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This defoliating insect, native to North America, is found throughout Canada and attacks hardwood species. Sugar maple and beech are the preferred hosts in eastern Canada and trembling aspen and willow in the west. Damage by this insect is caused entirely by larvae feeding on the tree leaves. However, defoliation is not sufficient to kill the tree because the larvae are not particularly active and very often will not defoliate an entire leaf. Defoliation of maple trees does not appear to affect the flow of sap adversely. The damage to trees depends on the insect population density and the degree of leaf development at the time the larvae emerge. Usually larvae hatch at the same time as buds are opening. However, if the buds' opening is delayed, the larvae will devour the bud.

Points of interest

• one generation per year
• first reported in Canada in 1903
• when hatched, the larvae will climb the tree, but if they are disturbed, they will spin down from the tree on silken threads
• because the females are wingless, the main means of dispersal occurs when the threads break and the wind carries away the larvae
• moths appear quite late in the season, around October or November
• average of mature larval or full-grown length is 18 mm

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.