INSECT ENEMIES OF WESTERN FORESTS 



103 



trees and red borino- dust in crevices and on the ground at the roots ; 

 later, by discoloration of the foliage, as it changes from normal 

 green to light 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 galleries 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. 









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Figure 50.— Lodgepole pine stand killed by the mountain pine beetle. 



Eggs 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 



