﻿30 



BULLETIN 1147, U. S. DEPARTMENT OF AGRICULTURE. 



RELATIVE TOXICITY OF COMMERCIAL LEAD AND CALCIUM ARSENATES. 



Since the preliminary experiments indicated that the commercial 

 acid lead arsenates do not differ greatly in toxicity, sample 39, one 

 of those first used, was selected as a standard by which to judge the 

 relative toxicity of other spray materials, because its arsenic oxid 

 content (32.93 per cent) approaches most nearly the theoretical 

 content (33.11 per cent). 



In order to obtain comparable percentages of toxicity for the three 

 arsenates tested against five species of insects, it was first necessary 

 to place all the daily percentages of mortalities on the same basis. 

 This was accomplished by subtracting the daily mortalities of the 

 control insects fed nonpoisoned food from the daily mortalities of 

 the insects fed sprayed food. Since the daily mortalities on any 

 given day vary too much to serve as a fair percentage of toxicity, 

 the average ol the mortalities on the third, sixth, and tenth days 

 have been taken. The records given in Table 13 under the twentieth 

 day show whether or not the insecticides used were efficient. To 

 test the effect of starvation on the insects, other controls without 

 food were used also. 



The results reported in Tables 13 to 21 are comparable only when 

 the same combination of data and the same number of sets of insects 

 have been used. Data on the number of sets tested and the varia- 

 tion and average number of insects used for each individual spray 

 material, other than those given in the tables, therefore, are stated. 

 For Table 13 these data are as follows: Silkworms, 1 set (variation 

 48-52, average 50); webworms (H. cunea), 2 sets (619-1224: 864); 

 tent caterpillars, 4 sets (711-1126: 897); potato-beetle larvae, 3 sets 

 (132-157: 145); and grasshoppers, 3 sets (368-482: 420). 



Table 13. — Relative toxicity of commercial lead and calcium arsenates on 5 species of 

 insects, after deducting mortality of control with food, 1919 and 1920. 













Percentage 



of insects dead within — 











3 days. 



6 days. 











ffi 









i 





83 









Arsenates and con- 









| 









*j 





C 









trols. 





^ 



C3 



•S 









*s 



03 



JS 













*-' 



a 



<s 









•-* 



H 



a 



Uj 





o 





a 



1 



<D 



I 



P. 



& 



■a 



Ui 



a 





a 



a 



s 



M 



p. 





a 



"a, 



a 



cfl 

 W 





o 



if 

 55 



It 

 l 8 



O 



a 



6 



03 



O 



tic 



C3 



a 



< 



o 



£ 



CO 



1? 



o 8 



o 



a 



a 

 Eh 



6 

 o 



P4 



o 



M 

 03 



> 

 < 



39 



Acid lead arsenate 



96.0 



39.1 



53.1 



61.5 



37.6 



57.5 



100.0 



91.7 



86.5 



72.3 



31.1 



76.3 



28 



Basic lead arsenate. . . 



61.3 



8.5 



53.6 



47.0 



33. 



40.7 



81.6 



45.0 



88.5 



66.2 



31.6 



62.6 



5 



Calcium arsenate 



96.0 



12.5 



54.3 



67.5 



63.6 



58.8 



100.0 



69.1 



89.6 



66.9 



32.6 



71.6 



7 



do 



11.3 



3.6 



49.7 



45.6 



48.0 



32.2 



28.6 



15.0 



85.2 



47.0 



32.6 



41.8 



56 



do 



59.6 



4.3 



51.8 



54.8 



62.4 



46.6 



94.3 



33.7 



87.6 



54.9 



32.6 



60.6 



57 



do 



64.0 



1.1 



43.9 



60.5 



61.6 



46.2 



86.0 



27.8 



82.9 



73.3 



32.6 



60.5 



58 



do 



12.5 



2.7 



45.1 



50.6 



42.6 



30.7 



18.7 



is. 7 



85.6 



70.4 



32.6 



45.2 



59 



do 



72.5 



12.2 



.0 



3.8 

 .0 

 .0 



60.3 

 .4 

 1.9 



57.8 

 20.1 

 14.6 



61.0 



51.1 



96. 1 



61.2 



.0 



42.1 



28. 6 



.7 



81.4 



15.3 



5.5 



60.8 

 43.7 

 20.7 



32.6 



62.6 





Control without food.. 







35.5 



10.4 



67.4 



18.9 



