, among the developing stamens.  She can lay one egg per seed head, or more.  The eggs hatch within three to four days (1) and live off of the floret of the plant all summer and fall.  The insect overwinters as a larvae in a gall in the seedhead and pupates in early spring.  The adults emerge timed with flower budding of knapweed in late spring/summer.  The adult form of the gall fly lives about fifteen days after the emerging.  The gall fly can produce two generations before a new year is up. (3)

Over Wintering State: In the over wintering stage the gall fly spends time as a mature larva in the seed heads of the plant. (3)

Egg Stage: After mating the female flies to a half grown bud and lays her eggs.  The eggs hatch in three to four days. (3)  She can lay up to 366 eggs but the average is around 130 eggs.  Each bud can hold close to 14 eggs.  (10)

Larva Stage: The larva is a white color and has a brown anal plate. (1)

Pupa: The larvae pupate in the galls within the seed heads in early to mid spring. (3 )

Adult Stage:  The adults emerge from pupa in spring and summer timed so that they can lay their eggs on flower buds. (3)

Damage to Host: The larva will feed on seeds and damage them and cause galls in the seed head that stress the plant. (2)  For ever gall formed 1.9 seeds are damaged in the seed head.   There are reports of the  U. quadrifasciata, with U. affinis, killed 95% of the seed heads in two British Columbia sites. These flies are most effective when combined with other bio-agents and including the root borers.  These flies them selves do not control knapweed spread in Montana. (3)

Host Impact: The adults lay their eggs in the developing stamens. Then when the larva hatches and eats the floret of the plants flower.  This effects the plant so it can't grow as well, spread seed or come back the next year as well. (3)

Release Habitats: The best places to release is where they can adapt and survive.  They mostly live in the Midwest and western states.  Some of this states are Arizona, California, Colorado, Idaho, Michigan, Minnesota, Montana, Nebraska, North Dakota, South Dakota, Utah, Washington, Wisconsin, and Wyoming.  Some eastern states are Indiana, Maryland, New York, Pennsylvania, Vermont, New Hampshire, Massachusetts, Rhode Island, Connecticut, and New Jersey.  They are well adapt to sunny areas rather than shaded sites.  The area you are releasing the flies on should be an area that won't be disturbed in at the least the next ten years.  The best time is in the spring. (3)  We find these where ever knapweed occurs in Montana and do not need to release them any more.  They can disperse them selves just fine now. (Mr. Breitenfeldt)

 How to collect: To collect the larvae you can hand pick the heads of spotted or diffuse knapweed in fall, winter or early spring.  Store these in a refrigerator until early spring and then set them out in tied bouquets so they can pupate and the adults can emerge at the proper egg laying time.  This is the most efficient way.
    Also, you can sweep net the seed heads for adult flies in the spring and summer.  Release these quickly onto new sites. (10)
    We find these where ever knapweed occurs in Montana and do not need to release them any more.  They can disperse them selves just fine now. (Mr. Breitenfeldt)

 Comments: Part of the floret well be ruined by the larva.  Because of this the gall forms a nutrient sink and the whole plant is effected. U. quadrifasciata can be obtained from almost any knapweed plant in Montana.  They fly great distances to get to the knapweed patches.  They spread into the U.S. from releases in Canada.  This is not the best defense against knapweed but it is still a well known agent that somewhat helps control the weed.  (10)  These seed head feeders in combination with the root borers is a good one-two punch that is working well (but slowly) on many sites in Montana!  (Mr. Breitenfeldt)

1)  http://www.bioimages.org.uk/HTML/R32172.HTM
2)  http://www.maes.msu.edu/nwmihort/cff_gallfly.html
3)  http://www.nysaes.cornell.edu/ent/biocontrol/weedfeeders/
4)  http://ag.montana.edu/warc/biocontrol_agents_of_knapweed.htm
5)  http://www.nysaes.cornell.edu/ent/biocontrol/weedfeeders/urophora_quad.html
6)  http://www.invasive.org/browse/detail.cfm?imgnum=1350080
7)  http://ucsub.colorado.edu/~honors/theses/s98/gregory.html
8)  http://cedarcreek.umn.edu/insects/album/029061003ap.html
9)  http://www.for.gov.bc.ca/hfp/noxious/Bioagents/Short/u3.htm
10) http://www.invasive.org/eastern/biocontrol/13Knapweed.html

(1)  Lang, R.F., USDA-APHIS-PPQ, Bozeman Biocontrol Facility, Forestry Sciences Laboratory, Montana State University, Bozeman, MT 59717-0278.last up date August 28, 1998. online:

(2) The Appearance of Two Non-Pest Tephritids in Michigan Orchardsunknown, last up date Tuesday ,January 02, 2000, Forest Practices Branch online:

(3) Bill Klein, weed feeders table of Content, skleinw@pilot.msu.edu   Last Revised: 3-5-99 online:

(4) Dr. Jeff Stewart, Section Head, Crop Sciences Section, Agriculture and Agri-Food Canada Lethbridge Research Central, Box 3000 5403 - 1st Avenue  Lethbridge, Alberta, CanadaT1J4B1.last up date 2000 12 28, online: http://res2.agr.ca/lethbridge/weedbio/agents/aurocard.htm

By: Mary Beth Sacry      3/15/02.
Updated by:  Ian MacMurdie 2/9/05

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