February, ’20] 
NEWELL: POISONING THE BOLL WEEVIL 
131 
When calcium arsenate was used (Table III) the mortality on pro¬ 
tected plants was 78.8 per cent and on “exposed” plants 73.8 per 
cent, the checks being as given above, giving a mortality, due to the 
poison of 64.8 per cent on dry plants and 56.6 per cent on plants ex¬ 
posed to dew, a gain of 8.2 per cent when the plants remained dry. 1 II) III) 
The foregoing results seem to show conclusively that, as the mor¬ 
tality on dry plants was perceptibly higher than on those exposed to 
the deposition of rain and dew, the presence of visible moisture is in 
no way necessary to the effectiveness of either lead or calcium arsenate. 
This forces us to the conclusion that the weevil is killed by ingestion of 
the poison in feeding and not when drinking dew or rain water as 
claimed by Mr. Coad. 
The investigation was, however, pursued along other lines, largely 
under laboratory conditions. 
The Toxicity of Dew from Poisoned Plants 
Investigations were also made to determine the amount of arsenic 
contained in dew which was deposited on cotton plants which had 
been treated with both lead arsenate and calcium arsenate. Upland 
cotton plants in the field were treated by dusting them with lead arse¬ 
nate in the usual manner, at the rate of about 8 pounds per acre. 
Other plats were treated in like manner with calcium arsenate. The 
dew was collected from these plants, early in the morning, by the use 
of shell or specimen vials. It was found that by carefully touching 
the lip of the vial to the dew drops suspended from the edges and tips 
of leaves that the dew could be, though rather tediously, drawn off 
into the vial and a sufficient quantity thus accumulated for laboratory 
experiments. Dew was collected only from leaves well covered with 
poison. 
Dew collected in this manner was submitted to Mr. S. E. Collison, 
chemist of the University of Florida Experiment Station, for quantita- 
1 The data secured in these experiments affords an interesting comparison between 
the effectiveness of lead arsenate and of calcium arsenate. 
On plants protected from moisture the mortality ascribable to lead arsenate (Table 
II) was 71.6 per cent and to calcium arsenate (Table III) 64.8 per cent, a difference 
in favor of the lead arsenate of 6.8 per cent, but the mortality ascribable to lead arse¬ 
nate on “exposed” plants (Table II) was 56.6 per cent and to calcium arsenate (Table 
III) also 56.6 per cent. 
In the case of application by the blast method, all experiments, lead arsenate gave 
a mortality of 88.6 per cent during ten days and calcium arsenate a mortality of 79.3 
per cent, a margin of 9.3 per cent in favor of lead arsenate. Applications by the 
cloud method, all experiments, gave a mortality with lead arsenate of 74.7 per cent 
and with calcium arsenate a mortality of 74.2 per cent. The mortality in the check 
was 16.1 per cent (see footnote, p. 9). 
