418 Forestry Quarterly. 



Among the influences other than climatic, affecting the multi- 

 plication of the beetles, forest fires and commercial cutting of tim- 

 ber may act favorably or unfavorably, depending upon the species 

 involved and in the latter case upon the time and method of cut- 

 ting. It is important that the principal cutting operations be 

 carried on during the period of hibernation, i. e., in the late fall 

 and winter, since during the following summer the stumps and 

 slash serve to attract the beetles away from the trees, and as the 

 new broods remain in the bark during the following winter they 

 can then be burned before the time of emergence in the spring, 

 When more than one annual generation occurs, as in the southeast 

 and Rocky Mountain region, it may be necessary to burn the 

 winter slash before the first of July. 



In fifteen of the species, removal of the bark from the main 

 trunk is all that is required to kill the broods which live in the 

 inner bark, and are killed on exposure to the drying influences of 

 the sun and wind. In the remaining eight species, it is necessary 

 to burn the bark, as in these species the larvae enter the outer bark 

 to transform into pupae. If necessary the barked trees may be 

 allowed to stand for several years without the value of the wood 

 becoming impaired. Various methods are also' suggested for the 

 destruction of the broods without removal of the bark, such as 

 converting the logs into lumber and burning the slabs, placing 

 the logs in water, etc. 



On the occurrence of an extensive invasion the affected areas 

 should be surveyed and mapped in the fall and the amount of in- 

 fested timber estimated, and logging operations should, when 

 possible, be concentrated upon the affected areas so that as large 

 a percentage as possible of the infested timber can be cut, barked 

 or otherwise treated before the broods begin to emerge. If this 

 course cannot be adopted, as much as possible of the infested 

 bark should be removed from the standing timber or from those 

 felled for that purpose. 



The trap-tree method of control is not recommended in the case 

 of Dendroctonus beetles. 



The introduction and protection of natural enemies such as 

 parasitic and predatory insects and insectivorous birds is another 

 important phase of the subject of the control of these insects but 

 has as yet received comparatively little attention. 



