The gypsy moth (Lymantria dispar) is...

...an invasive forest pest introduced from Europe that is one of the most damaging tree defoliators found in North America. Gypsy moth larvae are able to feed on as many as 500 host species, including evergreens and are present in early- to mid-summer. Primary long-distance spread occurs via egg masses laid on or in vehicles, especially on firewood carried from infested areas.

Gypsy moth was initially brought to the northeastern US for silk production and accidentally became an established forest pest. It is slowly moving west, with the border of the generally infested area in central Wisconsin and some satellite populations in eastern Minnesota.  "Slow-the-spread" management approaches that are currently applied to new invasive pests originated in early efforts to manage gypsy moth populations.

Why are gypsy moths a problem?

• They are voracious eaters and they often defoliate entire trees.
• Gypsy moth larvae prefer to feed on oak and aspen, two common tree species in North Dakota.
• Because gypsy moths are non-native, there are few natural enemies to keep their populations under control. 
• Repeated defoliation in an infested area can lead to the death of entire stands of trees, changing the mix of tree species and affecting plant species composition and wildlife.

What would be the main impacts of gypsy moth infestation in ND?

• Outdoor recreation may be impacted due to defoliated trees, caterpillar presence on trees and roads and caterpillar feces falling from trees.
• Oak, a favored food source of the gypsy moth, is a valuable tree to the urban and rural landscape of North Dakota.
• Tree losses can have an economic impact on landowners in ways such as decreased property value or increased heating or cooling costs.

More information about gypsy moths:
http://www.dnr.state.mn.us/invasives/terrestrialanimals/gypsymoth/index.html
USDA APHIS | Gypsy Moth