274 
JOURNAL OF ECONOMIC ENTOMOLOGY 
[Vol. 16 
from third instar larvae to full fed larvae. Later tests will be made to 
determine the lethal dosage for the young stage worms such as in 
nature are normally found feeding in the calyx end of the fruit. How¬ 
ever, it may be safely assumed that a dosage that kills the worms beyond 
the second instar will certainly kill first instar larvae. 
The following table shows the results secured by feeding larvae of 
varying sizes different quantities of arsenate of lead in determining the 
lethal dosage for larvae varying in age from the third instar to nearly 
mature larvae. In this work six different dosages were used varying 
from three and one-third millionths to five ten thousandths grams 
arsenate of lead. 
Table No. II 
Size of worms 
No. 
worms 
Dosage 
No. days 
observed 
Remarks 
Very small 
2 
.00000333 
2 
Almost dead 
One-fourth grown 
1 
.00000333 
5 
Almost dead 
Very small 
1 
.00000333 
4 
Alive 
Small 
1 
.000005 
3 
Dead 
One-half grown 
1 
.000005 
2 
Dead 
One-fourth grown 
1 
.000005 
2 
Nearly dead 
One-half grown 
1 
.000005 
2 
Alive 
14-% grown 
Va-Yz grown 
3 
.000008 
> 
Alive 
1 
.0000312 
4 
Dose repeated. Dead 
X-fij grown 
3 
.0000312 
6 
Dose repeated. Dead. 
One-fourth grown 
1 
.000125 
4 
Dead 
One-fourth grown 
3 
.000125 
4 
Alive 
Y to nearly grown 
4 
.000125 
1 
Alive 
2 mm. long 
1 
.0005 
2 
Dead 
y .2 grown 
1 
.0005 
2 
Dead 
yi-Yz grown 
2 
.0005 
2 
Sluggish-had eaten 
little. 
K-% grown 
1 
.0005 
1 
Dead 
Nearly mature 
1 
.0005 
2 
Alive-fed little. 
This shows that for the smaller larvae a dosage of only three and one- 
third millionths grams arsenate of lead may kill but that some of the 
nearly mature worms which fed but little were not killed with a dosage 
of five ten thousandths gram. However, where feeding was heavy this 
dosage killed all worms and may safely be considered as a killing dosage 
for all stages from the third instar to practically mature worms. 
Comparison of Lethal Dosage and Calyx Content 
If the lethal dosage for the older larvae is five ten thousandths (.0005) 
grams arsenate of lead then this is most certainly more than sufficient 
for the caterpillars of the first two or three instars which are the size of 
caterpillars which feed in the calyx cups. A comparison of the lethal 
dosage with the calyx content will show whether or not our ordinary 
spraying method places sufficient poison in the calyx cups to kill the 
young worms. 
The average of the nine above tests for calyx contents is .0001487 
