INSECTS AND FOREST MANAGEMENT — CRAIGHEAD 373 



southern Idaho and proved to be effective and economical. (Arrivee, 

 1930.) 



The possibility of injecting chemicals into the sap stream of the 

 tree and thus preventing the development of the bark beetle broods 

 and doing away with the costly operations of felling and barking 

 or burning the tree for the control of bark beetles has been experi- 

 mentally tested during the last few years. There appears to be some 

 promise in this field, both from control and salvage standpoints, 

 but it has a practical difficulty in that treatment is necessary shortly 

 after the beetles attack, i. e., before the blue stains in the sap wood 

 cut off conduction. (Craighead and St. George, 1938.) 



One of the disadvantages of bark beetle control has been the 

 loss of the lumber from the trees that are treated. Studies by Keen 

 (1931) of the salvage possibilities of beetle-killed timber have led 

 to some practical methods of treating this problem. He says : 



A great deal of attention has been devoted by our entomologists in the last 

 few years to the use of so-called salvage methods of control, and the Forest 

 Service and private timberland owners have cooperated heartily. In the pon- 

 derosa pine types of eastern Oregon and northeastern California when the 

 terrain permits caterpillar logging, prompt spotting and salvage of these trees 

 is feasible. [PI. 3, fig. 1.] 



It has long been desirable to have a method of treating infested 

 trees through the summer period, one that would be quick in action 

 and avoid the use of fire, which is so dangerous at that time of year. 

 After considerable experimentation several penetrating sprays were 

 developed which, when applied to the trees, promise to meet this 

 need effectively. The most satisfactory chemical is orthodichloro- 

 benzene carried in light fuel oil. This method is particularly well 

 suited to the control of mountain pine beetle broods under the thin 

 bark of lodgepole and white pines in the Rocky Mountain regions. 

 (Salman, 1938.) 



The lethal effect of low winter temperatures has been taken advan- 

 tage of to call off control work on projects already under way when 

 temperatures dropped to a sufficiently low level to destroy the broods. 

 (Miller, 1931; Keen, 1937.) 



RESULTS OF BARK BEETLE CONTROL 



A review of the control work against bark beetles in our forests 

 and an appraisal of its values were summarized by Craighead, Miller, 

 Keen, and Evenden in 1931. It should be explained here that con- 

 trol work is carried out only against a small percentage of the out- 

 breaks. In inaccessible timber, where new trees will replace those 

 destroyed before the area is logged or where commercial values do 

 not warrant large direct expenditures, control is seldom undertaken 



