342 AMERICAN FORESTRY 



INSECTS IN THEIR RELATION TO FUTURE SUPPLY OF TIMBER AND GENERAL PRINCIPLES 



OF CONTROL 



In the final circular of the series Dr. Hopkins states that investigations 

 conducted by him and his assistants in all sections of the country during the 

 past ten years indicate to them that the average percentage of loss in merchant- 

 able timber in the forests of the country to be charged to the insects is infinitely 

 greater than most people realize. The author's estimates for a ten-year period 

 have already been given. 



Insect-killed timber makes, as is well known, better fuel for forest fires 

 and fire contributes to the multiplication of insects which depredate on the 

 bark and wood of dying and dead trees, so that in forested areas where fires 

 are frequent, the damage to the wood of such trees is more severe, and fewer 

 injured trees recover on account of the abundance of secondary bark beetle 

 enemies which do not as a rule attack and kill living timber. Sometimes, when 

 the infested areas are swept by fire, the broods of insects are destroyed and 

 therefore complete fire control may easily conti'ibute to more extended depreda- 

 tions by insects on living timber, thus increasing rather than diminishing the 

 need for insect control. The setting of fires, however, or permitting them to 

 burn for the purpose of combatting insects, should never be undertaken or 

 permitted. Insect-killed timber could often be profitably utilized were it not 

 for the secondary attacks of wood-boring insects and the destruction of insect- 

 killed timber by forest fires. Injury by insects also often opens the way for 

 fungi, although certain species and groups of both insects and fungi are 

 trees. 



It is admittedly diflQcult to estimate losses in terms of board feet, or 

 dollars, there are so many contributing factors; but those estimates that are 

 made in these circulars are the best that can be presented on available evidence. 

 On this basis the author estimates the loss of standing timber killed or damaged 

 by insects at an equivalent of more than ten per cent of the quantity and 

 stumpage value of the total stand of merchantable timber in the United States 

 at any given time. Considering this in its various relations to the nation's 

 wealth and welfare and its effect on land values, it is difficult to estimate the 

 loss chargeable to insects. Considered from the standpoint of loss in cash 

 revenue, it means an annual loss in timber and its products of more than one 

 hundred million dollars. 



PREVENTION AND CONTROL 



It is, as a rule, useless to attempt to exterminate. The insect forces 

 must be weakened 75 per cent or more to have the control effective, and this 

 can be done by proper management. The author lays great stress upon forest 

 management, but urges that any adjustment or modification in management 

 or business methods should be based on expert technical knowledge of the 

 species, habits, life-history and natural enemies of the insects involved, supple- 

 mented by expert knowledge of principles of technical and applied forestry, and 

 by practical knowledge and experience as to local conditions. 



The value of natural checks and factors of control of injurious insects 

 without which such control would be impossible is dwelt upon. These natural 

 factors consist of parasitic and predatory insecls, diseases of insects, birds and 

 climatic conditions, and all of them play an important part which can be more or 

 less controlled by man in accomplishing the results. Finally he urges the 

 prompt utilization of all insect-infested timber, so that losses may be limited 

 as much as possible ; especially as by so doing we can contribute more, perhaps, 

 than in any other way to the reduction of the insects to or below their normal 

 numbers and thus provide against serious injui-y in the future. 



