A normal infestation under certain conditions 

 nay at any time "become epidemic. While epidemic infesta- 

 tions cause a greater annual timber loss for a certain lo- 

 cality, it is probable that the normal infestation, as a 

 whole, exceeds the epidemic in the total annual loss of tim- 

 ber and particular attention should be given by district rang- 

 ers to the control of this phase of insect depredations. 



Causes of Insect Infestations. 



Infestations have always existed in conifercnis 

 forests. Trees here anc< there have been dying from time to 

 time. These infestations before forests "/ere commercial^ 

 used increased locally, due to favorable conditions such as 

 a large number of windfalls, snowbreak, windbreak, and light- 

 ning fires or infestations from various species of fungi. 

 Nearly all freshly killed material breeds berk-boring insects 

 in large numbers. The epidemic runs through a certain number 

 of years and partially dies out. Sometimes this is due to 

 lack of food supply in the immediate vicinity, but more often 

 to attacks of enemies both predaceous anfl parasitic. Infesta- 

 tions may entirely die out or increase again after the para- 

 sitic and predaceous enemies diminish fron a lack of food. 



Since the forests have become popular eel by white 

 men these areas of infestation have increased in si?.e and be- 

 come more numerous. The reason for this nay be easily seen, 



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