What's Bugging Your Canola?

Thursday, October 26, 2023

Canola Swede Midge is the New Kid in Town.

By Stacy Berry

Agriculture has been around for over 10,000 years, and canola as we know it has been around for over 60 years – and new insect pest species are still being discovered.

Contarinia brassicola – now more commonly known as the canola flower midge (CFM) – was discovered in 2016. This was an accidental discovery by Dr. Boyd Mori, assistant professor and NSERC industrial research chair in the Department of Agriculture, Food and Nutritional Science at the University of Alberta. The discovery was actually a case of mistaken identity.

The swede midge, Contarinia nasturtii, is a pest that can send shudders through a crowd of farmers. This is an invasive pest of brassica plants – which includes the highly valuable canola and popular crucifer vegetables like broccoli and bok choy. "The swede midge was discovered in Ontario in the early 2000s," Mori explains, "and was quickly noted to be causing substantial damage – and has potential for more (damage)."

Dr. Meghan Vankosky is a field crop entomologist at the Agriculture and Agri-Food Canada Saskatoon Research and Development Centre. Vankosky explains that "swede midge attacks any growing point on the canola plant. In many crops, the growing points become the harvestable plant structure. In vegetable brassicas there is often only one growing point, so swede midge damage can cause 100 per cent yield loss."

With the risk of such damage, the Canadian Food Inspection Agency (CFIA) began regularly monitoring for swede midge on the Prairies. According to Mori, "around 2008, the swede midge was spotted in Saskatchewan and Manitoba." Fortunately, swede midge wasn't seen again, despite increased monitoring afterward. However, while monitoring for swede midge, CFM was discovered.

So, how does one go about accidentally discovering a new insect species while monitoring for another?

To monitor for swede midge, scientists will set up "emergence cages," Mori explains. "A dome tent with no bottom and a small hole in the top for light. A collection jar is at the top, that the insects will fly toward since they are positively phototactic – drawn to the light."

Mori expected to find lots of midge inside the collection jar and there were only a few. "Maybe the midge were just hanging out in the cage instead of being caught in the jar?"

Mori decided to make it more tempting and added a pheromone trap inside the emergence cage. This time, plenty of insects were caught in the emergence cage jar, but none were captured in the pheromone trap. "That definitely triggered the thought: I don't think this is swede midge."

However, this midge present in the field looked nearly identical to swede midge. So how to differentiate them?

Mori was going to have to go to the molecular level. "We decided to do DNA barcoding. We compare short fragments of DNA between species to determine how closely related they are. And it turned out the midge we had found was not swede midge!"

Mori called in some reinforcements to look at this insect: Dr. Brad Sinclair, a Diptera expert at the Canadian National Collection in Ottawa, and Dr. Rebecca Hallett at the University of Guelph. Upon close examination, morphological differences were seen. And even more exciting, Mori adds, the midge they were looking at "was not known in any other places in the world."

It was official – they had found a new insect species.

"I was just starting my career as this insect was discovered, so it's very exciting!" enthuses Vankosky. "There is so much to learn and so many questions to ask about it."

Where do you even start? Vankosky and Mori have been working together to study this new insect. "We knew nothing about it," says Mori. "All questions being asked about it are unique. However, it's an insect on canola, which is a major commodity, so there are concerns about its impact." This meant learning about this insect was paramount, but they also needed to start at the beginning. "You have to look at lifecycle, pheromones, habitat," explains Mori. "What about biology and distribution – what parts of the plant does it attack; where is it found?"

Several sites were selected across the Prairies to study and monitor for midge, and eventually some of the basic questions began to get answered. "Most CFM will emerge as adults in early summer, to lay eggs on canola as it comes into flower." This is how the CFM – canola flower midge – got its name: Larvae infest flowers of canola, creating a gall in which they feed, and prevents them from opening. "Some CFM may emerge as a second generation and lay eggs on later flowers, but most will remain as larvae in the soil to overwinter."

Larval feeding on the flowers also doesn't sound great for yields, but "CFM is only found in low densities across the Prairies." According to Mori, isolating CFM damage from other damages like drought and heat can be difficult, but CFM specific damage seems to be negligible.

However, that doesn't mean the questions and concerns end.

There is a parasitoid in Europe that keeps the swede midge population under control, and the avenue of biological control – using organisms to control other organisms in an environment – is of particular interest to Vankosky. "Biological control of the swede midge has been investigated, but the parasitoids that attack swede midge in Europe are not good candidates for introduction into Canada. However, there are parasitoids that attack CFM, and maybe these parasitoids could also be used to help manage swede midge."

Besides biological control options, there remains the question of controlling CFM at all. Currently, CFM damage levels are negligible; that doesn't mean that the CFM will always remain at these low levels.

Mori wonders if CFM might actually be a native species to North America. If that's the case, "what was its original host? Canola was bred for agriculture and does not naturally occur, so would CFM have expanded its natural range, or switched hosts completely?" Either way, it's a little worrisome – this insect has started to infest canola flowers. Will it do more than munch on a few canola flowers?

Vankosky: "Does it have pest potential? Could the population build up enough to cause economic damage? We still have important questions to answer."

Vankosky is the chair of the Prairie Pest Monitoring Network (PPMN) and is therefore hyper-aware of these types of questions. "The PPMN is a collaborative network of entomologists across the Prairies that conducts annual monitoring of insect pests in cereal, pulse, and oilseed crops," Vankosky explains. This is an invaluable resource. "The PPMN links entomologists, farmers, agronomists, and industry. We conduct research and collect data, and share information and results."

Vankosky urges everyone who has some connection to agricultural insect pests to utilize the PPMN and visit their website at www.prairiepest.ca. "There are tons of resources, including highlighting the ‘insect of the week.' As well, we provide a weekly update during the growing season to give farmers a heads up to time scouting and spraying." Really, that's the main goal of the PPMN – "helping farmers manage their time and make the best possible pest management decisions."

The PPMN also helps with the practices of good integrated pest management, and Vankosky can't stress enough that "scouting for pests in crop is key to knowing if you need to spray. Scouting is knowledge and can help you save money." So can the PPMN, Vankosky reminds farmers. "The website is free, you subscribe for free, and you can get information directly to your inbox." What's not to like?

That being said, the PPMN does need fields to monitor. "We really appreciate the farmers who give us permission to monitor insects on their land. The more sites we can visit, the better datasets we can produce for everyone."

Mori: "Are you interested in participating or helping out? Please, reach out! Let us know if we can monitor in or beside your field."

Vankosky echoes: "If you are interested in insect and pest monitoring, please contact us."

Mori also appreciates the farmers for allowing insect monitoring. "We are always looking for collaboration and access to farmers' fields. Although we do our best to avoid interference in farming activities, some of the stuff we do isn't the most convenient, and we can't express enough how much we appreciate farmer's willingness to allow us to study in their fields."

With more fields to look at, there will also be more opportunities to study the CFM and the endless questions that follow the discovery of a new species. Although not currently a worry, "CFM is something we should have on our radar so we can be proactive, not reactive, in case the situation changes," says Mori.

Additionally, "swede midge could be devastating if it establishes in the Prairies."

Either way, monitoring will continue to be crucial to their studies, and to learning about CFM and its future with canola on the Prairies. BF