170 REPORT 



weak dose. If the close 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 i)oison 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- 

 X3le, as the particles are thus driven into closer contact. 



After the i:)reliminary 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 b^^ Mr. G. N. Milco, of Stock- 

 ton, Cal., partly with imported insect powder made from Fyrethrum 

 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 test 

 their relative strength, Mr. H. G. Hubbard made the following experi- 

 ment: 



*^ 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 

 j)yrethrum 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 j full-grown worms showed the full effect of the poison 

 after several hours. In about three hours the smaller worms ax>peared 

 to be dead. The oldest worms did not die before night.'^ 



Pyrethrum can be applied — 1, as a dry powder j 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 pyretheuim as dry powder. — The following 

 experiments were made by Mr. Hubbard at Centreville, Fla., to ascertain 

 the minimum quantity of the dry powder that coidd be used with effect 



