22 THE SCOLYTID BEETLES. 



tree they are exposed to the frost or sun and drying winds, which is 

 sufficient to kill them, without the necessity of burning the bark. 



It will be seen from the foregoing that the periods in which control 

 operations must be conducted are indicated by the habits and seasonal 

 history of the species involved. In general, the work should be done 

 between the beginning of hibernation in the fall and the beginning 

 of activity in the spring, but in the case of certain species in which 

 there are one or more complete generations within the season of 

 activity, such as species 1, 2, and 4, it may be desirable under certain 

 conditions to dispose of the infested trees during the summer, as 

 well as during the winter, especially during the principal development 

 and summer activity of the first generation of larvse. In the case 

 of species 9, 10, and 11, the operations may be continued after activity 

 begins in the spring until late in June or the first of July. 



SECONDARY INJURIES TO THE TREES. 



Some of the losses resulting from secondary injuries or destruc- 

 tion may be mentioned in this connection. One of these which affects 

 the commercial value of the beetle-killed trees is the bluing of the 

 sapwood. This, according to Dr. Hermann von Schrenk, is due to 

 a fungus which finds its way into the wounds and galleries made by 

 the beetles and rapidly penetrates the sapwood to the heartwood, 

 causing at first bluish streaks and later a uniform bluish-gray appear- 

 ance of the wood. This bluing condition, especially in pine trees 

 infested with species 9 to 11, often prevails long before the leaves 

 of the beetle-infested trees show evidence of decline or death. 



Other secondary losses consist in abnormal decay of the sapwood 

 and heartwood, but the greatest losses of this class may come from 

 forest fires started in the beetle-killed timber, which may not only 

 complete the destruction of the old dead and the newly infested tim- 

 ber, but also spread into the healthy forests. But there is one 

 redeeming feature in the destruction of the beetle-infested timber by 

 fire, and that is the widespread destruction of the beetles in the 

 infested trees, thus preventing the rapid extension of their ravages 

 which would otherwise occur. 



FAVORABLE AND UNFAVORABLE CONDITIONS FOR THE BEETLES. 



It is quite necessary that we should have some general and detailed 

 information in regard to the influences upon the beetles of climate, 

 fires, etc., and how certain methods and practices in the manage- 

 ment of a forest, or in utilizing its resources, contribute to the mul- 

 tiplication of the destructive enemies of the living timber, and how 

 certain other methods may contribute to their reduction or destruc- 

 tion. There is considerable difference in this respect between dif- 



