172 REPORT 4, UNITED STATES ENTOMOLOGICAL COMMISSION. 
The practical application of such minute quantities in the open field is 
out of the question, and so is the use of the undiluted powder on a large 
scale, so long as its price is much higher than that of common flour. 
Mr. Hubbard continues: 
Experiments in the fields with the dry powder sifted upon the plants gave very 
unsatisfactory results unless large quantities of the powder were used. On August 28, 
a very windy day, I tried an application with the bellows, allowing the wind to carry 
the powder in fine clouds through the foliage, and. using about one pound to the acre, 
In this way, owing partly to the impossibility of securing an equal distribution, 
some worms were affected at a distance of ten or fifteen feet, while others, much 
hearer, were not affected at all. I have reason to believe that very few worms were 
killed outright at this trial. Some recovered in a few hours. A number of those 
which showed signs of pain, but had been very lightly dusted, I confined in vivaria, 
and all completed their transformations in the usual time. At the time the fore- 
going experiment was made the leaves were quite wet with recent rain, and another 
heavy shower occurred later in the day. 
Prof. J. P. Stelle carried out, during his stay at Calvert, Texas, simi- 
lar experiments with the same amount of undiluted powder and with 
the same unsatisfactory results. Fortunately it has been found that if 
unadulterated and fresh (which cannot be said in many instances of 
the powder sold at retail by our druggists) it may be considerably di- 
luted with other pulverized material without losing its deadly effect, 
the use of the powder thus becoming much cheaper. Of the materials 
which can be used as diluents, common flour seems to be the best, but 
finely-sifted wood-ashes, sawdust from hard wood, &c. — in short, any 
light and finely pulverized material which mixes well with the pyre- 
thrum powder — will answer the purpose. 
It has also been found that if the mixture of Pyrethrum and flour is 
applied immediately after preparation it is always weaker in effect than 
when left in a perfectly tight vessel for at least twenty -four hours be- 
fore use. In the experiments made in 1879 we found that a mixture of 
one part of Pyrethrum with ten parts of flour, applied immediately after 
preparing, is sufficient to kill the average-sized worms with which it 
comes in contact ; and that the mixture of one part of the powder to 
sixteen parts of flour is equally efficient after being kept for some days 
in a tight glass jar. The experiments made subsequently do not alter 
these results to any considerable extent. It would be quite superfluous 
to mention here the experiments made with very strong mixtures of 
Pyrethrum and flour, since they add nothing new to our experience, and 
we shall refer rather to those which were made to ascertain the minimum 
quantity of the powder necessary. The following series of experiments 
was made at Selma, Ala., by Mr. Schwarz : 
Experiment 1, August 27. — Pyrethrum powder, one part, mixed with twenty parts 
of flour, applied with the sieve immediately after preparing. Worms mostly more 
than half-grown. Only a small proportion of the worms came in contact with the 
mixture, though it was applied toward evening. These worms we're affected within 
the usual time, but upon examination, about ten hours afterwards, much more than 
half the number had recovered. The mixture in this proportion, and applied with 
tho sieve, is evidently a failure. 
