302 



THE MONTHLY BULLETIN. 



So far only the red aschersonia has been grown in pure culture for distribution. 

 To grow the yellow one would be unnecessary, since the red one can be used instead 

 of it on the cloudy-winged whitefly. 



The brown fungus has so far not fruited in pure cultures, and has not been grown. 

 The white fringe fungus could be produced in pure cultures, but the need for doing 

 this has not arisen. 



SPRAYING WITH INSECTICIDES. 



It is not generally understood that whiteflies can be almost perfectly controlled by 

 spraying with emulsions of oils or even solutions of soap. In order to successfully 

 control whiteflies by spraying, some knowledge of the life history and the succession 

 of broods is absolutely necessary. Even as late as 1906 extensive spraying, that 

 proved to be practically useless, was carried on in Florida. In order to spray suc- 

 cessfully against whitefly it must be done at a time when there are but few, if any, 

 adult whiteflies present. While it is easy to kill the adults that are hit by the spray, 

 so many escape by flying away that practical results are not obtained. The eggs, on 

 the other hand, are also not extensively destroyed by sprays. The ideal time, there- 

 fore, theoretically considered, in which to spray for whitefly is soon after the adults 



Fig. 102. — Group of pure cultures of the red aschersonia, or red whitefly 

 fungus. Cultures are grown on sterilized sweet potato and agar in wide- 

 mouthed pint bottles stoopered with plugs of cotton batting. (Original.) 



have quit swarming and the eggs have hatched. In practice, this works out just as 

 indicated in the theoretical conclusions. The directions given are to begin spraying 

 ten days or two weeks after the whitefly has quit flying, or swarming. The ten days 

 or two weeks allow time for most of the eggs to hatch, and the young, or larvae, are 

 then also in the younger stages, when they are easier killed. When spraying as just 

 indicated, the grower has three opportunities per year in which to effectively reduce 

 his whitefly to the extent of 90 to 99 per cent, namely, the latter part of April and 

 early May, during July, and again beginning with October or the latter part of 

 September. These dates are, however, not absolute, but will vary somewhat with 

 climatic conditions. Neither is July a good time to spray on account of the summer 



