24 ANNUAL REPORTS OF DEPARTMENT OF AGRICULTURE, 194 
to ail endemic status in which only a small amount of maintenance 
control work is necessary. Conditions are not so encouraging in the 
[ntermountain Region, especially on the Powell and Wasatch Nat tonal 
Forests in Utah. Over25,000 trees were treated by the Forest Service, 
part of the work being done by the penetrating-oil-spray method. 
Good results were obtained on the area- treated, but fund- were not 
available to permit as complete coverage as would have been desirable. 
It is likely that additional work will be needed to bring this outbreak 
under eont rol. 
Losses caused by the western pine beetle increased in parts of 
California and southern Oregon, and several control projects weir 
conducted by the Forest Service, the Office of Indian Affairs, and 
private timberland owners, following Bureau recommendations. 
Field work on the hazard-inventory survey of the commercial pon- 
derosa pine area in northeastern California was almost completed. 
This survey was based on the results of research in Oregon and Cali- 
fornia on the susceptibility of ponderosa pine to attack by insect-, 
particularly bark beetles. Forest stands or areas have been given 
hazard ratings based on the history of their recent losses from insects 
and on the present condition of the individual trees. The most sus- 
ceptible trees on the high-hazard areas may be marked for cutting. 
This will enable the owners to concentrate their logging operations 
in the areas where there is most danger of serious losses from bark 
beetles in the near future. The Forest Service and several large pri- 
vate operators in California and Oregon are making immediate use 
of the information supplied by the Bureau and are modifying their 
management plans to permit rapid and frequent coverage of their 
lands in an effort to take out susceptible trees before these are attacked 
by insects and rendered worthless. 
EFFECTS OF LOW TEMPER ATl'RKS ON THE BLACK HILLS BEETLE 
Laboratory studies to determine the effects of low temperatures on 
the Black Hills beetle are now completed. These studies, carried out 
♦ luring the last, four seasons, show the range of temperatures fatal to 
this insect and reveal that the species is well adapted to survive the 
minimum temperatures of its normal distribution. Analyses of tem- 
perature records from standard weather stations in or adjacent to 
forests where epidemics have occurred indicate that killing tempera- 
tures occur approximately once in 7 years in the ponderosa pine type 
Lethal low temperatures apparently occur less often in the limber and 
lodgepole pine types. Two instances of winter-Mil of the Black 
Hills beetle are on record. Both of these occurred in Colorado, the 
lirst on February when an estimated mortality of 50 percenl 
resulted from a low of —34° F.. and the second in November l ( .^ s . 
when a 29-percent mortality was caused by a minimum of —15°. It is 
evident, therefore, that low temperatures constitute one of the factors 
of natural control. No example of field mortality sufficient to alter 
conl rol projects is on record. 
Experimental data of particular interest in connection with the 
foregoing conclusions are as follows: During October and November 
the cold hardiness of overwintering larvae increases very rapidly, 
reaching a maximum by mid-December. The larvae retain this maxi- 
