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



or predaceous enemies. Though these are distinct methods of 

 approach, it is often necessary to utilize more than one of them 

 in the solution of some forest-insect problems. 



Forest-insect control in the Western States is at present 

 largely a matter of protecting mature timber stands from the 

 ravages of insects by applying direct remedial control measures. 

 But as mature timber stands are cut and brought under manage- 

 ment, there will be more and more opportunity to apply silvi- 

 cultural measures in the solution of forest-insect problems. The 

 application of biological methods will depend largely upon what 

 is discovered through further research work as to the various 

 interrelationships of the insects concerned. 



The control of introduced or foreign pests presents quite dif- 

 ferent problems. In the first place, every effort is made to prevent 

 their introduction into this country through rigid quarantine 

 inspections at all ports of entry. Such pests as escape detection 

 and become established in the country are hedged about with 

 domestic quarantines for the prevention of their further spread, 

 while every effort is made to exterminate them before they have 

 become so firmly entrenched as to make such efforts impractical. 

 If these efforts fail, a search is made in their native homes for 

 the specific parasites and predators that normally hold the pests 

 in check there, and these are introduced and their establishment 

 attempted in this country. Work of this sort has been highly 

 successful in controlling many foreign pests that have been 

 inadvertently introduced. 



SILVICULTURAL CONTROL 



When timber stands are brought under management, it becomes 

 possible so to regulate conditions as to make forests less vulner- 

 able to insect attack; or if insect damage does occur, to salvage 

 the timber without undue loss. The underlying aim is to maintain 

 a biological balance throughout the period of rotation. This task 

 is hardly as simple as it sounds and cannot be accomplished 

 without a thorough understanding of all the factors contributing 

 to insect abundance and the resistance of forest stands. The 

 possibilities in this direction have not as yet been fully investi- 

 gated, and there is still much to be learned about the manage- 

 ment of western forest types before thoroughly sound methods 

 of procedure can be recommended with complete assurance of 

 success (36, 93). 



It is apparent, however, that this field of silvicultural control 

 offers almost unlimited possibilities. In the older forests much 

 can be done to lessen insect damage by avoiding injury to the 

 trees from forest fires and other weakening influences ; by keeping 

 forests in a healthful condition through disposal of windfalls, 

 slash, and other insect-breeding places; and by selective cutting 

 operations to remove the trees most susceptible to insect attack, 

 and through these cuttings to regulate forest composition and 

 density. In new plantations consideration should be given to the 

 selection of the site and the planting of species and varieties of 



