THE GENUS DENDROCTONUS. 33 



• 



attention. While in exceptional cases it may be advisable to have 

 laws governing the treatment of timber infested with a dangerous 

 pest, such laws should be based on expert advice and should apply 

 to the more extreme and well-known cases only as a last resort. It 

 is probable that in most cases legislation will not be necessary, and 

 that more ultimate good will result without than with such laws, 

 especially when it can be made clear to the owner that his personal 

 interests demand that he take the proper action and that when nec- 

 essary his neighbors will render assistance, as is done in the case of 

 a forest fire. 



INACCESSIBLE AREAS. 



There are yet large inaccessible areas in the East and West where 

 it will not be practicable or possible to control the depredations by 

 these beetles, and which therefore must be left to natural adjustment. 

 While under natural control the matured timber will be lost, it will 

 usually be replaced by young growth, so that under normal conditions 

 the forest will be perpetuated. Under exceptional conditions and 

 combinations of detrimental influences, such as insects, fire, and 

 drought, extensive areas may, however, be completely denuded, never 

 to be reforested under natural conditions. This has doubtless hap- 

 pened in very many denuded and bare areas in the Rocky Mountain 

 region, which were at one time heavily forested. 



TRAP-TREE METHOD OF CONTROL. 



The well-known attraction of many species of European barkbeetles 

 to weakened, dying, and felled trees suggested to some of the earlier 

 writers on forest insects a method of barkbeetle control which since 

 that time has been widely recommended and under certain conditions 

 and for certain species of beetles has been successfully practiced. It 

 is the so-called trap-tree method, in which living trees are deadened 

 or felled at the proper time or season to attract the insects and induce 

 them to breed in the bark, where they can be easily destroyed by 

 removing the latter or burning the entire tree. Experience and 

 observations indicate, however, that while this method is successful 

 in attracting many species of bark and wood boring insects it does 

 not always attract those which are the most destructive to the living 

 trees, or at least not in sufficient numbers to justify its general recom- 

 mendation and adoption. 



Among the Dendroctonus beetles there are a few species which are 

 attracted to weakened and dying trees and to the stumps, logs, and 

 tops of recently felled living trees. These are species 1, 2, 4, 12, 13, 

 22, and 23 and, to a more limited extent, species 14 and 15, but ex- 

 tensive experiments have indicated quite conclusively that the Black 

 Hills beetle, the most destructive species of all, can not be success- 



89535— Bull. 83, pt. 1—09 4 



