134 



THE SCOLYTID BEETLES. 



GENERATION. 



The adults begin to attack the trees, excavate galleries, and 

 deposit eggs early in May, and continue to do so through June, 

 probably until August, though the principal period is in May and 

 June. Fresh attacks and eggs are also found in September, either 

 by adults of overwintered broods or those developed from eggs 

 deposited early in the spring. The larvae begin to hatch in May, 

 and probably continue hatching until in August, but the principal 

 period is in June and July. The principal period of larval develop- 

 ment is during June, July, and August. The larvae begin trans- 

 forming to pupae toward the last of July, and continue transforming 



probably until winter, but the princi- 

 pal period is in August and September. 

 The pupae begin to transform to adults 

 probably during the second week in 

 August, and continue transforming un- 

 til winter. The principal period of 

 transformation to adults is during the 

 month of September. The period re- 

 quired for the development from eggs 

 to adults is about three months. 



The more advanced broods of the 

 generation complete their development 

 by the last part of August and first 

 part of September, while the later ones 

 evidently pass the winter as mature 

 larvae and immature adults, to com- 

 plete their development the following 

 spring. There is, therefore, one com- 

 plete generation during the year. 



The fact that eggs and young larvae 

 are common in September indicates 

 that some of the broods of the first 

 generation may emerge in the fall and deposit eggs from which there 

 is a partial second generation, but it is not improbable that some of 

 the parent beetles of the overwintered broods may leave the trees 

 after they have completed the first set of galleries, and excavate 

 galleries in the same or other trees. If there is a partial second 

 generation the brood passes the winter in the larval stage, possibly 

 together with the parent beetles. 



habits. 



This species appears to prefer to attack the living bark on the 

 trunks and stumps of felled trees and on the trunks of those still 

 standing but weakened and injured. Apparently it will not attack 



Fig. 85.— The Sitka spruce beetle (Den- 

 droctonus obesus): Adult. Greatly en- 

 larged. (Author's illustration.) 



