108 THE SCOLYTID BEETLES. 



GENERATION. 



The overwintered broods of adults begin to attack the trees, 

 excavate new galleries, and deposit eggs about the middle of April. 

 The principal attack is during April, May, and June, but may con- 

 tinue into July or later. The eggs begin to hatch soon after they 

 are deposited, and the larvae begin to feed and continue to develop 

 during May, June, and July, into August or later, some retarded 

 individuals continuing to feed until cold weather. They begin to 

 transform to pupae and adults during the latter part of July and 

 continue their transformations during August until hibernation 

 begins. There is some evidence that a few of the more advanced 

 broods may emerge during September and October and deposit 

 eggs for the second generation during September and October, but 

 it is probable that these late-emerging broods are in the majority of 

 cases those developed from overwintered broods of young larvae or 

 from eggs deposited in the spring by overwintered parent adults. 

 It is very evident, however, that there is quite a complete develop- 

 ment of the first generation before the first of October, which accounts 

 for the passing of the winter principally as fully developed adults. 



HABITS. 



This species prefers to infest the stumps and logs of felled trees, 

 and injured and dying standing ones, in which it breeds in great 

 numbers, but in some localities and under favorable conditions it 

 will attack healthy living trees and cause their death. So far as 

 known, it breeds exclusively in the Douglas fir, bigcone spruce, and 

 western larch. The trunks of standing trees from a foot in diameter 

 to the large older ones are attacked from the ground to the middle 

 portion of the trunk, and sometimes to the lower branches. The 

 stumps, logs, tops, and larger branches of felled trees are favorite 

 breeding places and are usually thickly infested. 



The parent adults enter from the crevices and depressions in the 

 bark, excavate entrance burrows through the outer and inner 

 bark, and then extend their long, longitudinal egg galleries through 

 the inner living or dying bark. As the gallery is extended, the female 

 places her eggs in alternate groups along the sides, and when one 

 gallery is completed she either remains in the gallery until she dies or 

 leaves it to excavate a new one. The larvae, upon hatching, begin to 

 feed on the inner bark and to extend their food burrows at right or 

 oblique angles to the mother gallery. Instead of the burrows being 

 short and broad like those made by many other species, they are 

 often extended to a length equaling or exceeding that of the mother 

 gallery, and cross each other in such a manner as to completely 

 girdle the tree and separate the bark so that it is easily removed from 



