36 ’ WHITE FLIES INJURIOUS TO CITRUS IN FLORIDA. 
Taste VI.— Mortality of citrus white fly on umbrella China tree leaves. 








oath Live Dead 
Date. nue larvee larvee |Mortality. 
mo: land pupe.and pupe. 
Per cent. 
Oct. 28, 1906... 806 1 111 12.0 
July 8, 1908...- 497 338 192 18.7 
July 21, 1908... 113 256, 51 12 
Aug. 19, 1908.. 232 49 152 35.1 
Aug. 25, 1908... 312 169 70 13.4 
Total...| 1,960 813 | 596 | 18.2 

The record made on August 19, 1908, showing the highest per- 
centage of dead stages of the white fly, was based upon 10 leaflets 
selected from a single leaf and is not considered so typical of the con- 
dition throughout the tree examined as is the case in the other 
records. In contrast to the low mortality records as shown by. the 
insect forms present on the leaves of the umbrella trees, 26 records of 
mortality in citrus groves gave an average of 57.9 per cent dead on 
the leaves. These records were based on the examination of about 
2,000 leaves and over 100,000 white-fly forms. It should be noted 
that the mortality in the above records is based on the number of 
live and dead larve and pup, and of pupa cases present on the 
leaves at the times of the examinations. The actual mortality would 
be represented by the difference between the total live larvee, live pupe, 
and pupa cases and the number of hatched eggs. On umbrella China 
tree leaves this difference is slight and represented for the most part 
by the number of dead larve and pup found on the leaves. In the 
case of the citrus trees, on the other hand, the number of citrus 
white-fly forms on the leaves ordinarily represents only from 25 to 
30 per cent of the total number of eggs deposited. This disappearance 
from the leaves is discussed elsewhere. Its significance in this con- 
nection is that the actual mortality on citrus leaves is much higher 
than the average per leaf of 57.9 would indicate. The citrus white 
fly forms in the leaves show a mortality on the umbrella tree amount- 
ing to only one-third of the mortality on citrus trees. The considera- 
tion of the number of hatched eggs as a basis for mortality estimates 
would reduce this to about one-fifth. The figures refer to citrus groves 
where the citrus white fly is well established. In newly infested 
groves the rate of mortality is much smaller as a rule. 
The second important point established in the course of the investi- 
gations reported herein is that adult citrus white flies are so strongly 
attracted by growing leaves of umbrella trees that under certain 
conditions with umbrella and citrus trees growing side by side more 
adults collect on three or four umbrella leaves than are present on 
entire citrus trees of medium size. 
