158 OUR NATIONAL FORESTS 



The control of insect pests is a difficult matter. 

 On areas where insect depredations are conspicuous 

 and are liable to spread to nearby valuable timber, 

 control measures are undertaken in cooperation 

 with experts from the Bureau of Entomology. In 

 these control pro j ects, crews of men fell the infested 

 trees, strip the bark from them, and burn the bark 

 (usually at a time of the year when the young 

 broods of beetles are still in the bark, namely, fall 

 or winter) . Trap trees are sometimes resorted to. 

 In this method, trees are girdled with an ax and 

 thereby weakened to such a degree that beetles are 

 attracted to it. After such a tree has become thor- 

 oughly infested in this manner, it is cut down and 

 burned. In the case of a large, conspicuous infes- 

 tation, an insect reconnoissance is made, in order to 

 obtain an estimate of the percentage of trees that 

 have been killed by insects. When it is possible, 

 the timber is immediately sold. For example, on 

 the Lassen National Forest, the writer several years 

 ago made such an estimate of an infestation caused 

 by the mountain pine beetle, covering over 100,000 

 acres. The reconnoissance showed that about 35 

 per cent, of the trees above 12 inches in diameter 

 had been killed. The killed timber was subse- 



