18 
NATURAL CONTROL OF WHITE FLIES IN FLORIDA. 
DROPPING FROM LEAVES. 
Daily observations made on marked larvae from date of settling 
to emergence of adults, in connection with life-history studies, proved 
that a small proportion of larvae loses hold upon the leaves and drops, 
especially at molting periods. Of 231 marked larvse, 20 (or 8.6 
per cent) dropped before reaching maturity. This dropping occurred 
in nearly every case after the larvse had passed several da3^s in the 
plump condition preceding molting and were in no way pressed for 
room. While dropping is largely restricted to the earlier instars, 
one pupa has been known to drop after having shown developed 
eye-spots for nine days. Where infestation is excessive, dropping 
is more frequent than noted above, but is then due more directly 
to overcrowding, as shown under the following heading. 
MORTALITY DUE TO OVERCROWDING. 
The excessive overcrowding of leaves with eggs always results 
in the death of practically all the larvae that hatch, as it either becomes 
a physical impossibility for them to find suitable places for attach- 
ment, or, because of the closeness of the eggs, such spaces as they do 
find are far too limited to permit development to the pupal stage. 
Table V. — Effect of overcrowding upon development of the citrus white fly. 
Leaf 
No. 
Number 
of eggs 
deposited. 
Number 
live larvae. 
Number | Number 
live pupse. pupal cases. 
Per cent 
alive. 
1 
2 
3 
13.882 
14,000 
2,000 



2 
4 

0.01 
.03 
.0 
The data in Table V illustrate the inevitable outcome of over- 
deposition. The leaves on which these data are based were heavily 
infested with eggs, No. 3 being a very small leaf. Unfortunately 
this wholesale mortality is not so important a factor in the develop- 
ment and spread of the citrus white fly as in the case of the cloudy- 
winged white fly, since the habit of the female leads her to scatter her 
eggs over the older as well as over the more tender growth. With 
the former species on more than one occasion effective control has 
been observed to follow certain favorable conditions as to the rela- 
tive abundance of the adult insects and new citrus growth. It has 
been computed that the larvae hatching from the 13,882 eggs deposited 
on Leaf No. 1, would require about 25 times the surface of that leaf 
in order to reach the pupal stage should they settle with the view 
of utilizing the least possible space. Since the larvae do not show 
such discrimination in locating themselves, an even larger amount of 
leaf surface would be required. 
