DEFECTS IX TIMBER CAUSED BY INSECTS 



25 



and consequently reduce the structural strength of the wood, espe- 

 cially when cut into smaller dimensions; therefore timber having 

 such borer holes should be used in as large dimensions as possible. 



Fig. 27. — Western red cedar shingles badly damaged by grub holes and 

 burrows of flat-headed borers (Trachykele blondeli) . (7). a, Quarter- 

 sawn shingle showing both cross and longitudinal sections, c, d, of the 

 larval mines ; 6, bastard-sawn shingle showing larval mines 



GRUB-HOLE INJURY TO LIVING TREES; A NONPREVENTABLE LOSS 



Grub-hole defects in living trees can not be prevented by lumber- 

 men, since often these defects occurred many years before the tree 

 was cut. Sometimes the insect holes are partially healed over by 



