THE GENUS DENDROCTONUS. 



109 



the wood. The larvae transform to pupae and adults in individual 

 cells at the ends of their burrows, and when the adults are fully 

 matured they bore through the intervening bark and congregate in 

 broad cavities beneath the bark, remaining thus over winter, and 

 until they begin to emerge in the spring. Their habit of flight is 

 not well known, but they evidently fly or swarm in the evening or 

 early part of the night. 



Fig. 66. — The Douglas fir beetle. Egg galleries and larval mines: a, Beginning or basal sections of egg 

 galleries in bark; b, entrance; c, egg gallery; d, ventilating hole; e, egg nest; /, abnormal branch; 

 g, larval mines; h, egg gallery packed with borings; i, subsequent passage or inner gallery through 

 borings. (Author's illustration.) 



ECONOMIC FEATURES. 



The preference shown by this species for the bark of logs and 

 stumps of felled and injured trees makes it of less economic impor- 

 tance than the Black Hills beetle and some of the other species, but 

 in some of the localities, especially in Idaho and southward to southern 

 Colorado and northern New Mexico, it attacks the living timber and 

 causes extensive losses of the best as well as of the inferior Douglas fir. 



EVIDENCES OF ATTACK. 



The first evidence of attack on living trees is the appearance of 

 reddish boring dust in the crevices of the bark, lodged in the loose 

 bark on the trunk and around the base, and on the ground around 



