April, '12] 



WATSON: FUNGI AS INSECTICIDES 



203 



scales even when not aided by the grower apphes equally well to the 

 whitefly. It has long been recognized that even when no means were 

 taken to combat it, the grower could reasonably hope to get about 

 every third year a crop nearly free from the sooty-mold (Meliola) that 

 develops in the honeydew given off by the whitefly and constitutes 

 one of its chief injuries. Bordeaux mixture produces, here also, a 

 rapid increase in numbers when sprayed on trees. 



But the unaided spread of the fungi is often slow and very uneven. 

 This is true not only of its spread from grove to grove as would be 

 expected, but frequently from tree to tree in the same grove and some- 

 times from one part of a tree to another. As an illustration of this 

 some counts taken by the writer in December, 1911, will be cited. 

 Fifty leaves were taken at random from a grove with a conspicuous 

 amount of fungus and counts were made of the number of whitefly 

 alive, of the number surely killed by the Brown Fungus and Red 

 Aschersonia as shown by well-developed pustules, the number dead 

 from other causes including "natural mortality," and the number of 

 empty pupa cases showing successful emergence. Most of those in 

 column three were really killed by fungi which had not developed 

 sufficiently to show pustules. Recent study by the author has shown 

 pretty clearly that the so-called "natural mortality" is due to the 

 White-fringe Fungus that does not develop the characteristic fringe 

 as it does under favorable circumstances. The counts of some of the 

 leaves and the average of them all is given in Table II. 



TABLE II 



This table does not show the real mortality as it does not take into 

 consideration those that died and dropped off. It is not given as an 

 example of the efficiency of the fungi as it was taken in the most unfav- 

 orable time of year, but it shows the unevenness of the distribution. 

 It was shown, however, that even at this time of the year that the fungi 

 had made a clean sweep of the larvae on 19 of the 50 leaves. 



Because of this occasionally slow spread and uneven distribution of 



