﻿ARSENICALS. 



31 



Table 



insects 



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

 ts, after deducting mortality of control with, food, 191 9 and 1920 — Continued. 



Arsenates and con- 

 trols. 



Percentage of insects dead within— 



10 days. 



IS 





20 days. 



Acid lead arsenate. . . 

 Basic lead arsenate. . 



Calcium arsenate 



do 



do 



do 



do 



do 



Control without food. 

 Control with food 



30.3 

 98.1 

 98.0 

 22.9 

 100.0 

 71.5 

 .0 



84.5 

 74.8 

 84.0 

 24.4 

 52.4 

 50.3 

 22.2 

 69.4 

 83.3 

 14.4 



87.3 

 87.5 

 87.7 

 87.7 

 86.8 

 84.7 

 87.7 

 86.6 

 79.3 

 12.3 



52.5 

 47.0 

 53.7 

 40.6 

 43.8 

 51.5 

 53.2 

 52.3 

 37.4 

 42.5 



All. 

 All. 

 All. 

 All. 

 All. 

 All. 

 All. 

 All. 



81.1 

 76.3 

 81.3 

 45.8 

 70.3 

 71.1 

 46.5 

 77.1 



100.0 



"44.9 



100.0 

 100.0 

 29.2 



78.3 



17.3 



100.0 

 0.0 



All. 



All. 



All. 

 20.7 

 49.8 

 45.7 

 20.5 

 51.9 



All. 

 41.8 



All. 

 All. 

 All. 

 All. 

 All. 

 All. 

 All. 

 All. 

 All. 

 50.5 



All. 



All. 



All. 



All. 



All. 



All. 



All. 



All. 

 34.0 

 57.1 



71.6 

 59.9 

 70.6 

 39.9 

 59.2 

 59.3 

 40.8 

 63.6 



i5.*5 



100.0 



Table 13 shows the following: The average percentages of toxicity 

 of the acid lead arsenate (sample 39) and of one sample of calcium 

 arsenate (sample 5) on five species of insects are practically the same ; 

 the percentage of toxicity for another calcium arsenate spray (sample 

 59) is a little lower; those for two other calcium arsenates (samples 

 56 and 57) and for basic lead arsenate (sample 28) are practically 

 the same; while those for the remaining calcium arsenates (samples 

 7 and 58) are very low. Samples 7 and 58 were not efficient against 

 all five species of insects tested. The basic lead arsenate acted much 

 more slowly on the silkworms and webworms than did the acid lead 

 arsenate, but, as a rule, only slightly more slowly on the tent cater- 

 pillars, potato-beetle larva?, and grasshoppers. The quantity of food 

 consumed is inversely proportional to the toxicity, being least for 

 samples 39 and 5 and most for samples 58 and 7. The results in 

 this table also show that starvation had little or no effect on the in- 

 sects tested, but that the insects really died from the effects of the 

 arsenates. 



EFFECT ON TOXICITY OF ADDING LIME TO ARSENICALS. 



According to the preliminary experiments conducted in 1917 and 

 1918, the laboratory sample of calcium arsenate (sample 42) and the 

 same compound plus 0.3 gram of lime (sample 42A) killed 69 per cent 

 and 68 per cent, respectively, of the webworms counted on the 

 twelfth day. When the quantity of lime was doubled (sample 42B) 

 the mortality was 50 per cent, and when it was quadrupled (sample 

 42C), 40 per cent. In 1919 many other experiments, in which a 

 larger amount of lime was added to every 418 cubic centimeters of 

 another laboratory sample of calcium arsenate, were performed, using 

 silkworms, 1 set (variation 49-53, average 51) ; webworms (H. cunea), 

 2 sets (538-818: 622) ; tent caterpillars, 4 sets (785-1021: 943) ; web- 

 worms (H. textor), 1 set (181-325: 266); potato-beetle larvaa, 3 sets 

 (290-361:339); and potato-beetle adults, 1 set (37-41:39). De- 



