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How this tiny wasp is working to keep food on our tables

There's nothing like a crisis for sorting the important from the trivial.

That's been the case with the COVID-19 pandemic here in Canada — at least in the early days.

If you remember, flour disappeared from grocery stores and borders closed to temporary farm workers. Suddenly, Canadians feared not having enough to eat.

We realized we depend on a stable agri-food supply chain — the first link of which is the crop-producing farm — right here in Canada.

Nearly half of our daily calories come directly from plants, primarily from common food grains such as wheat, rice and corn. Even the animal proteins we eat rely on productive crop farms since most livestock are fed grains and oilseed meals.

Given that plants are central to our food security, it's no wonder the United Nations declared 2020 the International Year of Plant Health.

And a key factor in protecting plants now and in the future is science.

That's why Agriculture and Agri-Food Canada's Pest Management Centre (PMC) partners with researchers through its Pesticide Risk Reduction initiative. We support sustainable farming practices that increase crop yields while reducing environmental impact.

The case of the cereal leaf beetle is one such example.

The threat of a hungry beetle to our daily bread

Cereal leaf beetle

Cereal leaf beetle (Oulema melanopus) credit: Klaus Bolte

The story begins in 2005 when the cereal leaf beetle, an invasive insect native to Europe and Asia, began showing up in southern Alberta.

The cereal leaf beetle feeds on a wide range of grasses. But it loves cereal crops like wheat, oats and barley — important crops in Canada because of their use as flour and other food in our kitchens, as well as livestock feed in farmers' barns.

The beetle first turned up in Michigan in the 1960s and quickly spread throughout most of the United States. Reports emerged that the hungry pest decimated crop yields of winter wheat by 23%, with even higher losses in spring cereals.

Growers tried quarantining infested areas and used insecticides to control the pest. Yet the beetle continued to spread. So, researchers turned to classical biological control efforts — the attempt to introduce a foreign pest's natural enemies from its homeland to the pest's new home and thereby restore a natural balance.

Several species of small parasitic wasps were brought to the Midwest and mid-Atlantic states from Europe because, as natural enemies, they were known to kill the beetle and keep populations in check. The two most successful biocontrol agents were Tetrastichus julis and Anaphes flavipes.

Back to our story and the release of a killer biocontrol agent

Although initial numbers of the cereal leaf beetle in Alberta were small, researchers kept their eyes on populations, which multiplied year by year.

But as luck would have it, the beetle was followed into the province by its natural enemy, the non-stinging parasitic Tetrastichus julis wasp.

Because of the beetle's potential to damage cereal crops and without any registered products to control the pest (at least at the time), Agricultural and Agri-Food Canada research scientists like Héctor Cárcamo, PhD, in Lethbridge, sought to learn more about the survival, dispersal and populations of T. julis.

That's where the PMC enters the story.

So in 2013, in response to industry priorities and as part of its Reduced-risk strategy management of foliar insect pests of Prairie field crops (led by its Pesticide Risk Reduction team), the PMC provided Cárcamo the needed funds to collect, rear and relocate the wasps to new fields and cereal-growing regions where the beetle was emerging.

Working with provincial specialists throughout Western Canada, Cárcamo and his research team collected beetle larvae penetrated by the wasp and started rearing lab colonies at the Lethbridge research centre.

From 2013 to 2015, they released about 14,000 wasps (adults and larvae) to wheat fields in Alberta, Saskatchewan and Manitoba (and have continued to release many more wasps since).

The researchers also studied the landscape surrounding about 76 cereal fields to determine the features that affect beetle and wasp populations. They found that crop diversification and semi-natural habitats can reduce the beetle's presence in cereal crops.

But if no one hears about it

A truly successful biological control program depends in the end on the willingness of growers to adopt the practice and forego insecticides. It's a willingness that can be cultivated by scientists who share the fruits of their research — just as the UN prescribes they do to protect plant health.

Not surprisingly, that's just what Héctor Cárcamo and his team did.

Throughout the course of their work, they showed up at industry meetings, conferences and field days to spread the word about the cereal leaf beetle and the success of T. julis in managing it.

They published a factsheet called Biological control at its best, submitted several articles to agriculture magazines, and got information about the pest and its natural enemy included in the 2015 edition of the illustrated Field Guide to Pests and Natural Enemies of Prairie Field Crops.

The result has been definite interest among growers to use T. julis as a way to control the cereal leaf beetle.

Yet even then, Cárcamo knew more could be done.

While T. julis seemed to be keeping the beetle populations in check, Cárcamo wanted to give farmers still more options.

Like all parasitic wasps, the female bores into the beetle larvae and lays her eggs. When the wasp larvae hatch, they feed on the beetle from the inside out. Eventually, they emerge from the beetle host, killing it in the process.

The gruesome process takes about two-and-a-half to three weeks. This gives the developing beetle larvae plenty of opportunity to damage plant leaves through feeding.

So Cárcamo and his team sought other potential predators that would feed on the beetle eggs and larvae, and kill them instantly.

With further funding from the PMC, their search started in the lab before moving to the field. It confirmed that other predators (lady beetles, carabids, spiders, nabid bugs) will also eat beetle eggs and larvae, contributing another line of natural defence in the fight against the cereal leaf beetle.

Keeping our food supply chain safe

It seems that T. julis and these other natural predators are doing their job. Cereal leaf beetle populations have not caused serious losses in crop yield or impaired quality. Just as important, growers have not had to spray malathion, the only chemical registered to control the beetle, thanks to tiny T. julis and the work of scientists like Héctor Cárcamo.

Still, a scientist's job is never done.

With the recent hiring of Haley Catton, PhD, at Lethbridge, Cárcamo gained a partner in the continuing research on cereal pests. Together, the two scientists recently turned their attention to establishing a science-based economic or action threshold for when to start using insecticides to control the pest.

Farmers need such a tool since spraying insecticides regardless of risk or whether the pest is causing significant damage does not make financial sense. Especially since spraying will kill off T. julis and other natural predators, and enable the beetle to bounce back deadlier than before.

For the PMC and the UN, that's the ultimate goal: supporting and encouraging farmers to use crop and pest management practices that rely on natural enemies to keep our food supply chain safe. Practices that are, in short, effective, economical and environmentally sound.

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