10 NATURAL CONTROL OF WHITE FLIES IN FLORIDA. 
be entirely cleansed of sooty mold, leaving the fruit rinds and upper 
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 
tins 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. 1 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. 2 
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 pupae, which may be tentatively ascribed to weather 
conditions. Apparently associated with the mortality mentioned is 
the lower daily mean humidity and the greater daily rang? 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 pupae during the first emergence 
period of the year ordinarily ranges from 19 to 3S per cent. In one 
instance, however, this mortality amounted to about 92 per cent, 
with a strikingly beneficial result in the grove where observed. 
i Science, n. s., vol. 24, pp. 469-470, 1907; Fla. Agr. Exp. Sta,, Press Bui. 59, pp. 1-4, Jan. 15, 1906. 
2 Bui. SS, Fla. Agr. Exp. Sta., p. 69, January, 1907; Hep. Fla. Agr. Exp. Sta. for fiscal year ending June 30, 
1909, p. xliii. 
