30 



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



ing the newly planted trees nonresistant to their attacks, they pro- 

 ceeded to cause serious damage. 



The control of insects that feed on twigs and terminal shoots pre- 

 sents many difficult problems, and under forest conditions little of a 

 practical nature can be clone to control them, after they have become 

 established. Under management, however, much damage from this 

 source can be avoided by growing trees in dense stands or by keeping 

 the trees in as vigorous growing condition as possible. 



Under special conditions, Avhere the value of the young trees justi- 

 fies the expense, control can be accomplished by hand pickina' the 



Figure 11. — Group of young, thrifty ii'ii!.'! .i>a pim-.- killed by scale insects. (Group 

 killings of this type are most frequently caused by engraver beetles.) 



infested shoots and either burning them or placing them in cages 

 designed to retain the destructive species, but allow the escape of its 

 parasites. Recently one or two projects of this character have been 

 carried out with very satisfactory results. In the case of the isolated 

 Nebraska sand-hill plantations much good was accomjDlished by in- 

 troducing the native parasites of the tip moths. 



TWIG BEETLES 



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

 coniferous and broad-leaved 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.'' 



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

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



