66 THE SCHOOL BOOK OF FORESTRY 



of coniferous trees are the first symptoms of 

 infection. These beetles bore through the bark 

 and into the wood. There they lay eggs. The 

 parent beetles soon die but their children con- 

 tinue the work of burrowing in the wood. Fin- 

 ally, they kill the tree by making a complete cut 

 around the trunk through the layers of wood 

 that act as waiters to carry the food from the 

 roots to the trunk, branches and leaves. The next 

 spring these young develop into full-grown 

 beetles and come out from the diseased tree. 

 They then attack new trees. 



When the forest rangers find evidences of 

 serious infection, they cut down the diseased 

 trees. They strip the bark from the trunk and 

 branches and burn it in the fall or winter when 

 the beetles are working in the bark and can be 

 destroyed most easily. If the infection of trees 

 extends over a large tract, and there is a nearby 

 market for the lumber the timber is sold as soon 

 as possible. Trap trees are also used in con- 

 trolling certain species of injurious forest insects. 

 Certain trees are girdled with an ax so that they 

 will become weakened or die, and thus provide 

 easy means of entrance for the insects. The 

 beetles swarm to such trees in great numbers. 



