INSECT ENEMIES OF WESTERN POEESTS 



119 



mercial stands of Avestern Oregon and Washington seems to be quite 

 resistant to bark-beetle attack, and serious damage is rarely found. 

 At times, however, this tree suffers from bark beetles, even in this) 

 region of favorable groAvth. In the eastern portion of the Douglas 

 fir range, where growth conditions are less favorable and the timber 

 is of inferior quality, bark-beetle outbreaks of disastrous proportions 



^M^- 



FiGTiRB 58. — Typi(:;il KJiilenc.^ ;iiul c^s niches ol' I'LiutHj cues /o.n.m// w-f... 



are not an uncommon occurrence. The Douglas fir beetle (Dendroc- 

 tonus fseudotsugae) is the most common offender and causes the 

 bulk of the damage. Small Douglas firs are frequently killed by 

 the fir engraver beetles, particularly in situations where large num- 

 bers of these small beetles have developed in windfalls or slash. The 

 engravers usually responsible for this type of damage are Scolytus 

 unispinosus or Pseudohylesinus nebulosus. 



