Minnesota has imposed a quarantine on the gypsy moth to slow the spread of the destructive invasive species.

The caterpillar form of the pest can defoliate a variety of trees and has turned up in record numbers along the Lake Superior shoreline.

Minnesota agriculture department spokesperson Kimberly Thielen Cremers said the quarantine applies to Cook and Lake Counties in the northeastern part of the state.

The Pest Mitigation and Bio-Control supervisor said she wants visitors to keep a sharp eye out for the destructive moth.

“When [people] are travelling to an area that is under quarantine, they [should] do a self-inspection, particularly if they're in the area visiting, and they're going back home,” she said.

gypsy moth

A female gypsy moth lays an egg mass. Each mass contains thousands of eggs. (Minnesota Department of Agriculture)

“If they find anything suspect — whether it be an egg mass or a larva — [they should] remove it.”

Ontario's Ministry of Natural Resources reports the gypsy moth spreads mostly by people transporting egg masses, which are covered in a brown, chamois-like hairy covering.

It says the risk to the northwest is eggs, larvae or pupae being brought in from Minnesota on outdoor equipment, vehicles and firewood.

Very hungry caterpillars

Thielen Cremers said the moth is “a European insect introduced in the US in the 1800s [and] there's not a lot of natural predators to keep the population in check.

She noted the insect will feed on up to 300 different species of trees and shrubs.

“We're very concerned with it moving into the state and the impact it will have,” Thielen Cremers continued.

"We have not seen any noticeable defoliation [yet] and that is pretty typical. Within Cook and Lake County, even though we have detected very high numbers of moths in our traps, it may not be noticeable to the general public. It isn't going to be out in outbreak numbers where you see noticeable defoliation [until another] three to five years."

The goal of the quarantine is to educate people and to slow the spread to other areas of the state.

"You don't have to be an expert to know gypsy moths,” she said.

“If you see anything that shouldn't be on your outdoor items, simply remove it. If folks do want to know, the egg mass is round and quarter in size, buff in colour, and tends to be moved in the fall and winter time frame. Right now they are in the caterpillar stage."

Pheromones, insecticides used

Ontario MNR entomologist Taylor Scarr said Minnesota has been part of a US program to slow the westward spread of gypsy moth.

The program uses pheromone trap surveys to detect the insect, and then aerial spraying with insecticides such as the bacterium BTK. Large amounts of the pheromone are also released to confuse the males and prevent them from finding the females.

“The program has been quite successful in slowing the spread of the insect but, if areas do eventually have well established populations, then these areas are deemed infested and put under quarantine to reduce the chances of people moving the insect to un-infested areas,” Scarr said in an email to CBC News.

“Therefore the slow-the-spread program and the quarantines help protect adjacent parts of Canada from the insect.”