October, ’23] 
PARROTT & MACLEOD: TOBACCO DUST 
429 
tested may perhaps be explained on the supposition that the evolution 
of nicotine was slow. 
Relative Efficiency of Tobacco, Free Nicotine and Nicotine 
Sulphate Dusts 
This series of tests were designed to show the comparative insecticidal 
properties of dust mixtures, containing respectively fine tobacco dust, 
free nicotine and nicotine sulphate. The different preparations con¬ 
tained approximately 1 percent nicotine and were applied at the rate 
of 5 grams per plant. The results obtained with the dusts are indicated 
in Table III. 
On the whole, tobacco dust did not exhibit as high a rate of toxicity 
as did the mixtures containing free nicotine or nicotine sulfate, but the 
difference in insecticidal properties was, however, not very conspicuous. 
The free nicotine dusts were more rapid in their paralytic action than 
those containing nicotine sulfate, and tobacco dust was the least rapid 
in dislodging the insects. The mixtures in which kaolin was incorporated 
as a carrier of free nicotine or nicotine sulfate displayed a killing effi¬ 
ciency of less than 80 percent, while the preparations using sulfur and 
lime carbonate or hydrate as carriers of the nicotine were noticeably 
more efficient. 
Toxicity of the Fumes of Dusting Mixtures 
To obtain data relative to the toxicity of the fumes given off by the 
different nicotine dusts, applications of the materials were made to the 
walls of large bell jars, after which the jars were placed over plants 
heavily infested with aphids. In making these experiments care was 
exercised to prevent any of the particles of the various materials from 
coming in contact with the bodies of the insects. For the sake of com¬ 
parison several plants were dusted with the same preparations. ' The 
data are given in Table IV. 
The insects confined in the dusted bell jars exhibited no apparent 
signs of unrest, while those on the treated plants began to move im¬ 
mediately after the application and seemed agitated. The aphids began 
to fall from the dusted plants in half the time required to dislodge those 
subjected only to the fumes arising from the walls of the jars. Not¬ 
withstanding the greater speed with which the dusts in contact with the 
insects acted the final killing was more complete in the case of the en¬ 
closed plants. These insects were killed in situ and were usually attached 
to the leaves by the proboscis which had not been extricated at the 
time of paralysis. It is also interesting to note that only a very few 
