442 
JOURNAL OF ECONOMIC ENTOMOLOGY 
[Vol. 13 
for five or six days after the 20th, the temperature remained above 
freezing. 
Examinations of larvse were made during the period from December 
23 to February 28. It was found that wherever the minimum temper¬ 
ature had been lower than —25°, all larvse, with no protection other 
than bark or burlap bands, were killed. At the Bureau of Entomology 
Laboratory in Yakima, the minimum temperature was —25°, and 
several thousand larvse wintering in pupation sticks all succumbed. 
In orchards within two or three miles of the laboratory, and on higher 
ground, where the minimum temperatures ranged from —20° to —25°, 
80-90 per cent of the larvse were killed. On still higher ground, with 
minimum temperatures of —15° to —20°, the mortality was approxi¬ 
mately 70 per cent. Reports from the Wenatchee Valley, where the 
lowest temperature recorded was —20°, placed the mortality at from 
75-80 per cent. There was no opportunity of examining larvse in sit¬ 
uations where the minimum temperature was higher than —14°. In * 
all cases, these figures apply to the larvse wintering above the snow 
line. 
As the ground was frozen at the time of the earlier examinations, it 
was impossible to ascertain the condition of the large number of larvse 
which winter under the surface of the soil. In February, however, 
examinations were made of the larvse which spun their cocoons about 
the tree trunks an inch or two beneath the soil surface, where they were 
undoubtedly covered with snow during the cold weather. On Feb¬ 
ruary 28, a banded orchard was examined near Zillah, Wash., where 
the temperature had dropped to —24°, according to an unofficial 
record. The land was somewhat rolling, and it is probable that the 
drifting snow had accumulated in varying depths about different 
trees, as there was a marked variation in the condition of the larvse 
found on the various trees. The mortality ranged from 100 per cent 
on some trees to as low as 66 per cent on others, with an average for 
280 larvse counted, of 76 per cent. One interesting fact noted was that 
frequently, on tearing away the burlap band, one or two live larvse 
would be found in the midst of a number of dead ones. It seems im¬ 
possible, in these cases, that the live larvse had any more protection 
than the others. They must simply have had more vitality. 
All these records were obtained in the arid section of Washington. 
It would be interesting to know whether temperatures such as were 
experienced in this section would produce a similar mortality in more 
humid regions, such as the coastal sections of Washington and Oregon, 
or parts of the eastern United States. 
