18 
pair, probably until the principal flow of pitch is exhausted. The 
gallery is then extended (probably by the female) transversely or sub- 
transversely for a short distance (seldom more than an inch), and then 
longitudinally up or down the tree, but usually up, varying from a 
few inches to a foot and a half, the normal length being about 1 foot. 
As soon as the gallery has been extended 1 or 2 inches from the 
entrance and basal cavity, small notches, or cavities, are excavated in 
the sides of the gallery, in each of which an egg is deposited, and so 
on until the gallery is completed. As the eggs are deposited, the bor- 
ings, instead of being thrown out at the entrance, are closely packed 
in the entrance burrow, basal cavity, and gallery, except near the 
farther end, which is kept open, enlarged, or extended to one side or 
the other, as it is occupied by the parent beetles, after their work of 
constructing the egg gallery is completed, until they die (PI. I). 
The bark of an infested tree is usually occupied by one of these 
primary galleries in every 1 to 6 inches of circumference from near the 
base to near the middle of the trunk (Pl. VII, fig. 2). Therefore they 
effectually check the normal movements of the sap, and the larval 
mines, which radiate from the primary gallery, destroy the intervening 
bark and complete the girdling process. 
Ten or twenty, or even forty or fifty pairs of beetles, attacking a 
tree 6 or 8 inches in diameter, would have little or no effect on:its 
vitality if scattered over the trunk from the base to near the top, but 
if concentrated on a limited space on the upper part of the trunk, and 
distributed so that there is a gallery at intervals of about every 
inch of the circumference, forty or fifty galleries are sufficient to so 
seriously affect the tree that other insects are attracted to it, and it 
soon dies from the girdling effect of the primary galleries and brood 
mines. The marks of as many as seven galleries were observed in a 
single chip, 6 inches wide and 124 inches long (PI. ILL, fig. 2), cut from 
a tree that had been killed by the beetles. This, with many other 
observations relating to the number of pitch tubes on freshly attacked 
trees and the galleries in the bark of dead and dying ones, indicates 
that the average tree killed by the beetles has from one hundred to 
two hundred galleries in 30 to 40 square feet of bark from the middle 
to base of the main stem or trunk. The number of eggs deposited 
in each gallery depends on the number of galleries within a given 
area of bark and the success of the attack. They vary from one or 
two to about one hundred, but the normal number appears to be about 
forty to fifty. If only one-half of these develop to adults there are 
four thousand or five thousand beetles to emerge from a single tree 8 
to 10 inches in diameter. Therefore the number of beetles that may 
emerge from the thousands of trees that die in a single year would 
make a swarm of millions of individuals. Even if this number were 
reduced one-half, it will be readily seen how the trouble may be 
rapidly extended over vast areas of forests. 
