48 



THE SCOLYTTD BEETLES. 



It has been determined that this species can be attracted to girdled 

 and felled trap trees. Under certain conditions, therefore — as in the 

 case of the absence of logging operations and where only a few scat- 

 tering trees are infested — it may be desirable, as a means of main- 

 taining control, to provide a few trap trees to attract the first genera- 

 tion. This can be done by girdling two or three inferior trees to 

 the heartwood or by felling them in June. Then, if they become 

 infested with this beetle, the bark should be removed from the main 

 trunk and burned by the middle of August. Trap trees to attract 

 the second generation should be prepared in August and September 

 and barked before the first of the following May. Usually an aver- 

 age of one to three trees to the acre should be sufficient for this 

 purpose. However, the number will depend largely upon the preva- 

 lence of the insect. (See preceding reference to trap trees, pp. 33-34.) 



Fig. 11.— The western pine beetle: Distribution map. (Author's illustration.) 



Continued timber-cutting operations within an area of from 20 

 to 50 square miles usually provide sufficient breeding places in the 

 bark of the logs and tops of the felled trees to satisfy the requirements 

 of this species ; but if the living timber should be at any time threat- 

 ened by the broods emerging from the slash, or if it is desirable to 

 include in timber-sale and timber-cutting regulations certain provi- 

 sions for the burning of the slash, this work should be done about the 

 first of August for the slash of the winter and spring cutting, and dur- 

 ing the winter for that of the late summer and fall cutting; the latter 

 period, however, is preferable, on account of the danger of starting 

 forest fires by summer burning. 



