THE GENUS DENDROCTONUS. 127 
ACTIVITY OF OVERWINTERED BROODS. 
The adults begin to emerge from the bark and fly during May or 
June. They settle on felled or standing injured or on healthy trees 
and enter the living bark to deposit eggs (see fig. 78), which soon 
hatch into larvae. The broods of larvae feed in the inner bark and 
destroy that portion of it intervening between the egg galleries, and 
thus completely girdle and cause the death of the trees which were 
healthy when attacked. The medium to larger matured trees are 
the ones commonly selected by the beetle, and it is capable of killing 
all such timber within a forest. 
In the Black Hills of South Dakota, at an altitude of about 5,000 
feet, Mr. Webb found an adult flying on June 10. On July 30 adults 
were excavating galleries and depositing eggs, which hatched and 
had developed into nearly fullgrown larvae on October 14. It would 
appear, therefore, that the adults of this species come out a little 
earlier than those of the eastern spruce beetle. 
ECONOMIC FEATURES. 
This species, like the eastern spruce beetle, attacks only the larger 
or mature trees. It is evidently the most important enemy of the 
Rocky Mountain spruces, and from time to time has caused wide- 
spread destruction. 
In October, 1905, the writer found evidence of its destructive 
work (see figs. 79, 80) in the Pike National Forest, caused many 
years ago. At the time the observations were made the indica- 
tions were that the vast destruction of spruce in this reserve here- 
tofore attributed to fire was primarily caused by this beetle. This 
was particularly evident on the southern slopes of Pikes Peak, at 
an altitude of about 10,000 feet, where nearly all of the timber had 
been killed some fifty years ago. In the fragmentary patches of 
living timber, old felled trunks of a primitive matured forest of 
Engelmann spruce were found thickly covering the ground. On the 
weather-beaten surface of these logs the characteristic markings of 
the galleries of this beetle were so common as to leave little doubt 
that the trees had been killed during a destructive invasion by it — 
indeed, very conclusive evidence of this was found in the presence 
of dried resin in the egg-gallery grooves and on the surface of the 
wood, which would not be found there if the trees had been attacked 
after they were dying from other causes. 
This additional evidence, together with the known devastating 
work of this class of insects, makes it clear to the writer that there 
has been a most intimate interrelation of destructive barkbeetles 
and forest fires in the denudation of the vast areas of once heavily 
forested lands in the Rocky Mountain region, and that in very many 
