The emergence of a new canola gall midge in Ontario in 2021 has prompted researchers to re-assess swede midge data.
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The canola flower midge (CFM) was first noted in Western Canada in 2016. Researchers saw a significant number of midges bypass pheromone lures but also saw distinct canola gall injury. It was not the damage typically seen from swede midge.
Rebecca Hallett, a University of Guelph environmental sciences professor, told Ontario Canola Growers industry meeting that there is a small amount of research on the canola flower midge done by western Canadian groups that have tracked the pest for six years.
Why it matters: Until recently, swede midge was the only gall midge known to infest Ontario canola.
Once studies proved a new midge was damaging canola, researchers began to suspect flower gall damage noted as far back as 2012 was due to canola flower midge, not swede midge, she said.
“Boyd Mori (University of Alberta researcher) and others out west have done some studies looking at the types of damage CFM will cause,” Hallett said. “They’ve never seen these rounded caper-type galls, which is quite typical of swede midge bud infestation caused by CFM.”
Damage results in a gall where the buds fuse in an elongated bottle shape, unlike swede midge’s signature caper-like shape.
“In terms of the distribution of CFM in Western Canada, they (Mori et al.) had been conducting surveys over a number of years,” said Hallett. She displayed a map of larvae and damage to canola spanning 2014 to 2016.
“At that time, it was found throughout Saskatchewan and central Alberta, and subsequently, they’ve also found it in Swan River, Manitoba.”
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Ontario researchers have been looking for CFM in the field since 2016 but found none. Mori later found two records from the Peterborough area in the Barcode of Life database.
“They weren’t identified taxonomically, but the barcoding had been done and put … into the database,” Hallett said. “So, it’s been here for a little while.”
According to Mori’s 2019 publication and subsequent research, CFM is morphologically and genetically distinct from swede midge. However, both range in size from two to five millimetres. Identifying the two by appearance is challenging, but the critical factor is that CFM females have mottled wings or dark patches produced by wing-surface hair. The antennae of both species and genders also differ.
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The CFM’s pheromone is also distinct, which is why it bypassed swede midge pheromone lures.
Its lifecycle mimics that of the swede midge. Adults emerge from cocoons in late spring or early summer to coincide with brassica flower buds. Females lay egg clusters on the canola flower style.
“If you peel open a flower, (there’s) little larvae developing next to the style, but you can also see black necrotic lesions on the style of the flower,” said Hallett. “(That’s) feeding damage caused by the larvae.”
As a result, the flowers don’t bloom or produce seeds.
Like swede midge, there will be multiple larvae in one location, and mature larvae spring off the plant into the soil to create a larval cocoon. They emerge as the next generation or enter diapause to overwinter.
CFM leaves a dried older flower on the stem, which, according to a recent Saskatchewan study, results in a nine per cent potential yield loss per flower.
“That indicates that the CFM definitely has the potential to cause significant damage and yield loss in canola,” Hallett said.
Unlike swede midge, which is an alien invasive species, indicators suggest CFM is a native species that switched hosts to canola due to the dramatic increase of the crop on the Prairies over the last four decades.
“It’s likely something that has been in the landscape developing and feeding on some other plants and is now becoming an economic pest because it’s adapted to make use of canola,” Hallett said.
“From its widespread distribution and the population, genetic studies also suggest that this is a native species rather than an invasive alien species.”
Mori identified and synthesized CFM’s pheromone, and in 2021 and 2022, Hallett placed CFM lures in spring canola fields in Dufferin, Wellington and Bruce counties and the Kawartha Lakes region.
While researchers suspect there’s CFM in the untested counties, they chose to test the outer limits of canola production for established populations.
Hallett made two observations in areas with confirmed CFM populations. Emergence in Ontario is somewhat earlier than in Western Canada, occurring in early June. There are two emergence peaks throughout the summer, likely representing two generations.
More intriguing was the observation of CFM emerging from canola plants with injury considered characteristic of swede midge.
Hallett suggested CFM uses canola differently in Eastern Canada than in Western Canada, potentially due to regional climatic or environmental differences.
She theorized that swede midge interactions with CFM could affect the tissue available for use and the damage it causes.
“It’s possible some of the damage previously thought to be caused by swede midge could actually be CFM,” Hallett said. “Or maybe it’s caused by both of them.”
She has submitted a research proposal to define the distribution of CFM in Ontario, determine which part of the canola plant it favours and identify its damage symptoms. Additionally, the research would assess whether CFM was present in other host plants pre-canola, the existence of natural enemies and its susceptibility to pesticides.
Hallett said it’s critical to differentiate the two pests before adults emerge, especially if they are in the field on the same plant. Finally, she wants to see whether pesticide vulnerability differs from swede midge and how timing of pesticide application impacts efficacy.
“Does the timing of applications and the efficacy of compounds differ between the two species? We need to know what species we need to control – if it’s one or both – and what the timing should be if a pesticide application is warranted.”
Hallett said the differences between Western and Eastern Canada CFM could mean development, emergence and behavioural differences, so the study is vital for crafting best management practices.
“We need studies in Ontario to determine its pest status, the threat it presents to canola production and how we might best manage it,” she said. “Hopefully, with this information, we will improve the protection of canola yields from both of these midge pests.”
Even without funding, Hallett plans to do field research to see if CFM galls are typical of those in the west or unique to Ontario.
Anyone noting unusual or possible CFM galls is encouraged to contact Hallett or her assistant, Angela Gradish.