INSECT ENEMIES OF WESTERN FORESTS 163 



enemy of white, grand, red, Pacific silver, and possibly other firs 

 from California to British Columbia and eastward into Montana. 

 It makes a short horizontal egg gallery under the bark of dead or 

 dying firs, particularly at the extreme base or in the main roots. 



Some of the species of Dryocoetes are found working under the 

 bark of firs. While they are usually secondary enemies, they at 

 times attack and kill apparently healthy trees. 



The western balsam bark beetle Dryocoetes confusus Sw. (108) 

 is probably the most destructive member of the group and often 

 attacks alpine fir and sometimes other species of fir, spruce, and 

 pine. The adults are rather short, reddish-brown bark beetles 

 about y 8 inch long. They construct a small, circular nuptial cham- 

 ber under or in the bark, with several radiating egg galleries 

 which may score the sap wood (fig. 76). There is probably only 

 one generation a year. The species is distributed throughout the 

 Northwestern States from British Columbia southward in Oregon 

 and eastward to Colorado. 



Dryocoetes pseudotsugae Sw. is a secondary enemy of Douglas- 

 fir. The adults are reddish brown and are about % 6 inch long. 

 They construct short, irregular galleries in the inner bark of wind- 

 thrown and dying trees throughout California and northward to 

 British Columbia. The young adults gather in galleries in the 

 outer or inner bark, not in the cambium, to pass the winter. Adults 

 emerge early in the spring. Trees attacked in the spring produce 

 mature beetles by August. There is one generation and probably 

 a partial second each year. 



SPRUCE BARK BEETLES 



Spruce trees are attacked by a large number of bark beetles, 

 most of which are secondary enemies, breeding only in dying, 

 felled, or weakened trees. A few species, however, such as the 

 Engelmann spruce beetle and the Sitka spruce beetle, become 

 exceedingly destructive at times. Young trees are sometimes killed 

 by species of Ips, Pseudohyle sinus, and Dryocoetes, and by other 

 small engraver beetles. 



The Engelmann spruce beetle (Dendroctonus engelmanni 

 Hopk.) at relatively long intervals causes widespread destruction 

 of Engelmann spruce in the Rocky Mountain region. It will also 

 attack other species of spruce, and sometimes lodgepole pine, with- 

 in its range, which covers Oregon, Washington, Idaho, Montana, 

 Wyoming, the Black Hills of South Dakota, Utah, Colorado, Ari- 

 zona, and New Mexico. In endemic infestations large, overmature, 

 or mechanically weakened trees are preferred, with attacks seldom 

 extending below 6 feet above the ground. Distinct preference is 

 also shown for windfalls or logs. Blowdown areas are a primary 

 source of epidemic outbreaks. During epidemics trees of all ages 

 and diameters, except reproduction, are attacked, preference be- 

 ing shown for trees of larger diameter. The bole length of infesta- 

 tions varies, but averages from 18 to 20 feet in the lower bole 

 portion, from 2 to 3 feet above ground level. 



The adult beetles are about 14 inch long, dark reddish-brown to 

 black, the body sparsely clothed with long hairs. They excavate a 



