THE GENUS DENDROCTONUS. 
47 
than October and should be completed by the first of June. If at 
least 75 per cent of the infested trees are thus treated, sufficient 
numbers of the broods will be destroyed the first year to protect the 
remaining timber for several years. Then, if all patches of infested 
timber are subsequently located and barked before the broods emerge, 
it should serve to keep this enemy under complete control. 
Fig. 10.— Western yellow pine killed by the western pine beetle, Yosemite National Park. (Original.) 
Summer operations in the barking of infested trees are not to be 
recommended, except in special cases where it is desirable to destroy 
the broods of the first generation. In this case the work should be 
done during the period of principal larval development — that is, from 
the middle of July to the middle of August, or when the leaves of the 
infested trees are just beginning to fade. 
