44 WHITE FLIES INJURIOUS TO CITRUS IN FLORIDA. 
adults. If this were not so the pest would have become established 
in every grove of the State long before the present time. Except for 
spread by direct flight and on nursery trees and ornamental plants, 
the chances are against more than a few insects being introduced into 
a particular grove by any of the other methods discussed hereafter. 
In the case of a single adult there are two chances in three that it 
would be of the reproductive sex. If, as would be probable, the 
specimen were a female, there would be about one chance in three 
that it would not have been fertilized. In this case the second 
generation of adults would all be males, as shown by the observations 
recorded under the subject of Parthenogenesis. This would, of course, 
end the infestation directly due to the single specimen introduced, 
as the original female would have died several weeks before the first 
male matured. In case the originally introduced specimen were a 
female and fertile the chances of a male appearing among the second 
generation are not definitely known, but are with little doubt only 
small. The chances of such a male appearing at a favorable time to 
meet with and to fertilize a female of the same parentage are practi- 
eally negligible, though possible as a result of the great variation in the 
length of the life cycle as recorded under life history. The third 
generation would, therefore, in all probability, be all males, and the 
infestation ended. The chances that a single adult specimen intro- 
duced into an isolated grove or into a previously noninfested com- 
munity would successfully establish a permanent infestation are 
extremely small. The chances are only slightly increased by an 
increase to 5 or even 10 in the number of adults originally introduced 
into a single grove. 
From the foregoing considerations it is evident that two or more 
distinct introductions of even a few individuals at proper intervals 
during a single season might greatly increase the chances for the suc- 
cessful establishment of the pest. 
FiigHt or ADULTS. 
The flight of adults is the most important method of local distribu- 
tion and is also an important element in its association with spread by 
means of winds and vehicles, railroad trains, and boats. 
The distance to which the insect is capable of flying.—It would be 
almost impossible to obtain positive records on the distance the adult 
citrus white fly is capable of flying. Mr. W. W. Yothers, on April 29, 
1908, found on wild persimmon first and second generations of this 
species of fly at a distance of one-fourth of a mile from the nearest 
orange grove, Which was also the nearest point of the occurrence of a 
food plant upon which the insect could have passed the winter. The 
infested persimmons were in pine woods and the insects were in such 
numbers that it was evident that spread through pine woods might 
