INSECT ENEMIES OF WESTERN FORESTS 



159 



tacking the true firs in all the Western States and in British Co- 

 lumbia, and at times has been exceedingly destructive to white fir 

 stands in California and Oregon. The adult is a short, shiny black 

 bark beetle about y 8 inch in length, without a prominent spine on 

 the ventral declivity. The egg galleries are excavated in the inner 

 bark and cut transversely across the grain of the wood, which 

 they score rather deeply for a distance of 2 to 6 inches on both 

 sides of a central entrance chamber. 



Eggs are laid in niches along both sides of these galleries and 

 the larvae, on hatching, work up and down the bole (fig. 73), ex- 



Figure 73. — The fir engraver (Scolytus ventralis) : A, Egg galleries and 

 larval mines; B, adults, X 5. 



tending their individual larval mines for a distance of 5 to 7 

 inches. A brown stain of the cambium caused by a fungus is al- 

 ways found in the area in which the larvae feed. Pupation occurs 

 in the inner bark at the end of the larval mines, and the new adults 

 bore directly to the surface of the bark when ready to emerge. 

 Frequently green trees are attacked and new broods develop and 

 emerge without destroying enough of the cambium to kill the tree. 



