Second midge species identified

Key Result: Through this study, a second, previously unknown Contarinia midge species was discovered in Western Canada. Further work is underway on this new species, but overall, midge damage at the four Saskatchewan study sites was extremely low over the three-year project.

Project title, Principal investigators: “Monitoring of swede midge populations in Saskatchewan and determining the impact of swede midge on different growth stages of canola,” Julie Soroka and Owen Olfert, AAFC Saskatoon

Funding: SaskCanola, CARP

The swede midge, Contarinia nasturtii, is a significant pest of brassica vegetable crops and canola in Eastern Canada. It was first discovered in Saskatchewan in 2007, and now threatens the Prairie canola industry. In Ontario, there are usually four generations annually but the number of generations in Western Canada is not yet known.

A three-year study led by AAFC’s Julie Soroka and Owen Olfert was initiated in 2014 at four sites in northeastern Saskatchewan. The project objectives were to investigate the susceptibility of canola at different growth stages to infestation by swede midge and to determine the influence of seeding date and insecticide seed treatments on levels of infestation. Researchers also wanted to assess the effectiveness of adult insect sampling techniques (emergence and pheromone traps) throughout the summer to determine the natural cycle of swede midge populations.

During the study, Soroka and Olfert’s team discovered a second previously-unknown Contarinia midge species infesting canola. Because researchers were unable to differentiate the effects of each species, any assessed damage was considered to be caused by the Contarinia midge complex, including both swede midge and the new species. Two parasitoid species were also found to attack midge-infested flowers. If these parasitoids are attacking swede midge, this is the first report of parasitism in North America.

Overall, the research found that midge damage was extremely low over the three-year project. Early-seeded plots generally had higher injury ratings than late-seeded plots, but seed yield was not impacted. Seed treatment had no effect on midge damage and indicated either that these insecticides had dissipated and were no longer effective at the time of midge attack, or that midge damage was so low that no differences could be observed between the various treatments used in this study. Researchers would like to repeat the study in areas of high swede midge population levels such as those observed in Ontario.

Pheromone traps indicated extremely low or no swede midge population levels at the study sites. The newly identified Contarinia midge is not attracted to swede midge pheromone, but emergence traps provided some initial data on its lifecycle. This midge species has at least two generations on the Prairies, with only one appearing at the time of canola susceptibility during this study. Emergence traps also indicate that swede midge were not emerging from the soil at the four research sites. Future work is needed to clarify where swede midge is present on the Canadian Prairies.