264 REPORT OF THE DEPARTMENT OF ENTOMOLOGY OF THB 
them in every instance. The failure of the 25 per ct. to kill the 
scales does not agree with the results of Felt and Corbett who 
report success with a 20 per ct. emulsion. The reason for this 
is not readily apparent. It is to be noted, however, that 
although an examination of the treated trees made in the spring 
may indicate that the treatment has been successful, definite 
and final results cannot be obtained without several examina- 
tions during the following season. This is especially true in the 
latitude of New York State where a large percentage of the 
scales die during the winter so that during the spring but few 
live ones can be found. But later in the season after breeding 
begins the real condition can be much more easily determined. 
Taken as a whole the spraying experiments reported in this 
bulletin indicate the following: 
1. Vigorous trees are probably less liable to injury by crude 
petroleum than weak ones. 
2. Peach and plum trees are more sensitive to crude petro- 
leum than apples, cherries, or pears. 
3. There is less danger of injury if trees are sprayed in early 
spring than during the fall or winter. 
4. The 25 per ct. emulsion of crude petroleum and water can- 
not be depended upon to kill the hibernating scales in the lati- 
tude of Western New York, while the 40 per ct. has proven 
efficient. 
5. Much pains should be taken to avoid over-drenching the 
trees. Only enough of the emulsion should be applied to wet 
the bark evenly and thoroughly. 
It, KFUMIGATION EXPERIMENTS WITH HYDROCYANIC 
ACID GAS. 
INTRODUCTORY. 
Fumigation with hydrocyanic acid gas is now recognized as 
one of the best known methods of combating scale insects. The 
gas was first brought into prominence as an insecticide in 1886 
