THE CITRUS WHITE FLY: INJURY. 17 
connection with experimental work with the white fly. A review of 
all the literature to date shows that data have been published on the 
effect of kerosene emulsion on white-fly eggs, by Riley and Howard; 
on the subject of effects of cold upon white-fly larvae and pupae, by 
Prof. Gossard; on the percentage of trees infected by the spore- 
spraying method of introducing the fungous parasites, and on the 
amount of honeydew secreted by the larvae of the insect, by Dr. E. W. 
Berger; upon subjects related to fumigation, 1 by the senior author of 
the present bulletin; and on laboratory experiments with the fungous 
parasites, by Prof. H. S. Fawcett. Aside from the above, practically 
no data have been heretofore published. 
INJURY. 
Nature of Injury. 
The direct injury by the citrus white fly may be included under 
two main heads: (1) Injury by removal of sap from foliage, and (2) 
injury from fungous growth known as sooty mold (Meliola), which 
develops upon foliage and fruit on the excretions of the insects. 
The direct injury is principally included as loss in value of trees, 
extra expenses of maintenance, and losses from scale insects and dis- 
eases, which more seriously affect white-fly infested trees. 
LOSS OF SAP. 
The amount of sap extracted by the insects is not generally con- 
sidered an item of great importance compared with the injury from 
sooty mold. While the extraction of sap by itself probably would 
not cause sufficient injury to make the white fly rank as an important 
citrus pest, it is doubtless of considerable importance when combined 
with the lowered assimilative powers of the foliage due to the sooty 
mold. As mentioned more in detail under the subject of feeding 
habits, it has been estimated that the loss of sap per day amounts to 
about one-half of a pound for 1,000,000 larvae and pupae. 
SOOTY MOLD. 
Sooty mold is the principal evidence of white-fly injury, and is the 
most important element of damage, affecting both the foliage and fruit. 
(See PI. I, frontispiece.) No special attention has been given by the 
authors to its botanical aspects, but the following notes concerning it 
are taken mainly from Dr. H. J. Webber's report on this subject: 2 
1 Fumigation for the Citrus White Fly as adapted to Florida Conditions. Bulletin 
76, Bureau of Entomology, U. S. Department of Agriculture, Oct. 31, 1908. 
2 Bulletin 13, Division of Vegetable Physiology and Pathology, U. S. Department 
of Agriculture, pp. 5-11, 1897. 
59131°— Bull. 92—12 2 
