22 THE SCOLYTID BEETLES.. 
tree they are exposed to the frost or sun and diying 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 larvae. 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 
sap wood. 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 sap wood 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- 
