INSECT ENEMIES OF WESTERN FORESTS 



121 



larvae do not have time to complete their development before cold 

 weather overtakes them in the fall, and consequently they are obliged 

 to spend another winter in the host tree. One generation of beetles 



Figure 59. — Galleries of the Douglas fir beetle on inner bark surface. 



a year is probably the normal rate of development, but there are 

 considerable overlapping and retardation of broods, somewhat obscur- 

 ing the demarkation between generations. 



