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.
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