INSECT DEPREDATIONS IN NOETH AMERICAN FORESTS. 73 



ditions and facilities favorable and unfavorable for success in prac- 

 tical applications according to the recommended method or policy of 

 control. 



As has been shown, the mature or merchantable timber is the most 

 susceptible to injury or death from the ravages of insects. There- 

 fore, considered from the standpoint of insect control and the pre- 

 vention of one of the greatest items of loss, it is important that such 

 matured timber should be utilized before it begins to deteriorate, or 

 before it reaches the stage of unprofitable growth. 



For the greatest success in dealing with forest insects, it, must be 

 recognized that there are certain features in the habits and seasonal 

 history of each species which differ to a greater or less extent from 

 those of all other species, even of the "same genus; that there are cer- 

 tain features in the characteristics of the various species of trees 

 which differ from those of all other species ; and that as a rule it is the 

 technical knowledge, of these peculiar features or characteristics of 

 the trees and their enemies which furnishes the clew to successful 

 methods of'control. 



There are also many peculiar features in the prevailing conditions 

 in different localities, some of them favorable, others unfavorable, for 

 the practical application according to a given method, so that while 

 certain general advice may applj' in a broad sense and be available 

 for utilization by the practical man, whether owner, manager, or 

 forester, without further advice, it is often necessary to diagnose a 

 given case before specific expert advice can be given as to the exact 

 cause and the most effective method or policy to be adopted, just as a 

 physician must diagnose a case of illness or injury before prescribing 

 the required treatment for his patient. 



Therefore, in a consideration of the problem as to how far the 

 waste of forest resources caused by insects can be prevented and how 

 far the damaged timber can be utilized, we will attempt to give only 

 general statements based on the results of our observations relating to 

 some of the principal kinds of loss discussed in the first part of this 

 paper, namely, by insects which (1) kill the trees, (2) cause injuries 

 to the wood of living timber, (3) reduce future supplies, and (4) 

 cause injuries to the manufactured products. In addition, we will 

 consider the utilization of natural enemies of injurious insects, the 

 utilization of damaged timber, and the present conditions and 

 opportunities for success in the general control of forest insects. 



CONTROL OF-BARKBEETLES WHICH KILL TREES. 



The barkbeetles which kill trees attack the bark on the trunk and 



destroy the life of the tree by extending their burrows or galleries in 



all directions through the inner living bark. The broods of young 



grubs or larvae develop within the inner bark, on which they feed. 



61830°— Bull. 58—10 6 



