INSECT DEPREDATIONS IN NORTH AMERICAN FORESTS. 85 



UTILIZATION OF NATURAL ENEMIES AND FACTORS IN TIIK <»iNTI!<»L (»F 



IN.Ilinor.S INSECTS. 



AVerc it not for the luitunil checks and natural factors of control 

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

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

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

 complete. These natural factors in the control of the depredating 

 insects conssist of parasitic and predatory insects, diseases of insects, 

 birds, adverse climatic conditions, etc. While 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 the be.st 

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

 and the best tree species. The insects and birds which prey 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 frequently 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 prevail. 



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 

 rather than by efforts to nudve the natural enemies of the injurious 

 insects his allies through artificial introduction or dis.seminati(m. 

 The former is accomj)lished l)y the adoption of methods of combating 

 the invaders which 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 (he j^oint wheiv (hey nuist 

 occupy a defensive position again.st their natural enemies and be 

 dependent for their supplies of food and breeding places upon (hat 

 furnished through av()idai)le mismanagement of (he fores(s and manu- 

 facturing operations. Thus the owner of (he forest can contribute 

 greatly toward the preservation of a balance which will be (o his 

 .material i>enefit. On (he other hand, he may in the future, as in (he 

 past, contribute greatly to the midtii)lica(ion of the depredating 

 insects and to greatly increased losses causi'd by (hem. (hrough neglec( 

 or a disregard of available information on the fundamental prin- 



