NATURAL EFFICACY OF FUNGOUS PARASITES. 41 
are correctly treated in other 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, giving particular attention to their 
fungous diseases, Dr. Berger 1 (1909) summarized his observations 
concerning natural efficacy of the fungous parasites as follows : 
When left without assistance the fungi will practically destroy the white fly in a 
grove, on the average, once every three years; thus 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 the 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 'Tort 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. 2 
Mr. C. L. Marlatt, assistant chief of this bureau, after visiting 
various sections of Florida in the fall of 1907 and discussing the 
white-fly situation with numerous well-informed citrus growers, 
described the natural efficacy of the red and brown fungi as follows: 3 
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 fruit is 
clean and requires no washing. The following year the insect again flourishes because 
the white-fly fungi have disappeared, having during the clean year .-nothing on which 
to develop. Toward the end of this year, however, the fungi again begin 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 4 after 
a little more than one year devoted exclusively to white-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-third. 
* * * 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 this county. * * * As a natural consequence 
of the lack of abundant food for the fungous parasites in 1906, 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 find that individual groves vary 
considerably from the average condition of the groves in the county as a whole. 
i Bui. 97, Fla. Agr. Exp. Sta., p. 50, 1909. 
2 See explanation of this condition on p. 11. 
s Proc. Ent. Soc. Wash., vol. 9, nos. 1-4, p. 124, April, 1908. 
* Bui. 76, Bur. Ent., U. S. Dept. Agr., p. 64, issued October, 1908. 
