Sudbury trees are experiencing severe defoliation this summer and there's one bug to blame, according to the Ministry of Natural Resources.

The gypsy moth is an invasive species that's been causing damage in Ontario since the 1980s.

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Vanessa Chaimbrone, MNR forest health technician for part of the northeast region, is responsible for aerial mapping of defoliated areas. (Hilary Duff/CBC)

But this year it's worse than usual as the larvae are chewing away hectares of local forest.

Vanessa Chambroine, a forest health technician with the Ministry of Natural Resources, spent days in July mapping defoliation caused by gypsy moths across Sudbury.

She takes note of the damage from the vantage point of a helicopter, saying "It's very important to get up there and see the defoliation on a landscape level."

These days, young, white birch trees "look like white little toothpicks on the hilltops," she said.

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Gypsy moth larvae chew away at the leaves on many birch trees in northern Ontario. (Hilary Duff/CBC)

A bad two years

Gypsy moth invasions are preceded by warm, dry summers, similar to what northeastern Ontario has experienced over the last few summers.

An entomologist with the MNR said it's been a bad two years.

"In 2012 we had severe defoliation, mostly around Sudbury, and it totaled 8,123 hectares," said Taylor Scarr.

"A lot of it [occurred] south of Sudbury and a little bit to the east, a little bit to the west, and a few pockets down on Manitoulin Island."

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Taylor Scarr, a provincial forest entomologist with the Ministry of Natural Resources. (Hilary Duff/CBC)

Scarr said mapping this year will show whether the defoliation has spread. Ten MNR forest technicians across the province have been out mapping the defoliation caused by gypsy moth.

Aerial maps created by technicians like Chambroine can be used to determine if an area should be sprayed with a bacterial insecticide.

The gypsy moth population usually dies off after a few years from a naturally occuring fungus.

Scarr said there are a number of steps people can take to protect their yards while the bugs are in their larvae state.

"You can use the bacterial insecticide BTK and that can be purchased at nurseries or hardware stores," he said.

"Also products that can be injected into the tree. You can also use high pressure water to knock the caterpillars off the tree."