78 
THE SCOLYTID BEETLES. 
There is, therefore, but one generation annually, and it is probable 
that, like the roundheaded pine beetle, some individuals of the same 
generation may not complete their development until the second 
year, and that some adults may live over and deposit eggs the third 
3'ear. 
HABITS. 
The habits of this species appear to be similar to those of the round- 
headed pine beetle, with which it is frequently associated in the same 
tree. The character of the primary 
or egg gallery is distinguished by the 
larger, coarser appearance and by the 
Fig. 40.— The Colorado pine beetle {Den- 
droctonus approximate) : Adult. Greatly 
enlarged. (Author's illustration.) 
absence of exposed larval mines on the in- 
ner surface of the bark. The character of 
the primary galleries is shown in figures 
41 and 42. It appears that while some 
of the larvae may transform to adults in 
the inner bark, the majority of them 
transform in separate cells in the outer 
bark. The flight and food habits of the 
adults are evidently similar to those of 
the other species. 
ECONOMIC FEATURES. 
This species has been found attacking perfectly healthy trees in 
sufficient numbers to kill them. Therefore, if it should become 
isolated, and under favorable conditions multiply rapidly, it might 
easily become very destructive. As a rule, however, it prefers to 
Fig. 41.— The Colorado pine beetle: 
Single egg gallery. Reduced. 
(Author's illustration.) 
