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, While 

 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 wood; 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 larvae. 



