﻿ARSENICALS. 25 



Smith (48) did not find barium arsenate satisfactory again I one 

 species of army worm. 



Brittain and Good (7) used barium arsenate in 1917 againsl the 

 apple maggot, but did not recommend it because of h tendency to 

 burn the foliage. 



MISCELLANEOUS SPRAY MIXTURES. 



Kirkland and Burgess (21) determined in field experiments on the 

 gypsy moth that acid lead arsenate is slightly better than basic lead 

 arsenate. 



Wilson (51) reported that zinc arsenite killed tent caterpillars 

 (Malacosoma erosa and M. jjluvialis) more quickly and stayed in 

 pension better than the basic lead arsenate. The basic lead arsena t e, 

 while slow in its action, finally killed the insects. The same; arsenic 

 content was not used for both sprays. Lime-sulphur mixed with 

 arsenicals retarded the action of the arsenicals. Lime-sulphur used 

 alone was not of much value as a stomach poison. 



Robinson and Tartar (36) conducted tests with tent caterpillars 

 (M. pluvialis) on sprayed foliage in an open part of an insectary, 

 using an equal arsenic content. The acid lead arsenate killed more 

 quickly than did the basic lead arsenate which, however, although 

 slow, proved satisfactory because it killed all the caterpillars tested. 



Tartar and Wilson (50), also using tent caterpillars, determined 

 that acid lead arsenate (2-200) was more efficient than the basic 

 form (2-100). The acid lead arsenate had an arsenic content of 

 about 33 per cent, while the basic form had one of only 25 per cent. 



Sanders and Brittain (41), reporting tests on the toxic value of 

 certain arsenicals, both alone and in combination with fungicides, 

 against the brown tail moth, tent caterpillar, cankerworm, tussock 

 moth, and fall webworm in the field, report that calcium arsenate 

 is inferior to both acid and basic lead arsenates, and that barium 

 arsenate is still more inferior. Basic lead arsenate is inferior to 

 acid lead arsenate in all combinations except with Bordeaux mix- 

 ture. They think that Bordeaux mixture does not inhibit the 

 action of the basic form as much as it does that of the other ar- 

 senicals used. 



Lovett and Robinson (24 and 25) used the tent caterpillar (31. 

 pluvialis) throughout their experiments to determine the toxic 

 values and killing efficiency of the arsenates. Instead of examining 

 all the larva? daily to determine the exact number dead, they counted 

 the dead ones that dropped daily from the sprayed foliage in the 

 laboratory. These men also carried on preliminary field experi- 

 ments with calcium arsenate. They summarize their results as 

 follows : 



Lead hydrogen [acid lead] arsenate has a higher killing efficiency at a given dilu- 

 tion than either calcium or basic lead arsenate. It requires a longer period of time 

 to kill the nearly mature caterpillars than the small forms. All of the arsenic devoured 

 by the insects in feeding upon sprayed foliage is not assimilated, but a portion passes 

 through the intestinal tract in the excrement. The percentage amount of the arsenic 

 assimilated depends upon the arsenate used; lead hydrogen arsenate was assimilated 

 readily and most of the arsenic was retained in the tissues while much of the basic 

 lead arsenate was found in the excrement. It requires approximately 0.1595 milli- 

 gram of arsenic pentoxid to kill 1,000 small tent caterpillars, and approximately 

 1.84 milligram of arsenic pentoxid to kill 1,000 nearly mature tent caterpillars, irre- 

 spective of the particular arsenate used as a spray. 



27476°— 23— Bull. 1147 4 



