INSECT ENEMIES OF WESTERN FORESTS 



91 



B 



~9m 71 



Figure 36. — The Douglas-fir tussock moth (Hemerocampa pseudotsugata) : 

 A, Female laying eggs on cocoon; B, larvae, C, male moth; D, chrysalis. 

 Natural size. 



of this moth occurred at widely separated points in Canada, north- 

 eastern Washington, northeastern Oregon, Idaho, and Nevada. 

 The outbreak on the Colville National Forest, in Washington, 

 which reached a peak in 1929 and subsided in 1930, spread over 

 many square miles and killed at least 300,000,000 board feet of 

 Douglas-fir and true-fir. Many of the Douglas-firs that were not 

 killed outright by the defoliation later succumbed to the attacks 

 of the Douglas-fir beetle. One minor outbreak has been noted — 

 from 1937 to 1939 — which killed considerable timber over limited 

 areas of the Malheur and Umatilla National Forests in eastern 

 Oregon. Then in 1946 and 1947 a tremendous outbreak developed 

 over 500,000 acres in the fir forests of northern Idaho, northeast- 



