86 
THE SCOLYTID BEETLES. 
wood to blue long before the leaves begin to fade. Except for the 
secondary injuries by wood-boring insects, fire, etc., the keartwood 
of the larger trees will remain sound and valuable for several years. 
While, however, there may not be a very great loss from leaving the 
dead timber standing until the heartwood begins to deteriorate, the 
danger of destruction by forest fires is so great that, in order to insure 
Fig. 48.— Two giant sugar-pine trees killed by the mountain pine beetle, and one dying from recent 
attack, Yosemite National Park, Cal. Note horse and man by dying tree, indicating diameter of 
tree at base. Approximate diameter, 8 feet. (Original.) 
against complete loss, the attacked and infested timber should be 
felled and utilized before the broods of the beetle develop and emerge, 
or within two or three years. 
FAVORABLE AND UNFAVORABLE CONDITIONS FOR THE BEETLE. 
Favorable conditions for the multiplication and destructive work 
of this insect are found in so-called primitive forests with a predomi- 
nance of mature timber, and where trees are frequently struck by 
