INSECT ENEMIES OF WESTERN FORESTS 



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157 



Figure 71. — The Douglas-fir beetle (Dendroctonus pseudotsugae) : A, Gal- 

 leries on inner bark surface (natural size) ; B, larva; C, adult, X 4. 



A number of small bark beetles, belonging to Scolytus, Pseudo- 

 hylesinus, and related genera, commonly work under the bark and 

 score the sapwood of dying, broken, or felled firs, but at times 

 may attack and kill small trees. Beetles in this group are called 

 fir engraver beetles. 



Members of the genus Scolytus, are small, shiny, dark, or nearly 

 black bark beetles, which are easily recognized by the concave 

 appearance of the posterior ventral surface of the abdomen. The 

 adults feed for some time by making feeding pits in the twigs 

 and later attack in pairs and construct short egg galleries, usually 

 from a central entrance chamber. The larvae work out at right 

 angles from the egg gallery and bore through the phloem and 



