V ■•■ 4 J»«" -'-—--■" ^ — ■ ■ - »■■ i llUk ■ -i ' •* * Jb*~** ** • ^^P* ' ~-' : .".V " kf ■ i!Sp- •' Figure 2. — Eggs of the white fly. numerous th£y become. There were many thousands of such eggs on this leaf. Nearly every leaf on the trees in that part of town was similarly infested. These eggs are so small as to be scarcely visible to the eye singly, but the badly infested leaves appeared as though cov- ered with mold. While rather less than half of the town of Marysville is badly infested, still a careful examination would show the presence of a few eggs on nearly every tree in town. The eggs of the white flies are all very much alike and can be at once distinguished from every other known group of insects. The shape of the egg and of the stalk at the end by which it is attached to the leaf are sufficient to distinguish them. It is not, however, easy to distinguish between the eggs of the different species of white flies. The presence of an egg of this character on the leaf of an orange or lemon is quite conclusive evidence of the presence of the destructive white fly of Florida. According to Gossard, the egg requires from three to twenty days to hatch, according to the weather. In the hatching process the egg-shell splits in the manner shown in plate 1, figure 4. The Nymph.— The young insect on hatching very much resembles a. young scale insect, but can be readily distinguished by comparing a Figure 3. — Exuvium of the white fly and a young nymph.' carefully mounted specimen under a medium or high power of the microscope with the figure shown on plate 2, figure 1. Like the scale insects, the young white fly wanders over the twigs and leaves for a few hours, finally attaching itself by inserting its mouthparts into the leaf. After thus locating itself the young insect soon secretes a wax in sufficient quantity to fill the space between the body and the leaf. Because of the small size and transparency of the body and this cementing of the body to the leaf the insect is almost invisible. This makes it rather difficult to secure a good photograph of the insect. Figure 3 illustrates a partly grown nymph collected at Marysville produced from eggs laid this spring by flies appearing before the great majority had emerged. In structure and habits the nymph is so like scale insects that if seen at all they could easily pass as young scales. It is not safe indeed to depend on the use of a hand magnifier for the identification of a young or partly grown nymph until one is thoroughly familiar with them, and even then the use of a compound microscope should be resorted to. The details of structure shown by a properly mounted microscopical preparation of the various stages is well shown on plate 2. Figure 4. — White fly exuviae on leaf, much enlarged. Within the body of the nymph during the last stage wings are developed in both sexes and the whole internal structure reorganized so that when the skin is finally cast off a slender bodied, delicate fly- emerges. This is in striking contrast to the life history of scale insects where the male alone obtains wings. This makes the problem of the control of this insect entirely different and much more difficult than that of scale insects, as will be shown in the discussion of this subject below. The full grown nymphs have a very much thicker skin than the younger stages and this remains attached to the leaf after the molt. This dried skin is very much more conspicuous than the living insect and is the form illustrated in figures 1, 3, 4, 5, and 6. On some trees at Marysville most of the old leaves are well spotted over on the under side of these exuviae, as shown in figure 5. The Adult Insect. — The name white fly was given to the insects of this class on account of the appearance of the adult insect. Its snowy white color makes the insect very conspicuous notwithstanding its ex- tremely small size. In the spring they appear in great numbers for two or three weeks and then suddenly disappear after laying their Figure 5. — Leaf showing dirty condition when badly infested. eggs, only a very few belated individuals coming out after the others remaining in the trees. In mid-summer a second brood begins to ap- pear. There is no distinct swarm as in the spring, but during the whole latter half of the year the adult white fly can be seen on the trees in greater or less abundance. After the colder weather of winter begins the adults almost entirely disappear and are not seen again until the spring emergence. The life of any individual fly is very brief, averaging, according to Gossard, between four days and a week. During this time the eggs are laid, and as many as seventy-five have been deposited by a single female. *" EXPLANATION OF PLATE I. Aleyrodes citri. (This plate is reproduced from Bulletin No. 67 of the Florida Agricultural Experiment Station.) Fig. 1. — Adult female, with expanded wings, much enlarged. Fig. 2. — Adult female, with wings folded over the body in normal roof-like position. Fig. 3. — Egg and foot-stalk of same, greatly magnified. Fig. 4. — Egg-shell, showing the split through which the larva emerged. Fig. 5. — Tip of male abdomen, showing claspers. Fig. 6. — Antenna, showing annulated joints. Fig. 7. — Fore margin of front- wing. Insects sometimes mistaken for A. citri: Fig. 8. — Larva of Aleyrodes floridensis, greatly magnified. Fig. 10. — Greatly enlarged section of waxen fringe, surrounding A. -flori- densis. Fig. 11. — Outline of larva of Lecanium hesperidum. EXPLANATION OF PLATE II. (This plate is reproduced from Bulletin No. 67 of the Florida Agricultural Experiment Station.) Aleyrodes citri. Fig. 1. — Larva, first stage, greatly magnified. Fig. 2. — Larva, first stage, drawn to same scale as figures 3, 4, 5, 8, 9, and 10. Fig. 3. — Larva, second stage. Fig. 4. — Larva, third stage. Fig. 5. — Larva, fourth stage. Fig. 6. — Margin of advanced larva, greatly enlarged. Fig. 7. — Vasiform orifice of fourth larval stage, showing crenulated oper- culum with ligula in the center. Fig. 8. — Pupa, showing embryo and distribution of orange-colored areas. Waxen tufts extending from the breathing tubes are shown. Fig. 9. — Adult, with folded wings, emerging from the pupa case. Fig. 10. — Empty pupa case, showing split through which the fly emerged. PLATE I. + 1 ? PLATE II. 10 THE DETECTION OF THE WHITE FLY. At the present time the discovery of the presence of the white fly is of very great importance. After the insect has become so numerous that it is conspicuous either by its injuries or the swarms of the adult it is doubtful if eradication is possible, at least without very radical measures being employed. Much misapprehension can be avoided by getting a correct idea of the insect and of the things it is liable to be confounded with. Figure 6. — Red scale, adult and young, and exuviae of white fly. First it should be understood that the white fly is very minute. There is no other insect pest on citrus trees as small as the white fly, unless it be small individuals of the red or yellow scale. Figure 6 shows these two insects on the same leaf, and will give some idea of their relative appearance. The lighter spots are the exuviae of the white fly. There were a few young and eggs of this insect, but they could not be shown without magnification. The small dark spots are the young of the red scale. The structure of the scale is better shown in figure 7. The red or yellow scale occurs on the upper side of the leaf as well as below (see figure 8) and sometimes on twigs and fruit, H cT 11 Figure 7. — Red scale, much magnified. while the white fly confines itself exclusively to the leaves and almost exclusively to the under side of the leaves. No one will, however, confound these two insects if they see them clearly, for they are so Figure 8. — Red scale on upper side of leaf. 12 H«mr- &W * *&. ■ M . % 1a ' & Figure 9. — Bed scale on leaf, much enlarged. totally different in appearance. The comparison of figures 4 and 9 will show the differences that can be brought out by a hand magnifier between the exuvium of a white fly and the adult red scale, which might be confounded at first glance without the lens. Figure 10. — Bed and soft brown scale, much enlarged.