﻿36 BULLETIN 1147, U. S. DEJW I; ! \1K XT OF AGRICULTURE. 



The addition of Bordeaux mixture to the four arsenicals employed 

 reduced the percentages of toxicity against silkworms, webworms, and 

 honeybees, but- reduced the toxicity against the tent caterpillars little, 

 if any. The addition of lime-sulphur (sample 93) to the lead arsenate 

 (sample 30) reduced the toxicity against webworms, but seemed to in- 

 crease it against tent caterpillars. The addition of lime-sulphur (sam- 

 ple 94) to the calcium arsenate (sample 57) neither decreased nor in- 

 creased the toxicity against webworms, but appeared to increase it 

 against tent caterpillars. In the 1919 results, Bordeaux mixture and 

 lime-sulphur reduced the rates of toxicity in all cases. 



The following data are not given in Table 16: Silkworms, 2 sets 

 (each of 50) ; webworms (H. cunea), 1 set (variation 107-332, average 

 141); tent caterpillars, 3 sets (118-557: 301); and honeybees, 2 sets 

 (each of 50). 



To determine the percentage of arsenic borne by leaves sprayed 

 with the foregoing spray mixtures, many apple and mulberry leaves 

 were sprayed at four different periods. The parts of arsenic per 

 million parts of the leaves were as follows: Sample 39, 1,200; sample 

 91, 800; sample 93, 800; sample 57, 1,000; sample 92, 800; sample 

 94, 900; sample 23, 1,650; sample 54, 1,300; sample 25, 1,100; and 

 sample 55, 1,100. The general average of those containing neither 

 Bordeaux mixture nor lime-sulphur (samples 39, 57, 23, and 25) is 

 1,238 parts of arsenic, while those containing these two fungicides 

 (samples 91, 93, 92, 94, 54, and 55) have a general average of 950 

 parts of arsenic. According to these figures, the fungicides reduced 

 the arsenic content 23.3 per cent, whereas they reduced the general 

 average toxicity only 11.5 per cent. 



RELATIVE TOXICITY OF ARSENATES AND ARSENITES. 



Toxicologists report that arsenites are more toxic than arsenates. 

 Firrthennore, on the basis of equal percentage of arsenious oxid and 

 arsenic oxid, 16.2 per cent more metallic arsenic is present in the 

 arsenites than in the arsenates. To secure additional data on this 

 subject, a high-grade acid lead arsenate, a calcium arsenate, a sodium 

 arsenate, a zinc arsenite, and a Paris green were selected in 1919 for 

 comparison. The following insects were used: Silkworms, 1 set 

 (variation 49-54, average 51); webworms (H. cunea), 2 sets (818- 

 1725, average 1173); webworms (H. textor), 1 set (189-310, average 

 251) ; potato-beetle larvse, 3 sets (282-404, average 345) ; and grass- 

 hoppers, 2 sets (181-302, average 242). After deducting the mortali- 

 ties of the controls, the average percentages of toxicity were as follows : 

 Acid lead arsenate (sample 39) 66, calcium arsenate (sample 5) 63.9, 

 and sodium arsenate plus Bordeaux mixture (sample 55) 61.7, an 

 average of 63.9 for the arsenates on five species of insects; zinc 

 arsenite (sample 23) 57.6, and Paris green (sample 64) 65.5, an average 

 of 61.6 for the arsenites. Thus the Paris green tested is equal to 

 the arsenates in toxicity, and, as shown by the average, these two 

 arsenites are not quite as toxic to insects as are the tlrree arsenates 

 employed, although the comparison is not fair in all respects. The 

 smallest number of units eaten were sprayed with Paris green. 



