372 WEST VIRGINIA EXPERIMENT STATION. 



It will be seen from the above records, that with the excep- 

 tion ot a local cold spell in Pennsylvania in January, 1892, the 

 lowest temperature throughout the infested area for two years l 

 was late in December, 1892, and early in January, 1893, when 

 the mercury fell to 17 below zero in Maryland, 21 below in 

 New Jersey, 25 below in Pennsylvania and West Virginia, 26 

 below in Virginia and 6 below in the District of Columbia. 



In 1890, the minimum at the different Stations in the States 

 mentioned above, ranged from 22 above at Fortress Monroe, in 

 Virginia, to 18 below at Charlesville, in Pennsylvania, and 14 

 below at Tannery, in West Virginia; all in the month of March. 

 In 1891, the minimum in the same states ranged from 19 above 

 at Birdsnest, Va., in December, to 14 below at Corry, and Dy- 

 berry, Pennsylvania, in March, and 9 below at Pleasant Hill, 

 West Virginia, in the same month. 



The lowest temperature recorded from West Virginia in 

 1890-3 was 14 below zero in March, 1890; 9 below zero in 

 March, 1891, 10 below in December, 1892, and 25 below in 

 January, 1893. 



The excessive cola weather throughout the infested area dur- 

 ing the last days of December, 1892, and first days of January, 

 1893, it would appear, was sufficient to kill the insects if it were 

 possible for them to be killed by cold. And the fact that 

 this was the coldest weather that had been recorded through- 

 out the infested region since the trouble commenced, and that 

 it was followed by the extermination of the insect, is evidence 

 that the death of all of the individuals of this species was due 

 to unfavorable climatic conditions. 2 But when we come to 

 consider that the other species of bark beetles which were as- 

 sociated with Dendroctonus frontalis in the same trees and the 

 same bark were not killed, it would appear that if the death of 

 one species was caused by climatic conditions, the others would 

 have suffered also. Many examples of the turpentine beetle, 

 Dendroctonus terebrans^ (which does not associate wilh Den- 



1 Probably the lowest since 1885-6. See Annual^ Summary for 1892. 



2 "Nothing is better known than that exceptional freezes may kill off thousands of in- 

 sects- there must therefore be species whose successful hibernation is limited by 

 certain degrees of cold. 1 ' L. O. Howard, Pro. Ent So. W. Vol. Ill, No. 4. p 225. 



