Past and- Present Damage. 



Insect damage to the timber in our National For- 

 ests is supposed by some to be of recent origin. Evidence 

 shows, however, that it has always been present ever since 

 forests existed. 



Species of insects do not acquire food habits 

 suddenly unless introduced from other countries. All our 

 destructive insects in our virgin forests are indigenous, 

 and some, especially the bark beetles, are. peculiar to one 

 species of tree or to several allied species. Upon the let- 

 ter fact and upon the habits of the individual species of 

 insects our methods of control nork are based. In the past, 

 epidemics of infestation were probably caused by high wine's 

 uprooting or breaking trees, lightning, fires, snovbreak, 

 etc., or by favorable climatic conditions. Man has now sup- 

 plied other causes such as uncontrolled fellings, girdled 

 trees, cull logs, limbs and brush left over one season. Many 

 of the brush openings in timber supposed to be caused bjr fiin 

 are primrrily the result of epidemics of insect infestations. 

 Old logs on the ground generally show marks of tree -killing 

 beetles. In nany cases deep fire scars, where trees are burn- 

 ed a third or one half through, wore primarily caused by in- 

 sects killing a portion of the tree,* affording highly corn- 

 Bulletin 8'j, by Dr. A. D. Hopkins, page 151, Bureau of 

 Untonology. 



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