156 THE SCOLYTID BEETLES. 



May and June, and continue activity until hibernation begins in the 

 fall. The overwintered broods of large larvae evidently complete their 

 development to pupae and adults and emerge by July, while the young 

 larvae may not complete their development and emerge until in 

 September and October, and some individuals may pass the second 

 winter as adults. 



GENERATION. 



The overwintered broods of adults evidently begin to excavate 

 galleries and deposit eggs in the period from April to June, depending 

 on latitudes and altitudes, and continue their activity as successive 

 broods emerge, during June, July, August, and until September, or 

 later. The eggs begin to hatch probably within a week or ten days 

 after they are deposited. This process continues during May and 

 June or July, until September, or later. The larval development is 

 principally during July, August, and September, but continues until 

 hibernation begins. The more advanced larvae begin to transform 

 to pupae and adults in August, while some of the others continue trans- 

 formation during September and October, until cold weather, when 

 larvae of all stages, pupae, and adults are found. 



While it is possible that some of the more advanced broods in the 

 warmer localities may emerge in the late summer or early fall, it is 

 evident that by far the greater number pass the winter in the bark, 

 where they develop and emerge in the following spring and summer. 



The possibility of individuals of the overwintered parent adults, as 

 well as of young adults of the overwintered brood, excavating more 

 than one gallery, during the season, together with the probability that 

 some individuals of a single generation may pass through two or even 

 three winters, involves such an overlapping of broods of different 

 generations that even with extensive observations it has been impos- 

 sible to arrive at any definite conclusions regarding the normal period 

 required for the development and emergence of all of the broods of a 

 generation. 



HABITS. 



This species prefers to enter the bark of injured or dying trees or 

 that of the stumps and logs of those which have been felled, but often 

 attacks the perfectly healthy bark on the base and roots of healthy, 

 living trees. 



It has been found in practically all of the eastern pines and spruces 

 within its range of distribution, and in nearly all of the principal 

 western pines, but in none of the western spruces except the white 

 spruce in the Black Hills of South Dakota. It is probable that none 

 of the species of pine and spruce growing within its range is exempt 

 from its attack. We have no records of it in fir (Abies), or in Doug- 



