INSECTS AND DISEASES THAT DESTROY FORESTS 67 



When the tree is full of insects, it is cut down 

 and burned. In this way, infections which are 

 not too severe can often be remedied. 



The bark-boring beetles are the most destruc- 

 tive insects that attack our forests. They have 

 wasted enormous tracts of pine timber through- 

 out the southern states. The eastern spruce 

 beetle has destroyed countless feet of spruce. 

 The Engelmann spruce beetle has devastated 

 many forests of the Rocky Mountains. The 

 Black Hills beetle has killed billions of feet of 

 marketable timber in the Black Hills of South 

 Dakota. The hickory bark beetle, the Douglas 

 fir beetle and the larch worm have been very 

 destructive. 



Forest fungi cause most of the forest tree 

 diseases. A tree disease is any condition that pre- 

 vents the tree from growing and developing in 

 a normal, healthy manner. Acid fumes from 

 smelters, frost, sunscald, dry or extremely wet 

 weather, all limit the growth of trees. Leaf dis- 

 eases lessen the food supplies of the trees. Bark 

 diseases prevent the movement of the food sup- 

 plies. Sapwood ailments cut off the water supply 

 that rises from the roots. Seed and flower dis- 



