The following is excerpted from the Methow Valley Ranger District Douglas-fir Tussock Moth Suppression Project, 2010 Final Report of 2011 Followup Monitoring:
"The Douglas-fir tussock moth (Orgyia pseudotsugata) is a major defoliator of Douglas-fir and true firs. Its populations are cyclic, and during its periodic outbreaks it can cause substantial damage. In 2010 the Methow Valley Ranger District controlled a building outbreak by aerially spraying high-value infested sites with the biological insecticide TM-BioControl1, a naturallyoccurring virus of the tussock moth. This report documents monitoring of that control effort.
Population Viability Determination: Extensive cocoon and egg mass sampling was conducted in October, 2009 to predict 2010 DFTM larval densities. Sampling was conducted in areas of concern identified in the Douglas-fir Tussock Moth Final Environmental Impact Statement (2000). The blocks that were treated for DFTM control in 2001 were used to identify sampling areas. Fortunately, shapefiles for the 2001 treatment blocks were still available on the Forest. Additional sampling was conducted outside EIS areas of concern to identify sites that could be used to compare the effects of treatment with non-treatment.
A total of 288 blocks were surveyed, of which 104 had sufficient numbers of cocoons and egg masses to indicate suboutbreak or outbreak populations of DFTM. Sampling protocol can be found in the Project Entomology Plan. Based on fall cocoon and egg mass samples, suboutbreak populations were predicted in five Analysis Units (AUs): Mazama, Lucky Jim, Eightmile, Cub Creek, and portions of Twisp River. Mazama, Lucky Jim, Eightmile and Twisp River were identified as areas of concern in the EIS. Cub Creek was not an area of concern, but was used as a control area for monitoring.
Egg masses were collected from sampled areas so the natural level of virus and parasitism could be determined. A natural virus level greater than 25% indicates a population that is already about to collapse from an epizootic, so direct control is not necessary (DFTM Handbook 548).
A total of 67 egg masses were collected, from which 2,807 eggs were extracted for rearing. Egg extraction was done by Roy Magelssen at the Wenatchee Forestry Sciences Lab in Wenatchee. Rearing was done at the Washington State Department of Natural Resources (WA DNR) facility in Olympia with the help of WA DNR entomologist Glenn Kohler. The assay was completed in late March, 2010. Percent hatch averaged 82%, and virus level averaged 0.5%. Parasitism was about 1%. Overall the populations appeared healthy, and direct control for foliage protection was indicated."