Super corn borer resistant to Bt corn could infect Eastern Ontario first

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Attendees at the 2023 Eastern Ontario Crop Diagnostic Day near Winchester look for corn borer egg masses. Photo by Nelson Zandbergen.

by Nelson Zandbergen
courtesy of Farmers Forum

European corn borer is becoming resistant to the Bt corn varieties that have effectively repelled the pest for 25 years, and Eastern Ontario producers are likely to see it munching on their crop first before it attacks anywhere else in the Province, attendees were told at the 2023 Eastern Ontario Crop Diagnostic Day at OMAFRA’s Winchester research station.

While the corn borer larvae and moth was first discovered in Canada about 100 years ago, the Bt corn resistant borer, which first turned up in a Nova Scotia cornfield in 2018, has since been found in New Brunswick and in the Montreal area, according to presenters Tracey Baute, an OMAFRA entomologist, and Jocelyn Smith, entomology research scientist at the University of Guelph. It’s the corn borer larvae that bore into the corn stalk and cause rotting.

“Here in this region in particular, we’re extra concerned,” Baute said, noting that wind events can carry the European corn borer moth beyond its regular 40-km range after it pupates and emerges from corn stubble. “You guys are just close to any wind events carrying things in. If it’s going to happen in Ontario, it’ll be in this region first.”

A GMO success story, Bt corn handed producers revolutionary protection when it arrived in the marketplace 25 years ago. “If we lose Bt corn, it’ll be back to some old-school thinking or more expensive options,” Baute warned. “The reason why everyone moved to Bt is because spraying an insecticide is really difficult to do effectively and get the timing right to get those larvae when they hatch.”

Producers need to go back to scouting for corn borer, she said, an uncommon practice for decades. The small, cream coloured egg masses are laid on the underside corn leaves. The larvae get into the stalk and eat the plant from within, leaving holes.

Bt corn has done such a good job through the years that researchers, until recently, have had a tough time collecting corn borer specimens in the field. This year, however, an unprecedented number of egg masses turned up in a corn plot at the Winchester Research station. That doesn’t indicate Bt resistance, just that the species appears to be more prevalent in the environment this season.

“I’ve found more corn borer egg masses in this plot right here than I’ve ever seen in my life,” Smith said.

Veteran agronomist Gilles Quesnel similarly observed that it was his first time ever seeing corn borer egg masses.

The most advanced Bt corn contains four proteins that are toxic to the corn borer, and the latest tests on resistant corn borer at a site in Truro, Nova Scotia, showed that those larvae survived exposure to three of those proteins. Smith said that a new protein aimed at corn borer needs to be incorporated into Bt corn, but she estimated that this will take another eight years.

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