Hosts: Preferred hosts include oak, apple, birch, boxelder, hawthorn, linden, poplar, sweet gum, and willow
Evidence: The distinctive felt-like, tan egg masses may be seen on bark, branches, and in other sheltered locations throughout the winter. In early May, shot hole damage to leaves by young larvae is apparent. Large larvae, which are hairy and gray with five pairs of blue dots and six pairs of red dots, consume all but the larger veins and midvein (a,b). They tend to feed at night, and gather in protected areas during the day. They may even gather in nests of the eastern tent caterpillar.
Life Cycle: There is one generation per year, with winter spent in the egg stage. Eggs hatch at the time that shadbush (serviceberry) begins to bloom, and larvae feed until July. Pupation takes place in sheltered locations on tree trunks or branches, or under other objects such as rocks and picnic tables. Adults emerge about 2 weeks later to mate and lay eggs. Although the heavier white females (c) do not fly, the smaller brown males are very active fliers and often become a nuisance in infested areas.
Management: Gypsy moth outbreaks occur periodically. Egg mass counts can be used to predict spring infestation levels, with 10 or more masses per tree indicating that severe defoliation may follow. As egg masses remain somewhat intact for several years, be sure that the count includes only viable eggs. Viable eggs should be firm to the touch and "pop" when crushed. Should you desire to provide relief by scraping off egg masses, be sure to scrape them into a container so that they can be destroyed, not onto the ground where they may still hatch. Bacillus thuringiensis applied to very young larvae in May can provide good control. Residual insecticides are necessary if applications are made after mid- to late-May. Although barrier bands can afford some protection to individual ornamental trees, they should be used with great caution. Any materials applied directly to the bark may be toxic to thin-barked trees. Diseases and starvation become important control agents when populations are high.
Figure a: E. Bradford Walker, Vermont Department of Forests, Parks and Recreation, Waterbury, VT
Figure b: E. Bradford Walker, Vermont Department of Forests, Parks and Recreation, Waterbury, VT
Figure c: Ronald S. Kelley, Vermont Department of Forests, Parks and Recreation, Morrisville, VT
Drooz, A.T. 1985. Insects of Eastern Forests. USDA Forest Service Miscellaneous Publication 1426. p 229-233;
Johnson, W.T. and Lyon, H.H. 1991. Insects That Feed on Trees and Shrubs. 2nd edition. Cornell University Press. p 138-141;
Martineau, R. 1984. Insects Harmful to Forest Trees. Agriculture Canada Government Publishing Centre, Supply and Services, Ottawa. p 112-114;
Rose, A.H. and Lindquist, O.H. 1997. Insects of Eastern Hardwood Trees. Canadian Forest Service Publication, Forestry Technical Report 29. p 141 and 144-145.