June, *18] SWAIN: FUMIGATION EXPERIMENTS 323 
Table II —Chrysomphalus aurantii, February 19-20, 1917 
Time of ex¬ 
Number 
Number 
Percentage killed 3 
Percentage 
posure 
of lots 
of insects 
Mean 
Standard 
deviation 
difference 
60 
8 
800 
91.50dh .36 
1.50=1= .22 
11.25=1= .77 
30 
8 
800 
80.25d= .68 
2.86=1= .43 
60 
10 
1000 
96.30=1= .36 
1 .68=1= .26 
0.40=1= .55 
45 
10 
1000 
95.90=b .41 
1.92=1= .29 
60 
10 
1000 
87.30=1= .48 
2.24=1= .34 
0.30=1= .67 
90 
10 
1000 
87.60=1= .58 
2.73=1= .42 
The experiments with the red scale as the index gave results quite 
comparable with those in which the coccinellids were used. Between 
60 and 30 minute exposures there was a difference of 11.25±0.77 per 
cent which is comparable with that of the coccinellids; namely, 
11.00=1=2.53 per cent. Between 60 and 45 minutes the probable dif¬ 
ference was 0.40=1=0.55 per cent. In this case the probable error of the 
difference was larger than the difference, showing that there is no real 
difference. In addition to these, a series of experiments was carried 
on in which the exposures were 1 and If hours, with the result that the 
difference in favor of the 1| hour period was only 0.30=1=0.67 per cent. 
In other words there seems to be no advantage in an exposure of 1| 
hours over that of an hour. Nor is there any higher efficiency ob¬ 
tained by an hour exposure than by a 45 minute exposure. There is, 
however, a decidedly higher killing efficiency obtained in 45 minutes 
than in 30 minutes. These experiments, therefore, show that at 45 
minutes a killing efficiency is obtained which is not exceeded, by even 
twice that length of time. 
Commercial Fumigation 
To further verify these results, a study of the fumigation reports 
from Tulare County for the season of 1917 was made. Table III 
shows these results. 
Table III— Field Fumigation, Tulare County, July-September, 1917. Coccus 
citricola. 
120 Per Cent Schedule 
Time of exposure 
Number of 
orchards 
Number of 
acres 
Number of 
insects 
Percentage 
dead 
45 
15 
185 
34,495 
99.32 
50 
33 
455 
65,007 
99.28 
55 
77 
1225 
192,908 
99.21 
3 In determining the percentage of the insects killed only mature females were 
counted; the immature females and the males being omitted. 
4 
