10 NATURAL CONTROL OF WHITE PLIES IN FLORIDA. 



be entirely cleansed of sooty mold, leaving the fruit rinds and uppef 

 surface of the leaves bright and glossy. Straw on the ground around 

 the base of the trees and pieces of burlap hung in the crotches of the 

 main branches protect the eggs of the snails to a certain extent, but 

 birds and probably other natural enemies prevent their attaining a 

 position of reliable economic importance. Live white flies in any 

 stage are not eaten by the snails to any appreciable extent, the 

 destruction of a few being entirely incidental. Strictly speaking, 

 therefore, snails are not factors in the natural control of the white 

 flies, but in their effects they may appropriately be mentioned in 

 this connection. The species referred to above has been given the 

 common name of "Manatee snail " by Dr. E. H. Sellards, who has pub- 

 lished an account of its habits.^ Additional notes have been pub- 

 lished by Dr. Berger, who has also referred to another species of similar 

 habits, the "Miami snail," introduced into Manatee County from 

 Miami, Fla., by Prof. Rolfs.^ 



CLIMATIC CONDITIONS. 



An examination of climatic records for points in California where 

 both the citrus white fly and the cloudy-winged white fly have 

 been temporarily established shows conclusively that these destruc- 

 tive insects are dangerous under any climatic conditions in the United 

 States where citrus fruits are grown. The citrus white fly thrives on 

 privets (Ligustrum spp.) and Cape jessamine (Gardenia jasminoides) 

 out of doors in sections where winter temperatures are too severe for 

 citrus trees. Freezing temperatures therefore have no effect in 

 citrus-growing sections except through the shedding of the leaves of 

 citrus. In proportion to the thoroughness with which this occurs 

 both species of white flies are reduced in numbers, sometimes being' 

 entirely exterminated locally. In cool March weather heavy winds 

 accompanied by beating rains have been observed to destroy practi- 

 cally all the adults of the first broods. During March and April there 

 often occurs in Florida a rather high rate of mortality among the 

 overwintered pupas, which may be tentatively ascribed to weather 

 conditions. Apparently associated with the mortality mentioned is 

 the lower daily mean humidity and the greater daily range in humidity 

 than occurs at other seasons of the year. Strong drying winds seem 

 especially to characterize these periods of unusually high mortality. 

 (Plate II, upper record.) According to the observations made, mor- 

 tality among the overwintering pupte during the first emergence 

 period of the year ordinarily ranges from 19 to 38 per cent. In one 

 instance, however, this mortality amounted to about 92 per cent, 

 with a strikingly beneficial result in the grove where observed. 



1 Science, n. s., vol. 24, pp. 469-470, 1907; Fla. Agr. Exp. Sta., Tress Bui. 59, pp. 1-4, Jan. 15, 1906. 



2 Bui. 88, Fla. Agr. Exp. Sta., p. 69, January, 1907; Rep. Fla. Agr. Exp. Sta. for fiscal year ending June 30, 

 1909, p. xliii. 



