386 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1941 



For some time it had been recognized that a more systematic 

 study of the interrelationship of tree susceptibility and climate was 

 necessary in the ponderosa pine type. Any direct connection between 

 timber losses and deficiency of precipitation has been much more 

 diflScult to establish in the ponderosa pine type because of the lack 

 of adequate records in the timber areas and the apparent adjustment 

 of this pine to the rainless summers of the region. Three years 

 ago at our Berkeley laboratory R. C. Hall initiated such a field study, 

 establishing locations in several timber types and on several timber 

 sites, amply supplied with instruments to measure various environ- 

 mental factors. In these areas insect records and timber losses are 

 available over a long period of years. Already, after 3 years of 

 observation, very striking information (unpublished reports) has 

 been obtained indicating a close tie-up between climate, past timber 

 losses, and beetle activities, even definite variations within the 

 different sites of the ponderosa type. 



MANAGEMENT FOR INSECT CONTROL IN SECOND-GROWTH STANDS 



In the eastern States, particularly in some private forests, silvicul- 

 tural systems primarily designed to circumvent insect damage have 

 been applied in pine and hardwood stands. Such insects as the 

 gypsy moth, the white pine weevil, the locust borer, the turpentine 

 borer, and the bronze birch borer have each been the dominant factor 

 in shaping management plans of the forest types in which they are 

 active. 



Fiske (1913) was probably the first in this country to realize the 

 possibility of controlling the gypsy moth through forest management. 

 He suggests taking advantage of the preference shown by the larvae 

 for certain Sf)ecies of trees and removing these, especially oak, from 

 the stands. 



This possibility of control through adjustment of food plants stim- 

 ulated extensive studies by the Bureau of Entomology which were 

 published by Mosher (1915). Mosher classified the plants in the 

 regions into the following four groups: (1) Species highly favored 

 by all stages of gypsy moth larvae; (2) species that are favored food 

 for the gypsy moth after the early larval stages; (3) species that are 

 not particularly favored but upon which a small proportion of the 

 gypsy moth larvae may develop ; and (4) species that are unfavored 

 food. 



The gypsy moth develops normally and becomes destructive only 

 on plants of group 1. 



From the germ of Fiske's suggestion and the definite classification 

 proposed by Mosher, the possibility of silvicultural control gradually 

 gained recognition and resulted in a cooperative study between the 



