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



ficial in that the death and dropping of lateral branches leaves the 

 trunk of the tree freer from knots. In some cases, however, they 

 are injurious to small trees. 



Figure 13.- 



-Typical galleries of the pine twig beetle Pityophthorus rritidulus. 

 Natural size. 



FIR TWIG BEETLES 



Twigs of Douglas-fir and the true firs are frequently attacked 

 by several species and genera of twig bark beetles. These usually 

 are secondary enemies, attacking dying or felled trees, but occa- 

 sionally they have been found attacking small living trees in 

 crowded stands. The most common species found in twigs belong 

 to the genera Pityophthorus, Pityokteines, Carphoborus, Crypha- 

 lus, Crypturgus, Pseudohylesinus, and Scolytus. 



Species of Pityophthorus and Pityokteines make a central nup- 

 tial chamber from which several egg galleries radiate. One of the 

 most common species is Pityophthorus pseudotsngae Sw. (fig. 12). 

 Another common species found attacking true firs is Pityokteines 

 elegans Sw. The adults of both species are about y 8 inch long, 

 and the females have long, yellow hairs on the front of the head. 



