36 



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



parasites and finding the newly planted trees nonresistant to their 

 attacks, they caused serious damage. 



The control of terminal-feeding insects often presents an ex- 

 tremely difficult problem. Spraying, dusting, hand picking of dam- 

 aged shoots, and the fostering of parasites have been the methods 

 of control most frequently tried. Now that DDT and other new 

 insecticides are available, some of the terminal feeders can be 

 effectively controlled through airplane spraying. The cambium- 

 feeding insects can usually be controlled by felling and burning 

 the infested material, and leaf -feeding forms can be controlled by 

 spraying or dusting. Special methods adapted to the control of 

 each group will be mentioned under later discussions. 



TWIG BEETLES 



The bark and pith of the smaller twigs, and branches of various 

 coniferous and broadleaved forest trees, are frequently mined by 

 the smaller species of bark beetles of the family Scolytidae. These 

 small twig beetles are often very abundant in the branches and 

 twigs of dead, dying, or recently felled trees and in the twigs of 

 healthy trees in the vicinity of slashings. Usually they confine their 

 attacks to the twigs of trees of various ages and are commonly 

 referred to as "twig beetles." 



«£ 



- v ~ ,& 



Figure 12. — The Douglas-fir twig beetle (Pityophthorus pseudotsugae) and 

 its work in mountain hemlock. Natural size. 



The attack of the twig beetles on living trees (fig. 12) is indi- 

 cated by a small pitch tube or the exudation of fine boring dust at 

 the point of attack on the twig. Under this will be found small 

 tunnels of uniform width, free from packed boring dust, which 



