16 NATUEAL CONTROL OF WHITE FLIES IN FLORIDA. 
Unexplained mortality: 
5 lowest percentages averaging 66.1 per cent, 15.7 per cent survived. 
5 highest percentages averaging 76.1 per cent, 11.7 per cent survived. 
Fungous parasitism: 
5 lowest percentages averaging 10.2 per cent, 14.7 per cent survived. 
5 highest percentages averaging 20.5 per cent, 12.6 per cent survived. 
In the above summary the comparatively small difference between 
the five highest and five lowest records in each case makes the results 
less striking than are the results of the previous year. However, it 
is noteworthy that a difference of 10 per cent in unexplained mor- 
tality shows a corresponding difference of 4 per cent in the number 
surviving, while a difference of 10 per cent in the fungous parasitism 
shows a difference of 2.1 per cent in the number surviving. 
A fair estimate of the results produced by either unexplained 
mortality or fungous diseases must include a consideration of the 
increased degree of benefit from each if it had been the only factor 
concerned with the mortality of the larvae and pupae on the leaves. 
This point has been discussed elsewhere as to fungous diseases. 
Assuming that, in the 10 groves considered in Table III, the 12.4 per 
cent recorded as infected by parasitic fungi in 1908 and the 15.4 per 
cent in 1909 were actually destroyed by the fungi, 1 a large part of 
those infected by fungi would have died from unexplained causes if 
the fungi had not been present. Eighty-eight of every one hundred 
larvae and pupae were not infected by fungi in 1908 and 85 of every 
100 were not infected in 1909. Of these 84.1 per cent (73.7/87.6) and 
83.8 per cent (71.0/84.7), respectively, died from unexplained causes. 
It must therefore be assumed that if no fungous parasites had been 
present 84 and 83.8 per cent of the 12.4 and 15.4 per cent recorded 
in Table III would have died from unexplained causes, giving a total 
efficacy for unexplained mortality of 84.1 per cent and 83.9 per cent, 
respectively, for the years 1908 and 1909. This efficacy, combined 
with the effects of fungous diseases and overcrowding, did not result 
in a condition of satisfactory control in the average grove in 1908, 
with an average of about 24 live pupae per leaf, nor in 1909, with the 
average reduced to 11 live pupae per leaf. In each year there was a 
satisfactory condition of control in two or three of the groves under 
observation or a promise of such a condition the following season. 
In the opinions of the authors the data here given, representing a 
small selection of the large amount of similar data at hand, covering 
all sections of the State of Florida, conclusively show that the fluctua- 
tions from year to year in the proportion of white flies dying from 
causes as yet unexplained are of first importance in the periodical 
"cleaning up" of infested citrus groves. 
More attention should be given to a study of the cause or causes 
contributing to the unexplained mortality herein discussed. Attempts 
!As shown elsewhere, the brown fungus is known to infect dead as well as live insects. 
