ARSENICALS. 
47 
One drop would occasionally kill a large worm but more often two 
drops were fatal. In almost every case three drops proved fatal 
within 24 hours. Therefore, for these larvae three drops may be 
regarded as a minimum fatal dosage of acid lead arsenate. An 
analysis of 100 drops (4 sets) from the same pipette gave 0.0091 
milligram of metallic arsenic as an average per drop, making 0.0273 
milligram of arsenic a minimum fatal dosage for fully grown silk- 
worms. 
An analysis of 59 of the dead silkworms, each of which had eaten 
three drops of the arsenical, gave 0.0027 milligram of arsenic per 
larva, indicating that 90 per cent of the arsenic eaten had been 
voided in the feces before the larvae died. Silkworms which had 
received a maximum dosage of the same arsenical voided in the feces 
only 19 per cent of the arsenic eaten, and Ceratomia, which had 
received an average dosage of the same poison, voided 64 per cent of 
the arsenic with the feces. 
QUANTITY OF ARSENIC EATEN BY INSECTS IN FEEDING TESTS. 
During the feeding tests many samples of dead larvae were pre- 
pared for analyses, but only those of webworms (H. textor) and those 
of potato-beetle larvae were finally analyzed. The webworm is one 
of the most difficult to kill by arsenic, while the potato-beetle larva 
is one of the most easily killed. Some of the webworms were washed 
as described on page 44, but most of them were not washed. Also 
several samples of feces (more or less contaminated) were analyzed. 
The percentage of toxicity, as shown in Table 22, is the average of 
the mortalities recorded on the third, sixth, and tenth days for the 
one species concerned. 
Table 22. — Arsenic consumed by insects in feeding tests, 
1919. 
Species of insects 
Arsenicals and controls. 
Condition of 
larvae before 
being analyzed. 
Num- 
ber of 
larvae 
ana- 
lyzed. 
Arsenic 
per 
larva. 
Arsenic (parts 
per million) 
in— 
Tox- 
icity 
after de- 
ducting 
and sample No. 
Larvae. 
Feces. 
mor- 
tality 
of 
control. 
Webworms (£T. tex- 
tor): 
39 
Commercial acid lead 
arsenate. 
do 
Washed and 
dried. 
Dried... 
163 
400 
200 
400 
200 
180 
130 
160 
200 
200 
200 
200 
200 
200 
Milli- 
grams. 
0.0017 
.0025 
.0014 
.0024 
.0040 
.0033 
.0040 
.0027 
.0050 
.0016 
.0055 
.0050 
.0028 
.0053 
359 
385 
303 
481 
691 
436 
674 
399 
747 
303 
917 
911 
383 
613 
527 
1,114 
746 
1,125 
330 
851 
355 
365 
539 
818 
903 
946 
840 
306 
15 
39 
68.6 
5 
Commercial calcium ar- 
senate. 
do 
Washed and 
dried. 
Dried 
5 
59.1 
28 
Commercial basic lead 
arsenate. 
Laboratory calcium arse- 
nate. 
Sample 69 plus 1 gram 
lime per 418 cc. 
Laboratory barium arse- 
nate. 
Commercial magnesium 
arsenate. 
Laboratory sodium arse- 
nate plus Bordeaux 
mixture. 
Commercialzinc arsenite. 
Commercial Paris green . 
Laboratory aluminum 
arsenate. 
Laboratory copper 
barium arsenate. 
Control feces 
do 
do 
do 
48.9 
69 .*. 
15.1 
69B 
6.3 
71 
do 
31.5 
62 
do 
do 
36.5 
55 ... 
59.3 
23 
do 
do 
do 
do 
63.6 
64 
62.6 
73 
32.0 
74 
41.8 
