28 THE SCOLYTID BEETLES. 



ago indicates quite conclusively that the birds were rendering a most 

 valuable service as a natural check to the multiplication and destruc- 

 tive work of the eastern spruce beetle. The work of birds is common 

 in sections where species 1, 9, and 10 and other western species are 

 prevalent. Yet birds evidently render the greatest service where but 

 few trees are being killed, since their concentrated work may prevent 

 an abnormal increase of the beetles; but where many hundreds or 

 thousands of trees are being killed, the limited number of birds can 

 have little or no effect. Therefore, while the birds are among the 

 foresters' valuable friends, they can not, even with the utmost pro- 

 tection, always be relied upon to protect the forest from its insect 

 enemies. We must remember that there are most complex interre- 

 lations between birds, the injurious insects, the beneficial insects, the 

 enemies of the birds, etc., which do not always result in benefit to the 

 forest. In fact it is often quite the reverse. Therefore, in order for 

 the forester or owner of the forest to derive the greatest benefit from 

 the conflict, he must not only direct his efforts toward utilizing as far 

 as possible the natural factors which are contributing to his personal 

 interests, but whenever the enemies of the forest threaten to get 

 beyond natural control he must enter the fight and by radical artificial 

 means force them back to their normal defensive position. 



DISEASES OF THE INSECTS. 



While evidence has frequently been found of the work of fungous or 

 bacterial diseases in destroying the adults and immature stages of the 

 beetles, the matter will require detailed study by specialists on such 

 diseases before any definite conclusions can be formed in regard to 

 their economic relations or importance. 



DISEASES OF THE TREES. 



Evidence has been found from time to time that the primary cause 

 of the death of isolated large and small trees and saplings was some 

 fungous disease of the roots and base of the stem, and that the larger 

 trees so affected sometimes favored the multiplication of a destructive 

 insect enemy. Evidence has also been found that certain diseases of 

 the inner bark and sapwood, like the bluing fungus studied by Dr. Her-* 

 mann von Schrenk, are sometimes very injurious and destructive to 

 the developing broods of the beetles. It is also apparent that this 

 fungus, which is said to depend largely on the wounds made by the 

 beetles in finding its way into the living bark and sapwood of the 

 standing timber, may also contribute to the more rapid and certain 



a The "Bluing" and the "Red-Rot" of the Western Yellow Pine, with Special 

 Reference to the Black Hills Forest Reserve. By Hermann von Schrenk. Bui. 36, 

 Bureau of Plant Industry, 1903. 



