oct. 16,1916 Effects of Nicotine as an Insecticide 105 
webworm are branched, and they nearly close the entrance, while the 
entrance of a spiracle (PL 1, fig. O, sp) in the tomato worm (larva of 
Phlegethontius sexta Joh.) is closed by a hairy and porous plate (Pl. 1, 
fig. O, p), which has an oblong opening through its center. 
Shafer (20) colored kerosene with Sudan III; and after thoroughly 
spraying or dipping grasshoppers (Melanoplus femoratus Burjn.), tomato 
worms, and aphids into this oil and after dissecting these insects, he 
found more or less of the red oil in the larger tracheae. He colored kero¬ 
sene emulsion and the emulsions of the miscible oils with indigo-carmine 
and with safranin and found that they also enter the spiracles. Shafer 
repeated these experiments by treating aphids with creolin emulsion 
containing indigo-carmine. After fixing the insects in absolute alcohol 
and after studying the sections he observed plugs of “precipitated” 
indigo-carmine in the larger tracheae, which were sufficiently large to 
close them. 
Dewitz (7), in discussing contact insecticides, does not believe that 
either liquids or powders can enter the spiracles in sufficiently large 
quantities to cause the death of the insects by suffocation. 
Without attempting to apply the physical law governing the surface 
tension of liquids, the following experiment was performed to determine 
roughly the surface tensions of water, different solutions of 40 per cent 
nicotine sulphate, pure nicotine, kerosene, gasoline, and kerosene emul¬ 
sion. Fresh nasturtium leaves were spread out flat on a table, with the 
under surfaces upward. With pipettes drops of water, solutions of 
nicotine sulphate (1:500 and 1:100), undiluted 40 per cent nicotine 
sulphate, undiluted pure nicotine, pure nicotine solutions (1:500 con¬ 
taining indigo-carmine and 1:100), kerosene, gasoline, and kerosene 
emulsion were dropped upon the nasturtium leaves. Of all these liquids 
the surface tension of gasoline was weakest and that of water the strongest; 
that of kerosene was second weakest, while those of pure nicotine and 
kerosene emulsion were about equal, but still much stronger than that 
of kerosene. So far as practical work is concerned, the ability of 40 
per cent nicotine sulphate and its solutions and of the two enumerated 
solutions of pure nicotine to spread over the surfaces of these leaves is 
about equal to that of water. The drops of each one of these liquids 
upon striking the leaves form small spheres and are not retained when 
the leaves are somewhat inclined. 
In regard to the evaporation of the solutions of nicotine sulphate and 
of pure nicotine, the drops of the solutions of pure nicotine evaporated 
rather quickly while those of the nicotine sulphate did not disappear 
for some time. The more nicotine contained in the drops of the pure 
nicotine solutions, the more quickly they evaporated. The evapora¬ 
tion of the drops of the solution of nicotine sulphate (1:500) was about 
equal to that of the water drops. 
55857°—16 - 2 
