swede midge

Contarinia nasturtii (Kieffer, 1888)

Synonym(s): cabbage crowngall fly, cabbage gall midge

Swede midge is native to Europe and southwestern Asia. It was confirmed to be present in Ontario and Québec, Canada and has been detected in New York. Since the adults are weak fliers, it was most likely introduced through the movement of infested plants or soil. Hosts of this pest are plants in the family Brassicaceae: and includes plants such as broccoli, cauliflower, collard, kale, cabbage, and radish. The number of generations per year is dependent on the climate, with as many as 4 generations per year in parts of Europe and 3 per year in Ontario. Adults of the overwintering generation begin to emerge at the end of May. The female lays eggs in strings or clusters of 15-20 eggs on the youngest parts of the plant. The extremely small eggs are laid on a stalk. After three days, the eggs hatch and most larvae will start to feed near the growing point. The larvae are pale to lemon-yellow and legless. When full grown, they can be up to 1/16 of an inch in length. Their saliva digests plant tissue, resulting in the flower (i.e. head of broccoli or the like) becoming deformed and unmarketable. The damage by the insect also favors the development of plant-rotting fungi and bacteria. After 2-3 weeks the larvae drop to the ground and spin cocoons. Two weeks later the next generation of flies appear. Adults are 1/16 of an inch in length with iridescent wings. The abdomen has indistinct transverse stripes. The ovipositor of females is whitish and can extend to become pointed like a needle. The shield behind the head is slate gray with two lengthwise, shiny-black furrows. Females become inactive at temperatures below 68 °F (20 °C). During periods of drought, the larvae may become dormant, but growth resumes after a rainfall. Feeding damage is easily confused with mechanical injury from cultivation, feeding by other insects and animals, molybdenum deficiency, herbicide injury, genetic variation of the plant, and heat or cold stress.

Identification, Biology, Control and Management Resources

Contarinia nasturtii (Kieffer) - Swede Midge - Canadian Food Inspection Agency
Swede midge update (February 27, 2007) - Massachusetts Dept. of Agricultural Resources and the UMass Extension Agriculture and Landscape Program