Distribution and life history of Contarinia brassicola (Diptera: Cecidomyiidae) in canola (Brassica napus) grown on the Canadian Prairies

Contarinia brassicola Sinclair (Diptera: Cecidomyiidae) is a recently described species found infesting canola (Brassica napus L. and Brassica rapa L., Brassicaceae) in western Canada. There is concern that C. brassicola could have economic impacts on canola production. To learn about its biology, distribution, natural enemies, and potential impact, we conducted a prairie-wide survey in western Canada and field studies using emergence cages and plant dissections between 2017 and 2019. Results of a transect-based survey conducted in Alberta, Saskatchewan, and Manitoba indicated that C. brassicola is widely distributed in western Canada. Two species of parasitic wasp were reared from C. brassicola larvae collected during the survey. We found that C. brassicola can have multiple generations per year, with the first peak of adult emergence occurring in early July with the onset of the susceptible crop stage. Adult midge and larvae may be found from June until early autumn. Midge larvae appear capable of extended diapause over multiple years. During this study, we found that C. brassicola damage was restricted to developing flowers. In the vast majority of fields surveyed, C. brassicola occurred in low population densities and was unlikely to impact yield in those fields.