Pine Barl( Beetles 



431 



against the mountain pine beetle, the 

 Black Hills beetle, and Ips in lodgepole 

 pine and other thin-barked trees. New 

 insecticides, especially DDT, have 

 greatly increased the effectiveness of 

 oil-spray formulas. Burning unpeeled 

 infested trees with the aid of cheap 

 fuel oils, and even with "goop," de- 

 veloped for use in incendiary bombs 

 in the Second World War, also has 

 been tried. Infested lodgepole pines 

 have been burned while still stand- 

 ing by spraying the trunks with fuel 

 oil, igniting it, and following up with 

 more oil until the bark was thoroughly 

 charred. Where conditions permitted, 

 power saws and bulldozers have been 

 used to fell, move, and prepare trees 

 for burning. Mechanized equipment 

 has been used to haul infested trees to 

 the sawmill where the infested bark 

 was destroyed and the logs converted 

 into lumber. All these methods have 

 limitations. No one method has been 

 developed that can be used under all 

 conditions. 



INDIRECT CONTROL can help. About 

 1924, entomologists and foresters began 

 working on a different approach. They 

 studied the characteristics of trees that 

 were attacked by the western pine 

 beetle and found that the beetles pre- 

 ferred to attack slow growers and trees 

 below normal in growth functions. 

 Such trees could be distinguished eas- 

 ily from healthy, vigorous trees in the 

 form, density, and thrift of the crowns. 

 An off color of the needles and dieback 

 of twigs, limbs, and tops further indi- 

 cated susceptibility. The entomologists 

 learned from their studies and experi- 

 mental selective-logging operations 

 that losses could be lessened by remov- 

 ing part or all of these susceptible trees 

 from the stand. The term "sanitation 

 salvage" has come into use to desig- 

 nate this new type of control. Timber 

 companies, which were quick to try it, 

 found that the practice could pay its 

 way through the sale of lumber prod- 

 ucts from sound but vulnerable trees 

 that otherwise would be killed by 

 beetles and left to rot in the woods. 



Sanitation salvage has given excel- 

 lent results in controlling western pine 

 beetles. Areas so salvaged a decade ago 

 still show a substantial differential be- 

 tween the number of trees attacked and 

 the losses on untreated areas. This 10- 

 year period, however, does not include 

 any test of the method during an epi- 

 demic infestation. What will happen 

 then remains to be demonstrated. 



So far, the criteria by which high- 

 risk trees can be distinguished have 

 been developed only for the ponderosa 

 and Jeffrey pines found in forests east 

 of the Sierra Nevada and Cascade 

 Mountains. Studies are under way to 

 develop similar criteria for indirect 

 control of bark beetles affecting other 

 pine types, which for the present can 

 only be controlled through the applica- 

 tion of direct-control measures. A 

 method similar to sanitation salvage 

 has been developed and is being put 

 into practice for western white pine 

 stands in Idaho, where selective log- 

 ging of low-vigor trees reduces the 

 amount of timber killed by the moun- 

 tain pine beetle. 



The continuing search for new and 

 better methods to control the pine bark 

 beetles seeks to keep pace with the de- 

 velopment of sound forest-management 

 practices and is in the direction of im- 

 proving methods of surveys to detect 

 outbreaks in their early stages and to 

 determine the susceptibility or bark 

 beetle hazard of various pine stands, 

 developing better methods of direct 

 control, particularly through the use of 

 the newer insecticides, and developing 

 forest-management practices adjusted 

 to avoiding or limiting bark beetle out- 

 breaks. 



Use of the airplane in the surveys 

 is a new development that will make 

 possible the detection of small out- 

 breaks in inaccessible areas before 

 they develop into large ones. Surveys 

 from the ground will always be neces- 

 sary to follow up aerial observations. 



Of greatest value to the entire survey 

 system is the study and classification 

 of pine areas according to expecta- 

 tion of bark beetle infestations. This 



