158 MISC. PUBLICATION 273, U.S. DEPT. OF AGRICULTURE 



inner bark, usually deeply scoring the sapwood. Some members of 

 the genus are exceedingly destructive to true firs. Others work in 

 Douglas-fir, hemlock, spruce, or even in broadleaved trees. 



The Douglas-fir engraver (Scolytus unispinosus Lee.) is com- 

 monly found attacking weakened, injured, dying, or recently killed 

 Douglas-fir in the Pacific Coast States and British Columbia. 

 Sometimes it is a primary enemy of young Douglas-firs. The adults 

 are small, black, cylindrical, shining bark beetles about y 8 inch 

 in length, with a long spine projecting from the middle of the 

 nearly perpendicular face of the ventral declivity. The typical 

 egg gallery follows the grain of the wood and may range in length 

 from 1% to 3 inches. A short entrance tunnel leads into the main 

 gallery, at an angle of 45°, and a small nuptial chamber is con- 

 structed at the juncture (fig. 72) . The larvae work out at more or 



Figure 72. — Work of the Douglas-fir engraver (Scolytus unispinosus), 



less of a right angle from the egg gallery, and then work up or 

 down the tree so that the mines will not cross one another. The 

 winter is spent in the egg and young larval stages. Emergence of 

 adults takes place late in April, in May, June, and July. There 

 appear to be two generations annually. S. fiskei Blkm. is a closely 

 related species found attacking Douglas-fir in New Mexico and 

 Colorado. 



The fir engraver (Scolytus ven-tralis Lee.) (148) is found at- 



