UNEXPLAINED MORTALITY. 
15 
An examination of the data in the last three columns of the above 
table shows a striking relationship between the unexplained mortality 
and the insects which survived. In the case of the fungous parasites^ 
however, there seems to be no striking relationship of this kind. In 
order to make this point clear the six records (Nos. 1 to 6, inclu- 
sive) with the lowest percentages of unexplained mortality and the 
six records (Nos. 7 to 12, inclusive) with the highest percentages of 
unexplained mortality are here summarized and compared with a 
similar summary with regard to fungous parasitism rearranged from 
the same data : 
Unexplained mortality: 
6 lowest percentages averaging 58.2 per cent, 24.9 per cent survived. 
6 highest percentages averaging 81.7 per cent, 5.4 per cent survived. 
Fungous parasitism: 
6 lowest percentages averaging 8.5 per cent, 15.1 per cent survived. 
6 highest percentages averaging 21.1 per cent, 15.2 per cent survived. 
It appears from the above summary that a difference of about 24 
per cent in unexplained mortality in two groups of groves was asso- 
ciated with a difference of about 20 per cent in the insects which 
survived. On the other hand, a difference of about 13 per cent in 
the deaths due to fungous parasites was associated with no appreciable 
difference in the proportion of insects which survived. 
In December, 1910, Mr. S. S. Crossman, at the suggestion of the 
junior author, made a series of records to correspond with 10 of the 
12 included in Table IV. A summary of the 10 records for the two 
years is given in Table III. 
Table III. — Status of white flies in 10 groves at ends of seasons 1908 and 1909. 
Total num- 
ber white 
fly forms 
examined 
on 1,000 
leaves. 
Leaf averages. 
Percentages of totals. 
Year. 
Killed by 
fungus. 
Unex- 
plained 
mortality. 
Alive and 
matured. 
Per cent of 
fungous 
infection. 
Per cent of 
unex- 
plained 
mortality. 
Per cent* 
surviving; 
alive and 
matured. 
1908 
259,054 
107, 191 
34.0 
16.3 
203.1 
76.5 
33.5 
14.5 
12.4 
15.4 
73.7 
71.0 
13 9 
1909 
13.7 
In five groves a larger percentage of surviving insects was found in 
1909 than in 1908, in four groves a smaller percentage of surviving 
was found in 1909 than in 1908, and in one grove there was no 
appreciable difference in this percentage, as shown by the two exami- 
nations. Unexplained mortality ranged from 23.6 to 91.7 per cent 
in 1908 and from 61.8 to 78.8 per cent in 1909. The following is a 
summary for 1910 based on arrangements of the data to show rela- 
tion between unexplained mortality and fungous diseases to the 
number of insects surviving. 
