THE GENUS DENDKOCTONUS. 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 living 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 during 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 principal 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 
