70 NATUEAL CONTEOL OF WHITE FLIES IN FLORIDA. 



scale insects and wliite 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 injuiy from plant diseases citrus growers of 

 Florida are as a rule deterred from using fungicides on account of 

 the indirect elTect on the purple scale. A similar condition exists 

 to a certain extent in white-fly-infested sections where the fungus 

 parasites occur. That it is a mistake to allow hopes of possible 

 benefit from fungous parasites of the wliite 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. 

 Wlienever the white flies are controlled by fumigation or by spraying 

 the incidental control of the scale insects by the treatment primarily 

 directed at the wliite flies will permit the more extended use of 

 fungicides without fear of injurious secondary elTects. 



SUMMARY AND CONCLTJSIONS.i 



From our present knowledge of the effects of clmiatological con- 

 ditions upon the citrus white fly and cloudy-winged wliite fly, it is 

 necessary to conclude that climatic conditions offer no hope of 

 holdmg these insects in satisfactory control in any citrus-growing 

 region where they may be introduced. 



No true parasites of these species of wliite flies are known to exist 

 in tliis country and their numerous native predatory enemies are 

 usually of no material assistance in tlieir 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. Cilenn, 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 elfect 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-fun^s disease in Kansas," by F. K. Billings and P. A. Glenn, 1911. 



