34 WHITE FLIES INJURIOUS TO CITRUS IN FLORIDA. 
The difference in the degree of injury between orange and tangerine 
trees is less marked than between tangerine and grapefruit or orange 
and grapefruit, but the difference is nevertheless usually quite notice- 
able. The practical application of this difference in the degree of 
adaptation of the citrus white fly to the various citrus food plants 
will be discussed in a forthcoming bulletin dealing with the artificial 
control of the white fly. 
CHINA TREES AND UMBRELLA TREES, 
While China trees (Pl. IV) and umbrella China trees (Pl. V), when 
grown for shade and ornamental purposes, are, as has been pointed 
out, very injurious to citrus fruit-growing interests, the investigation 
of the utility of these plants as trap foods gives an increased import- 
ance to a definite knowledge concerning them as citrus white-fly food 
plants. Their injuriousness to citrus growers is very clear to pro- 
fessional entomologists, but not as generally appreciated by the citrus 
growers themselves as is desirable. 
The umbrella tree is recognized by pobenee as a variety of the 
China tree. This variety is the one most commonly grown except 
in a few localities, and observations reported herein Be tecciles refer 
to it and not to the China tree. The latter tree has, however, been 
under observation by the authors, and no noticeable difference has 
been observed between the two trees in their relation to the citrus 
white fly, and the data and observations are in the main fully as 
applicable to the one as to the other. 
The numbers of the white fly which mature on individual umbrella 
trees have been estimated in three instances and found to range 
between 25,000,000 and 50,000,000 where trees are favorably located 
with respect to nondeciduous food plants. Examinations were made 
by selecting 10 or more leaves at random and from each selecting 
a leaflet which appeared to represent the average condition of all 
the leaflets composing the leaf. In two instances it was found that 
the infestation was fully as great toward the top of the tree as on the 
lower parts. In one instance an extensive examination of different 
parts of an infested umbrella tree showed a decrease from lower 
branches to top branches of 50 per cent. In order to be fully con- 
servative, this percentage has been used as the basis of the calcula- 
tions, making the average infestation throughout the tree 75 per 
cent of the infestation of the leaves of the lower branches. Full- 
grown leaves were found to consist of about eighty-two leaflets. 
Complete records were made of eggs and of live and dead larvee and 
pup, but only a part of this data will be presented. The estimates 
and counts of both leaves and insects in the case of the first tree were 
made by the senior author; in the cases of the second and third trees 
the estimates of the number of leaves per tree represent the average 
