THE GENUS DENDROCTONUS. 
Ill 
EFFECTS ON COMMERCIAL VALUE OF THE WOOD. 
The commercial value of the Douglas fir trees killed by the beetle 
is not seriously impaired for several years after they die, except that 
the sapwood discolors and otherwise deteriorates, but the heartwood 
of large trees may remain sound for twenty years or more. On the 
other hand, if they are seriously attacked by wood-boring insects 
the wood may deteriorate rapidly. 
FAVORABLE AND UNFAVORABLE 
CONDITIONS FOR THE BEETLE. 
Favorable conditions for 
the multiplication and de- 
structive work of this bark- 
beetle ace found in the drier 
regions, where the growth of 
the trees is slow and where 
the older trees are frequently 
injured by fire, storms, land- 
slides, etc., as also in the 
more isolated sections of the 
forests in such a region where 
no continued timber-cutting 
operations are carried on. 
Unfavorable conditions for 
attack on living timber are 
found in moist regions, where 
the growth of the trees is vig- 
orous, as in the coast, Cas- 
cade, and Sierra sections of 
Washington, Oregon, and 
California, and especially in 
those sections in which con- 
tinued timber-cutting opera- 
tions are carried on under a 
system of lumbering or forest 
management which requires 
that the matured or older 
timber, as well as that which 
is dying and " beetle infested," be taken out, and where the younger, 
vigorous timber is protected from injury by fire and other causes. 
METHODS OF CONTROL. 
Whenever in a given locality it is positively determined that this 
species is attacking and killing the Douglas fir, bigcone spruce, or 
western larch, and that the bark of living and dying trees contains 
Fig. 6S.— The Douglas fir beetle: Section of log with bark 
removed, showing brood galleries marked and grooved 
on surface of wood. (Author's illustration.) 
