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MISC. PUBLICATION 9 0, U. S. DEPT. OF AGBICULTUKE 



because when it was discovered it was carrying on a very destructive 

 timber-killing campaign in the Black Hills of South Dakota. (Fig. 

 42.) This beetle was responsible for killing over 150,000,000 feet 

 of western yellow pine timber in the Kaibab National Forest, Ariz., 

 during the period from 1919 to 1925. 



For some unknown reason the bark beetles increase in great num- 

 bers during certain periods, and at that time kill a great amount of 

 timber. After the epidemic has run for a few years it usually dies 

 down, and the infestation goes back to normal. The causes for the 

 sudden increase and decrease are not known. 



Figure 42. 



-The Black Hills beetle (Dendroctonus ponderoscp) ; A, Adult ; 

 B, larva; C, pupa. (A, greatly enlarged.) 



The Engelmann spruce beetle is a brownish-colored beetle and is 

 about the same size as the other beetles. In Utah it infests nothing 

 but Engelmann spruce. It works in the same way as the beetles 

 described above. 



The Douglas fir bark beetle is a reddish-brown beetle of about the 

 same size as the others, and usually works in Douglas fir, but has 

 been found to a limited extent in a few other trees. 



The lodgepole pine beetle works almost entirely in lodgepole pine. 

 There is also a beetle which works in white fir, commonly called 

 balsam, but it has never been known to be very destructive. 



In combating bark beetles the infested tree is sprayed with oil and 

 burned, or cut down and the bark burned off, thus destroying the 



