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 onlv 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, a 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 
"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. 
