HERMAN H. CHAPMAN 45 



fungi, when they appear on infested trees, or by cutting 

 out the trees. Insects are sometimes fatal to trees. They 

 work either by defoliation, or by boring in the bark or 

 wood of the tree. The defoliating insects are occasionally 

 serious, since a tree cannot live without leaves. The ma- 

 ture tamarack throughout the Bast was practically all 

 killed by a sawfly within the last twenty years. The im- 

 ported gypsy moth and the brown tail moth may, if not 

 controlled, kill most of the trees in regions which they 

 infest, and the state of Massachusetts has for years em- 

 ployed an army of men to combat them, not altogether 

 successfully. Ordinarily, insects are kept in check by 

 their natural enemies, which are insect parasites and birds. 

 But the parasites of imported insects are not always im- 

 ported with them. 



Bark beetles often do great damage to standing tim- 

 ber, killing all the trees over wide areas. These beetles 

 are ordinarily found only in weakened trees. But when 

 in great numbers, they attack healthy trees, choosing the 

 larger and older rather than the small trees, since the 

 former are really not so vigorous. The most disastrous 

 attack of beetles of recent years was the recent visita- 

 tion in the Black Hills of South Dakota, where over 200 

 million feet of pine were destroyed. As in other instan- 

 ces, the beetles suddenly disappeared, killed probably by 

 a fungus disease. But such plagues can always be con- 

 trolled if taken in time, by cutting the infested trees and 

 burning the tops, the logs being either removed or put 

 in a stream and the beetles drowned. When only a few 

 beetles exist, woodpeckers and other enemies keep them 

 within their natural limits. 



