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Pat ay ; 7 a Eerimtlooties creeditls wpe a he, # ha os beidethtane me. opt itroate lion iBd sinav itn ee ae eb} maar, Jstsutig “7 ; - a 7 , a R i « 3s oo Orig FAT, 7 x * 7 at eo: . “7 ; ia v - " . Py sd a : i Ce ey . i oe a 4 P \ ‘i ' =F ? al _- . Me © f : a ; ae et i Pay ae oe, = ( F — = — “pay tea yg , aan s' ey RAL ’ ~ Fax VOC ¥ =. : ~s WARE as er S Settar, «eS Z ¢ Fz; I, é ‘ne Le Zt Issued April 16, 1913. US DERAR ELEMENT OF AGRICULTURE, BUREAU OF ENTOMOLOGY—CIRCULAR No. 168. L. O. HOWARD, Entomologist and Chief of Bureau. SPRAYING FOR WHITE FLIES. IN FLORIDA. ee BY W. W. YOTHERS, Entomological Assistant, SSS Gia a eee a tt ite eae ee) WASHINGTON : GOVERNMENT PRINTING OFFICE 197% BUREAU OF ENTOMOLOGY. L. O. Howarp, Entomologist and Chief of Bureau. C. L. Maruatt, Entomologist and Acting Chief in Absence of Chief. R. S. Ciirton, Executive Assistant. W. FEF. Tastet, Chief Clerk. F. H. CHITTENDEN, in charge of truck crop and stored product insect investigations, A. D. HoPKINs, in charge of forest insect investigations. W. D. HunNTER, in charge of southern field crop insect investigations. EF. M. WEBSTER, in charge of cereal and forage insect investigations. A. L. QUAINTANCE, in charge of deciduous fruit insect investigations. K. F. PHILLIPS, in charge of bee culture. D. M. RocGers, in charge of preventing spread of moths, field work, Roryia P. CurRik, in charge of editorial work. Mapret CoLcorD, in charge of library. Citrus Fruir INSECT INVESTIGATIONS. C. L. MARLATT, in charge. R. S. Wocitum, W. W. Yoruers, E. R. Sasscer, J. R. Horton, P. H. TIMBERLAKE, C. E. PEMBERTON, H. lL. SAN¥ForD, entomological assistants. BEULAH M. Boss, preparator. J. G. SANDERS, collaborator, Il CiRCULAR No. 168. Issued April 16, 1913. United States Department of Agriculture, BUREAU OF ENTOMOLOGY. L. O. HOWARD, Entomologist and Chief of Bureau. SPRAYING FOR WHITE FLIES IN FLORIDA. By W. W. YorHers, Hntomological Assistant. Citrus trees in Florida are subject to injury by four species of white flies, only two of which, however, the citrus white fly (Aley- rodes citri R. & H.) and the cloudy-winged white fly (Aleyrodes nubifera Berger), do sufficient damage at the present time to de- mand remedial measures. Of the two species considered the citrus white fly is by far the most injurious. THE CITRUS WHITE FLY. The citrus white fly is an introduced pest, having been brought to this country from Asia some time prior to 1879. Since its intro- duction it has spread over the entire citrus region of the State and westward throughout the Gulf region. At the present time it infests fully 60 per cent of the groves in Florida. It occurs on some 19 species of trees and shrubs, the most important hosts being the China trees, Cape jessamine, privet, and various species of citrus. Of native plants the only two which have been reported as being seri- ously infested are the prickly ash and wild persimmon. LIFE HISTORY AND HABITS. In completing its life cycle the citrus white fly passes through four stages, viz, egg, larva, pupa, and adult. The egg—TVo the unaided eye the eggs appear as minute particles of whitish dust. They are deposited on the underside of the leaves. To indicate the size of these eggs it has been estimated that 118 placed end to end would measure 1 inch, whereas 1 square inch would contain about 35,164, placed side by side. When examined 1 2 SPRAYING FOR WHITE FLIES IN FLORIDA. under a magnifying glass they resemble kernels of wheat in shape and appear as smooth, polished, greenish-yellow objects. After they are deposited, from 10 to 12 days are required for the eggs to hatch. The larva.—The newly hatched larva of the white fly is active, resembling that of a scale insect. After crawling for several hours it settles on the underside of a leaf, inserts its beak, and begins to take nourishment by sucking the juices of the plant. To reach the pupal stage it sheds its skin three times, the legs being reduced to mere rudiments after the first molt. The duration of the larval stages 1s approximately 23 days. The pupa—rThe pupa closely resembles the last-stage larva, but at maturity is thicker, more rounded, with a bright red spot on the ‘back. From 38 to 8 days before emergence the eyes of the adult be- come visible. The duration of the pupal stage varies from 13 days in the summer to a maximum of 304 days during the fall, winter, and spring. The larvee and pupe secrete honeydew, which drops on the leaves and fruit, furnishing nourishment for sooty mold. The adult.—The winged adults emerge from the pupal cases, which remain attached to the leaves. They collect most abundantly on the new growth and there they deposit their eggs. A single female has been known to deposit as many as 250 eggs, but the average is not more than 150 for each individual. The average life of the adult is 10 days. Seasonal history.—The citrus white fly passes the winter in the pupal stage, the adults of the first brood appearing in maximum numbers in March or early April, depending upon the season and location. After the practical disappearance of the last brood there is a period of about six weeks when adults are scarce. The second flight, or brood, of adults takes place in June. There is no marked absence of adults between the second and third broods, owing to the overlapping of these broods. The third brood reaches maturity in August, when the third and last flight of adults takes place. The eggs deposited by this third brood develop to the pupal condition and thus they remain on the leaves until the following spring. The third brood is by far the most numerous, and the larve and pupe following this flight, by the extraction of sap and the excretion of honeydew upon which sooty mold grows, cause the greatest damage to citrus trees. THE CLOUDY-WINGED WHITE FLY. The cloudy-winged white fly may be distinguished from the citrus white fly as follows: The eggs of the former are dark and have a reticulated surface. Those of the citrus white fly are greenish yellow SPRAYING FOR WHITE FLIES IN FLORIDA. 3 and smooth. The pupa case of the cloudy-winged white fly is thin and membranous and collapses after the emergence of the adult, while that of the citrus white fly retains its shape indefinitely. The adults are easily distinguished; the cloudy-winged white fly has dark markings on its wings, while the wings of the citrus white fly are pure white. The broods of the cloudy-winged white fly appear about a month later than those of the citrus white fly. INJURY FROM WHITE FLIES. The injury caused by the citrus and cloudy-winged white flies is much greater than is generally supposed. The damage occasioned by the loss of sap is considerable and is a serious drain on the tree, but is of secondary importance to the damage caused by the sooty mold which follows the white fly. The sooty mold affects both the fruit and leaves, blackening the former and covering the upper surface of the latter with a dark- brown coating which excludes the sunlight and clogs and checks the erowth. The reduction in yield from the white flies and sooty mold is variously estimated to be from 25 to 50 per cent. Tf the sooty mold forms a coating on the upper half of the orange, the rind underneath it may remain green indefinitely, while the lower half of the fruit becomes well colored. The retardation of ripening, delaying as it does in some cases the time when the fruit is market- able and materially increasing the percentage of culls, causes further loss, which is very conservatively estimated to range from 2 to 5 per cent of the value of the crop. It is customary to clean fruit noticeably affected with sooty mold. The process of cleaning causes many mechanical injuries which afford entrance to the spores of the blue mold with its resulting decay. SPRAYING. White flies may be controlled in two ways: (1) By subjecting the infested plants to the fumes of hydrocyanic-acid gas, or (2) by spraying with a contact insecticide. The latter method only is con- sidered in this paper and has the advantage of being comparatively inexpensive and adapted to grove conditions in Florida. APPARATUS FOR SPRAYING. In spraying, an extension rod, varying from 8 to 10 feet in length, should be supplied with each line of hose, the length depending upon the height of the trees. This rod may be an ordinary bamboo pole or a small gas pipe. The former is more suitable for this work in that it is hghter and more easily handled after becoming wet. 4 | SPRAYING FOR WHITE FLIES IN FLORIDA. A cut-off should always be inserted between the extension rod and the hose. This will enable the operator to cut off the spray at any time, either when going from tree to tree or in order to clean out the nozzle should it become clogged. If-a power sprayer is used it is also necessary to insert a cut-off between the hose and pump, which would relieve the pressure on the hose in case of a break.