92 
JOURNAL OF ECONOMIC ENTOMOLOGY 
[Vol. 16 
A few grades of tobacco dust purchased during the past summer were 
quite fine, but the larger number of samples contained a considerable 
amount of coarse material. Most preparations consisted of fine and 
coarse particles in varying proportions. A common constituent of 
tobacco was clay or dirt or other cheap adulterant substance or filler. 
In our experiments we used a tobacco dust which was guaranteed to 
contain 1 percent nicotine. The physical properties of tobacco dust 
were as follows: Less than 50-mesh screen, 18 percent; 50-mesh, 27 
percent; 100-mesh, 1 percent; 150-mesh, 10 percent; and 200-mesh, 
44 percent. 
To obtain larger amounts than were available of the more finely pulver¬ 
ized material, the tobacco dust was ground for six hours or more in a ball 
machine. This is not an entirely satisfactory outfit for the purpose 
because of the large amount of time required for grindingand its failure 
to pulverize completely all the coarse particles. Reminding, even with 
this machine, did improve greatly the physical properties of common 
grades of tobacco dust. This is shown by comparing the foregoing 
figures relative to untreated tobacco dust with the accompanying anal¬ 
ysis of a sample which was subjected to grinding for several hours:—- 
Less than 50-mesh, 1 percent; 50-mesh, 11 percent; 100-mesh, 2 percent; 
150-mesh, 12 percent; and 200-mesh, 74.5 percent. Supplies of tobacco 
dust of different degrees of fineness were obtained by passing the re¬ 
ground material thru screens of designated sizes. In the spraying opera¬ 
tions the reground tobacco dust was always used, and even with this, 
considerable difficulty was sometimes experienced in maintaining a uni¬ 
form discharge of the spray because of the clogging of the suction strainer 
and unseating of the ball valves. 
Experiments with the Spirea Aphis 
In this series of tests reground tobacco was compared with dust 
mixtures containing 1 percent nicotine. Sheets were attached firmly 
to the collar of each plant and “tanglefoot” was applied to the edges of 
the sheets to prevent the insects from escaping. Thoro applications of 
both kinds of dust materials were made. Twenty-four hours after treat¬ 
ment the number of dead and live insects were counted. With the ex¬ 
ception of the coarser grades of tobacco dust all or a majority of the 
aphids were usually dislodged by the applications, and there is little 
doubt that the plants received greater protection than is indicated by 
the recorded killing efficiencies. The data are presented in Table 1. 
