Insecticide-resistant insects have flown under the radar on the Canadian Prairies — but researchers are keeping an eye on a growing population of them in southern Alberta.
“We don’t have very many insects that are resistant to insecticides here on the Prairies, so luckily, it’s not that widespread of an issue,” said Boyd Mori, researcher and assistant professor at the University of Alberta.
“We have a very harsh climate, so most of our species only have one generation a year that we’re spraying with insecticide. Every time you’re applying an insecticide, you’re increasing selection pressure on those populations. We don’t have that here.
“So there are very few insects on the Prairies that have insecticide resistance or are tolerant to some insecticides.”
But very few is not the same as none, said Mori. In southern Alberta — and particularly in areas of alfalfa seed production — insecticide resistance is beginning to crop up in populations of alfalfa weevil.
“The issue of alfalfa weevil insecticide resistance really came to the forefront in about 2015 when growers and agronomists really noticed a lack of control with some of the synthetic pyrethroid products we’re using,” said Mori.
Further research confirmed that this lack of control was a result of insecticide resistance.
“It’s not widespread based on our work, but there are select regions in southern Alberta where we’ve noticed this resistance,” said Mori.
One of the goals of the ongoing research is to map where these populations are.
“It’s primarily in areas with high alfalfa seed production, around Rosemary and down toward Vauxhall.”
For those growers, insecticide resistance could leave them with few management options for alfalfa weevil, which can cause serious yield losses in alfalfa fields.
“If we’re having failure with insecticides, we’re going to either have to switch products — and unfortunately there aren’t a lot of good products available at the moment — or we’ll have to rely more on the natural enemies that are present in the field,” he said.
That’s something the research team will be looking at as well.
“Clearly we’re wiping out beneficial insects while we’re spraying insecticides,” he said. “But currently, the economic thresholds we use to determine if we’re going to spray don’t consider if there’s natural enemies present there to help control populations.”
Researchers know there are two parasitoids that help manage alfalfa weevil larvae populations, but it’s difficult to tell if larvae have been parasitized in the field.
“You can’t just look at a larvae and see that it looks sickly compared to other ones. It’s not that easy.”
So the team has created a molecular tool that will allow them to extract the DNA and determine if — and at what level — the larvae have been parasitized.
“What we’re hoping to do there is show growers that maybe they don’t need to spray an insecticide — maybe they have high levels of parasitoids that are going to help control these weevils, especially if we allow these parasitoid populations to build up year over year,” he said.
“That’s the ultimate goal — to be able to say that you have a parasitism level such that you don’t need to spray insecticide.”
That’s not possible to do right now with the existing economic thresholds, he added, but there’s a “big push” to move to what’s called a ‘dynamic action threshold.’
“For those action thresholds, not only would you be scouting for pests when trying to determine if you need to spray, you’d also be scouting for any natural enemies that are present,” said Mori.
“We know these natural enemies are there. We know they’re helping to control the populations. But we can’t necessarily say for certain that they’re taking out a certain percentage of our pests. That’s an area that really needs more work.”
But the economics of preserving this free labour could be a big boost to the bottom line, he added. One study from the 1990s valued the work of a wheat midge parasitoid wasp in Saskatchewan at over $248 million at that time. Another more recent study (this one from southeast England) found that predators and parasitoids of English grain aphid to be worth nearly $4 million a year in that area.
“That was just one parasitoid on one pest species. They can have huge impacts,” said Mori. “There’s a big push right now to conserve natural enemies, and we’re trying to get that information to growers.”