478 
JOURNAL OF ECONOMIC ENTOMOLOGY 
[Vol. 13 
is toward the top of the tent, which is also the point of the highest 
temperature, there is concentrated a maximum of influence for injury. 
Turning to the use of liquid hydrocyanic acid quite the reverse is 
true. The gas becomes weaker toward the top of the tent, the part 
of highest temperature, and the most concentrated gas is toward the 
bottom where the influence of the sunshine is less felt. Between these 
two factors, temperature and gas concentration, the latter appears to 
be the more dominant, for as a general rule the greatest injury to 
trees fumigated in the sunshine with liquid hydrocyanic acid is centered 
about half way up the tree on the sunward side. In all cases the 
injury is decidedly less than with pot-generated gas. The shaded side 
with its more normal temperature and without the sun-influence is 
seldom modified to any great degree either in point of injury or scale- 
kill over that normal to an equal temperature at night. 
Scale-Kill in Different Parts of a Tree Fumigated in the 
Sunshine 
The scale-kill is by no means uniform throughout a tree fumigated 
in the sunshine but rather irregular and reflects the effects of varying 
temperature and gas concentration at the different parts. This is 
shown in the following table which gives the results based on five 
trees infested with black scale which were fumigated March 3, 1920, 
with liquid hydrocyanic acid. The scale was in the rubber stage, 
approaching maturity, a condition in which they are very difficult to 
destroy and which require sharp influences to detect distinct differences 
in mortality. The insects were taken from outside branches and 
averaged 200 to 500 for each count. 
Table II —The Scale-Kill in Different Parts of 12-Foot Trees Fumigated 1 with Liquid 
Hydrocyanic Acid in the Sunshine with a Full Dosage Schedule for 50 Minutes, March, 
1920 
Tree No. 
• 
Per cent killed 
Sunward (S.) 
3 to 6 feet 
Top (N.) 
Shade (N.) 
2 to 4 feet 
1. 
75 
36 
47 
2. 
96 
87 
70 
3. 
94 
17 
20 
4. 
75 
11 
14 
5. 
84 
36 
25 
Average. 
84 
30 
27 
These results show the scale-kill on the sunward side of the tree at 3 
to 6 feet to be greatly superior to that on the shaded side both low 
down as well as at the top. In fact the mortality on the shaded part 
1 Jour. Econ. Ent., V. 12, No. 5, p. 361. 
