li^ATURAL EFFICACY OF FUNGOUS PARASITES. 41 



are correctly treatinl in otlicr respects I believe will live longer, yield better, and 

 give much larger net profits than they will do if fungi alone are relied upon for 

 protection. 



After three years largely devoted to investigations of the white 

 flies affecting citrus in Florida, gi^ang particular attention to their 

 fungous diseases, Dr. Berger * (1909) siunniarized his ohscrvations 

 concerning natural efficacy of tlio fungous ])arasites as follows: 



When left without assistance the fungi will practically destroy the white fly in a 

 grove, on the average, once every three years; tlius reducing the injury due to the 

 white fly by at least one-third. The destruction is not complete, so that the insects 

 increase again during tlie two succeeding years; but this is accompanied by rapid 

 increase of the fungi, until the white fly is again overwhelmed. This is the course 

 run by the white fly and the fungi when unassisted in those sections which have been 

 longest infested, such as Manatee County' TTott Myers, and Orlando. At Orlando the 

 fungi were in the ascendency during the summer of 1906, and this resulted in so far 

 reducing the white fly that an uncommonly large and clean crop of citrus fruit was 

 marketed in 1907. ^ 



Ml*. C. L. Marlatt, assistant cliief of tliis bureau, after visiting 

 various sections of Florida in the fall of 1907 and discussing the 

 white-fly situation with numerous well-informed citinis growers, 

 described the natural eflicacy of the red and brown fungi as follows:^ 



In Manatee County, where the fungi are fully established, they are able practically 

 to exterminate the white fly once in three years, so that every third year the fniit is 

 clean and requires no washing. The following year the insect again flourishes because 

 the white-fly fungi have disappeared, having during the clean yearaiothing on which 

 to develop. Toward the end of this year, however, the fungi again Ijegin to operate, 

 but not sufficiently to prevent the complete blackening of the foliage and fruit during 

 the following or third year. Nevertheless, during this year the fly is again reduced to 

 practical extinction, so that the year following is a year of clean foliage and fruit. 



The senior author of this bulletin, writing in the fall of 1907 •* after 

 a little more than one year devoted exclusively to wliite-fly investiga- 

 tions, discussed the natural efficacy at some length, in part, as follows: 



Data obtained from many orange growers and personal observation by the writer 



and other entomologists connected with the Bureau of Entomology indicate that the 

 fungi, without artificial aid, reduce the injury from the white fly about one-tbird. 

 * * * One year in three, it is the experience of the growers in this county (Manatee), 

 the fungi have so thoroughly cleaned up the pest that the fruit is clean and requires 

 no washing. * * * Considering the county as a whole in 1906, fully three-fourths 

 of the groves were so free from sooty mold as to require no washing of the fruit. It 

 was generally considered that this condition had never before been equaled since the 

 white fly first obtained a foothold in tliis county. * * * As a natural consequence 

 of the lack of abundant food for the fungous parasites in 190G, the situation in 1907 

 showed a complete reversal, with more than three-fourths of the groves thoroughly 

 blackened by sooty mold. It is not uncommon to fhul that individual groves vary 

 considerably from the average condition of the groves in the county as a whole. 



1 Bui. 97, Fla. Agr. Exp. Sta., p. 50, 1909. 



' Sec explanation of tliis condition on p. 11. 



3 Proc. Ent. Soe. Wash., vol. 9, nos. 1-4, p. 124, April, 1908. 



* Bui. 70, Bur. Ent., U. S. Dept. Agr., p. 64, issued October, 1908. 



