A minuscule pest has made its way from corn-belt states in the U.S. and is now slowly chewing its way through crops in Canada.

Entomologists aren't sure why the western bean cutworm began migrating, but can confirm the critter has popped up in Ontario and Quebec corn fields.

"This is the first year we're anticipating a significant problem," said Art Schaafsma, an expert in crop pest management at the University of Guelph in Guelph, Ont.

In just one year, there's been a proliferation not only in the insect's numbers but also in the number of regions where it's been found.

"We've been getting significant trap catches," Schaafsma said. "Last year it was more of a token catch."

Newly hatched larvae are a dull tan or pink colour with black heads. They feed on the plant's pollen, its silk and, later, on its developing kernels. Its feeding can open up the ear to other pests, diseases and fungal infections.

Farmers in Ontario and Quebec are being asked to scout for egg masses — pearly thumbtip-sized patches of eggs that turn purple before hatching — and for the larvae.

Schaafsma said the worst infestation he's seen so far was in one Ontario field. Eggs were found on 25 per cent of plants, an invasion he estimates could cost the farmer 10 to 15 per cent of his crop yield. "It hits the farmer in the pocketbook," he said.

Still, Schaafsma said farmers shouldn't panic. He cautioned that Canada's bug problem is mild compared to the cutworm invasion in some U.S. states.

Claude Parent, an agronomist with the Quebec Agriculture Ministry, agreed the contamination is — for now — on a relatively small scale. "We'll see some damage in a couple of fields," he said.

"But if we look at how it spread elsewhere, it starts small. In all the [U.S.] states we saw the population slowly increase."

The bugs moved into Ontario in 2008 and spread to Quebec a year later. The pretty adult moth, with its star- and crescent-moon wing markings, had flown northeast from Nebraska, Arkansas and Colorado.

Pest eats tomatoes, nightshade

The migration was first reported in Michigan a few years ago, and farmers in the border state are now reporting significant damage to their crops.

The insect also dines on dry beans — though not soybeans — and to a lesser extent on tomatoes and nightshade.

Corn farmers have two weapons in the battle against the cutworm: spraying with insecticides, or planting a breed of transgenic corn genetically modified to produce a specific insecticidal protein.

Entomologists are still studying the most effective way to spray the tough-to-kill pests, which can be hard to reach with chemicals once they've moved down into the ear of the corn.

They are also still trying to unlock why the insect suddenly started to settle in Canada. They do know it seems to prefer sandy soil into which it can burrow and survive the winter.

Schaafsma and Parent agreed the western bean cutworm is an unwelcome guest that's unlikely to leave any time soon. But they maintained the first few years of the infestation will be the worst.