82 



THE SCOLYTID BEETLES. 



GENERATION. 



The overwintered broods of adults begin to attack the trees, exca- 

 vate galleries, and deposit eggs about the &st of August and continue 

 to do so during August and September, until October or later, but the 

 principal period of attack is in August. The larvae begin to hatch 

 early in August and begin to transform to pupsB and adults in Septem- 

 ber and October. Under favorable conditions a few adults may 

 emerge late in the fall, but evidently it is the normal habit for the 



Fig. 45.— The mountain pine beetle: Egg galleries and larval mines in bark. Reduced. 

 (Author's illustration. ) 



broods of this generation to pass the winter as all stages of larvse, as 

 adults in pupal cases, and as parent adults, and it is evident that some 

 individuals of the delayed broods do not complete their development 

 until in the fall of the year following and that some of them pass the 

 second winter as parent and young adults. There is, therefore, but 

 one generation annually, with a possible overlapping of the generations 

 of three years during the summer. 



