INSECT DEPEEDATIONS IN NORTH AMERICAN FORESTS. 85 



tJTILlZATION OF NATURAL ENEMIES AND FACTORS IN THE CONTROL OF 



INJURIOUS INSECTS. 



Were it not for the natural 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 would evidently be 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 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 best 

 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 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 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 the point where they must 

 occupy a defensive position against their natural enemies and be 

 dependent for their supplies of food and breeding places upon that 

 furnished through avoidable mismanagement of the forests and manu- 

 facturing operations. Thus the owner of the forest can contribute 

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

 material benefit. On the other hand, he may in the future, as in the 

 past, contribute greatly to the multiplication of the depredating 

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

 or a disregard of available information on the fundamental prin- 



