70 NATURAL CONTROL OF WHITE FLIES IN FLORIDA. 
scale insects and white flies. In the case of fungous parasites which 
partially control the purple scale the disadvantage mentioned 
has been abundantly proved by the experience of many citrus 
growers. It is now recognized as necessary in most cases to follow 
up applications of a fungicide with applications of whale-oil soap 
or other insecticide suitable for checking the purple scale. Except 
in cases of extreme injury from plant diseases citrus growers of 
Florida are as a rule deterred from using fungicides on account of 
the indirect effect on the purple scale. A similar condition exists 
to a certain extent in wlrite-fly-infested sections where the fungus 
parasites occur. That it is a mistake to aUow hopes of possible 
benefit from fungous parasites of the white flies to interfere with 
the use of fungicides seems to the authors to be a clear deduction 
from the data herein presented regarding the efficacy of these diseases. 
Whenever the white flies are controlled by fumigation or by spraying 
the incidental control of the scale insects by the treatment primarily 
directed at the white flies will permit the more extended use of 
fungicides without fear of injurious secondary effects. 
SUMMARY AND CONCLUSIONS. 1 
From our present knowledge of the effects of climatological con- 
ditions upon the citrus white fly and cloudy- winged white fly, it is 
necessary to conclude that climatic conditions offer no hope of 
holding these insects in satisfactory control in any citrus-growing 
region where they may be introduced. 
Xo true parasites of these species of white flies are known to exist 
in this country and then numerous native predatory enemies are 
usually of no material assistance in their control. 
Two factors of natural control — overcrowding and unexplained 
mortality — have heretofore not been recognized or have been con- 
fused with the results of attempts at artificial control or with the 
effects of fungous diseases. The two factors named are in effect a 
reaction from excessive infestation. 
Bacterial diseases of the white flies are at present unknown but 
it is not improbable that they are the leading cause of mortality so 
far unexplained. 
1 The conclusions of Profs. F. H. Billings and P. A. Glenn, from their recent studies of the well-known 
and highly overrated chinch-bug fungus, are of especial interest in connection with the investigations of 
white-fly fungous parasites. In Press Bulletin 40 of the University of Kansas they say: 
"In fields where the natural presence of the fungus is plainly evident, its effect on the bugs can not be 
accelerated to any appreciable degree by the artificial introduction of spores. 
"Moisture conditions have much to do with the appearance of chinch-bug disease in a field; artificial 
infection nothing. 
"Advocating artificial infection or encouraging it by sending out diseased chinch bugs does not serve 
the best interests of the farmer, since his attention is thus diverted from other and truly efficient methods 
of combating the pests." 
See also Bulletin 107 ; Bureau of Entomology. U. S. Department of Agriculture, "Results of the artificial 
Use of the white-fungus disease in Kansas." by F. K. Billings and P. A. Glenn, 1911. 
