INSECTICIDES. 



461 



The poison acted very slowly, as none of the caterpillars 

 died for nearly three weeks, and one lived eight weeks. 



No. 70.— July 9, 1894. Ten caterpillars, of the fifth 

 molt, were placed on elm leaves which had been sprayed 

 with arsenate of lead, in the proportion of 2^ lbs. to 150 gal. 

 of water. One died the second day ; three died and one 

 pupated the fifth day ; one died and one Y)upated the sixth 

 and seventh days ; and one pupated the tenth day. 



Check experiment : two pupated the fourth, three the fifth, 

 one the sixth, seventh and eighth days ; and two were living 

 at the close of the experiment. 



No. 71 (field experiment).— July 9, 1894. Ten cater- 

 pillars, of the fifth molt, were placed on willow branches 

 which had been sprayed with arsenate of lead, in the propor- 

 tion of 2 lbs. to 150 gal. of water. One died the first day; 

 one pupated the third day ; one died the fourth and one the 

 fifth day ; one pupated the eighth and one the twelfth day ; 

 one died and one pupated the thirteenth day ; one pupated 

 the fifteenth and one the eighteenth day. 



No. 72 (field experiment). — June 21, 1893. A branch 

 of a small hop-hornbeam was sprayed with arsenate of lead, 

 in the proportion of 2 lbs. to 150 gal. of water, and ten fifth- 

 molt caterpillars were placed upon it. July 14, all were 

 dead. In this experiment the caterpillars died gradually, 

 the first one dying two days after the poison had been 

 applied, the last one living twenty-two days. The foliage 

 of the tree was uninjured. 



No. 73 (field experiment). — June 24, 1893. A branch 

 of apple tree was sprayed with arsenate of lead, in the pro- 

 portion of 2 lbs. to 150 gal. of water, and nine fifth-molt 

 caterpillars placed upon it. In this experiment the poison 

 was nearly all washed off by heavy rains soon after it was 

 applied. Four of the caterpillars molted and two pupated, 

 but all were dead August 2. Foliage uninjured. 



No. 74 (field experiment). — June 24, 1893. A branch 

 of apple tree was sprayed with arsenate of lead, in the pro- 

 portion of 2 lbs. to 150 gal. of water, and nine fifth-molt 

 caterpillars placed upon it. Six of the nine caterpillars died 

 before pupating, and, of the three which pupated, only one 

 emerged. Foliage uninjured. 



