THE CITRUS WHITE FLY: FOOD PLANTS. 35 
of three estimates—one by the senior author, one by the junior author, 
and one by Mr. W. W. Yothers. The counts and estimates of insects 
were made by the senior author in the second instance and by the 
junior author in the third. The data obtained in these examinations 
bearing on the number of insects the umbrella trees are capable of 
maturing are given in Table V. 
TasLe V.—Numober of citrus white flies developing on umbrella China trees. 





k Estimated 
Estimated | Number | Number eee oe pool 
Tre Date of exam-| number of | of pupa-| of live ze ot soa i: — ue a ed 
Wiele ination. leaves on cases pup pean a ae a aN f 
tree. Metileats |;penleat |e ee | see 
tree. examina- 
tion. 
- 1 | Oct. 28,1906 20,000 2,478 4.1 | 49,560,000 82,000 
2) Aug. 19,1908 25,000 1,910 13.2 | 47,762,000 330,000 
3 | Aug. 25, 1908 12, 000 2,230 | 4.0 26,760, 000 58, 800 



The three trees examined are not in any way exceptional as regards 
the degree of infestation, but may be considered as representative of 
the condition of China trees and umbrella China trees in localities 
where the citrus white fly is established. Tree No. 1 was located by 
the roadside near a 5-acre grove of newly bearing budded orange and 
erapefruit trees which were lightly infested by the white fly and on 
which it is estimated that not over 100,000 insects could have matured 
on any one tree during the season. Tree No. 2 was located most 
unfavorably for a heavy infestation, standing in a vacant lot in the 
business section of Orlando and having its source of citrus white-fly 
infestation in the spring almost entirely restricted to two neglected 
and worthless orange trees of small size growing within a radius of 
100 feet. Tree No. 3 was located in front of the laboratory at 
Orlando, with 36 orange and grapefruit trees on the grounds. The 
least conservative of the authors’ estimates would place the number 
of white flies which matured on any one of these citrus trees during 
the year 1908 as not over 500,000, with the average of the 36 trees at 
about one-half this number. It is estimated, therefore, that the one 
umbrella tree produced upward of three times as many adult citrus 
white flies during the year 1908 as the 36 citrus trees on the labora- 
tory grounds combined. The important relation of the remarkable 
multiplication of the citrus white fly on China and umbrella trees to 
the spread of tie pest will be discussed under the heading “Spread.” 
Two new points of importance have been established by the present 
investigations in regard to umbrella China trees as citrus white fly 
food plants. First, this insect shows in one respect a greater degree 
of adaptation to this food plant than to citrus plants, as shown by 
the very low rate of mortality in the immature-stages. Table VI 
gives the data obtained by five counts made at Orlando, Fla., during 
these investigations. 
