84 THE SCOLYTID BEETLES. 
surface of the wood of the main trunk. The larvae excavate short 
and broad, or long and slender food burrows at right angles to the 
primary gallery, and usually transform in their individual pupal 
cells exposed in the inner bark or between the inner bark and wood, 
the cells marking the surface of the wood. After the new broods of 
adults become matured, thev often bore out the bark intervening 
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between the cells and congregate under the loose bark before they 
begin to emerge: some of them, however, bore directly out from the 
transformation cells. 
Scarcely anything is known of the flight habits, but this species 
evidently flies in swarms late in the evening or at night. It is not 
improbable, however, that, like its near relative, the Black Hills 
beetle, it may at times swarm during the day. 
ECONOMIC FEATURES. 
While this species apparently prefers to attack injured and felled 
trees, it is in some localities often found attacking and killing the 
living timber over considerable areas. As a rule, the largest and best 
trees are attacked first, and their egg galleries and larval mines com- 
pletely girdle the trunks from near the ground up to the middle 
branches. 
The silver pine or western white pine (fig. 47) and lodgepole pine 
in Idaho and Montana, the sugar pine (figs. 48, 49) in Oregon and 
California, and especially the lodgepole pine in the Yosemite National 
Park, and in northwestern Oregon have suffered severely from its 
ravages. 
EVIDENCES OF ATTACK. 
The first external evidence of attack on living timber is the pres- 
ence of' pitch tubes on the outer bark of the trunk or of reddish bor- 
ings lodged in the flaky bark and around the base of the trees with 
normal green foliage. 
The second important external evidence of attack, and of infested 
trees, is the fading of the foliage in the fall and spring, followed by a 
yellowish or sorrel-top condition in May to June, and by red-tops 
during the period from July to September. The internal evidence is 
found by cutting into the bark and revealing the characteristic gal- 
leries occupied by the broods, but positive evidence of attack or 
infestation by this species is determined only by authentic identi- 
fication of specimens taken from the bark. Trees attacked for the 
first time early in August may have the foliage fading late in the fall. 
but as a rule the foliage remains green until the following spring. 
The broods begin to emerge by the time the leaves begin to change 
to the red-top condition, and are all out by the time all of the leaves 
are dead and red. Exceptions to this rule are frequently found, 
