The Douglas-fir tussock moth in the Northern Region : a cartographic history of outbreaks from 1928 to 1973

The Douglas-fir tussock moth, Orgyia pseudotsugata McD., periodically\ud defoliates Douglas-fir, true firs, and other host trees in forests of\ud the western United States. In the Northern Region, these infestations\ud occur about once every decade.\ud This history covers the earliest recorded outbreak in northeastern\ud Washington from 1928 to 1930 and includes information about outbreaks\ud in northern Idaho and eastern Washington from 1944 to 1947, northeastern\ud Washington and northern Idaho from 1950 to 1955, northern\ud Idaho and western Montana from 1961 to 1965, and the current outbreak\ud in northern Idaho, northeastern Washington, and western Montana which\ud began in 1970.\ud These outbreaks usually last from 2 to 4 years in forested areas and\ud typically go through a buildup phase the first year, an outbreak\ud phase the second year, and a declining phase the third year due to\ud parasites and/or polyhedrosis virus. Exceptions are: It may take\ud an outbreak 2 years to build up or occasionally natural control\ud agents can cause a population collapse at the end of the second year