170 EEPORT 4, UNITED STATES ENTOMOLOGICAL COMMISSION. 
weak dose. If the dose is not strong enough, the convulsions of the 
worm are much less violent, and it recovers fully within a few hours. 
The action of the poison depends, however, less upon the amount of 
powder used than upon the part of the body of the worm which it 
touches, and on the method of applying it. Very small particles placed 
upon the sides of larvae, especially near the anterior spiracles, produce 
a more marked effect than larger quantities dropped upon their backs 
or lodged among the hairs. The effect is also enhanced by driving the 
powder with force against the worms by means of a bellows, for exam- 
ple, as the particles are thus driven into closer contact. 
After the preliminary trials made in 1878. and the more extensive 
ones made in 1879, the encouraging results of which are recorded in the 
first edition of this work (pp. 62-64), we had the experiments vig- 
orously continued by the agents of the Commission in subsequent years, 
and at various points within the cotton belt. These experiments were 
made partly with buhach kindly furnished by Mr. G. N. Milco, of Stock- 
ton, Cal., partly with imported insect powder made from Pyrethrum 
roseum, and which had been liberally placed at the disposal of the Com- 
mission by Messrs. Lehn & Fink, of New York. There seems to be but 
little difference in efficacy between these two kinds of powder. To t£st 
their relative strength, Mr. H. G. Hubbard made the following experi- 
ment : 
u Sixty Cotton Worms were collected and divided into two lots as 
equally as possible, so that neither set should contain an undue propor- 
tion of old or young worms. Each set was placed in a Mason jar, and 
thoroughly dusted with a small quantity of powder, one jar with the 
buhach, and the other with the imported pyrethrum. The worms were 
immediately afterwards turned out upon newspapers spread upon the 
ground. Those dusted with buhach were paralyzed and unable to 
crawl about in from 15 to 20 minutes. Those treated with imported 
pyrethrum were similarly affected in from 25 to 30 minutes. In both 
lots the worms began to be affected in less than one minute, and nearly 
all died within 12 hours. Another experiment was made upon 100 
worms of all sizes in which the powder (imported) was applied in the 
open air by means of a bellows. Worms one-fifth to one-third grown 
were completely paralyzed in 10 minutes ; worms one-half grown, in 30 
to 45 minutes ; full grown worms show r ed the full effect of the poison 
after several hours. In about three hours the smaller worms appeared 
to be dead. The oldest worms did not die before night.' 7 
Pyrethrum can be applied — 1, as a dry powder ; 2, as a fume; 3, as an 
alocholic extract diluted; 4, by simple stirring of the powder in water; 
5, as a tea or decoction. 
1. Applications of pyrethrum as dry powder. — The following 
experiments were made by Mr. Hubbard at Centreville, Fla., to ascertain 
the minimum quantity of the dry powder that could be used with effect 
