18 THE BLACK HILLS BEETLE. 



value in its attractive influence on the Black Hills beetle to warrant 

 its adoption in efforts to control this insect. While many of the 

 trap trees were attacked, the percentage and density of the infesta- 

 tion were no greater than in near-by or distant healthy trees. On 

 the other hand, it was shown conclusively that the felled trap trees 

 were especially attractive to one of the most important secondary 

 enemies, namely, the Oregon Tomicus {Tomicus oregoni Eichh.). 



NATURAL ENEMIES. 

 INSECTS. 



WhUe a number of insect enemies of the Black Hills beetle have 

 been found during our investigations, they appear to have little effect 

 when the timber is dying over large areas, but under normal condi- 

 tions of scattering infested trees they seem to render valuable serv- 

 ice in preventing the rapid multiplication of the destructive beetle. 



BIRDS. 



The work of woodpeckers is frequently seen on infested trees, but, 

 like the beneficial insects, they do their greatest service, perhaps, 

 in helping to preserve the normal balance in the struggle of the trees 

 against insects and of the insects against their own enemies. 



DISEASES OF INSECTS. 



Evidence was frequently found of the destruction of part or all of 

 the broods in an infested tree by fungous diseases, but to what 

 extent this factor affects the decrease of the beetle has not been 

 determined. 



SECONDARY ENEMIES OF THE TREES, AND NEUTRAL INSECTS. 



Insects which attack only weakened, dying, or dead trees, and 

 those associated with a destructive or primary enemy are called sec- 

 ondary enemies. Insects which simply live under the bark or feed 

 on fungi, dead wood, and bark are in no manner responsible for 

 injury to the tree. Thus they are either neutral insects, scavengers, 

 or guests. 



There are so many of all of these classes of insects associated with 

 the Black Hills beetle in trees killed by it that it would require too 

 much space to discuss them in this connection; but it seems neces- 

 sary to say that the greatest care should be taken to avoid confusing 

 some of the species of secondary enemies with the primary one, and 

 that when there is the slightest doubt specimens should be sent to 

 this Bureau for identification. 



