FUMIGATION VERSUS NATURAL CONTROL. 65 



in producing the high degree of freedom from white-flj' damage at- 

 tained in 1906. Other conditions may have had minor influence. 

 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. 



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 ]\Iyers the 

 conditions 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. 

 There 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 WTiter'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 ^\^ll 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 has 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 little 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 fimii- 

 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. 



