264 Report of the Departmrxt of EntomoivOGy of the) 



them in eA'erj instance. The faihire of the 25 per ct. to liill 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 i^lum 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. Onl^^ enough of the emulsion should be applied to wet 

 the bark evenly and thoroughly. 



II. FUMIGATION EXPEROIENTS 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 



