14 



NATURAL CONTROL OF WHITE FLIES IN FLORIDA. 



important aids to the citrus white fly in regaining its normal abun- 

 dance after it has been reduced by any cause. 



Grove No. 6 in Table II represents the general condition of trees 

 in yards in Orlando aside from the groves 1 to 5. The important 

 point shown by this is that whether the parasitic fungi were present 

 or absent, the general condition in 1907 was practically the same 

 throughout the city. 



The foregoing general observations led to a more detailed investi- 

 gation of mortality from unexj)lained causes, and a largo amount of 

 data concerning the subject has accumulated. For the most part 

 these data cover too great a range of conditions to be briefly sum- 

 marized for this report. One series of observations, however, was 

 mad© especially with a view to securing records under uniform con- 

 ditions and sufficiently extensive to enable certain definite conclu- 

 sions to be reached concerning this important subject. The data 

 presented in Table II are based upon the examination of about 

 275,000 insects found on 1,155 leaves. All but No. 6 represent 

 citrus groves in Orange County selected on account ol the compara- 

 tive abundance of fungous parasites, or because common reports 

 placed a particularly high estimate on the effectiveness of the 

 fungous parasites in them. In several cases it had been generally 

 reported that the fungous parasites had brought the wliite fly into 

 complete subjection. No. 6 includes a mixed lot of leaves from 

 seven different points in the city of Orlando, representing town con- 

 ditions. The first record was made by the senior author on October 

 19, 1908, and the others were made by the junior author in Decem- 

 ber, 1908. The leaves were 1908 growth, and mostly midsum- 

 mer growth of that j^ear. For convenience in the discussion the 

 records in Table II are arranged in order of the percentage of unex- 

 plained mortality. 



Table II. — Study of causes of mortality of white flics near Orlando, Fla., in 1908. 



1 Represented on leaves examined by empty pupa cases. 



