Oct. i6 t 1916 
Effects of Nicotine as an Insecticide 
hi 
fig. E, ava ) in the thorax unites the pair of spiracles in the prothorax 
and aerates the subesophageal ganglion, whereas the posterior ventral 
arch ( pva ) connects the pair of spiracles in the metathorax and aerates 
the large thoracic ganglion. The two ventral arches are of the greatest 
interest, because they and a few other smaller branches carry nicotine 
fumes directly to the nervous system, and for this reason it is under¬ 
standable why the fumes so quickly paralyze aphids. 
Plate 3, figure E, is a reproduction of a combination drawing from 
five consecutive sections through the thorax of an aphid that had been 
fumigated with a solution of 40 per cent nicotine sulphate, showing the 
precipitate ( pr ) on the integument {ini), in the tracheae (tr), and in the 
subesophageal ganglion (sg). The large trachea was cut crosswise near 
the spiracle, and the branches are drawn in only their approximate posi¬ 
tions. It is to be noted that the anterior ventral arch (ava) passes over 
the subesophageal ganglion, but sends one of its branches under and into 
this ganglion. Another large branch from the main trachea also sends 
one of its branches to the same ganglion, penetrating its dorsal surface. 
These sections did not actually show the small tracheae penetrating this 
ganglion, but sections from several other aphids did. 
Plate 3, figure C, reproduces a combination drawing from six consecu¬ 
tive sections of the same aphid as above described, showing three tracheal 
branches entering the thoracic ganglion. Attention is to be called to the 
precipitate (pr) in these tracheae and in the ganglion. Often large gran¬ 
ules resembling precipitated particles lie in and near the ganglia. Three 
groups of them are represented in this figure, two being near the largest 
trachea and one by the smaller trachea. These fine particles may be 
either the precipitate resulting from fumes that had passed through the 
tracheal walls, or that from some other source. There can be no doubt 
about the large particles of the precipitate, because they are never found 
in aphids used as controls. 
While it is easy to find tracheae and precipitate in the ganglia, it is 
quite difficult to find them in the brain. This seems to be due chiefly to 
the absence of the larger tracheal branches in the brain. Plate 3, figure 
H, shows a small tracheal branch in the brain cut crosswise, containing 
three particles of the precipitate, and there are a few more scattered in 
the adjacent brain. Plate 3, figure G, shows a small tracheal branch 
running into an optical lobe, containing a few particles of the precipitate. 
A critical study of any given tissue would certainly show that it con¬ 
tains as much precipitate as found in the nerve tissue; but no other tissue 
was thus studied, because all the evidence indicated from the outset that 
nicotine kills insects by- paralysis. One more illustration from the aphid 
may be used to show that the precipitate may also be found in tracheae 
aerating other tissues. Thus, Plate 3, figure I, represents a tracheal 
branch containing the precipitate running between two ovaries. 
