18 



pair, probably until the principal now 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 (PL 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, tig. 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 or < 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, fort}' 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 niany as seven galleries were observed in a 

 single chip, 6 inches wide and 12^- inches long (PL III, 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 10 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. 



