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Of European origin, this defoliating insect is regarded as an important major pest due to its wide range of hosts (over 500 different plant species) and its capacity to kill or severely damage trees. Gypsy moth has established itself in Ontario, Quebec, New Brunswick, and Nova Scotia. It has also been found on the west coast. Preferred tree species are oak, white birch, larch, linden, willow, Manitoba maple, poplar, apple, and speckled alder, along with beech, hemlock, pine, and spruce (the latter when larvae are half-grown).

Infested areas are easily identified by the presence of egg masses on trunks and branches. After they emerge, it is the larvae that cause all tree damage, especially in the last 2 weeks of feeding (June). During severe outbreaks, all trees and shrubs in an infested area are completely stripped of foliage generally resulting in growth reduction for hardwoods (such as oak) and death within the first year for conifers (such as pine).

Points of interest

• one generation per year
• very common pest on most continents except for the Pacific islands
• first introduced in 1869 for silk production in the state of Massachusetts
• population levels fluctuate widely with long periods of scarcity punctuated with rapid increases to epidemic levels followed by sudden declines
• larvae feed mainly at night and rest during the day in a shaded spot
• females are flightless so natural spread occurs due to the caterpillar stage; further spread results from the transportation of objects onto which eggs have been laid
• average of mature larval or full-grown length is 40–65 mm

Additional information: Forest Pest Leaflet #75

References

Martineau, R. 1984. Insects Harmful to Forest Trees. Multiscience Publications Ltd., Montreal, Environment Canada, Canadian Forestry Service, Ottawa, and Supply and Services Canada, Canadian Government Publishing Centre, Ottawa. For. Tech. Rep. 32. 261 p. + x.

Rose, A.H.; Lindquist, O.H. 1997. Insects of Eastern Hardwood Trees. Natural Resources Canada, Canadian Forest Service, Ottawa. Revised edition. For. Tech. Rep. 29. 304 p.