﻿26 BULLETIN 1147, U. S. DEPARTMENT OF AGRICULTURE. 



Howard {19), experimenting with the spotted cucumber beetle 

 in the field, used equal amounts (by weight) of several arsenicals. 

 The average mortality on the fifth day, based upon the results of 

 two seasons' work, is as follows: Zinc arsenite, 24 per cent; acid 

 lead arsenate, 17 per cent; Paris green, 16 per cent; Bordeaux- 

 lead arsenate, 14 per cent; and calcium arsenate, 1 per cent. 



Sanders and Kelsall (43) give comparative figures for the toxicity 

 of several arsenicals. On the basis of one-half pound of metallic 

 arsenic to 100 gallons of liquid, they obtained the following percent- 

 ages of dead fall webworms on the eighth day : Sodium arsenate, 52 ; 

 Paris green, 72; acid lead arsenate, 36; zinc arsenite, 60; calcium 

 arsenate, 44; and white arsenic (As,0 3 ), 60. On the same arsenic- 

 content basis, but with the addition of Bordeaux mixture (10-10-100) 

 to the spray materials, they obtained the following percentages of 

 dead tussock-moth caterpillars on the eighth day: Sodium arsenate, 

 60; Paris green, 64; calcium arsenate, 48; and white arsenic, 60. 



Wilson (53), using five arsenicals against the potato beetle in the 

 field and laboratory, presents their rates of toxicity graphically as 

 follows: Paris green, 80 per cent; zinc arsenite, 65 per cent; acid lead 

 arsenate, 60 per cent; calcium arsenate, 50 per cent; and basic lead 

 arsenate, 20 per cent. He did not use the same arsenic content 

 in any two of them. 



EXPERIMENTAL WORK. 



In comparing the toxicities of the various arsenicals, fed to several 

 species of insects, equal percentages of the two oxids of arsenic 

 (As 2 3 and As 2 5 ) were used in the spray mixtures. 



PREPARATION OF SPRAY MIXTURES. 



Suspensions or solutions of each of the arsenicals used were pre- 

 pared on the basis of the presence of 0.076 gram of arsenious or 

 arsenic oxid per 100 cubic centimeters of distilled water. This 



f>roportion is at the rate of 1 pound of dry or 2 pounds of paste acid 

 ead arsenate to 50 gallons of water, it oeing assumed that 32 per 

 cent is the average arsenic oxid content of a dry acid lead arsenate. 

 On the basis of equal percentage, the mixtures made by using arseni- 

 ous oxid contained 16.2 per cent more metallic arsenic than did those 

 containing arsenic oxid. Each mixture, however, had either an 

 arsenious or arsenic oxid content of 0.076 per cent. All the laboratory 

 samples used in 1919 and 1920 were pulverized and passed through a 

 100-mesh sieve before being mixed with water, but the commercial 

 samples were used as purchased. When properly prepared, the 

 arsenical mixtures were placed in clean mason jars having rubbers 

 and tops. Each jar was then thoroughly shaken to dissolve, if 

 possible, and to distribute the arsenical, and subsequently the mix- 

 tures were sprayed on foliage which was eaten by insects. 



APPLICATION OF SPRAY MIXTURES. 



In all, seven species of insects were tested : Silkworms (Bombyx 

 rnori L.), two species of fall webworms (Hyphantria cunea Dru. and 

 H. textor Harr.), and tent caterpillars (Malacosoma americana Fab.), 

 belonging to Lepidoptera; the Colorado potato-beetle larvae (Lepti- 

 notarsa decemlineata Say), belonging to Coleoptera; grasshoppers 



