THE GENUS DENDROCTONUS. 



63 



cies, all of which extend their galleries from the entrance in a trans- 

 verse or sublongitudinal and tortuous course through the inner bark 

 (fig. 19). Those of different pairs of beetles frequently cross each 

 other so that the many primary galleries, independent of the larval 

 mines, serve to com- 

 pletely girdle the tree 

 and kill the bark. Thus 

 these winding galleries 

 cause a much more rapid 

 death of the bark and 

 foliage than do the 

 straight longitudinal gal- 

 leries, like those of the 

 spruce beetles and the 

 Black Hills beetle. The 

 trees are killed by the 

 girdling effect of the 

 winding primary galler- 

 ies in the bark of the 

 middle portion of the 

 trunk, which, it has been 

 demonstrated, is the 

 most vital part, or at 

 least has less power of 

 resisting injuries than 

 the lower portion and 

 base. Instead of the 

 leaves of the trees re- 

 maining green until the 

 next season, as they do 

 on trees infested by the 

 spruce beetle and the 

 Black Hills beetle, all 

 except those on the trees 

 attacked late in the sea- 

 son commence to fade 

 in a few weeks after the 

 trees become infested. 



Fig. 25.— White pine timber killed by southern pine beetle 

 Condition in October, 1894, of trees which died in 1891 and 

 1893. (Original, from photograph.) 



ECONOMIC FEATURES. 



This species may be considered as one of the most dangerous enemies 

 of the pine forests of the Southern States. It devastated the pine 

 forests over large areas in West Virginia and Virginia in 1891 and 1892, 

 and the extensive dying of pine timber in the Southern States during 



