564 
JOURNAL OF ECONOMIC ENTOMOLOGY 
[Vol. 17 
lower killing', even with the higher dosages. It may be that as the wire- 
worms become less active the effect of the gas upon them decreases. 
Results obtained at Toppenish, Wash., gave considerable promise, 
but difficulties were encountered owing to the lateness in the season, 
the hardness of the soil, and the increasing inactivity of the wireworms. 
Benefited by the experience gained in the fall, the experiments were 
begun at the first signs of wireworm activity in the spring, which was 
early in March. A special machine was designed by the American 
Cyanamid Company wdiich could be attached to the beam of a plow and 
set to feed a definite amount of cyanide in the furrow just ahead of the 
soil which is being turned over. Disc and hoe drills also were used in the 
application of calcium cyanide. Soil examinations were made both in the 
plots and in other parts of the infested fields. The percentage of killing 
was ascertained by sifting several cubic feet of soil in each plot and 
counting the dead and live insects. A summary of the experiments up 
to May 5 shows the following results : 5 
Table II—Showing Percentage of Wireworms Killed by Different 
Amounts of Granular Calcium Cyanide, Toppenish, Washington 
Pounds 
per acre 
Maximum 
Per cent killed 
Minimum 
Average 
Number of Total number 
experiments of worms found 
350-500 
100 
100 
100 
4 
35 
280-300 
100 
71 
93 
6 
141 
225-250 
100 
77 
89 
K 
D 
58 
180-200 
100 
21 
73 
11 
335 
130-150 
81 
16 
49 
8 
154 
Control 
0 
0 
0 
21 
579 
Here again it is at present impossible to explain the variations in re¬ 
sults but a study of the experiments suggest several contributing 
factors, among which are the following: 
(1) Temperature. During low temperatures the wireworms are in¬ 
active and probably not so greatly affected by the gas as when active. 
(2) Moisture. In several of the experiments where poor results were 
obtained the soil was wet. It is well known that moisture will absorb 
hydrocyanic-acid gas and that when too much moisture is present the 
calcium cyanide breaks down, forming ammonia and thus lessening the 
amount of hydrocyanic-acid gas given off. Probably this is what 
happened in some of these experiments. 
(3) Method of Application. In most cases better results were 
6 The type of soil at Toppenish is volcanic ash loam, and was practically uniform 
in all plots, varying only in its mechanical condition. 
