16 BULLETIN 255, U. S. DEPARTMENT OF AGRICULTURE. 
After the young larva has penetrated to the cambium, which 
usually occurs about August, cr at a time when the growing period 
of the tree for the season is ended, it excavates a tortuous tunnel 
from 1 to 2 inches in length, parallel with and transverse to the’ 
grain of the wood. The length of the tunnel at completion depends 
largely upon the growth of the infested tree. In slow-growing trees 
_ Fie, 10.—Pitch tube covering larve of the Douglas fir pitch moth 
the second year after infestation. Natural size. (Original.) 
it reaches occasionally a length of from 5 to 6 inches at the time of 
moth emergence, while in very vigorous growers the larva maintains 
its well-being within a circular-shaped pit, not more than 2 inches 
in width, deeply embedded in the woody tissues of the cambium. 
The surface of the wound is invariably covered by a pitch tube of 
the color of the bark. When the outer crust of the tube is removed it 
is found to contain pitch and the excreta of the larva. If the same 
wound is reinfested, soft pitch mixed with the old crusty pitch 
