THE GENUS DENDROCTONUS. 



95 



ECONOMIC FEATURES. 



This species apparently differs from all of the others in its decided 

 preference for living timber, in which it excavates its egg galleries in 

 such a manner as to kill the tree and make the conditions favorable 

 for the development of its 

 broods. It is, therefore, a 

 primary enemy of the first 

 importance, especially as 

 related to the western yel- 

 low pine in the eastern sec- 

 tion of the Rocky Moun- 

 tain region south of east- 

 ern Montana. It has de- 

 stroyed a vast amount of 

 the best timber in the 

 Black Hills National Forest 

 of South Dakota, and is 

 threatening the destruction 

 of practically all of the best 

 timber there, as well as much 

 of the reproduction. It is 

 also destructive to the pine 

 in Colorado, New Mexico, 

 and Arizona. There is evi- 

 dence that extensive forests 

 have been destroyed in Col- 

 orado by this beetle and by 

 resulting forest fires during 

 the past fifty or seventy- 

 five years. 



EVIDENCES OF ATTACK. 



The first evidence of at- 

 tack and infestation on liv- 

 ing timber is the appear- 

 ance of pitch tubes on the 

 bark of the main trunk, or, 

 in the absence of these, of 

 reddish borings lodged in 

 the loose bark and on the 



ground around the base of the trees. This is usually the only ex^ 

 ternal evidence from the time the trees are attacked in the summer 

 and fall until the following spring. Sometimes during the winter, and 

 especially in the period from April to June, the more noticeable evi- 



Fig. 55.— The Black Hills beetle: a, Pitch tubes on sur- 

 face of bark, reduced; b, same, two-thirds natural size. 

 (Author's illustration.) 



