9 8 
Journal of Agricultural Research 
Vol. VII, No. 3 
(e) VAPOR FROM A 40 PER CENT NICOTINE-SUIPHATE SOLUTION 
Fifty worker bees in an observation case were introduced into a large 
battery jar. A small quantity of a 40 per cent nicotine sulphate solu¬ 
tion in a Petri dish 10 cm. in diameter was placed inside the jar 8 inches 
beneath the case of bees. During all the following day the bees remained 
more or less inactive and appeared slightly stupid. The next day follow¬ 
ing they were still slightly abnormal in behavior, but none died. 
The upper surfaces of large dock leaves were heavily sprayed with 
two solutions of nicotine sulphate (1 : 100 and 1 : 500) in the greenhouse. 
The aphids on the under surfaces of these leaves apparently were not 
affected by the vapor from either solution. On the other hand, when 
a small amount of the stronger solution was placed on the under surfaces 
of nasturtium leaves near the aphids but not against them, most of 
the insects were found dead three hours afterwards. When a piece 
of cheesecloth wet with the weaker solution was placed an inch beneath 
the branches and leaves of a nasturtium, a few of the many insects on 
this plant were found dead. 
In view of the results of all the preceding experiments in which the 
spray solutions had been evaporated, it may be argued that many of the 
insects died of nicotine poisoning by eating the leaves which had previ¬ 
ously been treated with nicotine solutions. That these leaves still emitted 
a faint odor of nicotine indicates that their surfaces still bore many traces 
of the alkaloid. It is also probable that some of the nicotine passed into 
the tissues of the leaves. Since some of those insects that did eat the 
leaves died so quickly after being placed inside the jars, it does not seem 
logical that they died primarily from the effects of nicotine as a stomach 
poison, because a small amount of nicotine as a stomach poison acts 
slowly. In view of the preceding reasoning and since some of the insects 
did not eat the leaves at all, it seems safe to say that most of them were 
killed by the odoriferous particles of the nicotine passing into the tracheae. 
In all of those experiments in which the insects were subjected to nico¬ 
tine vapor, although they did not actually touch the nicotine solutions, 
there can be no doubt that the vapors killed the insects; and it is also 
probable that the vapors passed into the tracheae and killed by paralyzing 
the nervous system. These experiments demonstrate that nicotine spray 
solutions are not necessarily contact insecticides, although they are more 
effective when actually used as such, for by this means the insects are 
constantly brought near the vapor under the most favorable conditions. 
TRACING NICOTINE TO TISSUES 
Owing to the small sizes of the insects used, it was not considered possi¬ 
ble to operate successfully on live individuals in order to determine what 
particular tissue is vitally affected when nicotine is used as an insecticide. 
Drawing conclusions solely from the behavior of the insects dying of nico¬ 
tine poisoning, the author states in the preceding pages that they die of 
