FUMIGATION VERSUS NATURAL CONTROL. 65 
in producing the high degree of freedom from white-fly damage at- 
tained in L906. Other conditions may have had minor influence. 
As a natural consequence of the lack of abundant food for the fungous 
parasites in 190b, the situation in 1907 showed a complete reversal, 
with more than three-fourths of the groves thoroughly blackened by 
Booty 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. 
In the close vicinity of Fort Myers, in Lee County, the fungi have 
reduced the numbers of the white fly to a greater extent than observed 
at any Other place. The result of this is to cause a considerable 
variation from the usual succession of predominance of host and 
parasite, but in the course of a ten-year period the benefits from the 
fungous diseases under natural conditions will evidently be little if 
any greater than in Manatee County. In the town of Fort Myers the 
condition^ are not comparable with those in large commercial groves. 
In one such grove, however, located on the south side of the Caloosa- 
hatchie River, nearly opposite Fort Myers, the fungous diseases have 
proved more than ordinarily beneficial during the past two years. 
Then 1 is strong evidence even here that the white fly will regain its 
usual abundance in the course of the present season unless artificial 
methods of control are resorted to or experiments result in the dis- 
covery of a more satisfactory method than is now known of artifi- 
cially encouraging the growth and spread of the fungous enemies. 
The writer's observations lead to the conclusion that in 99 per cent 
of the groves in those localities where the fungous diseases are most 
effective, for every dollar expended for well-conducted fumigation the 
profits from the groves will be increased not less than $4, or at the 
rate of 250 per cent on the investment. If the expense of fumi- 
gation were doubled the adoption of this practice would still be 
profitable, at least until such time as the natural enemies at hand can 
be made more successful or new ones discovered to accomplish 
effective control. 
The spores and mycelium of the fungi are not affected by fumiga- 
tion, as far as lias been determined thus far. In experiments in the 
artificial dissemination of the brown and red fungous parasites the 
results obtained were as satisfactory when the material was collected 
from fumigated trees as when collected from those not fumigated. 
Ordinarily this point is of lit tie importance, since successful fumigation 
would always result in practically absolutely checking the further multi- 
plication of the parasites through the destruction of the host insects. 
The further multiplication of the fungous parasites following fumi- 
gation is therefore an indication of ineffectiveness of the treatment 
or of the increase in the numbers of the pest through migration from 
untreated groves. 
