Corn School: New Bt tolerance suspected in European corn borer

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A European corn borer (ECB) population in part of eastern Canada appears to have developed resistance to a Bt protein commonly used in North American corn hybrids for preventing damage from the pest.

On April 27th, the Canadian Corn Pest Coalition reported a sample of ECB collected near Truro, Nova Scotia, showed reduced susceptibility to the protein known as Cry1Ab. The sample was collected in the fall of 2022, and tested by Drs. Jocelyn Smith and Yasmin Farhan at the University of Guelph’s Ridgetown Campus.

The suspected case of resistance was found in the same area where resistance to the related Cry1F protein was discovered in 2018 — the first known case of ECB resistance to any Bt protein in the world.

It’s unknown how widespread the newly-found Cry1Ab-tolerant population is, but corn growers in other parts of Canada and the U.S. are encouraged to keep an eye out for ECB in their Bt corn, explains Morgan Cott, agronomy extension specialist with the Manitoba Crop Alliance, in this new Corn School episode.

“The messaging that we would like to get out is to certainly be scouting for European corn borer and excessive damage that might be outside of that 5 per cent refuge. So that’s what we’ll be looking for in the future,” she explains.

Resistance to the Cry1F protein was found in ECB samples in Quebec and Manitoba shortly after it was discovered in Nova Scotia in 2018, notes Cott, and that led the industry to remove hybrids that relied solely on the Cry1F gene from the market in 2020.

While the Cry1F protein was more common in short-season hybrids — which partly explains why resistance was found in Nova Scotia and Manitoba — use of the Cry1Ab protein is much more widespread in Bt varieties, she says.

Ideally, growers should plant hybrids that contain more than one effective Bt protein. Cultural management practices — mainly destroying corn stalks left on the soil and burying the shredded stalks — can also be effective in reducing ECB populations.

“Resistance is the first thing that we’re talking about nowadays. And so it just happens to be another thing that we really need to be working on — integrated pest management for insects,” says Cott.

The Canadian Corn Pest Coalition says it’s working on determining the level of susceptibility of ECB populations this year, and asks growers to scout and report any unexpected injury found in Bt corn to their provincial entomologists and seed providers.

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