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.) 
