374 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1941 



unless recreational or scenic values are at stake or unless outbreaks 

 in remote areas threaten commercially valuable stands. In general 

 only where utilization is anticipated in the next 10 to 25 years is 

 control economically feasible. 



The results might be said to be more or less in direct proportion 

 to the aggressiveness of the beetle. The Black Hills beetle, which 

 appears to be one of the most destructive of all species of Dendroc- 

 tonus, seems to build up into aggressive outbreaks rather suddenly 

 and, after locally killing extensive areas of timber, disappears quite 

 as rapidly. Control efforts against this species have been uniformly 

 successful if thoroughly applied. The southern pine beetle is 

 equally as aggressive. Its outbreaks have been definitely shown to 

 be tied in with deficiencies in rainfall extending over a period of sev- 

 eral months. Direct control is, however, more difficult here because 

 of the short duration of many outbreaks. The mountain pine beetle 

 in lodgepole pine behaves much like the Black Hills beetle and has 

 wiped out tremendous volumes of mature timber. Here, again, 

 control work has been successful when persistently applied. On the 

 other hand, this beetle's activities in the white pine type of the north- 

 ern Rocky Mountain region and the sugar pine type of California 

 are quite different. The western pine beetle in the ponderosa pine 

 type of Oregon and California may be classed as the least aggressive 

 of all these species, in that it seems to show a definite predilection 

 for certain weakened trees and its activities appear to run in cycles 

 associated with definitely unfavorable weather. This correlation 

 has been frequently noted and recently developed by Keen in a study 

 of tree growth, precipitation, and bark beetle activities. The climatic 

 influences that dominate the growth pattern undoubtedly have a 

 direct effect on the insects. (Keen, 1937.) 



CONTROL OF FOREST DEFOLIATORS 



Even greater efforts have been expended against some defoliating 

 insects. The gypsy moth is a European insect which reached eastern 

 Massachusetts in 1869. Some 20 years later it had become well- 

 established and attracted popular attention because of its widespread 

 defoliation of hardwood trees. The State of Massachusetts undertook 

 control work, which continued until about 1899. Then there was a 

 period when no work was done and the insect increased rapidly. 

 In 1905 the Federal Government stepped into the picture in an effort 

 to prevent its spread to other States to the south and west. Since 

 that time more money has been spent on the control of the gypsy moth 

 than has been spent on all other forest insects combined. In 1934, 

 total expenditures. State and Federal, to date were approximately 

 $40,000,000. Since then, through C. C. C. and relief funds, some $20,- 



