Generalist Defoliators Common in Alaska

Ghost looper- Epirrita undulata (Harrison)  
Great brown dart- Eurois astricta Morrison
Bruce spanworm- Operophtera bruceata (Hulst) 
Rusty tussock moth- Orgyia antiqua (L.)  
Speckled green fruitworm- Orthosia hibisci (Gueneé) 
Spear-marked black moth- Rheumaptera hastata (L.) 
Battered sallow moth- Sunira verberata (Smith) 

Current Status (2022 update)

Miscellaneous hardwood defoliation was recorded on over 1,000 acres during Aerial Detection Surveys (ADS). Most of this damage was along the south side of Kachemak Bay (815 acres), where notable alder defoliation also occurred. For more information on this defoliation event, see the alder defoliation update.

Symptoms, Life History & Impacts of Common Defoliators

The rusty tussock moth larva is a dark, hairy caterpillar adorned with four yellow “tussocks” of hair along the back. The caterpillars are generalist feeders on a variety of shrubs and trees, including aspen, willow, birch, cherry, and blueberry. The adult females are flightless, and the males are a rusty brown color with a white spot on each forewing. The adults lay eggs before winter, and caterpillars emerge from the eggs in the spring. High populations of these caterpillars can cause substantial defoliation. This moth is found throughout Alaska.  

The great brown dart larvae feed on aspen, cottonwood, alder, and birch in Southeast Alaska. Not much is known about this species, but larvae feed in spring and adults fly in late summer/early fall. The adults are marked with mottled grey/brown forewings. In June 2019, a local outbreak of the caterpillars was observed defoliating trees in Glacier Bay National Park, however, there was evidence that the caterpillars were infected with a baculovirus. By August the trees had re-foliated and recovered from the damage. 

The speckled green fruitworm larva is another generalist hardwood caterpillar that feeds on aspen, willow, birch, cherry, apple, and alder species throughout the state. The larvae is large, smooth caterpillar that is green in color with light stripes down the sides. The larvae overwinter as pupae in the soil, and adults emerge very early in spring (March – April). This is another caterpillar that can cause substantial local defoliation.  

The battered sallow moth is similar to the speckled green fruitworm, however, adults fly in late summer/early fall, rather than spring. The larvae are darker in color than the speckled green fruitworm, but also are generalist hardwood defoliators. In 2017, considerable hardwood defoliation was found along the Richardson Highway between Valdez and Glennallen. The battered sallow moth larvae (identified by DNA analysis) were severely defoliating alder, willow, balsam poplar, shrubs and some herbaceous species. 

Guidelines for Reducing Damage

Urban owners of ornamental hardwood trees and shrubs should insure the best possible growing conditions so that the trees can withstand periodic defoliation. Care should be taken to avoid injuring the roots with mechanical devices or soil compaction. To avoid moisture stress, trees should receive adequate water throughout the growing season.  

Content prepared by Alexandria Wenninger, Biological Technician, Forest Health Protection, alexandria.wenninger@usda.gov

For more information contact: Elizabeth Graham, PhD.  Forest Entomologist, Forest Health Protection, elizabeth.e.graham@usda.gov

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