342 YEARBOOK OF THE DEPARTMENT OF AGRICULTURE. 



wood by the parent beetle. It lives and feeds entirely within the 

 bark or wood until it attains its full growth, when it changes to the 

 pupa, or resting stage, within its burrow. The pupa later transforms 

 to a beetle, which emerges and flies in search of suitable places to 

 repeat the process of propagating the species. In nearly every in- 

 stance the entire damage is done while the insect is in the grub, or 

 borer, stage. This form is therefore the most important from an eco- 

 nomic standpoint. 



ECONOMIC IMPORTANCE. 



Some species of roundheaded borers kill trees outright by mining 

 in the bark, thus destroying the vitality of the tree, while others 

 injure the wood of dead, dying, or felled trees, or timbers manufac- 

 tured from such trees. Still others both kill the trees and injure the 

 wood for commercial purposes. The annual loss to owners of forest 

 trees and forest products from this source, if figured up in dollars 

 and cents, would amount to a sum far in excess of what the ordinary 

 individual would think possible. 



CHARACTER OF WORK. 



The work of this class of insects usually appears as irregular wind- 

 ing mines or " wormholes " in the bark and wood. The mine always 

 starts in the bark, where the minute larva just hatched from the egg 

 starts to bore and feed. At first the mine is very small, but gradually 

 becomes larger as the borer advances and grows in size. As already 

 indicated, the work of some species is confined entirely to the bark. 

 The work of other species is found in both bark and wood. In this case 

 the mine is continuous from bark to wood, the entrance into the wood 

 being a flattened oval hole. That part of the mine which is in the 

 wood may be long or short, according to the species. In general it is 

 more or less winding and irregular, contains borings and woody excre- 

 ment, and finally broadens out into a cell or " pupal chamber." At the 

 farther end of this cell the mine, or " exit burrow " as it now becomes, 

 usually leads directly to the surface by the shortest route. Upon the 

 surface it usually appears as a perfectly round " exit hole " (fig. 21, d). 



LIFE HISTORY AND HABITS. 



As a usual thing the adult female beetle lays an egg or a cluster of 

 eggs either in or upon the bark in the spring, summer, or early fall. 

 Sometimes the parent female excavates a pit in the bark with her 

 mandibles, through which the eggs are thrust by means of the ovi- 

 positor. In other cases eggs may be deposited in crevices of the bark 

 or under the overlapping scales of bark. In a few days after the egg is 



