INSECT DEPREDATIONS IN NORTH AMERICAN FORESTS. 85 



UTILIZATION OF NATIRAL KNKMIES AM) r.\( lOHS IN llli: CONTROL OF 



INJURIOUS INSECTS. 



Were it not for the natural chocks and natural factors of control 

 of sonic of the more destructive insect enemies of forest trees and 

 forest products, artificial control would in nuuiy cases be impossible, 

 and the depredations would evidently l)e far more continuous and 

 complete. These natural factors in the control of the depredating 

 insects consist of parasitic and predatory insects, diseases of insects, 

 birds, adverse clinuitic conditions, etc. AMiile one or more of these 

 beneficial factors exert a continuous and powerful influence toward 

 the prevention of a more extensive waste of forest resources, it has 

 been repeatedly demonstrated that they can not be depended on to 

 prevent widespread devastations or to otherwise work for tlu' best 

 interests of the private or public owner by protecting the best trees 

 and the best tree species. The insects and birds which i)rev upon the 

 depredating insects also have factors to contend against, consisting 

 of insects, birds, diseases, and climatic conditions. Therefore under 

 normal conditions the tendency is toward the preservation of a bal- 

 ance between the warring factors, but frecpiently the enemies of the 

 trees get the ascendancy and take on the character of an invasion, 

 which may continue for two or three or even ten years before the bal- 

 ance is again adjusted through the influence of the natural enemies 

 or diminished food supply. Thus a vast amount of timber or of a 

 given forest product may be destroyed before the factors of natural 

 control can i)revail. 



It is evident that the most effective utilization of the factors of 

 natural control will be through the alliance with them of the owner 

 of the forest in the artificial reduction of the enemies of the trees 

 ratlier than by efforts to make the natural enemies of the injurious 

 insects his allies through artificial introduction or dissemination. 

 The former is accomplished by the adoption of methods of couii)ating 

 the invaders wjiich will reduce and weaken their forces below their 

 power of prosecuting aggressive movements and attacks, or. as pre- 

 viously stated, to reduce their numbers to the point whei"e they nnist 

 occupy a defensive position against their natural tMieniies and be 

 dependent for their supjilies of food and l)i-eeding |)laces upon that 

 furnished through axoidalile mismanagement of the foi'csts and manu- 

 facturing operations. Thus the owner of the forest can contribute 

 greatly toward the preservation of a bahuice which will be to his 

 material l)enelit. On the other hand. In* may in the future, as in the 

 pa.st, contribute greatly to the nndtiplicati(»n of the dei)re(lating 

 insects and to greatly increased losses caused by them, through neglect 

 or a disregard of available information on the fundamental prin- 



