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MISC. PUBLICATION 273, U. S. DEPT. OF AGRICULTURE 



for the light, liairj^ caterpillars can be easity picked up and carried 

 b}^ air currents for long distances. When disturbed or when in 

 search of food, the larger larvae lower themselves to the ground by 

 silken threads and travel rapidly, but dispersion at this stage could 

 only be for short distances at most. Pupation takes place within a 

 gray cocoon made of silk mixed with larA^al hairs. These may be 



attached to the twigs, limbs, 

 or trunks of trees or on the 

 underbrush. These cocoons 

 are sometimes formed in 

 masses six or seven layers 

 deep, and in such cases tlie 

 moths from the lower ones 

 are unable to emerge. 



The Douglas fir tussock 

 moth {Hemerocampco pseu- 

 dotsugcDta McD.) {2) (fig. 

 32) is a defoliator of major 

 importance in the Douglas 

 fir and balsam fir forests 

 of eastern Oregon, Wash- 

 ington, and British Colum- 

 bia, and in Nevada and 

 Idaho. It was first dis- 

 covered in British Colum- 

 bia in 1918, where it was 

 severely defoliating Doug- 

 las fir, and since then local 

 damage has been noted at 

 several points. The species 

 was not recorded from the 

 United States until 1927, 

 when an outbreak occurred 

 in Nevada. Then in 1929 

 several outbreaks were 

 found in different sections 

 of Idaho, northeastern 

 Washington, a n d eastern 

 Oregon. The epidemic in 

 the Colville National For- 

 est, Wash., reached a peak in 1930, spread over many square miles, and 

 killed at least 300,000,000 board feet of Douglas fir and balsam fir. 

 The Douglas fir which was not killed outright by the defoliation 

 subsequently succumbed in many cases to the attacks of the Douglas 

 fir beetle. These extensive killings have been followed by some 

 disastrous fires. 



The Douglas fir tussock moth shows a decided preference for 

 Douglas fir and species of balsam fir and can increase to epidemic 

 numbers only when feeding on these preferred host trees. It will, 

 hoAvever, feed on other species of conifers when mixed with firs, 

 and even on the underbrush. Defoliation first occurs at the tops of 

 trees, and as this foliage is destroyed the caterpillars work down on 

 the lower foliage. 



Figure o2. — The Douglas fir tussock moth {Hemero 

 campa pseudotsugata) : A, Female laying eggs 

 on cocoon; B. lai'va ; C, male moth; D, female 

 moth. Natural size. 



