INSECT ENEMIES OF WESTERN FORESTS 



75 



Figure 31, — Ponderosa pines severely defoliated by the pine butterfly. 



ess. It is nature's way of disposing- of the old decadent trees to 

 make room for the younger, thriftier, growing individuals. Al- 

 though a natural process, this destruction is most wasteful from 

 the economic standpoint, since the old trees carry a large volume 

 of high-grade lumber. The prevention of this type of damage, 

 therefore, is an important phase of forest protection. 



When more of our forests come under intensive management, 

 and mature trees are utilized before they become decadent, much 

 of the present loss in virgin forests will be avoided. Until such a 

 time, the only alternative is the application of the control methods 

 discussed at the end of this section. 



Key to Recognition of Insect Injury to Mature Trees 



A. Foliage fed on; partially or wholly stripped from trees; or turning 



yellow or red. Trees sickly or dying. No insects working on 

 main trunk, branches, or roots Defoliators, p. 75 



B. Terminal shoots, laterals, or tips deformed or killed. Remainder of 



tree appearing healthy Twig feeders, p. 35 



C. Entire tree, or a large part, sickly, dying, or dead; foliage fading, 



turning yellow or red. Bark and phloem of main trunk or roots 

 mined by insects and killed Bark miners, p. 126 



DEFOLIATORS 



No other part of a forest tree offers nourishment to such a host 

 of insects as do the leaves. Literally thousands of insect species 

 feed on them in one way or another. Some mine within the needles, 

 some skeletonize the leaves, and others eat the entire leaf tissues 



