66 



THE SCOLYTID BEETLES. 



favorable conditions for the concentration of individuals from widely 

 scattered colonies and broods, and thus increases their power of attack- 

 ing and killing the surrounding living trees. By this means their 

 forces are greatly augmented, and much of the surrounding timber is 

 killed. If conditions favorable for the continued concentration of the 

 beetles prevail from year to year, an invasion like that of 1891 and 



Fig. 28.— Spruce timber killed by the southern pine beetle, mountains of Transyl- 

 vania County, N. C. (Original.) 



1892 may be started, which may far exceed any forest fire in the 

 history of the country, both in the extent of area covered and in the 

 number of trees of commercial value killed. 



Unfavorable conditions for the multiplication of the insect and its 

 destructive attack on living timber will be found in large areas where 

 the older matured trees have been removed and where continued 

 timber-cutting operations are carried on under some regular system of 



