INSECT DEPREDATIONS IN NORTTF AMEHIf'AN FORESTS. 73 



(litions and facilitios favorahlo and mil'axoraMc for success in prac- 

 tical applications according to the reconnnended method or policy of 

 control. 



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

 susceptible to injury oi' death from the rava<res of insects. There- 

 fore, considered from the standpoint ol" insect control and the pre- 

 vention of one of the p'eatest items of loss, it is important that such 

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

 before it reaches the stai;e of unprolital)Ie (growth. 



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

 recogniy.ed that there are certain features in the habits and seasonal 

 history of each species which ditlci- to a ijreater or less extent from 

 those of all other sjjecies. even of the same ^enus; that there are cer- 

 tain features in the characteristics of the various species of trees 

 Avhich dirt'er from those of all other species; and that as a nde it is the 

 technical knowled<;e of these jXH'uliar 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 prevailinir conditions 

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

 the practical application acc<)rdin<>: to a fjiven method, so that while 

 certain general advice may apply in a broad sense and be available 

 for utilization by the ])ractical man, whether owner, manager, or 

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

 given case l)efore specific expert advice can be given as to the exact 

 cause and the most ell'ectiv«' method or policy to be adopted, just as a 

 physician must diagnose a case of illness or injury before prescribing 

 the re(|uir(>d treatment for his patient. 



Therefore, in a consideration of the i)roblem 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 attem|)t to give only 

 general statements based on the results of our observations relating to 

 some of the principal Uind^ 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 li\ing timin'r. (:'») reduce futui'e supjilies, and (4) 

 cause injuiics to the manufactui'ed products. In addition, we will 

 con-^ider tlie utilization of natural enemies of injurious insects, the 

 utilization of damaged timlter, and the j)resent conditions and 

 opportunities for success in the general contiol of fore.st insects. 



CONTROL OK H \RKIU:i"ri.i:s WIIK II KM. I, IKKES. 



The barkl)eetles which kill trees attack the bark on the trunk and 

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

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

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



618.'W°— Bull. 58—10 () 



