Midges in canola

The Insect of the Week features Swede midge and the canola flower midge as doppelganger pests this week!

Two species of midges (Diptera: Cecidmyiidae) are known to infest canola in Canada. Since 2000, swede midge (Contarinia nasturtii) has been established in southern Ontario with serious levels of damage observed in several species of Brassicaceae, including canola by 2003. Swede midge is also established in Quebec, Nova Scotia, and Prince Edward Island. Across the prairie region of Canada, a separate canola flower midge (Contarinia brassicola Sinclair) was identified initially as larvae feeding within the developing flower that caused the formation of a “pop-bottle”-shaped gall (Fig. 1). To date, this is the only damage associated with the canola flower midge, and it has been minimal across the prairies.

Figure. 1. “Pop-bottle”-shaped galls created by the canola flower midge.
(c) 2016 Boyd Mori, AAFC

Because of the serious threat that swede midge poses to canola production, it is vital that monitoring for swede midge continues across the Prairies. Monitoring is underway for 2021.

Tips for scouting canola for midges:
• Watch for unusual plant structures and plant discolourations then follow-up by closely scrutinizing the plant for larvae.
• The growing tip may become distorted and produce several growing tips or none at all, young leaves may become swollen, crinkled or crumpled and brown scarring caused by larval feeding may be seen on the leaf petioles and stems.
• Flowers may fail to open.
• Young plants that show unusual growth habits should be examined carefully for damage and larvae; especially if the sticky liners have many flies resembling midges (swede midges are about the size of orange blossom wheat midge but are not orange).
• Larvae can be seen with a hand lens.

Access more information about midges in canola via these links:
Swede midge and canola flower midge: Doppelganger pests (2021; Wk 11)
New canola flower midge (2018; Wk 11)
Natural enemies of the canola flower midge (2018; WK 12)
Ontario’s swede midge fact sheet produced by Baute et al. 2016.
• Canola Council of Canada’s Canola Encyclopedia – Swede midge


In 2016, entomologists on the Canadian Prairies identified a previously unknown species of midge while conducting field experiments in northeastern Saskatchewan. The new midge was described in 2019 and is named Contarinia brassicola Sinclair (Diptera: Cecidomyiidae). It is known unofficially as the canola flower midge, although its host range includes mustard varieties.

Swede midge (Bugwood)

The full extent of the host range of canola flower midge has yet to be studied. Field surveys conducted between 2017 and 2019 found that the canola flower midge is widely distributed in Alberta, Saskatchewan, and Manitoba, with some pockets of higher population densities (i.e., northeastern Saskatchewan). The canola flower midge is morphologically similar to the swede midge: a doppelganger insect that damages the same field crops that canola flower midge does, as well as a variety of cruciferous vegetables (e.g., cabbage, cauliflower, Brussels sprouts) and Brassica weeds. Both species have much in common, but differences in the type of plant damage they inflect can help distinguish between the two.

Canola flower midge damage (AAFC)

Neither insect poses a threat to crops in their adult form, but both species have larvae that cause damage to their host plants. Canola flower midge larvae consume individual canola buds, resulting in characteristic galled flowers. In comparison, swede midge larvae are known to attack and consume plant material at any growing point on their host plants, affecting normal plant development.

Both midge species are quite similar in their physical characteristics. Adults are delicate, 2–5 mm long flies ranging in colour from light brown to grey. These insects have long legs, long beaded antennae and sparse venation on their wings. Larvae grow between 3–4 mm long. Young larvae are semi-translucent when they hatch and turn yellow as they mature.

Biological and monitoring information related to the swede midge in field crops can be found on our Monitoring page. For more information, visit the swede midge page in the Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and Management field guide. (en français : Guide d’identification des ravageurs des grandes cultures et des cultures fourragères et de leurs ennemis naturels et mesures de lutte applicables à l’Ouest canadien). For more information on the canola flower midge, check out this publication from the Alberta Department of Agriculture and Forestry, and previous postson the Prairie Pest Monitoring Network website.