110 
THE SCOLYTID BEETLES. 
its base, which is the only external evidence of attack or infestation 
until in the fall and winter, when the leaves on some of the trees will 
begin to fade and turn pinkish or yellowish, while on other trees 
they will not begin to change color until next spring, and on still 
others only the leaves of the top or lower branches on one side of the 
crown will die, while the remainder will continue green, thus indi- 
cating that only a portion of the bark is killed and infested. TVhile 
the fading and dying of the leaves result from infestation by this 
beetle, this may, and does, sometimes result from other causes, so 
that the only positive evidence of injury or destruction of Douglas 
Fig. 67. — The Douglas fir beetle. Egg gallery and larval mines: a, Egg gallery in bark and grooved 
in surface of Avood; b, larval mines in bark: c, larval mines marked and slightly grooved on surface 
of wood. (Author's illustration.) 
fir or western larch in any locality by this species can be determined 
only by cutting into the bark of the freshly attacked or dying trees 
and finding the characteristic galleries and larval mines occupied 
by authentically identified parent beetles or their broods. 
As a rule, the broods leave the trees before the leaves have turned 
reddish brown or fallen, and they never return to the trees to 
excavate galleries and deposit eggs for new broods after all of the 
bark is dead, since they must have either living or partially living 
bark for their eggs and young larva?. 
