THE GENUS DENDROCTONUS. 25 



on the lower and middle trunk is so scorched and killed that the 

 beetles can not live in it. Spruce, however, may be killed or weak- 

 ened from injuries to the base and roots by a surface fire, and thus offer 

 especially favorable conditions for the multiplication of the spruce 

 beetles. On the other hand, a forest fire in a forest in which the 

 majority of the trees are infested by broods of beetles and dying 

 from their injuries may contribute to the destruction of the insects 

 and the protection of the remaining living timber. 



MATURED TIMBER. 



Practically all of the more destructive species show a decided pref- 

 erence for the larger and best-matured trees, and as a rule these are 

 killed first, and the younger timber is not attacked until later, if at all. 

 This is particularly true of the spruce beetles (Nos. 14 and 15), the 

 southern pine beetle in the East and South, the western pine beetle, 

 and the mountain pine beetle of the West. 



COMMERCIAL CUTTING. 



The cutting of Uving timber for commercial purposes may offer 

 favorable conditions for the multiplication of some of the species, 

 like the Douglas fir beetle and western pine beetle, but if such cut- 

 ting, within a range of less than 50 square miles, is more or less 

 continuous, it appears to serve as a protection to the living timber 

 rather than otherwise. On the other hand, local sporadic cutting 

 may bring about more or less serious results. Some species, like 

 the Black Hills beetle, are evidently not attracted from the living 

 trees by cutting operations, while the southern pine beetle in the 

 Southern States is greatly favored by sporadic cutting, especially if 

 carried on dvu-ing the summer months. 



SUMMER CUTTING. 



The cutting of healthy trees, or even of living beetle-infested 

 trees, during June, July, and August, in a forest or section where 

 the southern pine beetle, the western pine beetle, the mountain pine 

 beetle, or even the Black Hills beetle, is present, is more or less 

 objectionable from the fact that the beetles are attracted by the 

 odor of the exposed bark and wood and often attack many healthy 

 trees in the immediate vicinity of the felled ones. 



WINTER CUTTING. 



When any of the more destructive beetles are present in a forest 

 it is important that the prmcipal timber-cutting operations should 

 be carried on during the late fall and winter months, and completed 

 in the spring before the beetles begin to fly. This is especially 

 important when there is a large amount of infested timber to be 

 utilized, because it is necessary to remove the bark from the trunks 



