244 MISC. PUBLICATION 273, U.S. DEPT. OF AGRICULTURE 



are rarely obtained in one season, and the work has to be re- 

 peated for several seasons, until the resistance of the stand has 

 improved through removal of beetle-susceptible trees or until 

 the trees are better able to resist attacks. In fact, during long 

 periods of drought and lowered tree resistance, almost continuous 

 work may be necessary to hold the beetle population down to 

 reasonable limits. 



In this work special consideration must be given to the natural- 

 control factors and an effort made to favor their effectiveness 

 while reducing the population of the destructive species. The 

 avoidance of burning around stumps where predators congregate, 

 the saving of certain infested trees to permit multiplication of 

 the beneficial parasitic insects present, and the improvement of 

 stand resistance are some of the ways in which natural control 

 may be encouraged (pp. 211, 215, 218, 220). 



CONTROL COSTS AND PROBABLE RESULTS 



The cost of control work varies with the size and type of 

 timber, the method of treatment, the intensity of the infestation, 

 the roughness of the terrain, the accessibility of the area, the 

 current cost of labor, and so many other factors that it is im- 

 possible to give any specific costs that might apply to a given 

 situation. Some idea of the approximate cost of the work, how- 

 ever, may be obtained from experience gained during the decade 

 from 1921 to 1930. 



In the ponderosa pine region of California, Oregon, and Wash- 

 ington the control of the western pine beetle cost on an average 

 about $4 per treated tree, with the cost dropping as low as $1.75 

 per tree. In the control of the Black Hills beetle in ponderosa pine 

 of the Rocky Mountain region the cost per tree averaged about 

 $1.50 with some costs as low as 75 cents per tree. 



The control of the mountain pine beetle in lodgepole pine 

 forests, where either the solar-heat method or the fell-deck-burn 

 method was used, cost on the average from 50 cents to $1 per 

 treated tree, depending largely on the intensity of the infestation. 

 Under similar conditions the solar-heat method is the cheaper 

 of the two. 



The control of mountain pine beetle infestations in western 

 white pine cost about $4.50 per tree, and in sugar pine, because of 

 its very large size, the costs sometimes amounted to as much as 

 $16 per tree. 



For the treatment of a few scattered trees around summer 

 homes or in inaccessible areas the costs will run higher than 

 on large-scale projects. 



Bark-beetle control work has been in progress in western 

 forests since 1911. The results of this work for the first 20 years 

 were summarized in 1931 (39). Since then much further progress 

 has been made in the development of materials and techniques of 

 application. 



Wherever bark beetles have been primarily responsible for the 

 death of trees, the application of control measures has resulted 

 in reducing the infestation or in restoring the natural balance 



