THE PINE INVESTIGATION. 



367 



TREES ATTACKED BY OTHER BARK BEETLES DID NOT DIE. 



In 1894, it was found that the living, healthy trees attacked 

 by D. terebrans in 1893, and threatened by other bark beetles^ 

 did not die, and the vitality of the trees was not impaired by 

 the attack. 



THE TROUBLE ENDED. 



The trees that were 

 seriously injured by the 

 destructive bark beetle 

 ( Dendroctonus frontalis } 

 in 1891 2 and did not die 

 then, gradually died dur- 

 ing 18936, the larger 

 number dying in 1893 and 

 fewer each subsequent 

 year until 1896, when but 

 very few trees died, and 

 with them the last effects 

 of the work of the de- 

 structive bark beetle up- 

 on the living trees was 

 obliterated, except the 

 defects in the wood 

 which will be found in 

 trees that were attacked 

 and are now living. 



Fig. LI. Table mountain pine on Allegheny 

 front, Mineral county ; seven years after it 

 was killed by the destructive pine bark 

 beetle. 



CONCLUSIONS. 

 THE CAUSE OP THE TROUBLE. 



The cause of widespread devastation in the pine and spruce 

 timber in 1890 to 92 was the primary attack upon living 

 trees by swarms of the destructive pine bark beetle Dendroc- 

 tonus frontalis. 



WHEN THE DESTRUCTIVE BARK BEETLE DISAPPEARED THE TIMBER 



CEASED DYING. 



The cause of the cessation of the trouble was the death of 



