INSECT ENEMIES OF WESTERN FORESTS 1038 
trees and red boring dust in crevices and on the ground at the roots; 
later, by discoloration of the foliage, as 1t changes from normal 
green to hight greenish yellow and then to red. 
The adults are rather stout, black, cylindrical beetles from one- 
eighth to one-fifth inch in length. They excavate very long, per- 
pendicular egg galleries (figs. 51 and 52) through the inner living 
bark, engraving both bark and wood. The ealleries may be nearly 
straight or slightly sinuous, and sometimes, particularly in sugar 
pine, ~ decidedly winding, and at the bottom of these galleries there 
is a short crook, or bend, 1 or 2 inches in length. The } perpendicular 
portion of the gallery ranges in length from 12 to 36 inches and 
nearly always follows the grain of the wood. 
FIGURE 50.—Lodgepole pine stand killed by the mountain pine beetle. 
Kggs are deposited singly in cells or egg niches on alternate sides 
during the construction of the egg gallery. These hatch in a few 
days, and the small white larvae excavate short feeding tunnels at 
right angles to the egg gallery. These feeding tunnels vary in 
length and are exposed on the inner bark surface. When full grown, 
the larvae construct small pupal cells at the ends of the larval mines 
and in these transform to pupae and then to new adults. These 
pupal cells are usually exposed when the bark is removed, but in 
thick-bark trees they may be concealed in the inner bark. The new 
adults may bore away the intervening bark between pupal cells and 
congregate beneath the bark, prior to emergence, or individual emer- 
gence holes may be constructed directly from the pupal cells. Two 
or more insects often use the same emergence hole, and the emerging 
beetles often take advantage of cracks in the bark or holes resulting 
from woodpecker work. 
The winter is passed in all stages of development except that of 
the pupa. These overwintering broods emerge in three well-defined 
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