398 
Journal of Agricultural Research 
Vol. XXVIII, No. 4 
Table IV.— Results, against the Colorado potato beetle, of spraying potato and 
tomato plants with cyanids 
Compound 
Application 
Number of insects 
Number dead 
Per cent killed 
Feeding 
Foliage 
injury 
Method 
CO ' 
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Zinc cyanid_ 
Dust... 
20 
3 
0 
0 
1 
o 
2 
30 
Slight. 
Yellowing. 
Cuprous cyanid_ 
...do_ 
20 
7 
2 
2 
3 
0 
70 
...do. 
None. 
Nickel cyanid. 
_do_ 
20 
1 
0 
1 
10 
None_ 
Wilted. 
Copper nitroprussid. _ 
Spray.. 
10 
20 
1 
2 
0 
0 
i 
0 
20 
Slight. 
None. 
Zinc nitroprussid_ 
...do_ 
10 
20 
0 
3 
0 
1 
i 
1 
30 
...do.. 
Do. 
Copper nitroprussid.. 
...do_ 
5 
20 
0 
0 
0 
0 
0 
0 
Medium.. 
Do. 
Zinc* nitroprussid. 
...do... 
2 
20 
0 
0 
0 
0 
0 
0 
...do.. 
Do. 
Ammonium nickel 
...do... 
10 
20 
2 
1 
0 
0 
1 
2 
30 
None_ 
Do. 
cyanid-aniline. 
Ammonium nickel 
...do— 
10 
20 
0 
0 
0 
2 
0 
0 
10 
Slight. 
Do. 
cyanid-phenol. 
Ammonium nickel 
...do_ 
10 
20 
0 
0 
0 
0 
0 
0 
2 
10 
...do_ 
Do. 
cyanid-benzene. 
Control__ 
20 
0 
0 
0 
0 
0 
0 
0 
0 
Heavy.... 
Nickel cyanid, although stable, as shown by long-continued spraying tests 
similar to the foregoing on glass plates, was not as toxic as zinc cyanid, and, 
moreover, did not have the physical properties of a good insecticide. 
Table V.— Results , against the Japanese beetle, of dusting plants with cyanids 
Compound 
Number 
of insects 
Number dead 
Per cent 
killed 
Feeding 
Foliage 
injury 
First 
day 
Second 
day 
Third 
day 
Fourth 
day 
Zinc cyanid_ 
20 
0 
0 
0 
0 
Medium. _ 
None. 
Cuprous cyanid_ 
20 
0 
3 
1 
20 
None_ 
Do. 
Cuprous oxid __ 
20 
0 
0 
0 
Heavy_ 
Do. 
Cuprous iodid_ 
20 
0 
0 
0 
0 
Medium.. 
Do. 
Cuprous thiocyan¬ 
20 
0 
0 
Heavy_ 
Do. 
ate. 
Lead thiocyanate .. 
20 
0 
• 
0 
_do. _ 
Do. 
Lead arsenate_ 
20 
1 
1 
2 
20 
Slight:.... 
Do. 
Control_ 
20 
0 
0 
0 
0 
1 
Heavy.... 
Do. 
Cuprous cyanid, CuCN, was tested in the same manner as zinc cyanid and 
was found to be stable for at least a month, when the glass-plate experiment 
was discontinued. This cyanid was the only nonarsenical tested which was 
approximately equal to lead arsenate in toxicity against the Japanese beetle 
(Table VI). Both the caterpillars and the beetles ate it very sparingly and 
succumbed quickly. It is hard to wet for a spray mixture. It adheres to 
foliage excellently as a dust, but is washed off easily by rain. It did not in¬ 
jure the foliage of wild cherry or that of smartweed, but in a special test to de¬ 
termine the point it did injure peach foliage. The writers did not have the 
opportunity to determine whether or not the burning was due to a trace of 
the free copper ion. 
Since cuprous cyanid was toxic to the Japanese beetle, and nickel cyanid 
equally stable, was not, it seemed possible that Cu was responsible for the toxicity 
rather than CN. Therefore other cuprous compounds were prepared and 
compared with cuprous cyanid. On tent caterpillars cuprous thiocyanate 
showed remarkable toxicity. It w T as even more toxic than lead arsenate applied 
at the same rate. But hopes for its success against the beetle were vain. It 
