50 WHITE FLIES INJURIOUS TO CITRUS IN FLORIDA. 
insect. The citrus white fly was without doubt introduced into the 
United States and distributed to the most important centers of 
infestation by this means. In Florida the white fly was probably 
introduced first on citrus nursery stock into some citrus grove on the 
St. Johns River in St. Johns County, and later by the same means 
into Manatee and Fort Myers. Gainesville, Ocala, Orlando, and 
Bartow were probably among the points to which the white fly was 
introduced on nursery stock. The distribution of the citrus white 
fly along the Gulf coast citrus-growing regions west of Florida has 
been largely due to shipments of infested citrus nursery stock, 
umbrella trees, privets, and cape jessamines. Of all methods of 
spread which are operative over greater distances than the flight of 
adults, introductions of live immature stages on trees or shrubs for 
transplanting purposes are by far the most certain to result in the 
successful establishment of the species. Fortunately it is practicable 
to prevent spread by this method by defoliating the trees as they leave 
the nursery. Much has been accomplished in the past by individual 
citrus growers, but more attention should be given to this matter in 
communities not now infested by both of the white flies treated in this 
bulletin. 
Accidental Spread by Man. 
Carriage oj the adult white flies on human oeings. — Man is doubtless 
responsible to a limited extent for the spread of adult white flies. 
During migrating periods, when in heavily infested orange groves or 
in towns where there are infested China and umbrella trees, adults are 
frequently observed on the clothing. Prof. H. A. Gossard states 
that he has carried adult white flies for nearly half a mile on his 
clothing after standing beneath a heavily infested tree. 
Introduction in pickers' outfits. — In some instances the citrus 
white fly is believed to have been introduced into previously unin- 
fested localities by orange pickers. In this case the principal danger 
lies in introducing live pupae on citrus leaves accidentally brought 
in with picking sacks and field boxes. The authors consider that there 
is practically no danger of the carriage of adults of the citrus white 
fly by pickers' outfits between December 1 and March 1. The few 
adults present in citrus groves during this period would rarely result 
in their transference to uninfested groves by such means, and the 
unfavorable factors heretofore discussed would almost certainly 
prevent the successful establishment of the pest. It would be 
almost impossible to conceive of any likely method by which a suc- 
cessful introduction of the citrus white fly into a noninfested grove 
could be accomplished by the carrying of leaves infested by eggs or 
larvae. Leaves infested with live pupae, however, particularly about 
the time of the beginning of emergence of the first spring brood, 
