298 THE MONTHLY BULLETIN. 



WHITEFLIES OF CITRUS. 



By E. W. Berger, Entomologist, State Plant Board, Gainesville, Florida. 



It is intended in this paper to give brief accounts of the injuriousness. life 

 history, and control measures of the common whitefly as it pertains to Florida. 

 Reference in these accounts will also be made here and there to the cloudy-winged 

 whitefly and the woolly whitefly, which, with the common whitefly first in the list, 

 are the three principal whitefly pests of citrus in Florida. 



Following these accounts will be added the list of 16 whiteflies at present known 

 to infest citrus in a greater or less degree in different parts of the world, giving 

 in each instance the origin, or probable origin, or distribution, food plants, and 

 degree of injuriousness. Of this list, nine are present in the United States, four 

 having been introduced and five being native. It is unnecessary to state that the 

 introduced species are the pests, while the native ones rarely occur in any abundance 

 on citrus. Of the 16, seven do not occur in the United States. 



WHAT ARE WHITEFLIES? 

 Whiteflies (Figs. 97 and 9S) are small, four-winged insects, measuring about 

 one-thirty-second to one-sixteenth inch in length. They belong in the same group, 

 or order, of insects with scales, plant lice, leaf-hoppers, cicadas, etc. 

 These insects are generally white, as the name implies, but some 

 have dark markings on the wings. In at least one instance the 

 wings are of a slate color. The bodies vary in color from light 

 yellow to brown or dark. The color of the immature stages, larvae 

 and pupa;, also vary from light yellowish to black, so that one might 

 truly speak of black whiteflies. 



Like the order of insects to which they belong, whiteflies have 

 sucking beaks in all stages, by means of which they penetrate the 

 leaves of their host plants and extract large quantities of sap for 

 food. 



INJURY. 



Cloudy-winged The common whitefly has been the principal citrus pest in Florida 



whitefly. and the Gulf Coast States since about 1880. Its injury is due. in the 



Enlarged first p i ace> t0 the extraction of large quantitits of sap from the 



fcourtesy Fla. ' leaves. In the second place, large quantities of the sooty mold, a 



Exp. Station,' black fungus that develops in the honey-dew excreted by the insects. 



Bui. 103. may s0 completely cover the leaves and fruit as to interfere with 



E WR) the proper physiological activities of the trees. Badly-infested trees 



get out of condition and produce small crops of insipid fruit. Fruit 



covered with sooty mold will also be retarded in ripening and belated in coloring. 



especially the upper part, which may remain green, when the rest of it has assumed 



the color of ripe fruit. A secondary injury to the trees may result from an excessive 



increase of the common scales of citrus, which find protection under the sooty mold 



that covers leaves and branches. Fortunately, the vigilant growers of Florida have 



learned how to largely obviate these injurious effects. 



What has just been stated for the common whitefly, holds true in about an equal 

 degree for the cloudy-winged whitefly and the woolly whitefly. The second named is 

 not regarded as quite so serious a pest as the common whitefly, while the latter 

 appears to offer better protection for scale insects. 



LIFE HISTORY. 



The life history of the common whitefly consists, briefly, of egg, first stage larva, 

 second stage larva, third stage larva, fourth stage larva, pupa, and adult or winged 

 insect. All stages live on the under sides of the leaves and the adults swarm freely 

 from dusk until after daylight. 



The eggs are minute, light colored when fresh and barely visible to the unaided eye 

 (Figs. 98 and 99). They are deposited in enormous numbers, as many as 20.000 

 having been estimated on a single citrus leaf. The surface is highly polished and they 

 are attached to the leaf by means of a short stalk. They hatch in eight to twenty-four 

 days, according to the temperature. 



The eggs of the cloudy-winged whitefly (Fig. 99) are covered with a reticulation 

 as though they were surrounded with a delicate net, which is easily brushed off. 



