372 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1941 



surveys, for making specific recommendations on the need of con- 

 trol work, and, when necessary, for the technical direction of con- 

 trol. This service was extended to private owners as well. A fine 

 spirit of cooperation between the several national agencies manag- 

 ing timberlands, namely, the Forest Service, the National Park Serv- 

 ice, the Office of Indian Affairs, and the Bureau of Entomology 

 (lately the Bureau of Entomology and Plant Quarantine) has facil- 

 itated this plan. 



Gradually these surveys have been developed to cover many of 

 the more important timber types in the western States although 

 the job is still far beyond the appropriations available. During 1940 

 the Bureau of Entomology and Plant Quarantine covered in these 

 surveys over 23 million acres in all types of forests. Much of the 

 country was covered by general reconnaissance surveys, while certain 

 areas required intensive detailed estimates. These results were re- 

 ported to the agencies administering these timberlands and in many 

 cases recommendations for control were suggested and carried out. 



As this control program increased, it stimulated new ideas and 

 technique and provided large-scale tests for these developments. 



To quote Craighead et al. (1931), 



Control methods necessarily must be based upon Information regarding the 

 seasonal history and habits of the insects, and also, until thoroughly tried out 

 in practice, upon certain conceptions and theories. Each species of bark beetle 

 presents its own special problem, and even the same species may present prob- 

 lems which differ in different regions. 



Control of bark beetles is admittedly expensive. (PI. 3 ; pi. 6 ; pi. 

 7, fig. 1.) According to Craighead (1938) , 



It involves the spotting of infested trees in the forest, followed by felling, 

 barliing, and often burning of the bark to destroy the beetles and thus pre- 

 vent new broods from emerging from infested trees and attacking nearby 

 green trees. Usually the largest trees in the forest are attacked and the labor 

 required for spotting, felling, barking, and burning costs from $2 to $20 per 

 tree, depending on its size, accessibility, type of timber, and other factors. 

 Such costs are a limiting factor in the application of control, as frequently 

 the expenditures run too high to make control economically feasible. In recent 

 years several new methods have greatly reduced these costs. 



The so-called solar-heat method was tested out on a large scale 

 in lodgepole areas in Oregon by Patterson (1930) and found to be 

 successful under certain conditions. It consists of simply felling the 

 tree and exposing the trunk to full sunlight, later turning the log 

 to expose the underside. The heat generated under the bark by the 

 direct rays of the sun is sufficient to kill the brood. In California 

 the thick bark of yellow pine and sugar pine is first peeled and then 

 spread out in the sun. 



About 1926 a method was devised for burning the infested bark from 

 standing lodgepole pines. It was tested on several large projects in 



