404 



WESt VIRGINIA EXPERIMENT STATION. 



Fig. LXXI. Completed primary and secondary galleries of 

 Dendroctonus frontalis. 



beetles bore directly through the bark to the wood and proceed 

 to excavate the preliminary gallery through the inner bark. 

 In this operation in healthy, living bark filled with turpentine, 

 it is necessary for one of the beetles to continually move back 

 and forth in the burrow, in order to keep it open and push out 

 and dispose of the borings and inflowing turpentine, as shown 

 in Fig. LXXII. 



Thus the excavation of the entrance through the living bark 

 is a slow and tedious process. In fact, a pair of beetles must 

 often spend their lives under the most unfavorable conditions, 

 affecting an entrance and the excavating of a gallery one or 

 two inches in length. From the time they penetrate the outer 

 layer of living bark, there must necessarily be an incessant 

 struggle with the sticky, resinous mass which is constantly 

 flowing into the burrow and threatening to overcome them. It 

 is often the fate of the leaders in the attack to be imprisoned in 

 their borrows and killed in this manner, or if not killed, may 

 be compelled to abandon their work before the condition of the 

 bark is favorable for them to deposite eggs. While these ad- 

 vance forces may fail in their object of depositing eggs and 

 perish in the effort to overcome the resistance of the invaded 

 trees, they make the conditions favorable for the success of 



