8 



beetles during the flight period. When the material is sawn, practi- 

 cally all the beetles are destroyed, and in the logs that are left in the 

 woods during the winter a very high mortality of beetles occurs, so 

 that the emerging beetles are much fewer than those attacking. At 

 the same time the cull logs and tops furnish good breeding material 

 for certain borers (Acanthocinus) and predatory species which are 

 detrimental to the development of the Dendroctonus broods. As *^ 



these enemies increase with this abundance of breeding material they 

 tend to concentrate on any standing trees which are attacked, and 

 thus hold the infestation at a minimum. Under these conditions it 

 is doubtful whether disposal of the larger slash would not in fact be 

 more injurious than beneficial to neighboring standing timber. 



In both the Rocky Mountain and the Pacific regions Dendroctonus 

 valens Lee. breeds in stumps and butt logs, and to a limited extent 

 it attacks the base of live trees. This injury is not often severe 

 enough to warrant the expense of special control methods, such as 

 piling brush over stumps, prompt removal of logs, and barking of cull 

 logs. 



In Arizona, New Mexico, and south of the Colorado Plateau, some 

 outstanding cases of losses to reproduction resulting from insects 

 breeding in slash have been called to our attention. Craighead 

 reports that two species of Ips were found breeding in cull logs and 

 larger tops of western yellow pine on timber sales. The spring 

 generation of beetles is confined to this felled material, whereas the 

 summer generations attack and kill pine reproduction in clumps of 

 from one-tenth to 1 acre. At some places these repeated attacks 

 have materially thinned out the stands of second growth. Modifi- 

 cations of logging operations will be necessary to prevent these losses. 



JEFFREY PINE IN CALIFORNIA 



The Jeffrey pine beetle {Dendroctonus jefreyi Hopk.), although 

 often a very destructive insect in living Jefl^rey pine (Pinus jeffreyi) 

 in California, is only weakly attracted to the slash of this tree. This 

 species and other bark beetles, such as Ips, breed very freely in wind- 

 falls and large pieces of slash material. On large windfall areas they 

 may occasionally breed up to the point where they become very 

 destructive to adjacent full-grown timber, saplings, poles, and the top 

 of mature trees. Such epidemics are, however, characteristically spo- 

 radic, and their control is not economically feasible at the present time 

 except in cases where high timber values are involved. As far as injury 

 by insects is concerned Jefi'rey pine slash is usually of but slight 

 importance. 



LODGEPOLE PINE 



The mountain pine beetle {Dendroctonus monticolae Hopk.) is a very 

 serious enemy of lodgepole pine {Pinus murrayana), often killing 

 hundreds and even thousands of acres of the standing timber. Here ^^^ 

 is another case, and a very striking one, of an insect which is strongly 

 attracted to the vicinity of logging or clearing operations, yet rarely 

 attacks the felled trees. Clearings for summer homes or hotels have 

 often brought about such a slaughter of lodgepole pines in the vicinity 

 as to mar the beauty of the site. Even control operations are not 

 immune, and in one instance such a heavy concentration of beetles 

 followed control cutting as entirely to wipe out the effect of the work. 



