44 



THE SCOLYTID BEETLES. 



pupae about the middle of August, and continue transforming until 

 cold weather, the principal period of transformation being from the 

 middle to the last of August. The pupae begin to transform to adults 

 after the middle of August, and continue transforming until cold 

 weather, but the principal period of transformation is between the 

 middle of August and the middle of September. 



The adults begin to emerge from the trees toward the last of 

 August, and continue to come out until in October, or later, but the 

 principal period of flight appears to be from the last of August to the 

 middle of September. While the majority of the broods of this 

 generation emerge before cold weather, it is evident that some of 

 them overwinter in all stages from larvae to young and parent adults. 



SECOND GENERATION. 



The records of observa- 

 tions indicate that the ear- 

 lier emerging adults of the 

 first seasonal generation 

 begin to deposit eggs about 

 the last of August, and 

 that the principal period 

 of attack is from the last 

 of August to the middle of 

 September. The larvae be- 

 gin to appear about the 

 first of September, and 

 continue to hatch until in 

 October, or later. No evi- 

 dence has been found that 

 the larvae of this genera- 

 tion transform to pupae 

 before winter, but it ap- 

 pears that the broods pass 

 the winter in all stages of 

 larvae, together with some of the parent adults. Thus, there is one 

 complete generation annually and a partial second one. 



Fig. 8.— The western pine beetle: Bark showing, a, a, pupal 

 cells; 6, exit burrows; c, pitch tubes. Reduced. (From 

 Webb.) 



HABITS. 



The adults attack the living bark on healthy, felled, and weakened 

 standing western yellow pine and sugar pine. They excavate long, 

 winding galleries (fig. 7) through the inner layers of bark, along the 

 sides of which single eggs are deposited at intervals of one-half inch 

 or more. The larvae ^normally do not excavate their mines through 

 the inner layers of bark, but through the middle or outer portion of 

 the inner bark. When the larvae have fully developed, they bore 



