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 Fig. 25.— White pine timber killed by southern pine beetle 
in a few weeks after the %?£££2Z$!££Z "^ " * ™ "* 
trees become infested. 
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 
