52 JOURNAL OF ECONOMIC ENTOMOLOGY Vol. 4 



1113 forming a white crust which lifted the scale covering so that it 

 might easily be washed or brushetl from the tree, thus exposing any 

 helpless insect, not already dead, to weather conditions. 



Sulphur dioxide could not be detected coming from a surface treated 

 with lime-sulphur wash, unless when nearly dry, the surface was ex- 

 posed to temperatures high enough to rapidly vaporize the free sulphur 

 present. It would seem therefore that under natural conditions sulphur 

 dioxide is not formed in sufficient quantity to be of any insecticidal 

 value. 



If carbon dioxide is dissolved in lime-sulphur wash, hydrogen sul- 

 phide will be formed. This gas is poisonous to insects; but no 

 means was found of proving its presence in effective amounts be- 

 neath scales treated with lime-sulphur. 



It was not found with certainty, in any case, that lime-sulphur wash 

 penetrated into the body of the insect, although it would kill the cells 

 of a small part of an insect's body touched by it, while other parts of the 

 body remained alive for a time. 



The experiments therefore, seem to show that with lime-sulphur 

 wash, it is mainly the combination of the three properties or conditions 

 already described which makes the insecticide so efficient against 

 scale-insects — especially against San Jose scale which winters in a 

 partially grown condition. 



Mr. Headlee: I have enjoyed this paper very much, and wish 

 to thank Mr. Shafer for it. It is a type of work we ought to have 

 more of. A few thoughts occurred to me while this paper was in process 

 of being given, and one of them is this: Why does the author think 

 that gasoline dissolved out parts of the fat body? Is it not possible 

 that something else entered in and produced the same morphological 

 result? 



Mr. Shafer: Mr. President, I think the gasoline affected the "fat 

 body," because in every case where it, alone, was tested for the right 

 length of time, gasoline dissolved the fat body. If kerosene were used 

 it would leave the fat body intact after two hours' treatment. This 

 did not affect the fat body very rapidly, but after a certain number of 

 hours, say eight or ten, I found that the "fat bodj^" began to be 

 dissolved, and in the case of gasoline, if the insect be left in for say 

 twenty-four to thirty hours it will dissolve practically all the fat of the 

 "fat body." The fat will be in solution in the gasoline, so that we can 

 say that is the agent bringing about this result. 



Gasoline and kerosene, however, kill the insect before any noticeable 

 solution of the fat body takes place. It is the alkaline wash that can 

 dissolve the "fat body" in one portion of the body of an insect while 

 the other portions of the body are still alive and able to move for a time. 



