Introduced Pests Outreach Project

Swede Midge
Swede midge update (February 27, 2007)

(Click on an image below to see the captioned full-size version)
Figure 1
Figure 2
Figure 3
Figure 4
Figure 5
Figure 6

Scientific Name: Contarinia nasturtii
Common Names: Swede Midge, cabbage crowngall fly, cabbage gall midge

Known Hosts:
Cruciferous vegetable crops including broccoli, cabbage, cauliflower, Brussels sprouts, kale, collards, rutabagas, and radish. The highest levels of damage have been seen on broccoli, Chinese broccoli (gai lan), Brussels sprouts, cauliflower, Chinese cabbage, and other Asian greens.
Cruciferous weed hosts include wild mustard, shepard’s purse, stinkweed, field peppergrass, and yellow rocket.

Key ID Features (Adults, Larvae, Eggs):
The adult is a small (1.5-2mm) light brown fly with hairy wings. (Figure 1)
Adult population emerge from the beginning of May through the middle of October in Ontario, Canada with 3-5 peaks in population during the year.
Full-grown larvae are 3-4 mm long and yellowish in color. (Figure 2)
Eggs are very small (0.3mm) and laid on the youngest parts of the plant (e.g. flowers buds, leaf bases) often near the growing point of the plant. Eggs are transparent when first laid and change to a creamy white color as they mature. (Figure 3)

Description of damage:
No head will form if damage occurs to a young plant. (Figure 4)
Young shoots and leaf stalks may be swollen, distorted and crinkled.
Heart leaves are crinkled and crumpled. (Figure 5)
Brown scarring on the head and along leaf stalks. (Figure 6)fs
If the main stem is destroyed, the development of secondary stems can result in a multi-stem plant.

Similar species or symptoms:
Swede Midge is difficult to distinguish from other midges.
Plant damage caused by Swede midge looks similar to other problems with crucifers including molybdenum deficiency, mechanical injury from cultivation, hormonal herbicide injury, genetic variability of seed and heat or cold stress.
Suspected plants need to be examined for the presence of larvae. Examine with a hand lens or force the larvae to leave the plant tissue by placing the affected plant part in a black plastic bag in the sun for several hours or placing damaged tissue in 70% alcohol.

Fact sheets and references:
Swede midge: An introduced pest of crucifer crops
Massachusetts Introduced Pests Outreach Project

Cooperative Agricultural Pest Survey Swede Midge Pest Page: Information on surveys in the US and links to other resources

Swede Midge Information Center for the United States

Cornell University Swede Midge Fact Sheet

Swede Midge: A New pest of Brassica Crops in Canada
UMass Extension Vegetable Notes. September 16, 2004. 15(21)2-3.

The Swede Midge- A New Pest in Crucifer Crops in Canada
Ontario Ministry of Agriculture and Food (Excellent swede midge photos)

Swede midge informational PowerPoint: University of Vermont

last reviewed December 22, 2014

Massachusetts Department of Agricultural Resources
The Massachusetts Introduced Pests Outreach Project is maintained by staff at the Massachusetts Dept. of Agricultural Resources. This website was made possible, in part, by a Cooperative Agreement from the United States Department of Agriculture's Animal and Plant Health Inspection Service (USDA APHIS). It may not necessarily express APHIS' views.