New and notable Prairie crop pest insects

Haven’t heard of canola flower midge? Can’t identify those RED BUGS showing up in your fields? Didn’t know alfalfa weevil populations are developing insecticide resistance? Everything you need to know about new insect threats

Most Prairie farmers know more than they might want to about common crop pests like grasshoppers, cutworms and flea beetles. However, nature likes to throw curveballs, and pests are no exception. Here’s what you need to know about several new-to-you pests currently catching Prairie farmers by surprise.

Alfalfa weevil

While alfalfa weevils are familiar to Prairie forage producers, their ability in some fields to withstand insecticide applications is a new and worrying reality. Scientists have confirmed alfalfa weevils are exhibiting pyrethroid (i.e. Decis) resistance in a small number of southern Alberta fields, making them one of the very few pests across the Prairies that have overcome certain pesticides. Resistance was first noticed in 2015 and confirmed each year since then.

Alfalfa weevils are widespread across the Canadian Prairies. No studies have yet been conducted for pyrethroid resistance in Saskatchewan or Manitoba alfalfa weevil populations. Similar resistance has been confirmed, however, in several regions in the United States.

While alfalfa weevils are familiar to Prairie forage producers, their ability in some fields to withstand insecticide applications is a new and worrying reality. Scientists have confirmed alfalfa weevils are exhibiting pyrethroid (i.e. Decis) resistance in a small number of southern Alberta fields.
photo: Larry Grenkow, AAFC

“This isn’t an entirely new problem. Resistance is happening in the U.S. as well, but my guess is that resistance in Alberta is likely a homegrown issue,” says Boyd Mori, assistant professor of agricultural entomology at the University of Alberta.

Organophosphates (such as malathion and dimethoate) are a viable alternative given the right conditions. Unfortunately, alfalfa weevil larvae typically appear early in spring when conditions are cool — malathion is more effective at temperatures above 20 C.

“If they’re producing hay, producers can cut early and not worry about an insecticide application. But there are limited options out there if you’re growing for seed production,” says Mori.

If you’re only scouting for the insects you know, emerging pests might gain the upper hand.

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Alfalfa weevil populations are biologically controlled by at least three parasitoid species. Currently, a research project through Agriculture and Agri-Food Canada (AAFC) and the University of Alberta is attempting to map insecticide-resistant populations and their corresponding parasitoids in order to determine whether producers should be relying more on natural enemies.

Red bugs

In 2017, small, conspicuously red insects started gaining increasing attention in Saskatchewan.

The bugs are actually the nymph (juvenile) stage of three distinct insect species: the twice-stabbed stink bug, the white-margined burrower bug and the insect Peritrechus convivus, which does not yet have a common name. Most reports over the past few years have involved damage inflicted by the red bug P. convivus. These insects appear to have a very broad range of hosts and can cause damage quickly.

Nymph stage of the white-margined burrower bug.
photo: Patrick J. Alexander

“Red bugs are not widespread, but they can be regionally very damaging,” says James Tansey, Saskatchewan Agriculture’s provincial insect and vertebrate pest specialist. “Both in 2018 and 2019, 10-acre-plus cornfields in Saskatchewan were flattened by these (pests). We got some reports of heavy damage in flax that was initially mistaken for cutworm damage. And one canola grower lost a half section to them in 2018.”

To date, scientists are still working to gain knowledge about these bugs, though they were first described about a century ago. No control products are currently registered. Tansey says there does appear to be an anecdotal correlation between seeding low-lying and often wet areas with increased populations.

Red bugs are a good example of growers being caught unawares, says Tansey. “They do seem to pop up rather mysteriously, and when they do, it’s in very high numbers.”

Though Mori hasn’t heard of any red bugs being identified in Alberta fields yet, he says they’re “definitely one to keep an eye out for, for sure.”

Most reports over the last few years have involved damage inflicted by the red bug Peritrechus convivus (nymph shown above), which does not yet have a common name.
photo: AAFC

Canola flower midge

Canola flower midge is a recent, though as yet, small problem on the Canadian Prairies. Crop damage occurs by larval feeding, which creates a distinctive, bell shape in canola flowers.

If you haven’t yet heard of canola flower midge, you’re not alone. Despite the fact that the insect is widespread across the Prairies and may actually be native to those regions, it’s only very recently been identified as a potential Prairie crop pest.

If you haven’t heard of canola flower midge, you’re not alone. Despite the fact that the insect is widespread across the Prairies and may actually be native to those regions, it’s only very recently been identified as a potential Prairie crop pest.
photo: Jonathon Williams, AAFC

“Is it new? That’s the ultimate question. We think it’s a native species that has potentially switched hosts, but what its original host is we have no idea,” says Mori. “It’s very widespread but exists at very low numbers. Of the 50 or 60 fields we surveyed in Alberta over the past three years, there might have been one field that suffered economic damage.”

Mori and his research colleagues suspect the midge has existed on the Canadian Prairies for a long time because they have already identified a couple of parasitoids that attack it.

“Usually, if it’s an invasive species, you don’t find natural enemies right away. That leads us to believe it’s either native or that it’s been here for a long time and that we just never noticed it before.”

AAFC, together with colleagues at the University of Alberta and the University of Greenwich in the United Kingdom, have successfully identified a pheromone for the midge. The researchers’ plan now is to distribute pheromone traps to colleagues here at home and in other parts of the world to determine population spread and confirm whether the insects are native to Canada or imported.

At first, researchers thought the insect was a different, more destructive pest.

“We originally thought it was swede midge, which is a devastating pest,” says Mori. “In northern Ontario, swede midge are so bad that they asked for a three-year moratorium on canola production to try to control the population. Producers are applying multiple insecticide applications per year. So, the fact that what we found is not swede midge is a very good thing.”

How much of a concern could canola flower midge be in the future? That answer is very hard to know.

“I think it’s a wait-and-see game,” says Mori. “They’re similar to wheat midge in that the canola needs to be at the right stage when the canola flower midge emerge in order for the bugs to be successful. And, it does have a lot to do with the weather: in wetter conditions, we’ve seen higher numbers. But, as far as what the population is going to be like into the future, that I just don’t know.”

If producers find red bugs, canola flower midge, insecticide-resistant alfalfa weevil, or any other unusual or unexpected pests in their fields, contact the experts.

“If anything odd shows up, I strongly encourage growers to notify experts at their Ministry of Agriculture, the universities of Saskatchewan or Alberta, or at Agriculture and Agri-Food Canada. One of us would be happy to take the call and we all benefit from the information,” says Tansey. “The only way we can stay on top of emerging issues is to know what’s out there.”

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