APPEAKANVK OF LARV2E AND IM I'.l. \\ 1 1 I . N DESTROYED. 
51 
turbing the insect or detaching the leaf from the tree. String tags 
attached to leaves upon which are specimens classed as doubtful 
will enable examinations of such specimens from time to time until 
their condition is positively determined. A careful examination of 
normal specimens and direct comparisons of these with those on 
leaves of Fumigated trees will assist in the ready identification of the 
dead insects. 
DENSITY OF THE GAS AT VARIOUS HEIGHTS ABOVE THE GROUND. 
It is natural to presume that owing to the fact that hydrocyanic- 
acid gas is lighter than air, its density during the process of fumiga- 
tion is greater toward the top of the tree. In four of the nine obser- 
vations on the comparative effect of the gas at different heights 
above ground the results of this variation in density are not evident. 
In the other five observations the results are quite striking. In the 
six experiments in which observations were made 10 feet or more 
from the ground, the average percentage of insects killed up to 6 
feet above the ground was 04, while from 10 to 18 feet above ground 
the average percentage killed was 71. The data concerning the 
effectiveness of the gas at various distances from the ground is sum- 
marized in Table XL 
Table XI. — Efficiency of gas as affected by height above ground. 
Ex- 
peri- 
Distance 
above 
ground. 
Number of 
white fly 
Per cent 
Ex- 
peri- 
Distance 
Number of 
white fly 
Per cent 
ment 
No. 
pupae ex- 
amined. 
killed. 
ment 
No. 
ground. 
pupae ex- 
amined. 
killed. 
Feet. 
Feet. 
30.4 
4-G 
427 
89 
30.1 
4-0 
74 
21 
14-15 
244 
98.3 
12-14 
909 
36 
18 
120 
100 
40.3 
4-6 
822 
80 
20.1 
4-fi 
087 
91.9 
12-14 
445 
90.8 
12-14 
1,000 
90.8 
30.3 
2 
396 
92.8 
20.7 
4-5i 
222 
77 
3i-7 
159 
78 
10 
300 
60 
40.7 
2 
93 
80.6 
40.12 
2 
3§-5 
4-6 
112 
728 
541 
64 
98.4 
26.4 
4-0 
139 
79.2 
14-10 
136 
50 
The results show that when examining for the results of fumigation, 
the most significant effects are those within a few feet of the ground. 
The observations concerning the results of the experiments upon 
which the recommendations in this bulletin are based were made in 
all cases within 7 feet of the ground, and included examinations of 
insects on leaves closest to the ground in all cases. 
EFFECT OF FUMIGATION ON Tl IK TREES. 
During the months of December, January, and February, until the 
appearance of the new spring growth, fumigation for the white fly 
with the dosage herein recommended will rarely occasion appreciable 
