8 INSECTS AND REDUCED TIMBER SUPPLY. 



Utilization 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 

 comj)lete. These natural factors in the control of the depredating 

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

 birds, adverse climatic conditions, etc. "Wliile one or more of these 

 beneficial factors exert a continuous and powerful influence toward 

 the prevention of a much greater 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 ma}' 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 supj)ly. 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 agencies of 

 natural control will be through the alliance a\ ith them of the owner of 

 the forest by his efforts toward an artificial reduction of the enemies 

 of the trees rather than by efforts to make the natural enemies of the 

 injurious insects his allies through artificialintroduction or dissemina- 

 tion. The former is accomplished by the adoption of methods of com- 

 bating the invaders which will reduce and weaken their forces below 

 their power of prosecuting aggressive movements and attacks, or, as 

 previously 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- 

 ciples of insect control in the management of forests and manufac- 

 turing enterprises. 



[Cir. 129] 



