168 MISC. PUBLICATION 273, U. S. DEPT. OF AGRICULTURE 
Trees that have been felled by wind or snow and those struck by 
lightning furnish favorable breeding places for a great many destruc- 
tive bark and wood borers. Such material is probably the natural 
habitat for many species that at times become excessively abundant 
and attack living trees. Many severe bark-beetle epidemics are 
known to have originated in areas of wind-blown timber. 
SLASH 
The debris left from the cutting of trees in the forest is a suitable 
and attractive breeding ground for a great many forest insects, some 
beneficial and some harmful (37, 67, 84). When slash is freshly 
produced, the dying inner bark is attractive to many species of bark 
beetles that are commonly found breeding in standing trees. Usually 
these bark beetles select in the slash or stumps the type and size in 
which they normally breed. Thus the limb- and twig-feeding bark 
beetles go into the brush and smaller pieces of slash, trunk-breed- 
ing bark beetles go into the cull logs and butts, and those that nor- 
mally work at the base of the tree attack the stumps. The abundance 
of the progeny depends a great deal upon the moisture and temper- 
ature conditions within the slash and the requirements of the differ- 
ent species of beetles. The red turpentine beetle, which breeds readily 
in pine stumps, frequently develops in such numbers as to do serious 
injury to adjacent forest trees. The trunk-breeding pine beetles 
rarely find suitable conditions in the cull logs and butts, and the 
progeny which they produce under such circumstances seldom cause 
any trouble in neighboring forests or to the reserve stand, especially 
where logging operations are continuous. The engraver and twig 
beetles, which breed in the smaller pieces of slash, frequently emerge 
in such enormous numbers as to kill patches of young trees and 
sometimes the tops of older trees. 
The wood-boring species that breed in slash must be considered 
generally beneficial, in that they help to decompose the wood and 
reduce the slash with its accompanying fire hazard. 
They may become injurious, however, and in order to avoid or reduce 
a possible menace from slash-breeding insects special considerations 
in slash disposal are frequently necessary. When a logging operation 
is continuous, and a fresh supply of slash is furnished throughout 
the flight period, the emerging progeny is repeatedly absorbed in the 
slash and in the logs removed to the mill, and no special precautions 
need be taken. But if a cutting operation ceases or is intermittent, 
as in the case of road and power-line development, then some damage 
from slash-breeding insects may be expected and should be avoided 
if possible. Burning the slash is beneficial provided the large limbs, 
cull logs, and stumps are included and the burning done before the 
insects emerge. In many cases this would mean that the burning 
would have to be done in the middle of summer or early in fall, and 
this would not be safe from the standpoint of fire hazard. Spreading 
the slash so as to receive the direct rays of the sun is effective in 
disposing of a high percentage of the insects in the more southern 
latitudes where high temperatures can be attained in and under the 
bark in this way. 
