6 Farmers’ Bulletin 1154. 
Trees of from 2 inches up to the largest diameter are attacked by 
this borer. The large trees are frequently attacked close to the limbs, 
while smaller trees are attacked from the base up. 
One of the characteristic features of the injury caused by this in- 
sect is that it is concentrated on trees that have been previously in- 
jured. In every clump of aspens trees heavily infested, or what may 
be called “brood trees,” can be found. This feature tends to limit 
the destruction by this borer by confining it to such trees, and at the 
Fic. 3.—A summer home on Cheyenne Mountain, Colo., 
being constructed from aspen logs. These trees were 
cut within a radius of 200 yards of the structure. Hle- 
vation at this point, 9,000 feet. 
same time it destroys many of the insects, in that these brood trees 
are frequently broken off by the wind or attacked by a fungus and a 
large percentage of the borers within fail to mature. 
One of the chief causes of the rapid deterioration and death of 
trees attacked by this insect is a wood rot® or fungus which follows 
the work of the borer and destroys the heartwood. Following the 
opening made through the bark this fungus rapidly penetrates and 
destroys the heartwood, and so weakens the tree that it is broken off 
by the wind. The development of this disease is often so rapid that 
it envelops and destroys the borer larva before it matures. 
5 Fomes igniarius. 
