THE GENUS DENDROCTONUS. 55 
and adults before cold weather, but evidently no adults emerge before 
winter. 
It is very evident that there is only one partial generation annually, 
and that some individuals may not complete their development 
until' the second year. It is evident, also, that the most retarded 
adults of the first generation may live over and deposit eggs the 
third year. 
HABITS. 
So far as known, this species confines its attacks to the western 
yellow pine, but it is probable that it will attack other species of 
pine growing within its range. It is nearly always associated with 
the other species of Dendroctonus and other barkbeetles in injured, 
dying, and felled trees. The adults enter the living to dying bark 
on the main trunk of the trees and excavate long, slightly winding, 
longitudinal, oblique, or nearly transverse and sometimes branched 
galleries through the inner bark, and often groove the outer layer 
of wood. In contrast with other species of Dendroctonus which 
are usually associated with it, except the Black Hills beetle, the larval 
mines are usually, but not always, exposed in the inner bark, and 
often mark the surface of the wood. Some of the larvae may trans- 
form to adults in the inner bark, but as a rule they enter the outer 
corky bark for this purpose. The young adults remain there until 
time for them to emerge and fly. Nothing is known of the food 
and flight habits, and many other facts are obscure, owing to the 
confusion of this with other species before it was recognized as 
distinct. 
ECONOMIC FEATURES. 
The fact that this species is usually associated with one or more 
of species 2, 3, 5, 8, and 10 renders its specific relation to the death of 
trees doubtful. It is evident, however, that if it should become iso- 
lated from the other species and occur in large numbers, it would be 
fully capable of killing trees on its own account. During the past year 
it was found associated with the Black Hills beetle in the destruc- 
tion of a large amount of timber, with evidence that some of the 
trees were killed by it alone. 
METHODS OF CONTROL. 
Whenever it is found that this species is causing the death of 
timber or is associated with other species in doing so, the bark should 
be removed from the main trunk of the infested trees and burned. 
The work should be done between the first of October and the middle 
of the following June. (See also "General methods of control," pp. 
29-35.) 
