426 
JOURNAL OF ECONOMIC ENTOMOLOGY 
[Vol. 16 
Less than 50-mesh, 1 percent; 50-mesh, 11 percent; 100-mesh, 2 percent; 
150-m.esh, 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. 
Toxicity of Coarse and Fine Tobacco Dusts 
In this series of tests commercial tobacco dust and reground tobacco 
of different degrees of fineness was applied at the rate of 5 grams to 
each spirea, the material being applied carefully in order to insure 
thoro treatment. 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. Twenty-four hours after treatment the 
number of dead and live insects were counted. With the exception of 
the coarser grades of tobacco dust all or a majority of the insects 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. 
A study of the foregoing data shows plainly that the finer grades of 
tobacco dust possessed greater killing powers than the coarse preparations. 
The 200-mesh material obtained from the leground tobacco was superior 
to other grades in its toxicity to the aphids and in its physical condition. 
Tobacco dusts of 50-mesh fineness or coarser displayed low killing power 
and poor adhesive properties. 
Effects of Hydrated Lime on the Physical and Insecticidal 
Properties of Tobacco Dust 
Chemical analyses demonstrated that hydrated lime in combination 
with tobacco dust promoted the liberation of nicotine. Observations 
also indicated that the incorporation of light fluffy material such as 
lime hydrate of 200-mesh fineness improved the physical condition of 
tobacco dust. To determine the influence of these factors a series of 
tests were undertaken, the results of which are indicated in Table II. 
It will be observed that in general the mixing of hydrated lime with 
tobacco dust resulted in decreased toxicity, and that the loss of insecti¬ 
cidal efficiency increased proportionately with the amount of lime added. 
Mixtures containing 10 percent lime hydrate were not as effective as 
undiluted tobacco dust but they were more toxic than those containing 
25 percent hydrated lime. On the other hand the physical properties 
of tobacco dust, especially the coarser grades, were considerably enhanced 
by the addition of lime hydrate. Altho lime tends to liberate nicotine, 
its failure to affect appreciably the insecticidal properties of the mixtures 
