32 WHITE FLIES IXJURI0I7S TO CITRUS IX FLORIDA. 
public sentiment. These food plants favor the rapid dissemination of the white fly 
from centers of infestation and their successful establishment in uninfested localities. 
They seriously interfere with the success of fumigation, as well as of all other remedial 
measures, by furnishing a favored breeding place where the white fly can regain 
its usual abundance in a much shorter time than would be the case if it were entirely 
dependent upon citrus fruit trees for its food supply. The plants mentioned, together 
with Citrus trifoliata (except where used in nurseries), and all abandoned and useless 
citrus trees should be condemned as public nuisances and destroyed in all communi- 
ties where citrus fruit growing is an important industry. 
Xot only is a knowledge of the relation of the various noncitrus 
food plants to white-fly- injury of great importance, but it is also of 
considerable importance to growers to know the capability of the 
insect for multiplying on the different citrus fruit trees in order that 
advantage may be taken of it in the arrangement of new groves and 
the improvement of old groves. 
It is a matter of common observation that injury from the white 
fly is most marked on citrus fruits of the Mandarin group. This 
group includes the Tangerine, Satsuma, and King of Siam. The 
sweet oranges are next to the mandarins in this respect, followed by 
the kumquats and grapefruits. 
The relatively less injury to grapefruit by the citrus white fly 
{A. citri) is sometimes obscured by the presence of A. nuhifera. 
Blackening of foliage and fruit by the citrus white fly is more notice- 
able on grapefruit trees when they are surrounded by or are otherwise 
unfavorably located in respect to oranges or tangerines. Solid 
blocks of grapefruit trees rarely show more than slight effects of 
white-fly infestation when only the citrus white fly is present. An 
example of this is the Manavista Grove at Manavista, Manatee 
County, Fla. This grove consists of 22,000 grapefruit trees, and 
appreciable blackening of the foliage is rarely seen except occasionally 
where orange groves adjoin. Only one record, based on actual 
examination of leaves, illustrating the difference in the degree of 
infestation of adjoining blocks of grapefruit and orange trees is 
available. The grapefruit block consisted of about 400 trees located 
immediately north of a block of 200 or 300 orange trees and separated 
on the west by a public road from a grove of about S00 orange trees. 
On April 23, 1909, after practically all the overwintering pupa? had 
matured, an examination of 100 or more leaves collected at random 
from each grove, counting the pupa cases, showed an average of 8 
insects that had reached maturity on the grapefruit leaves. 27 on 
the orange leaves of the block south, and 56 on the orange leaves of 
the block west. Xo studies have been made to determine the differ- 
ent degrees of susceptibility to white-fly injury among the different 
varieties of grapefruit, but the Royal variety appears to be more 
