INSECT ENEMIES OF WESTERN FORESTS 245 



so as to bring the outbreak under control. With such aggressive 

 tree-killing species as the mountain pine beetle and the Black 

 Hills beetle, control work has been very effective in quickly 

 suppressing outbreaks wherever a high percentage of the infested 

 territory could be covered in a single season and the results were 

 not nullified by migrations from distant areas. Western pine 

 beetle epidemics have so frequently been partly dependent on a 

 weakened condition of the host trees that the results from control 

 have not been so clear-cut. Infestations have been reduced, but 

 unless the work is continued or conditions bring about improved 

 tree resistance, the reductions brought about by control efforts 

 are difficult to maintain. 



At best, remedial bark-beetle control is only a temporary ex- 

 pedient, or a method of suppressing outbreaks that have been 

 brought about through some interruption, disturbance, or failure 

 of the biological balance. The only permanent protection is 

 through the management of forest properties so as to maintain 

 the natural balance, or if this is broken by forces beyond man's 

 control, to be able to salvage the killed timber quickly enough to 

 prevent excessive loss. 



