THE GENUS DENDROCTONUS. 
45 
out into the outer corky bark to pupate and transform to adults. 
After the adults are fully matured, and the proper time has come for 
them to emerge, they bore out of the bark (fig. 8) and fly to other 
trees, there to start a new at- 
tack. While very few observa- 
tions have been made on the 
habits of flight, it is probable 
that the beetles swarm during 
the evening and at night. 
ECONOMIC FEATURES. 
While it appears that this 
species prefers to attack weak- 
ened and felled trees, or isolat- 
ed healthy ones, it often attacks 
large numbers of healthy trees 
and causes extensive depreda- 
tions. It is especially destruc- 
tive to the western yellow pine 
(see fig. 10) in central Idaho, 
and in the mountains and 
higher valleys of eastern Wash- 
ington, Oregon, and California. 
It must therefore be classed 
among the important primary 
enemies of the pines within its 
range. As a rule, the largest 
and best trees are attacked, 
and the winding egg galleries 
beneath the bark serve to com- 
pletely girdle them and cause 
their death before the broods 
have developed and emerged. 
EVIDENCES OF ATTACK. 
The external evidence of at- 
tack by this species on healthy 
trees is the presence of pitch 
tubes (figs. 8, 9) at the entrance 
of the galleries, or reddish bor- 
ings lodged in the flakes of 
bark on the trunk and around 
its base. Trees attacked in 
Fig. 9, 
-Work of the western pine beetle: Pitch tubes 
on bark of tree. (From Webb.) 
