17 



when .stored in yards and factories. The seasoned and finished prod- 

 ucts, especiali_y those from sapwood, may he infested and dosti'oyed 

 by a number of species of so-called powder-post beetles. Construction 

 timbers and lumber, either before being utilized or while in the sti'uc- 

 ture, are su])iect to injuries b3Miian3' injurious and other species. The 

 old lumber and timbers of barns and outl)uildings, old log and frame 

 dwelling houses, are also infested and injured by forms which are 

 peculiar to such material. 



THE ECONOMIC RELATION OF INSECTS TO FORESTS. 



The preceding references to the insect fauna of forest trees and their 

 products are suggestive of the vast numbers of kinds, groups, and 

 societies of insects and the kind and character of injuries to be studied. 

 This leads us to a consideration of the economic relation of insects to 

 American forests under the varying conditions which prevail before 

 and after the country is settled and its resources developed. 



The relation of Injurious Insects to tJie priiidtive forests. — The rela- 

 tion of insect enemies of a forest before its resources are available to 

 civilized man is of little or no economic importance. They are simply 

 factors in the general struggle for existence between insects and trees, 

 and between the individuals of the forest community in which the 

 destruction of an individual tree by insects is a benefit to other insects 

 and other trees. If a matured or old tree is killed, it gives more room 

 for the development of the younger and more vigorous ones. The 

 injured, declining, and old individuals furnish breeding places for 

 successive comnumities of insects, which contribute to their death and 

 rapid decay. Thus the young tree growth is favored by light and 

 plant food, and soon fills up the vacancy. Invasions of destructive 

 insects ma}^ cause the death of one kind of tree growth over vast areas. 

 This favors the enormous multiplication of the insect fauna until the 

 destructive species perishes for lack of food supph% or from the mul- 

 tiplication of its natural enemies. This proves to be a calamity to the 

 other insects which have depended upon the destructive species to 

 furnish, in the dying and dead trees, the required conditions for their 

 existence. The dying and dead trees and the fallen and decaj^ed 

 branches, bark, and roots contribute to a more vigorous reproduction, 

 so that the forest found ])v the pioneer settler has lost nothing from 

 its insect enemies. 



The relation of the insect enemies of trees to the pioneer settler in a 

 forested country may be more beneficial than otherwise, so far as his 

 immediate needs are concerned. The forest must be cleared from the 

 land that is desiral)le for agricultural purposes, and in this process the 

 depredating insects may be decidedly beneficial. They contribute to 

 the death and rapid decay of the girdled trees in the clearings and 

 hackings. Invasions which cause the death of the large timber over 

 7796— No. 37—02 2 



