448 JOURNAL OF ECONOMIC ENTOMOLOGY [Vol. 14 



to the pine timber far over shadows the insect loss prevailing in the other 

 tree species. The m.ajor pine species involved in the Pacific Slope insect 

 depredations are, in order of their importance: western yellow pine', 

 sugar pine, western white pine and lodgepole pine. Only two species of 

 Dendroctonus are of primary importance in the wholesale killing of these 

 four species of pine; namely, the western pine beetle {DendroctonMS 

 hrevicomis Lee.) and the mountain pine beetle {Dendroctonus monticolae 

 Hopk.). The western pine beetle infests only the western yellow pine 

 while the mountain pine beetle kills with equal ease the four species of 

 pine we have enim^.erated. Nevertheless the volume of western yellow 

 pine killed in this region by brevicomis undoubtedly exceeds the total 

 monticolae depredations in all the four species of pine under discussion. 



Ordinarily one finds only relativeh- unimportant evidences of the 

 activity of these two species of Dendroctonus in our yellow pine, sugar 

 pine, white pine and lodgepole forests. .Small and scattered attacks of 

 this type are known as nonnal infestations and in the present intensity 

 of forest protection no control work is done on such infestations. How- 

 ever, thev should be carefully watched for any evidences of increase in 

 the severity of the attacks. Occasionally the killing of trees by these two 

 Dendroctonus beetles proceeds at an alarming rate and in such cases the 

 prompt destruction of the beetles in the infested trees must be undertaken. 

 These concentrated and heavA' attacks are called epidemic infestations. 

 Since existing epidem.ics have their origin in normal or endemic situ- 

 ations, it is not at all improbable that eventually, when forest protection 

 becom.es more intensive, the so-called normal infestation will come in for 

 its share of control work. 



It has been demonstrated that the safe control of epidemics is not a 

 one year or even a two or three year m.atter. It is true that the effort 

 is made to help the natural forces to break the force of the infestation 

 bv large scale control operations in the first year or two, but it is just 

 as important that this initial control work be followed up by a certain 

 amount of so-called m.aintenance w^ork year after year. This mainte- 

 nance work is inexpensive and ser\^es to prevent the recurrence of the 

 epidem.ic conditions. As our pine stands become more and more valu- 

 able, they will be divided into control units and a definite permanent 

 plan of insect control will be worked out for each unit. In the Sierra 

 National Forest, in California the Bureau of Entomology already has 



^Western yellow pine -Pinus ponderosa 

 Sugar pine -Pinus lambertiana 



Western white pine -Pinus monticola 

 Lodgepole pine -Pinus contorta 



