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- Title:
- Whitefly studies in 1908
- Series Title:
- Bulletin - University of Florida Agricultural Experiment Station ; 97
- Creator:
- Berger, E. W.
- Place of Publication:
- Gainesville, Fla.
- Publisher:
- University of Florida Florida Agricultural Experiment Station
- Publication Date:
- 1909
- Language:
- English
Subjects
- Subjects / Keywords:
- Fungi ( jstor )
Insects ( jstor ) Eggs ( jstor )
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- Source Institution:
- University of Florida
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- All applicable rights reserved by the source institution and holding location.
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FEBRUARY, 1909.
Florida Agricultural Experiment Station.
WHITEFLY STUDIES IN 1908.
BY
E. W. BERGER, Ph.D.
Fig. 1. Eggs and Adults of A1oyroi.s ciri.
X 2. From Bulletin 67.
The Bulletins of this Station will be sent free to any address in Florida upon application to the Director of the Experiment Station, Gainesville, Fla.
The Record Co., St. Augustine, Fla.
BULLETIN No. 97.
BOARD OF CONTROL.
N. P. II, VAXN, Chairman, Jacksonville, Fla.
t'. K. YoNi.:, Pensacola, Fla.
T. B. KING, Arcadia, Fla.
J. C. B.\1 nF;N, Live Oak, Fla. F. L \V\ RTM .XNN, Citra, Fla.
STATION STAFF.
1P. 11. RoLus, M. S., Director. A. NNV. ltLAM, A. Al., Chemist. JOHN Al. ScOTT, B. S., Animal Industrialist. C. \V. BERGER, PH. D., Entomologist. 1H. S. FAWxC.:TT, Al. S., Plant Pathologist. Bl. F. FLoYD, A. M., Assistant Plant Physiologist. R. Y. \VINTY.S, B. S., Assistant in Botany. R. N. \VIL.ON, A. 11., Assistant Chemist. JoHN kELLINC, B. Sc., Assistant in Horticulture. MIRs. E. W. BERGcE, Librarian. [K. II. GRAHx\isi, Auditor and Bookkeeper. J T. BLRv \RD, JR., Stenographer. Al. Cos.ws, Farm Foreman. ALFRED:1) DiCKINSON, Gardener.
Temporary Assistant.
IMPORTANT FACTS.
1. It is easy. in Fborida, to inTfect the whitetix larvae with the parasitic fungi by spraying on the spores at the proper time.
-2. The proper time to spray with fungus spores is when there are many young larym )n the leaves and the weather is both moist and xxari.
31. The fungi should be put on the trees as early in the season as possible. in order that their growth ma Ile helped by the summer rains.
4. If the fungi are applied late in the season, they will probably not increase suncient tiuntil the next Year.
. During g the wiiter it is sometimes advisable to spray badly infested trees with contact insecticides.
G. It is much cheaper to keep the whitefly out of a community or out of a grove, if possible, than to control it after it has once entered.
The Experiment Station has no funds available for distributing the whitetfl ftngi. These fungi can !i, i)btained. however, from 1)1 ivate individuals.
CONTENTS.
Page.
Introduction . 43 M eans of Control . 43 Fungus Parasites of W hitefly . 43 H ow Fungi Propagate . 44 Methods for Introducing Whitefly Fungi . 45
Spore-spraying M ethod . 45 1,eaf-pinning M ethod . 46 Tree-planting M ethod . . 47 Conditions Favorable for the Fungi . 4 W hen to Introduce Fungi . 48 Success in Introducing the Fungi . 49 Efficiency of the Fungi . 50 Plan of Cam pain . 50 W here Fungi can be Obtained . 51 T he F ungi . 51
Red Fungus of W hitefly . 51 Yellow Fungus of W hitefly. 52 Brown Fungus of W hitefly . 53 White-fringe Fungus of Whitefly . 54 Cinnamon Fungus of Whitefly. 55 Sporotrichum Fungus of W hitefly . 56 Fungus Super-Parasites . .56
S ooty M old . 5 A rtificial M eans of Control . 58 Q quarantine . . 59 Food Plants of W hitefly . 60 Plants to be Condem ned . 61 W hitefly Living on Fallen Leaves . 62 R esults of D efoliation . 63 Honeydew . 3 Life-history of W hitefly . 64 Two Species of Citrus W hitefly in Florida . 6 ' R eferences . 70
WHITEFLY STUDIES IN 1908.
By E. W. BERGER, Ph. 1).
INTRODUCTION.
The present bulletin includes a revision of Bulletin 88S, issued in January, 190',.1 and also a report of progress.
During 1908 the whitetix has continued to spread to citrus-growing sections of the State which had not hitherto been infested. Vehicles, railroad trains, and infested nursery stock are perhaps the chief means by which it is spreading to all those parts of the State where citrus fruit is crown, or where its other food plants are found. Vxhile a few citrus-growers still treat the spread of the whitetx as insignificant, and believe that it will disappear of its own accord, this 1nnlber does not include the owners and managers of the larger properties. These are gLreatly interested in and read to adopt such meals as promise relief.
MA,\NS OF CONTROL.
The means of conurl are first, natural enemies: aml second, artificial methods.
Among the natural encnies o insects are fun-i. bacteria, and predaceous insects. Ilacterial diseases of the whitefly are at present unknown, hut the known fuinis diseases of this insect are seven in number. Several prelaceous insects are also kwxii to feed oii the larva of the whitefly.
The artificial means for controlling insects include contact insecticides, stomach poisons, and fumigation with a poisonous gas. The whiteflv can not be killed Lv stomach poisons,. such as compounds of arsenic, since it is a sucking insect and draws its food from the interior of leaves ly ieaiis of a beak. Spraying solutions which kill the insect I contact, and fim igation, are therefore the artificial methods for combating this pest.
FUNGUS PARASITES OF WHITEFLY.
Fungi are among- the lowest plants known. They are devoid of the green coloring matter which is characteristic of higher plants. Mushrooms. toadstools, mildews and molds are familiar examples.
As regards their metlhods of feeding, fun-i may he either parasites or saprophytes. Fungus parasites infect and often destroy living plants or animals. The xxithertip fungus of citrus trees ald the rust of tomatoes are familiar examples of fungi which live on plants. The seven fungus parasites of the whitefly, also the red-headed scale fungus, the white-headed scale fungus, and the black scale fungus, are examples of fungi infecting insects. Saprophytic. fungi are those that grow only on dead organic matter. These include most of the fungi growing on rotten wood, or on the ground in fields or forests. Toadstools. mushrooms, and the molds of bread are familiar examples.
Florida Agricultural Experiment Statioll
The fungus body produced on a whitefly larva is spoken of as a iungus pustule. Such a pustule is limited in its growth by the amount of food furnished by a single larva, so that the pustules can not increase beyond a certain size. Their size varies with the size of the larva attacked. The largest pustules are about three-sixteenths of an inch in diameter, while the smallest are smaller than a pin's head.
Six fungus parasites are at present known to infect the larvae of the whitefly, and a seventh infects both larve and adults. The following table gives the common and scientific names of these fungi, with the dates of their discovery on the whitefly in Florida:
1. Red fungus of whitefly (Aschcrsonia a/ cyrodis Webber) 1893 2. Brown fungus of whitefly . . I.1b9.
.3. Red-headed scale fungus (Sphaerostilbe coccophi/a Tul.) 1903.
4. Yellow fungus of whitefl\ (Aschersonia /a1zo-citrina
P. Henn. ) . 1906.
5. White-fringe fungus of whitefly (Ilicrocera sp.) . 1907.
6. Cinnamon fungus of whitefly (VIerticillium hetorocladomi Penzig) . 1907.
7. Sporotrichitm sp., similar to the chinch bug fungus
(S. globiiferum), infects the adult whitefly and
som e of the larvw . 1908.
The first six fungi, when present, are found on the under surfaces of whitefly-infested citrus leaves, and kill the larvae, transforming them into pustules which have the color and appearance characteristic of the particular fungus. The red-headed scale fungus is only occasionally found infecting whitefly larve. and will not be further discussed in this bulletin. So far, no fungus capable of infecting the eggs of the whitefly has been discovered. "WVith regard to these seven fungi, reference may be made to Bulletin 94, and also to Special Studies, No. 1, University of Florida.2
HOW FUNGI PROPAGATE.
Fungi more generally propagate by spores than in any other way. The spores of fungi are niinute microscopic bodies produced in countless millions, and are mostlv used when we desire to start a new growth of fungus. They take the place of the seeds produced by the higher plants, but do not have the same structure as seeds. A single spore is invisible to the unaided eve. The spores of two of the fungus parasites of the whitefly, the red and the yellow fungi, .are boat-shaped and pointed at both ends. About 1,700 of them ,could be placed end to end along a line one inch long, and more than 8,000 could be arranged side by side along the same line. About 13,600,000 of these spores could thus be arranged upon the surface of a square inch. Thousands of spores are borne in each bright red or yellow pustule of these fungi. These spores are washed out when the Aschersonias are placed in water. Some fungi may
Bulletin 97
also be propagated by portions of the thread-like growths which make up the mass of the fungus. This method of propagation is analagous to the propagation of the higher plants by cuttings. A good illustration of this is the use of "spawn" for propagating the common mushroom. This spawn consists of dry fragments of the underground growth of the mushroom embedded in manure or other vegetable matter. \\hether any of the fungus parasites of the whitefly are propagated in this wax has not been demoiistrated; but the peculiar network of threads of the brown fungus which extends over the citrus leaves, and even over the leaf-stalks, suggests that this fungus may perhaps be propagated by fragments of these threads being carried by the wixnd, by insects, or otherwise, from one leaf to another.
METHODS FOR INTRODUCING WHITEFLY FUNGI.
There are three methods which have been used for introducing these fungi into whitefly-infested trees. These are the spore-spraying method, the leaf-pinning method, and the tree-planting method. These methods are based mainly upon experiments with the red. yellow, and brown fungi.
SPORE SPRAYING METHOD.
This method is the best one of the three. It consists in washing the spores froin funguLs pustules by means of xxater, and then spraying the mixture of spores and water onto the under surfaces of the xxwhiteflv-infested leaves. (The writer's earlier successful experiments with this method were made at Lake City in July, and at Leesburg in August 1)00, with the spores of the red Aschersonia.) About forty of the bright red or yellow pustules of the fungus should be used to a pint of water. This will be about the same as one or two ftngus-bearing leaves to a quart of water. More fungus may be used if procurable. but the amount indicated has been found to give good results. Immerse the fungus-bearing leaves in water, and stir occasionally during ten or fifteen minutes, then strain the liquid through clheesecloth or fine wxire gauze. While spraying the mixture of spores and water onto the under surfaces of the whitefly-infested leaves, look well to the newer oowth, especially the water sprouts. This young growth is generally most infested with the younger whitefly larvxe, since the winged females always seek out young leaves when depositingg their egg>. It should be remembered that the younger larve are more easily infected with the fuutls than the older larv'. If the supply of fungus is limited, spray only the worst infested twigs and branches: for the fungus will infect some of the lary, and the adults maturing from those not infected, together with other adults migrating there, will carry the fungus spores to other parts of the tree and to other trees. It is considered better practice to spray tile infested parts of all trees with a weak mixture, than to
Florida Aloricultnral Elxperiinct Station
spray only a part of the trees in a grove with a strong.mixture. Use a new spraying outfit, preferably one of the compressed air type (3 or
-P gallons capacity), with no copper or brass about it excepting the nozzle. The finer the spray, the better; since it is only necessary just to wxet the leaves, and whatever liquid runs off is lost.
Ol no account should the spraying solution be permitted to stand in a copper or brass vessel, since an exceedingly small amount of copper in solution will retard or destroy the germinating power of the spores. D~o not use an outfit which has been previously used for spraying Bordeaux or other strong fungicide, since a very small amount of fungicide left in the machine may kill the spores. An old spraying outfit which has been used only for soap solutions or oil emulsions, may be employed; but it should be well washed out. A larger specially made spraying machine mounted on a barrel may be llsed when many acres are to be sprayed and when an abundance of fungus is available.
A\ simple modification of the spore-spraying method consists in flirting the liquid against the under surfaces of the leaves by means of a tilt cup. A wisp broom has also been employed, or a bunch of small twigs dipped into the liquid.
Cost of introducing fnus by this method.-This will varv with the size of the trees. One correspondent reports that it has cost him two cents per tree to spray his -rove of medium-sized trees. In another case it is costing one cent per tree to spray; but, in this instance, the fmgus was procured at the slight expense of picking it from other trees. 'li'e i writer helped to spray 1It medium-sized trees during the last week of September, 1MS, with spores of the red fulgtls, usilo- about one .gallon of liquid per tree. About eight fiugus-bearing leaves were used to prepare a gallon of this liquid. The leaves cost $1 per thousand. This made the total cost per tree. for fungus and labor, about 5 cents. \l all-iroll spray-p l)l,
mounted oii a barrel. was used for spraying this grove. This method is applicable to all the funtigus parasites of the whiteflix when they are in the spore-bearing stage. The brown fungus does not always have spores ; hence there is more or less uncertainty when one attempts to introduce it by the spore-spraying methodl. Some excellent
growths of the brown fungus have, however, been started hx this method.
LI, A-'IN N 1NC, xi1ET]it ).
This method is considered second best. Ilt introducing fungus by this means, the writer has usually piined from two to a dozen fugus -covered leaves to the under surfaces of leaves of a whitefly-infested tree. In Bulletin 8S81 the writer recommended that each leaf should be pinned x\with its under, or fungus-covered surface, facing downward. Later observations have confirmed this as the proper xxax to pin the leaves, since the adult whiteflies creeli over the under
Bulletin 97
surfaces of the leaves. and in so doing probably get many of the spores attached to their feet, and then carry them to other leaves. For the same reason the'leaves should be pinned to those parts of a tree where the adult whiteflies are most abundant" that is, on the newest growth. It might also be well to pin the leaves so that the drip from them, when it rains, will run onto a cluster or several clusters of leaves beneath them. \t all events, we sometimes find that fungus starts to develop on the leaves of clusters underneath the leaves pinned on.
Since the adult wx hiteflv appears to be instruimental in the distribution of fung-,us (this probabl applies mainly to the red and yellow fungi) we w outd expect to get the best results with the leaf -pining method at those times when adults are most ahtmdant in the trees. Such is the case: for late in the fall wheii no adults or only a few were about, no growx tli of ftgus, or oiily a very poor growth, resulted froii pinning on the fung-us-covered leaves while ili most instances promising growths of ftingus resulted from spraying the spores. Similar observations were made at other times when few adults were on the wing: and then onlx a restricted growth of funglis resulted from pinning on leaves, while a wide-spread growth came as a consequeice of spraying the spores. Other crawling and flying insects are also probably instrumental in distributing fungus spores. (The leafi-pinning method may he used with all the whitefly fuingi.) Te (l'C-l'ANTING AlEI, tW).
Small whitefixinfested trees, having an abundance of a whiteflydestroying fungus on their leaves, have been temporarily planted by some of the citrus-growers, so that their foliage came in contact with that of the-infested trees iito which it was desired to introduce the fumgns. -When necessarv. these trees were planted in pots or tubs, and elevated on platforms. This inethod of introducing the fungi, although useful, is not so adviantageotis as either the spore-spraying or the leaf -)inning iiiethods, and is of course. much more expensive. It requires considerable care in the xxay of vatering to keep the small tree from dropping its leaves while the fuigus is spreading to the tree ii which it is wanted. Like the leafi-pinning method, this method is probably dependient mainly upon the adult whitefly and other insects for spreading the fungi, especially the red and yellow fungi, froin one tree to aiiother. This method is applicable to all the fungi of the whitefdx.
CONDITIONS FAORAILE FOR THE FUNGI.
All fungi thrive best in the presence of abundant moisture. Observations show that the fungus parasites of the whitefly are most effective in destroying this pest when the atmosphere in a grove is most humid, as it is during the period of summer rains. On page 55 of Bulletin 88,' the writer called attention to the desirability of
48 Florida Agricoltiiral E.pcriiet Stationl
arranging conditions in a citrus grove to promote dampness of the air about the trees. Plenty of vegetation trees , shrubs, tall grasses, etc.) around and iu a grove will do this to a great extent. Trees and shrubs should be arranged as windbreaks, while grasses or1 beggarweed should he permitted to grow tall and rank, as a cover crop at the proper time. Mulching around and between the trees will also help to conserve moisture. Wherever an irrigatin.- outfit is emplo yed, tie treqnent wetting of the trees or the soil in dry weather would add to the efficiency of the fungi. Snch a use of the irritaIig outfit \v N also reduce "'red spider" and rust-mite, and favor the activities of [he st-ails which feed on the sooty mold.
Warmth is a necessary condition for the rapid development of the fungi, This condition is generally realized in Florida from the beginning of April until October. During this period the fungus parasites of the whitefly thrive xxell if the wvarm weather is accompanied by enough rain. Careful observations during the cooler
months, from SeptemLer or October to March, indicate that the fungi grow and spread but slowly during this period, notwithstanding that either rains or heavy dews may supply much moisture.
WHEN TO INTRODUCE FUNGI.
The period of sumner rains, which often lasts from June to September, is generally the hest time in which to bring the fungi into a grove; but the stage of development of the whitefly larve is also important. Experiments with the red and yellow fungi, by the sporespraying method, on January 17 and March 1,, 19108, in trees in which the whitefly had advanced to the fourth larval or to the pupal stage, did not result in any growth of fungus. Similar experiments made on1 October 3, 1 16(, and November -29, 1907, with the same fungi and the spore-spraying method, resulted in some growth of fungus notwithstanding that the conditions of moisture and temperattire were no more favorable for fungus growth during these months than durilig January or -March. But young larve are present in considerable numbers until December and sometimes later, and these are apparently more easily infected than are the older larve or the pupie. This may account for the failure to yet a growth of fungus in January or March, when young larvae are very scarce or absent. No experiments have been made during December and February, but these two months resemble january and March so closely both in regard to climate and the condition of the xwhitefly larve, that probably little or no success wxoulld be obtained. Expei luents with the same fungus by the same method at DeLand on April 21 and '22, 1908, in trees in which the whitefly was mainly in the first and second larval stages, just after the disappearance of the spring brood of adults, resulted in a heavy growth of fungtis, and by the 17th of the following June a third to a half of the whitefly larve had become infected and were dead. Showers of rain immediately followed or preceded some
Bulletin 97 49
of these spore-sprayings, and were probably factors in bringing about the result.
To slun up: the best time to apply the fungi by the spore-spraying method is when the larvae are young (that is in the first, second, and third stages) and abundant. This time extends from April or earlier. ntt November and perhaps December. During a short time in .\lay or June, just ILefrea anwl during the period of issuing of the s1L iii brood of adult whitelie-s. when the progeny of the first brooI ,e mainly in lie fourth larval and the pipal stages of development, but little success can I-e expected. With the leaf-pinning and the treeplanting rietho Is, the best time extends from the (late in March or April when the adults begin to swarm about abtindantlY, until sometime in September: after which but few adults are about. There will be a short batren period for the leaf-pinning method in May or June. when few or no adils are about, and the larvae have advanced to the older stages. \Vhile successful growths of fungus can be started during the fall months, vet they will generalHy not develop and spread to any great extent until the following summer. It is therefore desiral'he to get a good growth of ftmngus started early in the season, either in \piil or as soon as yomg larva are abundant, in order to benefit fro- the fungus as soon as possible. It may not 1-e possilil. (-boswever, for want of material, to introduce fungus be ne the middle of summer or even later.
SUCCESS IN INTRODUCING THE FUNGI.
IBy taking into account she cloiclusions just set forth, and introducing the fungi in a methodical way, it should le possible to get a good growth of fungus in nearly every trial. These concltsions are based upon many experiments carried on during the past two years and a hal at Lake City, Leesburg. St. IPetersburg, Kissitmee, New Sinsrna, DeLand and Gainesville. About fifty experiments have been coAcluded, and several hundred trees have been treated. When the conditions set f- rth in the preceding sect in were observed. soi gm-ti of fmgus xa- iivrinaily ol taimed when fresh fungus was iiel, and when the spores were not inj ured hs the use of a spraying machine cmtaminated wvith Rordeaux mixture.
Several citrus-growers have treated thousands of trees (ltring the past sunuler. \imong these, Air. Frank Stirlin , of Debaud, in a communication of December 1, 1908, states that lie has been successfti in stating the ftngi, having sprayed between eight and nine thu isand trees with the red, yellow, and brown ftligi since Aug-ust, 1!8iS. He has also grown thi red and brown fungi on infested cape jasnie, chiuaberr and privet. NMr. . B. Stevens, of l)eLand, reports that the application of the brown fungus by the spore-spraying method in July has apparently resulted in infecting nearly all the whitefly larve. Leaves sent to the Experiment Station had every larva killed by the fungus. Mr. Edwin W. Johnson, of East Palatka,
00 Fl-ida Ig ricultural Experin cut Station
sends an account of his success in infecting the whitefly in his grove ixith the red and brown fungi, and states that, in many cases, the fungus growths on the sprayed trees were equal to those on the leaves used for preparing the mixture of spores and water. Ile expects to repeat the spore-spraying as soon as young larvme are present in the spring, and finds it an easy and incxpensive treatment.
EFFICIENCY OF THE F-UNGI.
Our investigations show that the whitel-v is not an ouStlrloOtlltable obstacle to the profitable growing of citrus fruits. When left without assistance, the fungi will practically destroy the whitefly in a grove, on the average, once every three years; thus reducing the injury due to the whitefly by at least one-third. The destruction is not complete, so that the insects increase again during the two succeeding years but this is accompanied by a rapid increase of the fungi, until the wliteflx is again overwhelmed. This is the course run by the whitefly and the fungi when unassisted in those sections which have been longest infested, such as Manatee county, Fort \Iyers, and O)rlando. At Orlando, the fungi were in the ascendency during' the sulnier of iPOhi, and this resulted in so far reducing the whitefly that an uincommonly large and clean crop of citrus frnit was marketed in DOth?. The writer believes, however. that by diligently following the recomenndatious made in this bulletin it would he W1 easy matter to double the efficiency of the ftun-i; in other words, to give us clean fruit on the average, for two years out Of thirce.
PLAN OF CAMPAIGN.
whe writer's plan of campaign, based upon experiments in the field, is as follloxws: If a grove is thoroughly. infested xw ith xhitefly, an(l sifFcient seed-fung us is available, spray it through hly into all the trees hut if the supply of seed-fungus i> limited, spray onlv a small amount into each tree. Later o, when abundant seedt-fungus can be procured, the trees or parts of trees not previously treated max he attendfled to. A second, and even a third treatment may le -iven to the trees in the same season in order to get the most thorough dissemination of fungus. So long as only a few fungus pustules are visible on those leaves of a tree which bear the niost fungus and wvhitefly larve, it will be advisable to iiitrodtice more, especially should ax abundance of seed-fungus le rea(ily ohtainahhe. The reater the amotint of ftngus growth which is successfully started in a grove, the more rapid will be the destruction of the whitefly. These insects have a habit of congregating ox water-sprouts ani other tender growth of citrus, consequently we should give particular attention to introducing the fungi into such parts of the trees. The xw' irk should he done methodically and not in a haphazard way.
The plan of campaign for a grove just becoming infested with whitefly, or only infested in part, would lbe to introduce fungus into
Bilctin 97 51
all those trees sufficiently infested (that is, a score or more of larve on each leaf), and later on into other trees as soon as they become sufficiently infested. This operation should be repeated each year. or whenever the whitefly is observed to be in sufficielit abundance to allow of a good growth of fungus being started.
WHERE FUNGI MAY BE BOUGHT.
The Experinient Station has no funds available for collecting and distributing fungi. The money approplriated by the U. S. Congress for the maintenance of Experiment Stations is for the purpose of defraying the expenses of actual experiments and investigations pertaining to agriculture. As the collecting and distributing of well-known fungi is not an experiment, it could not be carried on with this money. The State- Legislature would appr-opriate money for such work, if the citrus growers considered it desirable to do so. But sufficient fungus material can generally be obtained from private sources. The following gentlemen have consented to furnish fungus whenever they have it available. The cost will vary, but from two to four dollars will generally pay for an amount sufciemt to treat an acre of grove. Red, yellow. and brown fungi: C. A. Boone, Orlando, Fla. Red and brown fungi A. J. IPettigrew. Manatee, Fla.; A. F. Wyvnan, Bradentown. Fla.: F. D. \aite, Palmetto, Fla. Red and fellow fungi: C. B. Thornton, Orlando, Fla. Red fungus: Frank H. Davis, Apopka, Fla. John F. Carlton, Sparr, Fla. Yellow fungus: W. H. Maxw ell, Titusville, Fla. It may be mentioned here that 3,000 orange leaves will loosely fill a bushel measure.
THE FUNGI.
rD FUNGUS OF WIJITEFLY.
Fig. 2. Red Fungus of Whitefly. x1%.
52 Florida Agrictltural ]Lrperimcnit Station
As the name implies, this fungus is red and when at its height of spore-formation bright red, this extra redness being due to the mass of spores. Before it reaches the spore-producing stage, it is yellowish in color, and becomes a faded pink when the spoies have been washed away. This fungus growth or pustule is generally surrounded by a lighter-colored fringe closely appressed to the leaf, while the pustular part projects. The exact details of the process by means of which a whitefly larva becomes infected by this fungus have not been observed, but that the infection proceecls from the development of a spore of the fungus, lodged on or near the larva, has been demonstrated beyond doubt by hundreds of experiments with the spore-spraying method. Figures 3-5, taken from Dr. I1. J. Webber's bulletin7 show many details in regard to the manner of development of this fungus in the body of the whitefly larva.
Fig. 3. (After fV-bber.) Fig 4. (After Webber.) Whitell larvawtilhled Li elue t ace. The fiuig IT Fig. 5. (After ftebe.) Still filitgli1 (a) gromting il- liread are s(ei gi-mv- later ,t a 'e Tho f i-Or sideithody. Tie larva intmtottu thedead latva. eas- s C--rll ai ll'ut ri ng ' is dying or dead. X 1. X 15. rttld the dead itl Ia X 15.
This fungus appears to thrive equally on both speck> of the citrus whitefly, but has most frequently been observed upon the sp-cies with the smooth e--> (Alcyrodcs citri). The red fungus can be introduced by any one of the three methods already described, and is very effective. It requires about three weeks for this fungus to make visible growth, but under the most favorable conditions growth has several tines been detected in ten (lays.
YELLOW FUNGUS or WHITEFLY.
This fungtus is so much like the red fungus that what has been writteii and figured in regard to the latter holds true for the former. Its color, however, is a rich lemon yellow, so that it can easily be distinguished frot the red, especially when both are in the spore-producing stage. It was first described from specimens obtained on guava leaves in Brazil, and was first recognized in Florida by Professor P. H. Rolfs in September, 1906. This fungus appears not to thrive so well upon the smooth-egged species (Alcrodcs citri) of th@
Bulletin 97 53
citrus whitefly. Whenever the writer observed it effectively infecting whitefly larva, it was on the species with reticulated eggs. All efforts. on the part of the writer to introduce it effectively on the species with smooth eggs have so far failed. It has been found possible to infect a few larve, but the fungus did not increase and thrive, and this happened when the red fungus, introduced at the same time and close by, grew and throve well. This fungus can be introduced by any of the three methods and has been observed to be very effective on the whitefly with reticulated eggs (Aleyrodes nubifera). The spore-spraying method is to be preferred.
BROWN rUNGUS OV THE WHITEFLY.
This fungus develops into pustules of a glossy chocolate brown, although sometimes it is quite light in color. It resembles in color and shape the Florida red scale of the orange, Chrysomphalus (Aspidiotus) ficus, and may easily be mistaken for this insect. The brown fungus differs in one remarkable respect from all the other known fungus parasites of the whitefly. The fungus growth which develops upon a single whitefly larva, instead of being limited in its, activities to this one larva, sends out hundreds of ramifying fungusthreads (hyphae), which will infect other larvae if they are sufficiently near. From these infected larve more threads ramify until the whole under surface of the leaf is covered with a network of fungus threads, which when peeled off, has much the appearance of very thin tissue
Fig. 6. Brown Fungus of Whitefly. xl y.
paper. This fungus tissue may also spread to the upper surface of the leaf and down along the leafstalk, even onto the stems o~f the twigs.
The brown fungus appears to thrive on both species of whitefly,. but has been more frequently observed upon the smooth-egged species (Aleyrodes citri). It has been successfully introduced by means of
Florida Agricultural Experinhciit Statiou
all the methods described on a former page ; but since the red and yellow Aschersonias lend themselves more readily to experimentation because of the ease with which their spores may be obtained, these have naturally been experimented with first, possibly to the neglect of the brown fungus. That the latter can readily be introduced onto non-infected whitefly larve by the spraying method, has been demonstrated a number of times by the writer and others. The most successful of these introductions have probably been made by Mr. H. B. Stevens, at DeLand, during JTily, 1908, and by Mr. Edwin NV. Johnson, at Fast Palatka. E]xperiiuents so far indicate that we have the most favorable conditions for introduciug the brown fungus during July and August. Until more definite information in regard to the spores uf this fungus is at hand, tile writer recommends that the fungus be scoured off the leaves by ieans of a little sand and water, and the resulting mixture of fungus particles and water used as a spray. About the same relative quantities of fuugus and water should be taken as recommended for tile red and fellow Aschersonias, and if necessary tihe mixture may be strained.
'WHI FE-II-I qINGE FUNGiUS O11 \IIFLF .
Fig. 7. White-fringe Fungus on Whitefly (Aleyrodet, nbitfera).
Sooty mold round several larve.
This fungus has been only recently recognized as an effective parasite of whitefly larve.2 It was observed that from 70 to 90 per cent. of the larva in certain trees were dead, apparently through infection by this fungus. The white-fringe fungus is not conspicuous to the unaided eye, as are most of the other fungus parasites of the
Bulletin 97 55
whitefly, but it can be made out with the use of a hand lens. It appears as a delicate white fringe about the margin of the larva, which fringe soon disappears when the leaves dry. The (lead larva have a white or light-pink papery appearance.
The fungus has been successfully introduced by the spore-spraying method, and in two weeks it was plainly evident upon previously healthy larv-in this instance, those of the smooth-egged species (Alcyrodes citri). The fungus can probably also be introduced by the other methods. It will apparently thrive on both species of whitefly, but has so far been observed as most effective upon the species with reticulated eggs (Alcyrodcs on bifera). This fungus being of comparatively recent discovery, and being besides rather evanescent and inconspicuous, much remains to be observed in reg;ar, to its life-history and its effectiveness in checking the whitefly. It seems to be pretty generally distributed in the citrus-growing sections of the State, as specimens have been identified from widely separated groves.
CIXNA\ION YUNG'S or WHIlTErLY.
Fig. 8. Cinnamon Fungus on Whitefly. x l1%.
This fungus much resembles the brown fungus, except that the surface of its pustules has a powdery appearance and a cinnamonbrown color. A layer of white interwoven threads spreads a little distance over the leaf from the pustules, but this layer does not spread over the whole leaf, as it does for the brown fungus. The cinnamon fungus produces an abundance of spores, and may be introduced by the spore-spraying method. It appears to be widely distributed in small quantities and on both species of whitefly. While
-56 Florida Agriclt-al Expcrime"I Station
-this fungus is useful, and may frequently 1e introduced, especially in connection with the brown fnins, yet it does not occur in sufficient abundance to allow of its I being preferred to the brown fungus or to the Aschersonias. It has also been observed on several scale insects ncluding a Lecanium and a Diaspis.
SPOROTRICHU FUN(;XS oF" \VIIITEIFLY.
This Sporotrichulin is a .species of fungus closely related to the chinchbug fungus. The plant pathologist of the Station, Prof. H. S. Fawcett, has several times observed this fting us on adult whiteflies in different parts of the State, first in a small orange grove near 'Gainesville during last August. Dozens of the adults xcre found
-dead, attached to the under surface of the leaves, with tl grayish fungus threads penetrating the lod)-wall and hearing thousands of � spores. As just stated, this fungus infects the adults, but it has also been observed on the larvte. It has so far been found only on the species of whitefly with smooth eggs (1lcvirodcs citri). This fungus may prove to be a valable adjunct to the other fungus parasites. especially since it attacks the adults, which the other fungi are not known to do.
FUNGUS' SX'PEtI',\ RASITS.
rCladosporiom sp.-An olive-green fingus of the genus Cladosporium frequentix overruns and destroys the red and yellow Aschersonias, chang-ing their colors to olive-o-reen. Attention was first directed to this fungus by Dr. A. W. Alorrill in an article to the Timcs-Umci, of Jacksonville, Fla., April 14, 190,. According to the .present writer's olservaticus, this ftlgts strong glx attacks the red and yellow Asclersonias onix towards fall and during winter and spring, ,when these fungi are inactive and are probably undergoing ldegener:ative changes. The chief injury caused by the Cladosporium, in the writer's opinion, inay consist in its destruction of the spores of the Aschersonias, at a time when these should be conserved for the infection of the spring brood of xxhitefiT larve. The writer is not aware, however, that the Aschersonias are seriouslx retarded b-y the Clado>porium, since their spores are in a great ,-wisure lost, in any case, by the weathering and rain of the winter and spring. At all events, the wx riter has so far given no heed to the Cladosporiumn in conducting his experiments. The yellow Asehersonia is more generally infected by the Cladosporium than the red As -bersonia. This Cladosporiuni also occurs on dead insect remains, and may overrun the sooty mold fungus.
Coaiothy'nim sp.-Shortly after Dr. Morrill had noticed the Cladosporitm, he directed the writer's attention to another fungus in Manatee county, which he believed to he a superparasite of the brown fungus. It was identified by Prof. 11. S. Faxvcett, as belonging to the genus Coniothvrium. It occasionally overruns the pustules of
Builetim 97 57
the brown fungus, and much resembles a certain stage of the black scale fungus, Jlyriaugion Duriaci, but it has a decided shade of green in the black. The writer regards this fungus also as attacking the brown fungus chiefly after the latter has become old or weakened from drought or cool weather.
SOOTY A1O-D.
This mold (a species of Meliola is of a sooty black color, as its name implies. It is found whenever whitefly or other insects occur that excrete a sweet solution {honeydew). As this honeydew nearly always collects on the upper surfaces of leaves, it follows that the mold which thrives in this secretion occurs mainly on the upper surface. Insects that are accompanied by the sooty mold are: whitefly. rnealybugs, plant lice (aphides), soft scales (Lecanium), wax scales, cottony cushion scale, etc. The presence of sooty mold on a tree is therefore not a sure sign of the presence of whitefly. This fungus does not ordinarily become visible until after the trees have been infested bv the whitefly for some months. Not infrequently this sooty mold occurs also o the undler surface of the whiteflv-infested leaves, either completely covering them or forming a black fringe about whitefly larve Fig. 9 ) When this condition occurs, it is due, in the first place, to an a' normal or disease(d state of the larvae, which results in the honey(ew collecting al-out and underneath them, instead of being projecte'l away. The nuolcl then develops in this honeydew, and probably completes the destruction of the larve. Larwe wet with their own honevdlew are frej mently observed before the mold has made any visible growth. Sometimes the diseased condition of the larve resulting in this v etting is recognized as being due to an infec-
Fig. 9. Sooty Mold overgrowing Whitefly (.1 iii'odes citr,).
Also eggs, larve, and pupa cases. x l".
58 Florida Agricultural Exrperilni t Statiol
tion with one of the fungus parasites of the whitefly, but at other times no cause can be assigned.
ARTIFICIAL MEANS OF CONTROL.
SPRAYING WVITH CONTACT JNISECTICIDES.-For More complete directions in regard to the preparation of contact insecticides, the reader is referred to Bulletin 1 6 of the Florida Experiment Station, on Insecticides and Fungicides, which also contains general direction> for spraying and fumigation. Judicious spraying with contact insecticides would be effectual in reducing the ravages of the whitefly, provided a grower can persuade his neighbors to spray at the same time. or if the grove is isolated. If a grove is not isolated and one's neighhors do nothing to check the whitefly, the latter will keel) coming in from the infested trees. When chinaberry trees, privet, or othcr food plants are about to aid in the breeding of the adults, an isolation of a nile will hardly be sufficient to keel) whiteflies from coming in when they begin to swarm out of such trees as chinaberry and umbrella trees dnrino Augu st and September. Spraying is difficult and almost impracticable, except when the trees are small-not over five to seven years old-since the larger the tree, the more difficult it is to do the work thoroughly.
December, jJanuary and February are the best months to spray for the whitefly, as this insect is then in one or other of its larval stages, and there are very few or no adults present to escape. It is practically useless to spray the adults, since the females may lay their eg-gs when they are eighteen to thirty hours old, so that the gr power would have to spray every day duringg the swarming periods to insure killilg- them before theY laid their egg>. The eggs- are not readily killed either iy spraxg or fumigation. Spraying to be most effective should, furthermore, be really thorough, and one such spraying in winter, after the fruit is picked, will be worth more than several less thorough applications. The spraying should be postponed until danger from frost is past: since if the leaves should be cut off by a frost, but little if any spraying would be necessary during that season. Summer spraying may be practiced when conditions require it. The difficulty with spraying lies not so much in getting an insecticide that will kill the insect, as in the application of it so that all, or at least a very large percentage of the whitefly larve will he killed. Any of the contact insecticides, such as whale-oil soap, kerosene emulsion, resin wash, and a number of proprietary brands which are generally used for destrovin z insects on citrus leaves, will be found effective. I-Towever, all sl)raying w ith emulsions and other chemical compounds generally in use is more or less injurious to orange trees. Of these. whale-oil soap is probably the least injurious. Before spraying, all excessive foliage should be removed from the trees by a thorough pruning. Spray ing with insecticides is also more or less harmful to
Bu/Ictiio 97 '59
the fungi so that having once decided to adopt the fungus method, spraying should be discontinued. Soap solutions and plain emulsions of oils do least injury to the fungi, unless used in a very concentrated formu.
FUMIGATION \VITH IJYDROCYANIc ACID G &s.-Those desiring information on fumigation are referred to the bulletin on this subject by Dr. A. NV. Morrill.'; Those who require copies of this bulletin may sectire them through their cong ressmen. Dr. Morrill saxs further in the "Florida Fruit and Produce News," November '?0, 1908: "In the country if a -rove is isolated by a distance of two or three hundred feet from all other infested groves, fumigation can be practiced without fear of its being made unprofitable bl mig rations of the adults."
QUARANTINE.
The whitefly canl be kept out of non-infested groves in localities sufficiently isolated, for a considerable length of time. The fact that thousands of dollars may lie saved in this way to a grower or a commtity, should be an incentive for all, whether directly interested or not, to co-operate in keepiig the whitedly out, or in checking its spread.
Several methods of procedure are available. 1>' closing all private roads and gate. especially against vehicles coming from infested districts, much could be, and in fact has been. accomplished. The property should le "posted," which would have the effect of keeping out many individuals xxho ixay be carriers of w hitefly, since the latter has frequently been founi concealed on the clothing of persons after they had left infested localities. No nursery stock should le admitted except after it has been completely defoliated (leaf and leaf-stalk), and cut back to the extent of removing the tender greencolored growth. To complete the protection, the stock should furthermore be fumigated with h-drocyanic acid -as. Vhen it is know l for a certaint that the section front which the stock is ordered is free from whitefly, the previous l)recantiomls need not be taken; but the stock should be completely enclosed to protect it fronx becoming infested while in transit through infested districts. Pickers' implements from infested districts have been excluded by grower s in certain noi-infested sections. This was a perfectly proper course to follow, since it is easy to conceive of the newly hatched larve or the adults being carried by such means. Stic illplements could, hoxxever, be made safe ibv a thorough spraying with some contact insecticide. When implements are sprayed, every effort should be made to saturate all crevices. The picking bags and outer clothing of pickers should also be treated, either xvith carbon bisulphide or xvith hydrocyanic acid gas, in some air-tight receptacle or room. Three ounces (about one-fifth of a pint) of carbon bisulphide wiIl be sufficient to fumigate a space about the size of a barrel, the fumigation being
Florida Agricultural E.xperimcnt Station
allowed to continue from thirty minutes to several hours. If a futiiigating box is at hand, such as is used for fumigating nursery stock, the implements and other objects may be fumigated in this, using an ounce of potassium cyanide, two ounces of sulphuric acid and four of water. The water and acid are first nixed in an earthenware vessel of double the necessary capacity, and then the cyanide is added. The gas is evolved immediately, and is dangerously poisonous. The fumigation should last for thirty minutes or longer. The picking bags and clothing of the pickers should be arranged loosely and with spaces between them to insure a circulation of the vapor or gas used for fumigating. See bulletin 76 of the Bureau of Entomology.5 and bulletin 76 of this Station, for further directions on the use of hydrocyanic acid gas.
FOOD PLANTS OF THE WHITEFLYY.
Some people still imagine that every tree, bush, and shrub in our hammocks is a food plant for the whitefly. This is erroneous. The number of food plants is very limited when conipared with the number of native species of plants. As a matter of fact, the native species capable of supporting the whitefly in dangerous quantities are quite few. The number of plants, however, which become only occasionally infested, may be greater than we at present know.
CLASS I.-1OOD PLANTS PRLEFFR;RED;ax 'BHEV1 W-IIT1FLY.
Native Species:
Prickly ash (Fa.-ara Chua-fT'rculis).
Wild persimmon (Diospvros T 7rgin/ann
Introduced Species:
Citrus (all varieties).
Chinaberry (Melia A Iedarach .
Umbrella (Mclia -.Cdarach in cn ILfca).
Cape j asmine (Gardenia jasm . )1o1dcs)
Privets (Ligustrum spp.).
Japan persimmon (Diospyros Kaki).
CLASS II.-FoOD PLANTS SOMEUI'IMI'S INFESTED UT NOT PREFERRED BY THIL W-IITEFLY.
Native Species:
Cherry laurel or Mock orange (Lauroccrasns sphacrocarpa and
L. Caroliniana).
Smilax (Smila-r sp.).
Blackberry (Rubus sp.).
Water Oak (Qercus n/iJra).
Scrub palmetto (Sabal megacarpa).
Viburimu nudum.
BuHcti 97
Introduced Species:
Coffee (Cofea Arabica.
Pomegranate Pit ica ranatit).
Allamanda IA/alamaida ncriiiolia .
Honeysuckle (I oniccni japonica iaHia/n
Ficts altissina.
Ficus sp. (from Costa Rica .
Oleander (.ctron 0[cadcr).
Cultivated pear I -'rts sp.).
Lilac 7S3ltbga sp.
Banana shrub hic/lia inscata).
Camellia, often called Japonica, Catomc/a Japonica).
Prickl, ash and mcck orange Pave again been observed infested with whitefly during October. 1 908, both at Lake City and at Gainesville. and the former has been put in Class I. Both are undoubted food plants, but the latter is leas frequent infested. A pomegranate Lush. growing near infested citrus trees in a small grove at Leesburg. was observed to be thoroughly infested during December, 190-, and again in August. 191,--whitefly in all stages being present at the time of the second observation. Coffee, allamanda, camellia. and bmna shrub were observed at Lake City in October. 19ttS, and found variously infested with whitedv. The coffee tree w a> thoroughly infested, having as many eggs on its leaves as citrus trees nas have. All larval sta;-es and the pupze were also observed. bit n empty pupa-caes. Eggs and lane were abundant on the allamanxia, and a few enipty itupa-case> were also found, indicating that some wx hiteflies had matured. Egg and firststage larx Mely were founld m the caimellia, but some eggs with all four stages of larva! were on the banana shrub, together with a doubtful pupa-case. Several larvs and two empty pupa-cases were found on smnilax near a chinalherrv tree in a small grove by Gainesville, in August. 1908. Blackberry and honeysuckle are reported as host plants of whiteflarve in winter, hy Dr. E. Ii. Sellards in the Annual Report of the Fdorida Fvperiinent Station for 1905. The water oak has 1been repoi-ted as a focodc, plant ly Quaintance and Gossard. but it is nct stated that the insect ever reaches maturity on this tree. The writer has never been able to find either e-s or larve on oaks. Professor Gossard also mentions having taken two or three larvre advanced to the third and fourth stage on scrub palmetto,3 but the writer has so far been unable to duplicate the observation. Oleander, culdtivated pear and lilac are listed by Dr. Morrill.)
PLANTS TO BE CONDEMNED.
The following plants should be destroyed by every citrus grower, and by all the people in every colmnunityx where citrus growing is an industry. These plants are, the cape jasmine, the chinaberry tree, the umbrella tree, the pricklx ash. all privets, the trifoliate orange
62 Florida A,,,riciltiral Experiment Stationl
(Citruts trioliata.), and any useless and abandoned citrus trees. The mock orange, or cherry laurel, should also be included in this list whenever it is observed to become infested. These plants are generally of little value, and can well be surrendered and replaced by others not subject to attack by whitefly. They should be cut down and immediately burned to prevent the whitefly from transforming and migrating to other food plants. It may seem akin to vandalism to sacrifice some of the ornamentals, but all successful warfare consists, in some degree at least, in reducing the number of the enemies' strongholds. One cape jasmine and two or three umbrella trees in a certain yard in New Smyrna appear to have been responsible for the spreading of the whitetly in that place, and the consequent loss of hundreds of dollars, while the plants themselves were not worth a thousandth part of the cost of the damage.
Chinaberry and umbrella trees are no doubt the two food plants of the whitefly which are most to be feared by citrus-grow ing colmtnities. It has been observed that the adult whiteflies instinctively leave these trees in August and September, or at the time when the fall brood of adults matures. This accounts for the great number of adults which swarm about the trees of some of our towns and in their immediate vicinity. Alyriads of adults were observed during A-ugnst and September, 1908, fully a mile from their presunied breeding places in and about Gainesville. The citrus trees on the Experiment Station grounds, which were previously free from whitey, became literally alive with them. These citrus trees are at least a mile from the nearest chiunaberrx and umbrella trees previously infested1 with wx hitefl). The adults were observed everywhere, in houses, on windows, and on garments ail some plants, such as collards and beans, which are not food plants, were swarming with them, but no e-s or larve were discovered on these plants. Examination during autnuin of the leaves of some of the infested umbrella trees in Gainesville, as well as in several other towns, revealed the fact that relativel few eggs ( only a dozen or two per leaf ) were being depositedl on these, while the leaves of citrus and privet were covered with thousands of e,,-s. In spring the situation is reversed, and then some of the whiteflies migrate to the chinaberr and umbrella trees from such evergreens as cape jasmine, privet, and citrus.
W\lITEFLY LIVING ON FALLEN LEAVES.
While making inspections of whitefly-infested trees at DeLand. On November 20 and 21, 1907, the writer, with the aid of Mr. R. Y. 'Winters, Assistant in Botany at the Experiment Station, made careful examinations of considerable quantities of (lead and dried leaves found under cape jasmine and citrus trees. Special attention wat given to those leaves found in small hollows, or otherwise somewhat protected against complete drying up. The result was that wellmatured larv and pupe, apparently healthy and alive, were found
Billctin 97 8
ol dead and brown leaves, which had either retained, or had been supplied with, sufficient moisture to keep them flexible. Also a living adult was found emerging from its pupa case. Some of these leaves were taken to the laboratory at the Experiment Station, and after a few days winged whiteflies emerged. On January 17, 1908, some of the fallen leaves under the cape jasmine were again examined, with similar results. Several fresh leafs twigs were collected at DeLand from the cape jasmine and taken to Gainesville. Some were placed in a cloth sack, and lightly covered ,%-ith earth at the foot of a magnolia tree. Live whiteflies emerged on March -2, when some of the leaves were still green. Other twxigs were kept under a belljar with open top, covered with cheesecloth. on moist sand in the greenhouse. Live adults were obtained at the end of txx o months, and a few of the leaves were still green. There remains no doubf. therefore, that some whitefly larve and pupe can continue to live oni leaves that have dropped from the trees during winter, and that these may mature sufficiently late in the spring to imuest time memx leaves.
RESULTS OF DEFOLIATION.
It appears from the observations just stated, that one Cause of the reinfestation of the citrus trees after defoliation at DeLand durmug the summer of 190H; was the presence of live whitefly larvae and pupmt on somc of the fallen leaves beneath the trees. All infested citrus and other food plants at DeLand had been carefully defoliated during February, 19(17, after the partial defoliation by frost in the previous )ecember, and precautions had been taken to burn the leaves. Nc doubt, however, some leaves were overlooked. Some of the trees ill which the whitefly reappeared in greatest abundance had been banked
-Ith earth, and these banks must have been appropriate places �,r preserving leaves with live larx and pupae. It is, of course, possible that some whitefly lived over the winter on other plants, but careful search in November and January revealed no plants with whitefly on them. Nevertheless, defoliating the trees at Deland xxas productive ofi much good, and prevented a damage that would have equaled manx times its cost. The results were equal to a season's spraying, Or one fumigation.
Defoliatim as a moans for checking the whitefiy in a grove cam hardhx be recommended, except when the defoliation has already been in a great measure accomplished bv a preceding freeze, or whe n one has only a few small trees. The best time in which to defoliate i. probably iln January or February, before the trees start to grow.
HONEYDEW.
A convenient method for collecting honeydew consists in placing a loaf infested with whitefly larve between two glass plates, or on I glass plate or other smooth surface, so that the honeydew projected by the larse will fall upon the glass or other surface. The honeydew
64 Florida Ag ricultural Epelruurnt Stationl
is deposited in small drops, and in case the glass is above the larwe it may be projected upwards for a distance of one-eighth of an inch. Pnpe ready to transform into adults secrete honeydew, as do larve of all stages. Larvae of probably the third and fourth stages of growth excreted at the rate of .0005 gramne each in 48 hours. One million larwe would thns excrete about a poud of honeydew in 48 hoeirs. This would be at the rate of 15 pound per month, or 1io pounds per year. \When we recall that thousands to millions of whitefly larve may inhabit one tree, xwe get some idea of the amount of sap stolen from an orange grove by this pest.
LIFE HISTORY OF WHITEFLY.
(Figs. 1, 9, 10, 11, 12-19.)
The name whitefly is a misnomer, the insect in question not being a fly, hut a member of the order i temiptera, to which the plantlice and scale insects belong. The fact that the whJbitefly has four Wings at oice separates it from the order Diptera, or flies proper.
There are three well-defined broods of white.ly, with an interva: between each brood of several clays to several weeLks, when few oi none are seen on the xxing. The first brood generally appears sone time in March, April, or May, varying with the latitude and with the temperature of the spring. The second brood emerges iin June. July, or August, and the third in \ugust, Septeinier or October. Some people have supposed that they had exterminated the whitefly by some treatment (such as the application of copperas), whn one or other of the broods had disappeared from the xxing.
Larvae (the young stages) or pupC (the transformation stage) of the whitefly can nearly always be found on the under surface of the leaves. The larva are scale-like (Figs. 9, 1l, 14-18), and closely appressed to the leaves. They vary in size from the recently hatched larva, just visible to the unaided eve, to the full-grown larva, which are one-cighteenth of an inch in length. The larva are light-colored, with a tinge of yellow, translucent, and almost ill visible on the leaf. By rubbing the under surface of a leaf length-,vise with the finger, the l rve will appear as flattened whitish scales. The pupa (Figs. 9 and 11 ) is the transformation stage from the larva to ti adult winged in sect. The l)upe are rea(lilY visible as Yellowishwhite, plump, oval bodies, with a dark reddish spot on the back. From the pupa emerg-es the adult wigcd fly. The little white cases, with a T-shaped split on the back, found on the under surface of the leaf, are the empty pupa-cases from which the adults have emerged (Figs. 9 and 11). The eggs (Figs. 1, ,. 10, 12 and 13) are just visible to the unaided eve as a fine dust on the under s-rfaces of !he leaves. An ordinary band lens or magnifying glass will show them as little bodies resembling grains of wheat. There are, therefore, four stages in the life of the whitefly: the egg, visible as a fine particle of dust;
Bulletin 97
J
//
1. '\ \, \i ,
Fig. 10. (From Bul. 67.) Whitefly (A1eyrode, citri) and insects sometimes mistaken for it. Much enlarged. No. 1. Female whitefly with expanded wings.
No. 2. Female whitefly with folded wings. No. 3. Egg and footstalk. No.
4. Empty eggshell. No. 5. Tip of abdomen of male showing claspers.
No. 6. Antenna of whitefly. No. 7. Front margin of forewing of whitefly.
No. 8. Larva of guava whitefly (Aleyrodes foridsio). No. 9. Margin, and No. 10, wax fringe, of larva of guava whitefly. No. 11. Soft scale (Lecanium
l.'.peridum. )
Florida Agricultural Experiment Station
I 6
Fig. 11. (From Bul. 67.) Larval and pupal stages of whitefly (Aleyrodes citi).
No. 1. First stage larva, much enlarged. No. 2. First stage larva. No.
3. Second stage larva. No. 4. Third stage larva. No. 5. Fourth stage larva. No. 6. Margin of advanced larva, much enlarged. No. 7. Orifice of fourth stage larva, much enlarged. No. 8. Pupa, showing orange-colored areas, and wax tufts from breathing tubes. No. 9. Adult whitefly, with wings folded up, emerging from pupa skin. No. 10. Empty pupa case
with T-shaped slit.
\ 11
ww' y
Bullefin 97
the larva, a flattened scale: the pupa, plump and easily seen; and the adult winged insect. These stages are nearly always found on the under surfaces of the leaves.
The following facts are taken from Prof. H. A. Gossard's
bulletin:3 Twenty thousand eggs have been estimated on a large orange leaf. From observation made in the laboratory, egg-laying begins when the female is from eighteen to thirty hours old, and from seventeen to twenty-five eggs are deposited. [The number of eggs is doubtless greater.] The length of life of the female has been estimated at from three days in warm weather, to three weeks in cool weather, and the complete length of the life cycle from egg to adult at from forty to fifty days in summer to six months in winter.
This brief sunimary of the life-history of the whitefly applies, in its details, to the species with smooth eggs (Alcvrodes citri) ; but also in a general way, as far as is known at present, to the species with reticulated eggs (Aleyrodcs mubifera).
Fig. 12. Eggs and eggshells of A I~rodi v ubifera. Netted surface and wide opening.
Enlarged about 90 times.
TWO SPECIES OF CITRUS WHITEFLY.
(Figs. 1, 9. 10, 11, 12-19.)
There are two distinct species of the citrus whitefly of Florida, each of which seriously infests citrus trees. In order to facilitate
Florida Agricultural Experiment Station
reference to the two species in question, it should be stated that the species with the smooth eggs is Aleyrodes citri, Riley and Howard. It is to this species alone that the citrus whitefly of Florida has until reFig. 13. Eggs of Aleyrodes cirri. Smooth surface. Enlarged about 90 times.
cently been referred. The other species, with reticulated eggs, has now been named. Aleyrodes nubifera n. sp. The reticulated egg was figured in 1893, by H. A. Morgan, in a special bulletin of the Louisiana Experirnent Station.4 Attention was first directed to an undescribed species about a year ago, when some eggs of whitefly were being examined by means of a compound microscope. A delicate net, or reticulation, consisting of five- and six-sided meshes, and which can be easily removed. was then definitely made out (Fig. 12). Comparison of specimens from different localities showed that some eggs were always perfectly smooth (Fig. 13), while others always had this net. Examinations of the first stage larva of specimens hatched from the smooth eggs, and from the reticulated eggs, brought out distinct differences between them (Figs. 14 and 15).
Fig. 16 shows an older first stage larva of the reticulated egg type, with a delicate waxy fringe about the margin. This fringe varies with the age of the larve, being absent in the very young, and about as broad, when fully developed, as the lateral bristles are long. The larve of the fourth stage (Figs. 17 and 18) and the pupa also show distinct differences. Differences between the second and third stage larva of the two species have not been made out. The empty pupa cases (Fig. 11) of the species with smooth eggs (Aleyrodes citri) are firmer and
Bulletin 97 69
remain expanded, with the T-shaped slit through which the adult emerged generally wide open; while the empty pupa cases of the species with reticulated eggs (Alevrodes nubifera) collapse when the adults have emerged. and the edges of the T-shaped slit become more or less folded inwards.
Fig. 14. First stage larva of Aleyr les Fig. 15. First stage larva of A(leynubfera befbn e development of the rodes itri. Enlarged about 100
waxy fringe. Enlarged about 100 times.
times.
The adults of Alelyrodes citri have immaculate wings, while those of Aleyrodes nubifera have a smoky-colored area near the end of the wing, easily visible in the living insect with the aid of a lens.
~j)
1/
Fig. 16. First stage larva ofA Aly"rades nubifera, witl %N axy fringe. Enlarged about 1 0 ties.
Fig. 17. Fourth stage larva of Aleyrodes citri. Photographed by transmitted light. Enlarged 45 times.
70 Florida Agricultural Experimcnt Stationt
The distinctive characters of the eggs and first stage larva can
only be satisfactorily seen by the use of a compound microscope; the remaining characters can be observed with a good hand magnifier. The following characters can be made out without the use of any magnifier.
The eggs and empty egg-shells of Aleyrodes citri generally appear like a whitish dust on the leaves, and the tendency is for them to be collected near the mid-rib (Figs. 1 and 9), except when the eggs are very
numerous on the leaves.
The eggs of Alevrodes ni bif era (tfae
cloudy-winged whitefly) generally have the appearance of dark or black (lust particles, and the tendency is for them to be distributed away from the mid-rib and towards the margin of the leaf (Fig. 19).
Aleyrodes n7ibifera
is at present known to occur at the following places: Bartow, Bayview, Clearwater, Geneva, Largo, Maitland. Mims, Orlando, Ozona, Riverview, Sutherland, Titusville and Winter Park. Until the present time, Ale v rods iiiibifera has been ob.____served only upon citrus t-rees, and both species Fig. 18. Fourth stage larva of Aleyrodes vubifer . may occur together in
Photographed by transmitted light. Enlarged the same tree, as at Bar,/ about . 4 times, tow, Largo, Maitland,
Orlando, Ozona, and Winter Park. That the yellow Aschersonia appears to thrive only on Aleyrodes nubifera, anl that the white-fringe fungus has been observed to be especially effective against this species
of whitefly, were referred to in the accounts of these fungi.
REFERENCES.
1. Berger, E. W.-Whitefly Conditions in 1906. Fla. Exp. Sta.
Bul. 88, 1907.
2. Fawcett, H. S.-Fungi Parasitic upon Aleyrodes Citri. University
of Florida, Special Studies, No. 1, 1908.
3. Gossard, H. A.-Whitefly. Fla. Exp. Sta. Bul. 67, 1903.
Bulletin 97 71
4. Morgan, H. A.-The Orange and Other Citrus Fruits. La. Exp.
Sta. Special Bulletin, 1893.
5. Morrill, A. \V.-Fumigation for the Citrus W1hitefly. U. S. Dept.
of Agr., Bur. of Entomology, Bul. 76, 1908.
6. Rolfs. P. H., and Fawcett. H. S.-Fungus Diseases of Scale
Insects and Whitefly. Fla. Exp. Sta. Bul. 94, 1908.
. Webber, H. J.-Sooty Miold of the Orange. U. S. Dept. of Agr.,
Div. of Veg. Physiol. and Path., Bul. 13, 1897.
Fig. 19. Eggs of whitefly (Alerode.x nubifera), showing distribution on leaf. x 2.
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Full Text |
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BULLETIN No. 97. FEBRUARY, 1909. Florida Agricultural Experiment Station. WHITEFLY STUDIES IN 1908. BY E. W. BERGER, Ph.D. Fig. 1. Eggs and Adults of Alcym,fe8 cit,i. x 2. From Bulletin 67. The Bulletins of this Station will be sent free to any address in Florida upon application to the Director of the Experiment Station, Gainesville, Fla. The Record Co., St. Augustine, Fla.
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DO , \l{D OF CONTRO L. N. P. l:1 1L \ .\', Chairman, Jackso11vill e, Fla. P. [(. Yo N Ct •:, Pen sa cola , Fla . T. n . K, NC, A r cadia, Fla. J. C. R\l '. ' OF.N, Live Oak, Fla. E. L \ \! , \u n1.\NX, Citra, Fla . STATION STAFF. P . H. RoLF S, I \'f. S., Dir e ctor. A. \V . HL AIR, A. l\I.. Chemi s t . JnH N" M. Scon, B. S., Animal Industri a li st. E . \V. BtRG E R , PH. D., E nt o mol o gist. H. S. F ,\WCT-:TT, M. S . , Plant Patho l ogi s t . n . F. FLorn, A. M .. Ass i stant Pla nt Ph ys i o l ogis t. R . Y. \ V 1 NT l S: R S, B. S .. Assistant in Bot a ny. * R N . W1L " O N , A. D., Assistant Chemist. Jor IN B1:LLI NG, B.Sc . . Assistant in Horti c ultur e. l \IR s. E. \ V. B E RCr-:H, Librari a n. K. l I. GtnH r\;'1-1, Auditor and Book keep e r . J . T . nERi'i A RD, JR. , St e nograph e r. \1 . CREWS, Farm F o reman. Acnn-:n D1 c K1:--; soN, Gard e n e r. * T emporary Assistant.
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DI P ORT.--\ :: \T F.--\CTS . 1. It is e as, . in Fl or icl a . t o in fe ct the whitethlan-,e ,,ith the para sitic fungi by s pr ay in g o n th e s pores at th e proper tim e . . , The proper time to sp ray ,Yith fungus spo r es i s wh e n there ar e many young lary,e on th e l ea n :s and th e \\ -Ca th e r i s b ot h moist and warm . :3. The fungi sh o uld b e put on the tre es as earl y in th e season a s po ss ibl e . in order that their grcmth may Le h e lped by the s ummer rain s . -1 . If th e fun g i ar e app li ed late in the ~eason. th ey \\ ill probably n ot in c rea se s uffi cie nt]~ until the next year. ,j _ During the 11 i11ter it is somet im es ad vi ~a bl e to s pr ay badly infest e d trees with c on tact in sect i c id es. G. It is much cheap er t o k ee p the whiteHv o ut o f a community or out of a grove. if p oss ibl e. than to co iltrol it after it has onc e enter ed. The Ex p e rim e nt Station has 110 fond~ aY a ilahle for d istribut in g th e \Yhitctly fungi. Thes e fungi can \.o btained. h o\\eve r. from p1 ivatc indi,idual s.
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CONTENTS. Introdu c tion ........... .. ..... ... .. . .. ... ..... .. ........ . Means of Control. ... ... . . .... . . ..... . ... .. .... . . ........ . . Fungus Parasites of \Vhitefly .. . .. . ..... .. ....... . ......... . How Fungi Propa gate .................... . .... . .......... . 1'fethods for Introducing whit efly Fungi .. . . ..... .. . ........ . Spore-spraying M e thod ......... _ ...... .. .......... . .. . . Leaf-pinning :'.\' Iethod . . ...... . ...... . ......... .. ...... . Tree-planting Method .. .. .. .. . .. ... ....... .. . .. . .. . ... . Conditions Favorable for the Fungi ......................... . \Vhcn to In t roduce Fung;i ..... .. ...... . ... . . . .......... . ... . Success in Introducing the Fungi . .... .. .. .. .. ..... .. ... .. .. . Efficiency of th e Fungi ..... .. . .. . ...... . ................. . Plan of Campaign .............. . ....... . ................. . here Fungi can be Obtained .. . ... ..... ...... .. .. .. ...... . The Fungi ....... .... .... . .. .. ......................... . . Reel Fungu s of " Whitefly ... . .. . .. . ... .. ..... . ...... . . . . . Yellow Fungus of Vvhitefly ... . . . ... ..... ... . ........ .. . Brown Fungus of \,Vhitefly . . .. . . .. ... .......... . ...... . \i\/bitc-fringc Fungus of \Vhit efl y . .. ......... . ...... . ... . Cinnamon Fungus of whitefly . ...... .. .. . ..... . ... . .. . . Sporotrichum Fungus of \Vhit e fly . .... . . . ... . ... . ...... . Fungu s Super-Par as ites .......................... . ... . Sooty Mold ..... .. .. .. ... ... ... ... . . .. . ........ ... .. . A rtificial Means of Control ... . .. .... . . . ........... .. . . . ... . Quarantine . ... .... .. . .. .. ........ . ....... ... . . .......... . Food Plants of whitefly ........... ... ................. .. .. . Plants to be Condemned .. . . ........ .. ..... .. .. ............ . \,Vhitefly Living on Fallen Leaves . . ...... . ...... . .......... . Results of Defoliation .... . ............. . ......... . ....... . Honeydew ........... . ......... . ... . . ... . . .. ..... ... . . . . . Life-history of Whitefly ... . ............................... . Two Speci es of Citrus vVhitefly in Florida ........ . ..... . ... . References ......... . .. ...... .. . ...... . ...... ...... . . . Page. 43 43 44 45 45 46 48 49 50 50 51 ,51 51 53 5-1 ,55 5G 56 58 ;""59 60 61 G2 63 li ,q ,) 64 67 70
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WHITEFLY STUDIES IN 1908. RY E. \\ " . BERGER, Ph. D. l:'.\'fRODCCTIO X . The pre s ent bulletin includ e s a revision of Bulletin 88, i ss ued in January, rno~. 1 anc\ also a rep o rt of progre s s. During HlOS the \\hiteHy has c o ntinued to ,;prcacl to citrus-gro1Y ing s ection s of th e State 11 hich hac\ n o t hith e rt o b e en infest e d. V e hicles, railroad train s . a nd in fr ,-;tccl nur se ry ,;t o ck ar e perhap s the chief m e ans by which it i s ,prcading t o all those parts of the State where citru s fruit is g-r o 1Yn. o r ,rhe1 e it s o t her fo o d plants arc fo und. \Vhi] e a few citrn s -gro\\ c r,; s till tr e at the s pread of the , rhitcfly as in s ignificant. and b e lieve that it 11i1! dis a pp e ar of its o wn accord. this numb e r does n o t includ e th e 0 1n1 e r s and mana~ er s of th e large r prop erties. The s e are g reat]~int e rested in and rc:1d y to aclnpt s u c h mean s a s rromi s c r e lief. }JL\:'.\ S O F C O:\'TROL. Th e m e an s of c o ntrol a re fir s t. natural en e mi e s: and se cond, artificial method s . . \.m o ng th e n a tur a l e ncrnic . , of ins e cb arc f t111g i. bact e ria. and pr e da c c o u s inse c b. l\act e rial di,-ca,s cs of the 1Ybitefly ar e at pres e nt 11nkn o wn , hut the known fu11g11 s di s ea se s o f thi s in se ct ar e seven in number. S e veral pred a cl us insect:-; ar e abu k1101y11 tu feed o n the larv~ of the whitefh . The artifici a l ;11e a 11s for c o ntr u lling insect,.; incl11d e contact in secticide s , stom a ch p o isons. a nd fumig ati o n 1yith a p o isonou s gas. The whitefly can n o t b e killed by s t o mach p o is o ns. s u c h a ,; c o mp o unds of ar s eni c . s inc e it is a s ucking in se ct and draw s it s fo o d from the interi o r o f J e an ' s by mean s of a be a k. Spraying solutions 11hi c h kill th e in s ect h) co ntact. and fumiga t ion. arc th e r e fore the artificial m e thods for combating thi s p es t. FVNGlTS PARASITES OF WHI'I'EFLY. Fungi are a mong th e lowc;;t plant s knQwn . Th e y are devoid o f th e green coloring matt e r which i s characteristic of high e r plant s . }J ushro o ms. toadst oo l s, rnild e \\'s a nd m o ld s ar e familiar example s . As regards th e ir method s of fe e ding. fungi may he either par a sit es o r s aprophyte s . Fungu s parasi te s infe c t a nd o ft e n d e stroy living pl a nt s or anirn a b. Th e ,Yith c rtip fungu s of citrus tree s a nd th e rn s t of tomat o es a re familiar e x amples of fungi which liv e on plants . The s e ven fungu s p a ra s it es o f the whitefl y , als o th e r e d headed sc a le fungu s , the white-headed s cale fungu s , and the black s cal e fongu s, ar e examples of fungi inf e cting insects . S a prophytic . fungi are tho s e that grow only on dead org a nic matter. The s e inclncle most of the fungi growing on rott e n wo o d. or o n the ground in field s or fore ~ ts. Toadsto o ls, mushro o ms , and the molds of bread ar e familiar e xampl e s .
PAGE 6
44 Fl o rida Agricultural E.ipcri1n e nt Station The fongus body produced on a whitefly l a rva i s spoken of as a fungus pustule. Such a pustule is limited in it s growth by the amount of food furni s hed by a single larv a, so that th e pustules can not in crease beyond a certain size. Their si z e varies with th e si ze of the larva attacked. The l a rg est pustules are about three-sixteenths of an inch in diameter, while the sma ll est are sma ller than a pin' s h ea d . Six fungus parasites are at present known to inf e ct th e l a rv ::-e of the whitefly, a nd a seve nth infects both larv ::-e and ad ults. The follow ing table gi v es the com m on a nd scientific n a m es of these fungi, with the dates of their discovery on t h e w hit efly in Florida: 1. Red fungus of w hitefl y (,-lschcrso11ia alcyrodis vVebber) 189:1 2. Brown fungus of whitefly ..................... . .. . . 189!i. :3. R ed -headed scale fungus ( S phacrost!/be cocco phila Tul.) 1 9 0 8. 4 . Y e llow fungus of whitefly (Aschersonia tlm 1 0-citrina P . Henn.) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 190G. 5. White-fringe fungus of whitefly (M irroccra s p.).. . .. 190,. 6. Cinn a m on fungu s of whitefly ( Vc rticilliu1n hctcro cladu11t Penzig) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1907. 7. Sporotrirlw1u sp . . , similar to the c hin c h bugfungus ( S. globnlifermn), infects the aclt1lt whitefly a ncl s ome of the larv::-e . . . . . . . . . . . . . . . . . . . . . . . . . . . 1908. Th e first s ix fungi, when pr esent , a r e found on th e under surfaces of whitefly-infested ci trus l eaves, and kill the larv~ , tr a n sfo rming them into pustules w hich ha ve the color and appearance characteristic of the particular fungus. Th e red-headed sca l e fungus i s o nly o cc a si on ally found infecting whit efly larv~. and will n o t be further di s cussed in this bulletin. So far, no fnngu s capable of infectin g th e eggs of the whitefly ha s be e n di scovere d . \,Vith regard t o th ese seven fungi, r efere n ce may b e mad e t o Bulletin fl L" a nd also to Special S tudie s, No. 1, l: niver s ity of Fl o rida. 2 H OW FUNGI PROPAGAT E. Fungi m o r e generally propagate b y spo r es than in a n y ot h e r way. The spores of fungi are minute microscopic bodies produced in countless millions. a nd a r c m ost l v u sed w h en we desire to s tart a n ew growth of fungu s . They take" the place o f the s ee d s produced : by the hi gh er pl a n ts , hut d o n o t have the same s tructur e as seeds. A singl e spore i s in vis ibl e to t h e unaided eye. The sp ores o f two of the fungus parasites of the whitefly. the reel a nd th e y ell ow fungi, : are boat-shaped and pointed at both ends. Abo ut 1, 7 00 of them •could be placed end t o en d al o ng a line one inch lon g , and more than 8,000 c o uld be a rr a n ged side by side along th e s ame lin e. About 13,600 ,0 0 0 of the se s pores cou ld thus be arra n ge d upon th e surface of a squa r e inch. T h o us a nd s of spores are borne in e ach bright red or yellow pustule o f these fun gi . Thes e spores are washed out when the Aschersonias a r e plac ed in water. Some fungi may
PAGE 7
Bulletin 97 al so be pro pa ga t e d by porti ons of the thr e ad-lik e g ro, , hs which m ake up the m ass of t he fon g u s. This method o f propagati o n is an a l agous to the p ropaga ti on of th e high er plant s by cutt in gs. A go od illu st ration of thi s is the use of "sp aw n" fo r prop ag atin g the common mushroom. T hi s spa wn co n s i s t s of dry fragm e nts of the und e rg roun d gr o wth of the mushro o m em bed ded in manur e or ot her v eget abl e matter. 1 Yh et her any of the fun gus par a5 ites of the white fl y are p ropag at ed in thi s ,, ay ha s n o t be e n d emo n s tr ated; but the peculiar nct,York of thr ea ds of the bro\Yn fungus ,, hich exte nd s ov er th e citrus leav es. and e ven o ,er the leafsta lks. s ugg ests that t his fungus may p e rh aps b e propagated by fragments o i these thr ea d s b e in g carri e d by th e ,,ind. by i nsect s , o r ot h e nyi se . from o ne l eaf to an ot her. METHODS FOR I~TRODCCI::.ZG \\ ' HITEFLY FL::\GI. Ther e are three methods ,, hich have been u se d for introdu c ing th ese fun g i int o whitefly-inf este d tr ees. Th ese ar e the spore-s pra yi ng m e th o d, the leaf-pinnin g method. and the tr ee -plantin g m ethod . T hese m et hods are ba se d m a inly u po n experiments with the reel. y ello w, and brmvn fun g i . SPORE SPR.\ YI XG l\fETHOD. Thi s method is th e best one of the thr ee. It co nsist s in wa s hing th e s pore s from fungu s pnstul es b y m ea n s of wate r , a nd t h e n spray ing th e mix t u1 e of s pores a nd ,vat er on to th e und er surfaces of the whitefly-inf e sted l e ave s . ( Th e writer's earli er su cces sful ex perim e nts with thi s meth od \\'ere mad e a t Lake City in Jul y , and at L ees burg in A.u gu st HIO G, \\ ith the spores of the reel A sc hers on i a.) . -\bo ut fort y of the bri g ht r eel or yellow p u s tule s o f th e fongu s sh o ul d be u sed t o a pi nt of \Yater. Thi s w ill b e about the sa me a s o ne or two fungus-bearing l ea \'e s to a quar t of water. :\l ore fu ng u s may be u se d if proc urabl e . but the amount indicat e cl has bee n fo und to g ive good r es ult s. I mm e r se the fungus-bearing l eaves in \Y ate r , and st ir occasio n a ll y dtffin g ten or fifteen minutes, th en s train the liquid th ro ugh che esecl o~ h or fine wire gau ze . v Vh ile spraying the mi xt ure of spo re s and wate r o n to th e under s urfa ces of the whi tefly -inf es ted l eaves, l oo k \Yell to the nc1\'er growth, esp ec ially t he water sprouts. Thi s youn g g ro 1yth i s gen e rally most in fes ted w ith the y o unger ,, hitefly lan a~ . s in ce th e ,, ing e cl fem ales ah, ays seek o ut you ng leaves when dep os itin g their eggs. Tt sho uld b e r emem b ered th at the y ot mger l a n-,e a r e mor e e asil y infected with the fun g us th an th e o lder l arvx. T f th e s upply of fungus i s limit ed . .;p r ay o nly the ,1 r s t in feste d tw igs and br anc hes: fo r th e fungus will infect so me of the lar v~ . and the adults maturing from those n ot inf ec ted, together with ot h er adult s mi g ratin g there , will carry the fun gus spores t o o ther part s of the tr ee and t o other tree s . It i s considered b ette r pr ac tice to sp ray th e inf es ted parts o f a ll tr ees with a w eak mixture, than to
PAGE 8
Floridc, Agrrnlt11ral Ex perim en t Statio11 spray only a part of th e tre es in a grove with a stro ng mixture. Cse a n ew spray ing ou tfit , preferably one of th e co mp resse d a ir typ e ( ;{ or J ga llon s ca pa city) . with n o copper or br ass about it exce pting the n ozz le. The fin e r the sp ray, the bett e r; sin ce it i s o nly necessary jttst t o wet th e l eave,;, and wh at eve r liqni ll nm s o ff is l os t. On no account s h o uld the sp r ayi n g so luti on b e permitted t o stand in a copp er or brass vessel, since an e xceedingly sm all amount of co pp er in so luti o n w ill retard o r destroy th e ge rmin ati ng power of the spo res. Do not use an out fi t which has b een previously u sed for spra y ing Bordeaux or othe1 str o ng fon gi cicl e, s inc e a very s mall a m o unt of fun g i ci de left in the machine m a) ~ kill t h e spo r es. , \n old spray in g o utfit w hich h as been u se d only for soap so lut io n s o r oil emulsions, may b e empl o yee\ ; but it should be well wa she d out. A larger spec iall y made sp ra yi n g machine m o un ted on a barrel may b e used when many acres arc to be spraye d an d when an ab und ance of fungus i s avail a ble. A . si mpl e m od ifi catio n of the s pores praying method consists in fli rting t h e liqu i d against the under su r faces of the le aves by means of a tin c up. A wisp broom has a l so be en employed, or a bun ch of sma ll twi gs dipped int o the liquid . Cost of in troc lu cing fttngus by this methocl. ~ Thi s will va ry w ith th e s ize of the t r ee s. One corr esp on dent reports that it has cost him two ce n ts p er t ree to sp ra y hi s grove of m edi ums ized trees . In a n ot h e r case it i s costi n g one cent per tree to spray; b ut. in thi s in sta nc e . the fungus was pr oc ured at th e s light ex pen se of picking it from othe r trees. 'J' he w rit e 1 h elped to spray ,i;;o mediums ized tre es du ring the last week of September . 1 !10:-i, wit h spores of the r ed fungu,;, using a bout o ne gallon of liquid per tr ee. "" \bout e ight fungus-bearing leave s ,, re used to prepare a ga ll o n of this liquid. The leav es cost $ I p e r t hou sa nd. T hi s made the total cost per tr ee. fo r fun g us and lab or . ab out ;; ce nts. .\ 11 all-iron s prayp ump. m o unt ed o n a b a rr e l. was u sed for sp rayi ng t hi s grove. ' l'his m et hod is a ppli cab le t n a ll t h e f1n1:u s parasites uf the w hitefl y: when they are in th e spor e -bearin g stag e . 'l'h e brown fun gus do es not a lway s h ave spores: h e n ce th ere i s m o r e o r l ess nncertaint y w hen one attempt s to i nt roduce it b y the spore-s p raying method. Some excellent growths of th e brow n fttn gus ha ve, how ev er. been started b _v this m et hod . u,;.\F1 '1:\'!\l l ,\'(; ~ JJ ('l'Jlt>JJ. This meth od is con sider e d se co ncl b est. I 11 introdu ci ng illngus by this means . the writer has u sua ll y pinned from two to a doze n fungus-covered l e aves to th e under surfaces of l ea ves of a whit e fly in fes ted tree. In Bull et in 88 . 1 the writer recommenclecl t hat ea c h leaf s h o uld be p inn ed with it s und e r . o r fun g u s -cover e d s ur face , facing d ow nwar d. L ater obse r vations have con firme d t hi s as the proper w ay to pin th e leaves, si nce t h e adult whit efl ies creep over th e under
PAGE 9
B11llcti11 97 s urface s of the leave:;. and in so doing pr o bably g e t m a ny of th e spores attach e d to th e ir feet, a nd then carrv th e m to other leav es . For the sa m e r easo n the l e aves s h o uld b e pi,;ned to those part s of a tree wh ere the adult whit e fli es ar e m ost abundant: that is, o n the n ewe:; t gro,vtl1. lt mi g ht a l so b e ,v e il to pin th e lea ves so that th e drip from th e m, wh en it rain s, ,1 ill run onto a clu st er o r se ver a l clu s t e r s of l eaves ben ea th them. . \t all eYe nts. ,re so metime s find t hat fnn g us st arts to develop o n t he l ea v es of clusters underneath the l e av es pinn ed o n. Since th e adult \\ hitefly appea rs to he i nstrurne nt al in the distri lmti o n of fun g u ,; ( thi :=probably applies mainly to the re d a nd yellow fungi) \\ e , rn utd e xp ec t t o get the bc,;t results ,vith the l ea f-pinnin g meth o d a t th o;;e time s ,1h e n adult s a r-c most abundant in the tree s . Such is the cas e: for late in the fall wh e n 110 adults o r o nh a f ew ,ver e a b out . n o grn,vth of fungHs. or o nly a v er y p oo r growt h, r es ult e d frorn pinning on the fu ngu s -c ove r ed lea ves: whil e in mo s t in sta nc es promising grO\rth s of fun g n s re s ulted from spraying t he spo r es . Similar o bsenati ons e re mad e a t o ther time s \\hen f e 11 ad ul ts wer e o n th e ,ving: and th e n on !:, a rest ri c t ed g-r o 1vth o f fungu s resulted from pinnin g o n l ea n•;;, "hile a ,1id e -spr ca d grm,th came as a co n se quen ce of spray ing th e spore,. Ot he r c ra ,v lin g and flying insect s a re a lso probably instrum e ntal in distributing fun g u s s pores. ( Th e l eaf-p inn i n g mcth ot l may b e t1 se d with a ll th e \Yhitefly fun g i.) TRJ.; J : -PL\ ?\' 1'1 ~G )11 \' l'H OD. S m a ll whitclfr infc s ted trees, having an a bundanc e of a whitefl destroying fungu ~ o n their lea ves, hav ~ b ee n t e mp o raril y planted b y ;c;ome of the cit ru s g rcmcrs . so th at their foliar;e came in c o ntact with that o f the in fested tr ees i11to , d1i c h it ,ra ,; desired to introdu ce th e fun gu s. , \'h e n n e cess a r,1. t he se tr ees \Y e rc plant e d in pot s or tub s , a nd elevated on platform s. Thi s m e th o d of introdu ci ng the fun g i. a lth o ugh us efu l. is n ot so a
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-l-8 Florida Agrirnlf 1t ral Expcri111 en t Station arranging condition s in a citrus g rove to prornotc d a mpne ss of the air ab o ut the tr ee s. Pl e nt y of v eg etation ( tre :.:s . shrubs, tall grasses, etc.) around and in a grov e will d o this to a great e xt e nt. Tree s and shrubs s hould be arranged as windbreaks. while grasses or beggarweed sh o uld be permitted t o grow tall and rank, as a c o ver crop at th e prop e r time. Mulching aro und a nd betwe e n the t ree s w i ll al s o h el p to conserve moisture. Wh e rev e r a n irri g atin:s m 1tfit i s emplo_\-ecl. tli e tr c cp e nt wet tin g of the tr ee s o r tli e s o il in clry weather would a cld tD the e ffi c ien c y o f th e fun!?,"i . Such a use of the irril':_a '.i ng o utfit w i ll also r e du ce "red spider'' 'anti ru st -mit e . a nd fav o r 'the 7tctivitics of th e s1 1 a ds w hich feed on th e s oo ty m o ld. \ V an n th is a n e ce ss ary condition fo r the rapid . developm e nt o f th e fungi . This c on diti o n is g en e 1all _y re ali z ed in Fl o rida from th e beginning of April until O ct o ber. During this period th e fungu s pa ras ites of th e whitefl y thriv e well if the warm weather i s ac c om pani e d b y enough rain . C a reful o b ser vations cl nring th e cooler m o nth s . from Septeml:.er o r Octob er to March, indica te that the fungi g row and s pr ea d but s l ow l y durin g thi s p e ri o d. notwith s ta11din g that either rains o r heavy d e w s ma y s upply much moi st ur e. WHEN T O INTRODUCE FL '.NG I. The period o f summer r a ins. which of ten l as ts fr o m June to September. i s generally the be st time in which to brin g th e fungi into a grove: hut th e stage o f dev e lopm e nt o f t he whitefl y larv, e i s al so import a nt. E xp e rim e nt s with the reel and y e llow fung i , b y th e spore spraying method. on J anua r y 1 7 and March \ ?. HJ08. in trees in which th e whitefl y had a d va nc e d t o the fourth lar va l o r to the pupal stage, did not r es ult in an y growth o f fungus. Similar e xp e riments made o n October :3. lHOG, and Nove mb e r ; !!). l!HI ';' , with the s am e fungi and th e s p o r e-sp ra y ing m e th o d, r es ulted in some growth o f fungu s . n ot withstandin g th a t the comlitions of moi s tu re a nd temper ature were n o m or e fa~orablc for fungu s g-rowth during th ese m o nth s than during Januar y or I\1arch. But yo ung larvce are p1 c sent in considerable number s until D ec ember and som et im es later. and the se ar e appar e ntl y m o r e easily infected t han are th e o ld e r larv ce or th e pup ce. Thi s ma y account for the failure to get a g-r owt h of fungus in Jannar y or M a rch. when y o nn g larv x ar e v e ry s carce o r a bs en t. No e xp e rimen ts hav e b ee n m ad e during D ece mb e r and Febrna1y: but th ese two m o nth s r es embl e J a nu a r y . and :\lar c h so closely both in reg a rd to c limate a nd th e condition of th e whitefly larv ce , th a t probably littl e o r n o s ucc es s would be r.>btained. Experiments with th e sa m e fungu s b y th e sa me method at D e Lancl o n A pril n and 22 . 190 8. in tre es in which th e whit e fly wa s mainly in the first and s e cond larval s tages, ju s t af ter th e disappearance of t h e s prin g brood of adult s . re s ulted in a hea vy grow th o f fun g u s, and by th e 17th of th e following Jun e a third to a half of the whitefly larvx had b e come infected and were dead. Shower s of rain imm e diately followed or pr ece d e d so me
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B11ilcti11 97 49 of these s por e -spr a yin gs . and \\ re probably fa ctor s 111 bringing about the r es ult. To sum up: the b es t time t o apply th e fungi by th e spore-spraying rne t h o d i s e n the lan a? are young (that is in the fir ,t, seco nd, : 111d third stages) a nd abundant. This tirne e xtends fr o rn _\pril or earlier . until :S-:ov e mb c r a nd p er hap s D e cemb e r. During a s h o rt t i me in .\l ay o r June. just before and durin g th e period of i ss uin g of the S<'L'
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; j(J Florida .-lgrirnltural E xpcri111cut Statiou s ends an account of his success in inf e cting th e whitefl y in his g ro ve with the r e d and brown fungi. a nd s tates that, in m a ny cases, th e fungu s growths on the sprayed tree s were equal to tho se o n th e l e ave s u s ed for pr e paring th e mi x ture of spores and water. H e ex pect s to repeat th e spore-spraying a s s o on a s _young l a rv a: are present in the spring, and find s it an ea sy and inexpensive treatment. EFFICIENCY OF TH E FU:\'GT. Our inve s tigati o n s show that the whitefly is not an insurmount a bl e o bstacl e to th e profitable growin g of c itrus fruit s . \Vh e n l e ft without a ssist a nce. th e fun g i will practic a ll y destroy the whitefly in a grove, on the average, once every thr ee yea r s; thu s r ed n c ing th e injury due to the whitefly by at lea s t on ethin!. The destrnction i s not complete, so that the in s e ct s increa se a ga in during the two s uc ceeding y e a rs: but this is a c co mpani e cl by a rapid incr e as e of the fungi, nntil th e whitetl _ 1 1s again overwh e lmed . This is the c ours e run by the whitcJly and t h e fungi when un ass ist e d in those sect i o ns which have bce11 long es t in feste d. such as l\f anatee county. Fort 2\Jyers. an d u ce more . , e:-pec ially should an abundan c e o f see d-fungu s be readily o btain a ble. The 1:;reater the amount of fungus growth which i s suc ce s s fnlly s tart e d in a grov e , t h e more 1apicl will be th e rk,-truction of the whitefly. Th ese ins ecb hav e a habit o f c o ngrega t ing; on water-sprouts and other tender growth of ci trns. eonseqnently we should givc parti c ular att e nti on to i ntroducing; the fungi int o s uch part s of the t r ees. 'l'b c wnrk shou Id h e don e me t h od i ca ll y a nd n ot in a hapha za rd way. The plan o f camp a ign for a grov e just b e c o ming infested with whitefly. or only infested in p a rt. w o uld be to introdu ce fungus int o
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Bnl/ e tin 97 3 1 all tho se tr ees s ufficiently in fested ( that i s, a s core o r more of larv ~ on each l eaf ), and later on into othe r tr ees a s soo n a s they become s ufficiently infe s t e d . Thi s o p e rati o n s h o uld be r e p ea ted each year, or w h enever th e wh it efly i s o b e rv ed to be in s uffici e pt abundance to a ll o w of a good g rowth of fungu s b e in g s tarted. WHERE FUNGI M Y BE BO U GHT. The Experiment Statio n h as n o fund s available for co ll ect ing a n d di s tributing fun g i. T h e money app r o priat ed by th e U. S. Congre ss fo r the maint e nance of Experiment Station s i s fo r the purpo se o f defrayi n g th e expe n ses of actua l expe rim e nt s and inv e ti gations p e r taining t o agricultur e . As th e c o ll ec ting and di s tributing of well-kn ow n fungi i s n o t an expe rim e nt , it co uld not b e carr i ed o n wit h thi s m o n ey. The State Legi s l at ur e wo uld apprnpriate money fo r s uch w o rk . if the c itru s growe r s co n s id e r ed it desirable t o do so. But s uffici e nt funo-u s mat e rial ca n ge n e rall y be o btain ed fr om pri v at e so urc es. The fo ll owi n g gentlemen h ave co n se n ted to furni . h fung u s whenever th ey ha ve it ava il a bl e . The cost w ill vary. but from two t o fo ur dollar s wi11 ge n e rall y pay fo r an amount s uffi cie n t t o tr ea t a n acre o f grove . R eel . ye ll o,,. and brow n fun g i: C. A . l:loone. Orlando, F l a . Red a nd brown fu n gi: A. J. Pett i g r ew, :'.\Ianatee, Fla.; A. F . vVyman, Bradentown. Fla.; F. D. \ i\ T aite . Palmett o . Fla. Reel and ye ll o w fun g i: C. D. Th o rn to n . Orlando. F l a. Red fungu s : F r a nk H. Davi s, A p opka, F la .; J o hn F. Car l ton . Sparr, F la. Ye ll o w fu n g u s : \ i\T. H. ::vraxwell, Titusv ill e, Fla. It may be m en tioned h e re that 3.000 ora n ge l eaves wi ll l oose l y filJ a b u s hel m eas ure . TH E F UNG I. RED F UNGUS OF WHI'l ' EFLY . Fig. :3. R e d Fungu s of Whitefly. x l .
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52 Fl or ida A g ricultural Experiment Station As the nam e implie s , th is fungus i s red and when at it s height of spore-formation bright r e d, this ext ra r e dn ess being clu e to th e mass of s por e s. Befor e it rea c hes th e spore-producing stage, it is yellowish in color, and b e come s a faded pink w h e n th e s p o re s ha v e b ee n washed away. This fungu s growth or pustule is ge n e rall y sur rounded by a l ig hter-c o lored fring e cl os el y appr ess ed to th e leaf , while th e pu st ular part projects . Th e exact det a ils of the proc es s by mean s o f which a whit e fly lar va becomes inf ec ted b, th is fungu~ have no t be e n observed, but th a t the inf ect ion p ro c eeJs from the devel op ment o f a sp or e of the fungus, l o d ge d o n or n e ar th e larva, h as been clemon s trated bey o nd doubt b y hundred s of e x periments with the s p ore -spraying method. Fi g ur es 3 5 , taken fr o m Dr. H. J. V/ebb e r 's bull e tin! s ho w many details i n r e gard to th e manner of d ev el o pm e nt o f thi s fun g u s in th e body o f th e whitefly l ar v a. F ig. 8. (Art e r 11Pbb e r.J \\'hit e!l v l1trva wilh 1 e d fun g 11 s (o) g-rowing ln c'id e its h o dv. T he h tr, a is ctyiug n r'den.d. x 1 : -,. fl . s: -1 . ( After \Yebl.> e r.) Lut e r .-.. ta ,!!e. Th e f11ngn..; 1ltr catls A. r e tH :t~ II _ gri . 1w in~1,utuftlted eu d la 1Ta . X 1 h . Fi!.(.t1. 1A ft r\rehher. ) Rt ill lu te r ~ 11 1 . ~e 'f!J"' s po r e mas~c ls f,,rm n hruke11 ri u r1,1111d t h e d e 11d lnnn . X 1 5 . T hi s fun g u s appea r s to thri ve eqnall y on both sp e ci es of the c itru s whit c tly, but has mo s t fr e quently be e n ob s er ve d upon th e sp ec ie s wit h th e s mooth eggs ( A fry rodes ci tri). T h e red fungus c an be introduc e d b y an y o ne o f the thr ee m e th o ds alr e ady cl esc rib e cl. and is very effecti v e. It re q u ires ab o ut thr ee week s fo r thi s fun g u s to mak e vi s ible growth. but und er th e m os t fav o rabl e c o nditions growth h as s e veral times been d e tect e d in t e n clays. YE I ,LOW FUJ\"CliS OF WHITEFLY. T hi s fun g u s i s so much lik e th e r e el fungT1 s th at what ha s be e n writt e n and figured in r eg ard to t h e latt e r h o ld s tru e for th e for m er . It s color. how eve r . i s a ri c h l e m o n ye llo w , so th a t it ca n easi l v be di s tingui s h ed fr o m t he reel. esp e ci a llywhen b o th are in the s 1 i or e -pro ducin g sta g e. It w as first cle sc rih e cl from spec im e n s obta in e d on guava lea ves in Brazil, a nd wa s fir s t r e cognized in Fl o rida by Pro f es sor P. H. Rolf s in S ep te m ber. Hl06. Thi s fungus ap pe a r s not to thriv e so we ll up o n the smoot hegg ed s p ec ie s (Alcyrodcs citr i) of tlrn
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Bitlletin 97 53 citrus w hit efly. Whenever the wr it e r o b e r ved it e ffectiv e l y inf e cting:: whitefly lar vc.e, it was o n th e spec i es w ith r et i c ulat e d eggs . All effor t s. . o n the part of th e w r iter t o introduc e it effect iv e ly on the species with s mo o th eggs ha ve so far fa il ed. It ha s b een found possible to infect a few larv c.e, but th e fungu s did n ot incr eas e and thrive, and this. happen ed when the red fungu s, int rod u ced at th e same time and close by , grew and th rove we ll. This fungu s can be i ntroduc ed by any of th e three method s and h as been o b served to be ve r y effec tiv e o n the whitefly with r e ti c u lated eggs ( Aleyrodes nubi fera). The spo r e s pray ing m et h od i s to be preferred. BROW FU_ GUS OIi THE WHITEII L Y . Thi s fun g u s develops into pustu l es of a g l ossy chocolate brown~ a l though some ti mes it is quite light in co l o r. It r esemb l es in co lor and s hap e the Florida r ed sca l e of th e ora n ge, Chrysompha lus (Asp idiotus) ficus, and may eas il y be mistake n for this in sect. The brown fungus differ s in o n e r ema rk ab l e r es pect fr om all th e o ther kn o wn fungus para s it es of the w hitefl y. The fungus growth w hicli . d eve l o ps up on a s in g l e whitefly l a r va, in stead of b eing li mited in it s. activitie s to thi s o ne lar va, sends out h un dreds of ramifying fungus thr ea d s ( h yphae), which will inf ect o th e r larv c.e if the y are s uffi cien tly n ear. From these inf ected lar vc.e mo r e thre ads ramif y until the w hole un de r s urfa ce o f the l eaf is covered with a n etwo rk o f fun g us threads,. which whe n peeled off, has much the appearance o f ve r y thin tissue F i g. 6 . Brown Fungus of Whit e fly. X l . pap e r. Thi s fun g u s ti ss u e may also s pr ead t o t h e upper s urface of the l ea f and down along the l eafsta lk, even o nto the s tem s of the twi gs . Th e b rown fungu s appears t o th ri ve o n b ot h species of but ha s been mo r e fr eque ntl y obse r ved up on the s mooth-egged spe cies (Aleyrodes citri). It h as b een s u ccessfu ll y introduced by means of
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Florida rlg ricult11ral Expcrimc11t Station a JJ the methods described on a former pa ge; but s inc e the r ed and yellow Asc h e rs o nias lend th e ms e lve s m ore readily to experimentation because of the ea se with which th eir spo r es m ay be ob tai ne d , th ese hav e na t urall y b ee n exper im e nt ed with first, possibly to the neglect of th e brown fungu s . Th at th e latt e r can readily b e introduced onto non-infected whitefly lar va: by the sp ra y ing m e th od, ha s be e n demon st rat ed a numb er of times by th e writer and other s. The most su ces sful of th ese introductions h ave probably been made by !\fr. H. 13. Stevens, at DeLand . during July. mos. and by Mr. Edw in \ V . J ohnson, at E as t P alatka. E.,p eriments so far indicate that we have th e mo s t favorable conditions for introdu c in g th e b row n fungu s durin g Jul y and A u g ust. Until more d efi nit e in fo rm a ti on in re ga rd to the s por es ':l f thi s fungus is at hand, th e writer recommends that the fungus be sco ur e d o ff the l eaves b y means of a little sand and wate1. and the r es ulting mi xt ur e of fungu s p a rticl es an d wat er used a s a sp r ay . A b ont the sa m e relative quantities o f fungus a nd water s hould be taken as rec o mm e nd e d fo r t he red a nd vcllow Aschersonias. a nd if neces s ary th e mixture may be strai n ed . W HI ' .l'J~ 1-'RINGF, FU!sCl J S OF WIII'l' l ~ FLY. Fig. 7. Whit.e-tringe Fungus on \Vhitefly (Ale!Ji'()i/c. q nulr i fcrn) . So oty mold round se v era l l ar vre . This fun g u s ha s b ee n o nly recently r ec og izecl a s an eff ec tiv e parasite of whitefly l a rv ce. 2 It was o b served that fr o m 70 to DO p e r cent. of the larva: in certain tr e es wer e dead, appar e ntly through infection by this fun g us. Th e wh i te-frin ge fungus is not conspicuous t o th e unaid ed eye, as are m os t o f the o ther fungu s parasit es of the
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Bull e tin 97, 55 whit e fly , but it ca n b e made o ut w ith th e u se of a hand l e n s . It appear s a s a d e li cate w hit e frin ge abo ut th e mar gi n of th e larv a, which fringe soo n di sa pp ea r s whe n th e leaves dry. T h e dead larv a'. hav e a white or li g h t p ink pap e r y appea ranc e. The fun g u s h as b ee n s ucc ess full y introduc e d b y th e s pores pray ing m e th od , a nd in tw o weeks it was plai nl y ev id e n t up o n previously h ea lth y lar vcein t hi s in s tanc e, th ose of th e s m oo th-egged s pecies ( Ale yro d e s citr-i ) . Th e fun g u s ca n probabl y al so b e introduc ed b y th e o t ner m et h ods. It wi ll apparently thriv e o n b o th s pecie s of w hit e fl y, but h as so fa r be e n observed as mo s t effect iv e up o n the s p ec i es with r e ticulat ed eggs ( A l ey rodcs 1111bif era). T hi s fungu ,:; b e in g of compa r atively r ecent discove r y, a nd bei ng be s i des r athe r e vane s c e nt a nd in co n sp i c u o u s, muc h r e mai n s t o be obse r ved in r e,;:1 r , : , to it s lif e -hi s t o r y am l it s effect iv e n ess in c f:i ec kin g th e whitefly. It see m s t o b e pre tt y ge n e rall y d i s tributed in th e citrus-growing sec ti o n s o f th e State , as s pecimen s h ave b ee n id e ntifi ed from wide l y se parat e d groves . cr:-rNAMON FUNGUS OF WHITEFLY . Fig. 8. C inn amo n Fun g u s o n Whit e fl y. x l . Thi s fungu s much r esemb l es t h e bro wn fung u s, excep t that the s ur face of it s p u s tul es h as a powdery appea r a n ce and a c inn amon br o wn c o l or. A l aye r of wh it e interwoven thr eads sp r ea d s a littl e distance o v e r t h e l eaf fr o m th e pu s tul es, but thi s l aye r do es n ot s pr e ad over th e whole l e af, as it do es fo r th e brown fun g u s . Th e cinnamon fun g u s produce s an abundanc e o f spores, a nd ma y b e introduc e d b y th e s p o r e s praying m e th od. It appears t o be widely di s tribut e d in s mall quantitie s and o n b o th s pecie s o f w hit e fl y. \ i\T hil e
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-56 I'-lorida , .J.grirnltura{ Expcri111c11/ Stati o n :this fun g us i s u se ful , am! ma y frequently be introduced , es p ec ially in conn ec tion with the br ow n ft11 Pl 1 S, vet it does n o t occu r in s ufficient ;abund a nce to a ll o w of it s being prefe'rred to the br o wn fun g u s or t o the Aschersonias. It ha s a lso b ee n observed on seve ral scal e insect s -...ncludin g a L eca nium and a Di asp i s. ~P OlW'l'Rl CfiG M FUNCU S 01" WfIITEl'L\". This Spor o triclnu n i s a spe c i es of fungus cl ose l y relat ed to the chinchbug fun g u s. Th e plant path o logi st of the St ati o n , Prof. H . S . Fawc e tt, ha s seve ral times obs e r ved thi s fttngns on adult whiteflies in di ffere nt parts of th e State, first in a s mall orange grove near :Gain esv ille during last A ugust. Dozens of the ad ults w ere found ~Jead , attached t o the und e r s urfa ce of th e l e ave s, with th e g rayi s h fun g us thread s pe net ra tin g the body-wall a n d hearingthousands of spor es . As just s tated, this fun g u s infect s the adult s, but it has also been obse rved o n the l arv~. J t has so far been found on l y o n th e -;;pecies o f whitefly with s m oo th eggs ( .1 /,; y ro dc s citri). Thi s fungu s may prov e to be a val t tabk adjunct to t h e other fungu s parasites, especi a lly sinc e it attack s the adults, which the other fnn g i ar e not known to d o . FU XGL1S St'PERl' , \IL\ SI'l'ES . f[.7nd o.i}ori11111 sp.-A . n oliv e -gr e en fungus of t h e genu s Clado spoiium frequ e n t ly ov e rruns and destroys the reel a nd yellow As cher sonias, c hangin g their co lors to o live-gr ee n. ; \ttention was fiist direct ed t o thi s fungu s by Dr . :\. w. ?d o rrill in an arti c l e to th e Ti111c s U 11io11, of Jacksonville. Fl a . . April l+ . 190~. According to th, : : present writer' s o bervati c ns, thi s fun12;us st r o ngly atta cks th e red and _ yellow As cb e r son ias o nl y t o ward s fa ll and during wi nter a nd sp rin g. when these fun gi are in active and a rc pr oba bly und e rgoin g degener :ative c hanges. The chi d injur y caused by t he Claclosporium, in th e writ e r' s opinion. may c o nsist in i ts destru c tion of the spor es of th e Asch c r s o nia s , at a tim e w h e n th e se ~ h o ulcl be conse r ved for the i nfec tion of the s prin g bro o d of whit e fly lar va:>. ' l'hc write r is n o t aware , how eve r, that t h e Ascb e r so nia s a r e seriouslv retard e d lw the Claclo s porinm, since t heir spo res are in a g reat n ,,, ; 1snre l ost . in. any cas e, h y the weathering a nd rain o f t h e w in te r and s pring. A t all eve nt s, the writ e r h as so fa r g iven no heed to t he C!a<1o s porii1111 in conducting hi s exp er im e nts. The yell ow , \scb crso nia i s more cn e r a lly in fecte d by the Claclosporium than t h e reel As c hcrsoni a . Thi s C l a closp ori1 1m als n occur s o n d ea d in s e c t re main s . a nd ma v ove rrun the sooty mold -fungu s . Co niotltyri11111 sp.S h o rtly afte r Dr. l\Jorrill bad n otice d th e Clacl ospo rium , h e direct e d the writer's att entio n t o ano ther fungus in Manat ee count\ , whi c h he beli e ved t o b e a s up e rparasit e o f th e brown fungu s. It wa s id e ntified b y Prof. H. S. Faw ce tt, a s belonging to the genus Coniothyrium. It occ asion a lly overruns the pustules of
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B 11 /lc ti n 97 5 7 th e b ro wn fun g u s, a n d mu c h r ese m b l es a ce r ta in s tag e of th e bla c k s . c a le fun g u s, Ni ' yria 11 gi u m D nriaei, bu t it ha s a d ec i ded s had e o f g r ee n in th e bl a c k. Th e w rit e r r ega rd s thi s fungu s a l so as attackin g th e brown fun g u s c hi e fl y aft e r th e l a tt e r h as b e c o m e o ld o r w ea k e n e d fr o m drought or c oo l w e ath e r. SOOTY MOLD. Thi s m o ld ( a s p ec i es o f Mel i o l a ) i s of a soo t y bla c k c o l o r , a s it s nam e impli es . It is fo un d w h e n eve r w hit e A y o r o ther in sec t s o ccur that exc r e t e a s we e t o luti on ( h oneydew) . As thi s h o n ey d ew n ea rly al ways co ll ect s o n t h e u pper s u rface s of l eaves, it fo ll o w s t h a t the m o l d whi c h thri ves in t hi s sec r e'.: i o n occ ur s m a inl y o n t he up pe r s urfa ce . In se cts th a t a r e accom p a ni ed by th e soo t y m o ld a r e : w hit e fl y, m ea l y bu g , p l a nt li ce ( a phi cles), so ft s ca l es ( L e canium ), wax s ca l es , c o tt o n y c u shio n sca l e . e t c . Th e p r esence o f soo t y m o l d on a t r ee i s th e r efo r e n o t a s ur e s i g n of t he prese n ce o f w hit e fl y. Th i s fun g u s d oes n o t o r d in ar il y b ecome v i s i b l e until af t e r th e t r ees h ave b ee n inf este d b y th e w hit e fl y fo r ome mo nth s. No t infr e qu e ntl y thi s soo t y m o ld oc cur s a l so o n th e un de r s u rface o f th e whit e fl y -inf es t e d l e a ves, e ith e r com pl etely c o ve rin g th e m o r fo rmin g a bl ac k frin ge ab o ut whi te fl y l a r vze ( Fig . 9 ) . \ Vhen t h i co n d i t i o n o c c ur s , i t i clu e, in th e f11 t p l ace . to an a b n o mal o r di . eased s ta t e o f t h e l a rvae, w h i c h T es ult s in the h o n ey d e w co ll e ctin g al : o ut and un derneat h t h e m, in tea d of b e in g p ro j e c te d away . Th e m o l d th e n d e ve l ops in t hi s h o n ey d ew, and prob ab l y comp l e t es th e de s tru ct i o n of th e l a rv ze . L a rv ze w e t with th e ir ow n h oney d ew a r e fr eq, 1 e n t l y obse r ved b efo r e th e mo ld h as made a n y v i s ib l e growth . S o met im e th e d i se a se d co n d i t i on of th e 1arv ze r esu l t in g i n thi s wetting i s r ecog niz e d as b ei n g cl u e t o a n in fec F i g . \l. Soot , y Mo l d ov e rg r o wi n g Whitefly ( . 1 1 , ,,r-nd es ci tr,). Also eggs, l arvre, and p u pa cases. x 1 % .
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F l o rida . .J.grirnltural Experiment Station tion with one of the fungus p arasi t es o f th e w hitefl y, but at other ti me s n o cause ca n b e assigned. ART IFI CI AL M EA NS OF CONTROL. SPH.\YING WITH CoN1\\C'f J NSF. CTICIDES.Fo r m o re complete directions i n r eg ard to the preparation of contact in sec ticid es. the r ead er i s referred to B ulletin : G of t he Florida Ex peri me nt Station. on Insecticides an d Fun g icid es . w h ic h al so co ntai ns general dir ec tions for s pra y ing and fumigation. J uclicious spraying w i t h contact in se cti cid es would be eff ectual in r e ducing the rav ag es of the whitefly , pro vid e d a grower can per s uad e hi s nei gh bor s to spra y at th e sa m e time . o r if th e grove i s i so lat e d. l f a grove is n o t is.olat e d and o n e's n ei gh b o r s do nothing to ch ec k th e whitefly, the l at ter will k eep coming in fr o m th e infest ed tr ees. \ Vhen c hinah c rr y tr ees, pri vet . nr o the r foo d plant s are about to aid in the br ee d i ng of th e a dults , an i so l a tion of a mil e will h a rdly be suf nc i e nt to keep whitefli es fr om coming i11 w h e n th ey begin to swa rm out of s uch tr ees as chinab cr ry and umhr e ll a tr ees du r in g Au g u s t and Sept e mber. S pra yi ng i s difficult a nd alm os t impracti ca ble. exc ept whe n the tre es a re sma ll -no t ov er five to sev en yea r s old-si n ce the l a rger t h e tr ee, the more diffi c ult i t i s to do the work th oro ughl y. Dec e mber. Januar y and Fe bru ary ar e t he b es t mon t h;; to ::;pr ay for the w hitefl y, as thi s in sect is the n in o ne or ot her of it s l a rval s tage s , and th ere a r c very few o r no adnlt s pre se nt t o esc ape. It i s pr act icall y usel ess to spray th e a dul ts, s inc e t he females may la y t heir l'ggs when the y a r c eig h teen t o t hir ty hour s o ld, so th at t he grow er wo uld hav e to sp r ay eve ry d ay dnr in g the s war min g period s t o ins ure killing th e m b efore th e _ \' laid their eg gs. T he eggs ar c not r ea dily k ill e d eit h e r b y s pra y in g o r fumigati o n. Spra y ing to be m ost eff ect ive s h ou l (l. furt herm o r e , h e really th orough , and one s n c h s pray i ng in win te r. afte r th e fruit is pick ed . will be w ort h m o r e than se ver al !cs, th o r o u g h a ppli cat i o n s . Th e s pra y ing s h o uld b e p ostpo ned until danger from fr ost is past: s in ce if th e lea ves s h ou ld b e c ut off b y a fr ost . bnt little if any sprayin g woul
PAGE 21
the fungi : so that haying once decided to adopt the fungus method, spraying should be discontinued. Soap solutions and plain emulsions of oils do least injury to the fungi, unless used in a very concentrated form. Fuc\1IGA'l'lOX \\"ITH H YDROCY,\:\"IC A.cw G.\s.-Those desiring information on fumigation are referred to the bulletin on this subject by Dr. A. \V. :\lorrill:' Those \\ho require copies of this bnlletill may secure them through their congressmen. Dr. :\Iorrill says further in the "Florida Frnit and Produce :\:e\\"s.'' :\:ovember ?O, HJOS: "In the country if a grove is isolated by a distance of two or three hundred feet from all other infested groves. fumigation can be practiced ,vithout fear of its being made unprofitable by migrations of the adults... QL-\IL\:\:TI:\:E. The whitetly can be kept out of non-infested groves 111 localities sufficiently isolated. for a considerable length of time. 'l'he fact that thousands of dollars may be saved in this \Vay tu a g-rmver or a com rnunitv. should be an incentive for all. whether directh interested or not. to co-01)cratc m kee1Jinuthe \\hitetl, out, or in ~hecki1w its r spread. Several methods of procedure arc available. l\y closing all pri vate roads and gates. especially against vehicles corning from infested districts, much could be. and in fact has been. accomplished. The prnpert1 should be '"posted." ,1bich ,nmld have the effect of keeping out many individuals who mav be carriers of whiteth. since the latter ha~ frequently been founcl conceale
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60 Florida Agrirnlt11ral Expcrimcnt Station allowed to continue from thirtv minutes to several hours. If a fumi gating box is at hand, such ai is used for fumigating nursery stock. the implements and other objects may be fumigated in this, using an ounce of potassium cyanide, two ounces of sulphuric acid and four of water. The water and acid are first mixed in an earthen ware vessel of double the necessary capacity. and then the cyanide is added. The gas is evolved immediately, and is dangerously poison ous. The fumigation should last for thirty minutes or longer. The picking bags and clothing of the pickers should be arranged loosely and with spaces between them to insure a circulation of the vapor or gas used for fumigating. See bulletin 7G of the Bureau of Ento mology,5 and bulletin 76 of this Station, for further directions on the use of hyclrocyanic acid gas. FOOD PLANTS OF THE WHITEFLY. Some people still imagine that every tree. bush. and shrub m our hammocks is a food plant for the whitefly. This is erroneous. The number of food plants is very limited when compared with the number of native species of plants. As a matter of fact, the native species capable of supporting the ,vhitefly in dangerous quantities are quite few. The number of plants. however, which become only occasionally infested, may be greater than we at present know. CLASS I.-FOOD l'L\N'l'S PREFJ.;tmED DY 'l'HF, WHITEFLY. Native Species: Prickly ash ( Fagara C/aVi1-Hcrc11/is). \Vile! persimmou ( Diospyros Virp,-iniana). Introclucecl Species: Citrus ( all varieties). Chinaberry ( M clia A.c:cdarac!z). Umbrella ( Jfc/ia ,-1::;cdaraclz 11111brarn/i/cra). Cape jasmine ( Gardenia jas111i11oidcs). Privets (Lig11str11l11 spp.). Japan persimmon (Diospyros Kali:i). CLASS IT.-}'O(lll PL.\NTS SOME'l'IMI~S 17\Fl~STF,D nuT -:SOT PIU:FJ<:RRED DY 'l'In; WIIITEfLY. l\ative Species: Cherry laurel or .\Tock orange (Laurocerasus splzacrocarpa and L. Caroli11ia11a). Smilax ( Sm ila.r sp.). Blackberry (R11b11s sp.). \Vater Oak (Quercus 11igra). Scrub palmetto ( Sabal 11zegacarpa). Viburnum nudurn.
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B11l/cti11 9 7 Introdu ced Spec ie s : Coff ee (Coffca . --lrab ica). Po m egra nate (Punica .1/ra 11 at11111) . . \llamanda I .-l!lamancla naii fo/i a J . Honeysuck l e ( Lo11icNa }af> o11 ica JJ,1 /lia11a). F icus altissi111a. Firns sp . ( from Costa Rica I. Oleander (cYcriu111 Of,,and cr ). Cu l tivated pear ( Pyrns sp.) . Lila c ( Syringa sp. ) . Ba n ana s hrub ( Ji ichclia f 11 sca ta). Ca 111 e llia. ofte n called J a p o ni ca, ( Ca m e llia Jap o nica ). Gl Pr i ck ! :, a s h and rn r , ck ora n ge l ~aH again b ee n o b se rv e d in f es t e d \ Yit h ,Yhitetly durin g Oc t o b e r. 1 ! 10 8, both a t Lake City and at Gainesville . and the for 1 11 er ha s been pnt in Cla ss I. Bo th are und o ubt ed foo d planb. but th e l a tt e r i ~ less frequentl y inf es t ed . A p omeg-ranatc Lush. ,-;TO\Ying n ea r infe s ted citrus tre es in a sma ll g-rov e a t Lees burg. ,,-as obs e ncd to b e thoroughly inf es t e d during Dec e mber. Jf l(J;', and ag;ain in .-\ ugu s t. lf)11S-1,hitefiy in a ll stages b e in g pr ese nt a t the ti1~1e of th e seco nd o bsenation. Coffee . a lla mancla. came llia. aml banana slir ub \Y e r e obsen•ecl at L a k e City in Octobe r . l!H)8 . and found , ri n u s l y infested \\ith \\"hit efly . The coffee tree 11 as thoroughly in fe~ t e d. ha y ing a s man y eggs o n it s l e a ves as c itru s tr ees ma Y haY e. . \II lan al s ta ges and th e pupze \\' C r c a l so ob:;;ened. but 11, j e mpt _,. pupac a se,; . Egg s and l arva': ,r e re abundant 0 11 the allamanda. ,1 nd a i e\\ t'm pty pupacases \\ r e a ls o foun d . indicating that some \\ hitefl ie~ h ad matured. Eggs and fir s s t age l an,e , mh \\Tff fonHl nn t h e camell ia. but some eggs with all fou r s t age., of lan,-e \\ -e r e o n th e ban a na shrub, to get h e r w ith a doubtful pupa-case. Sever a l l a r v;l' ancl two empty pupa -cases were found o n smi l a x near a cbin a l ~e rr _v tr ee in a small grov e by Gai n es ville. in A u g u s t. mos. Bla ckberry and honeysuckle ar e r epo rt e d as ho st p l ants o f \\hiteRy larv a:in winter. by Dr. E. I-I. Sdlard s in the .\nm1 a l R e p o rt o f the fl o rida Exper im e n t Station for Hl05. The ,rat e r oa k ha s h ee n 1 -cporte d a s a foo d p lant by Q u ai nt a n ce a nd Gos . q rcJ . but i t i ,n o t s tated th at th e in se ct eve r rea c h es maturit y o n thi s t r ee. The ,niter ha., n e , r b ee n able to find e ith e r egg:; o r l a rv ;e o n oa k s. Profc ,~cir G, ,s5a rd a l so m e ntion s ha v in g t a k e n two o r t hr ee l arv~e advanced t o th e third a nd fo urth ~tage on sc rub p a metto .3 but the writer has so far b ee n un able to dupli cate th e o bserva tion. Olea nd e r, cultivated pear a nd lilac a rc listed by Dr. l\forri]Lu PLANTS TO DE CONDE MNED. Th e fo ll ow ing plants should be d es troyed by every citru s g r owe r, and by a ll th e people in every comm unity where citrus growi n g i s an indu st ry. These p lants are. th e cape ja~mine. the chinab e rry tr ee , th e umbr e ll a tree, the prickly as h . a ll privets, the tri fo liat c orang ,:
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Florida Agricultural ExperiJ11c11t Station ( Citrns trif oliata), and any useless and abandoned citrus trees. The mock orange, or cherry laurel, should also be included in this list whenever it is observed to become infested. These plants are gen erally of little value, and can well be surrendered and replaced by others not subject to attack by whitefly. They should be cut clown and immediately burned to prevent the whitefly from transforming and migrating to other food plants. It may seem akin to vandalism to sacrifice some of the ornamentals, but all successful warfare con sists, in some degree at least, in reducing the number of the enemies' strongholds. One cape jasmine and two or three umbrella trees in a certain yard in New Smyrna appear to have been responsible for the spreading of the whitefly in that place, and the consequent loss of hundreds of dollars, while tbe plants themselves were not worth a thousandth part of the cost of the damage. Chinaberry and umbrella trees are no doubt the two food plants of the whitefly which are most to be feared by citrus-growing com nmnities. It has been observed that the adult whiteflies instinctive!\ leave these trees in August and September, or at the time when th~'. fall brood of adults matures. 'fhis accounts for the great number of aclnlts which swarm about the trees of some of our towns and in their immediate vicinity. :11Iyriad., of aclnlts were observed during .-\ugnst aml September, 1D08, fully a mile from their presnmed breed ing places in and about Gainesville. 'l'he citrus trees un the Experi ment Station grounds, which \\'CIT previously free from whitefly, be came literally alive with them. These citrus trees are at least a mile from the :1earest chinaberry and mnhrella trees previoush infester] with whitefly. The aLlults ,vere observed everywhere, in houses, on windows, a1~d on garments; aml some plants: such as collards and heans, which are not food plants. were S\l'arming with them, but no eggs or larva: were discovered on these plants. Examination clnring autumn of the leaves of some of the infested umbrella trees in Gaines ville. as well as in several other towns, revealed the fact that rela tively few eggs ( only a dozen or two per leaf) were being depositec: on these, wh1le the leaves of citrus and privet were covered with thousands of eggs. In spring the situation is reversed. and then _-;ome of the whiteflies migrate to the chinaherry ancl 11mhrella trees from such evergreens as cape jasmine, privet, ancl citrus. WHITEFLY LIVING ON FALLEN LEAVES. \Vhile making inspections of whitefly-infested trees at DeLanrl. on i\ovember :20 and ?1, 1!-J0,, the writer, with the aid of llfr. R. Y. VVinters, Assistant in Botany at the Experiment Station, macle careful examinations of considerable quantities of dead and dried leaves found under cape jasmine and citrus trees. Special attention wa~ given to those leaves found in small hollows, or otherwise somewhat protected against complete drying up. The result was that well matured larv~ and pup~. apparently healthy and alive, were found
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B11/lcti11 9 1 l ,., ),) o n d ead and brown leaves. which had either retained. or had been s uppli ed with, suffic ient moisture to keep them flexibl~. .-\!so a liv ing adult was found emerging from its pupa case. Some of these leave s were tak en to the laboratory at the Ex perim ent Stati on. and after a few day s ,yingecl whitetlies emerged. On January 1-;-. lDOS. some of the fallen leav es under the cape jasmine \\"ere again exam inecl. with simil ar results. Several fresh leafy t\Yi gs \\Tre co llected at D eLam l fr om the cape jasmine and taken to Gainesyi l! e . Some ,,ere placecl in a cloth sack. and li g htly coye recl :1it h earth at th e foot of a magnolia tree. LiYe ,d1iteflies emergecl 011 :\larch :!!. "hen some of the le aves ,Yer e sti ll gre en. Oth er t11igs ,1cre kept under a bclljar with open top. covered \Yith ch eescclo t-h. 011 moist ,;and in the gree nhou se. LiYe ad ult s \\ r e obta in ed at the end of t1 yo months, and a few oi the leav es were still green. There remains no doubf, therefore. that som e ,Yhit efly lanx and pup;e can co ntinu e to livt on le aves that h aYe dropped from the tr ees cluring \\"inter. and that tlwse may matur e s uffici e nt ly lat e in the spring to infest the ne1, leaves. RESCLTS OF DEfOLL\1'10\". It appcars from th e obsc ryati ons just state d. that unc cau.sc oi the rein festat i on of the citru~ tr ee,; after defoliation at De Land du ingthe s umm er of 1 1 10; ,ms the presencl' o i Jin \Yhitctl _, l an,e and pupa: on so me of the fall e n lea,Ts beneath the trees . . \11 infes ted citrus an d other food p l ants at Dela nd had bcen care flllly defo liated durins February, rno-;-, afte z the partial defoliation by fr ost in th e preYiou-c December. and precautions had been taken tu bu rn the lean :' -'. .\"c doubt. l ICl 1,cn-r. some l eans ,1tr e o,e rlotlk ed. Som e nf the trees in 1d1icl1 the \\hitet-l_1 reappeared in grcatest alrnncl anc c had be en banked th eart h. and tht>c banks 1ml::' t h aYe be e n ap pr opria te plac e s prescning Jcaye:,; 11ith liYe la ;-e and pnp,e. I t is. o i course. possible that some whitefly Jiyccl ove r th e \\"intcr on ut her plants. hu t car eful .,carch in c'\ovcmber and January revcalecl no plants with whitetly on them. 1\' eve rth e l ess . d efo li at ing thc trees at DeLand was productive of much good. and prevented a damage that would have equa led manv t imes its cost. The re,:ults were equ a l to a seaso n's spraying. or 0;1e fumigation. Defoli,:iion as a means for chec kingthe ,,-hiteth in a gro,e can harcll v he rec omme nded . except ,1 he11 the defoliation ha s already been in a great measure acco mplish ed by a preceding freeze, or \\he;, o ne has onlv a few small trees. The best time in ,Yhi ch to defoliate 1, probably in. Janu ary o r Feb ruar y. before the trees start to gro1,. HO~EYDEW. A con veni ent method for coll ect ing h oney dew cons ists in placing a leaf infested w ith whitefly larv ~ between two glass plates. o r on ;_i g-Jass plate or othe r smoot h surface, so that the hone ydew projected hy the larvze ,1ill fal l up on the glass or other su rfac e. The honeydew
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64 Florida Agricultural Expcrilllcnt Station is deposited in small drops, and in case the glass is above the larva: it may be projected upwards for a distance of one-eighth of an inch. Pupae ready to transform into adults secrete honeydew, as clo larva: of all stages. Larvae of probably the third ancl fourth stages of growth excreted at the rate of . OOO;"i gramme each in 48 hours. One million larv~ would thus excrete about a pound of honeydew in -k-i honrs. This would be at the rate of 15 pounds per month. or 180 pounds per year. vVhen we recall that thousands to millions of whitefly larv~ may inhabit one tree, we get some idea of the amount of sap stolen from an orange grove by this pest. LIFE HISTORY OF WHITEFLY. CFigs. l, 9, 10, 11, l.'.!-l!J.J The name whitefly is a misnomer, the insect in question not being a fly, but a member of the order 1-Iemiptera, tc1 which the plant lice and scale insects belong. The fact that the whitefly has four wings at once separates it from the order Diptera, or flies proper. There are three well--clefinecl broods of whiteJly, with an interva: between each brood of several clays to several ,ve2ks, when few 01 none are seen on the wing. The first brood generally appears som,~ time in March, April, or ~\fay, varying with the latitude and with the temperature of the spring. The second brood emerges in June. July, or ,-"\ ug-ust. and the tl1ircl in A. ugust, September or October. Some people have supposed that they had exterminated the whitefly by some treatment ( such ,,s the application of copperas), ,vhcn one or other of the broods hacl disappeared from the wing. Larv;e ( the ymmg stages) or pup,e ( the transformation stage) of the whitefly can nearly always be found on the under surface of the leaves. The larvx are scale-like ( Figs. !I, 11, 1--18), and closely appressecl to the leaves. They vary in size from the recently hatched larvx, just visilile to the unaided eye, to the full-gTown larvx. which are one-eighteenth of an inch in length. The larva: are light-colored, with a tinge of yellow, translucent. and almost in visible on the leaf. By nibbing the under surface of a leaf length wise with the finger, the larvae will appear as tlattrned whitish scales. The pupa ( Figs. !) and 11) is the transformation stage from the larva to the adult winge(l insect. The pnp;e are readily visililc as yellowish white, plump, oval bodies, ,vith a dark reddish spot on the back. From the pupa emerges the adult wingwl tly. The little white cases, with a T-shapecl split on the back, found on the under surface of the leaf, arc the empty pupa-cases from which the adults have emerged ( Figs. 9 ancl 11). The eggs ( Figs. 1. 0. 10, 12 and la) are just visible to the unaided eve as a fine dust on the under s 1 irfaces of ~he leave~. An ordinary 11.and lens or magnifying glass will show them as little bodies resembling grains of wheat. There are, therefore, four stages in the life of the whitefly: the egg, visible as a fine particle of dust;
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Bulletin 97 G5 i. ) ) i t I 3 1 ? f s -,,-----=-J O Fig. 10. (From Bui. 67. ) Whitefl y (Al e y ro d es ci tri) and in s e cts somet im es mis ta k e ,n for it. Much e nlarged. No. 1. Fernal e whit e fl y with expanded wings. No. 2 . Female w hit e fly with fo l ded wings . No . :,. Egg and footsta lk . No . 4. Empty eggs hell. No. 5. Tip of abdomen of male showing c l aspers. No . Ii. Antenna of whitefly. No. 7. Front margin of forewinp: of whit e fly. No. 8. Larva of guava whitefly (AleiJrodes Jlorici e ns i. ,). No. 9 . Margin, and No. 10 , wax fringe, of l arva of guava wh i tefly. No. 11. Soft sca l e (L e cuni'Urn /, p . •perid u m.)
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66 Florida Agric ultura l E:rpcrim c 11 t Statio11 I 1/ 1/ 00 .. 0 l --------------I Q ~ w. \ :;:=::::: /, ~-,.------...._ _ I ~/ L~ _/ "-\ 1 ,~ \ j ! \ I,. .,,,,..-"'( > ' \ \ -V, l J I \ ~i @, } --~ / \~./~ Fig. 11. (From Bu i. 67 . ) Larv a l a nd pu pa l stages of whitefly ( Aleyi od e s ci tr i ) . No. 1. First st ag e lar v a , much e n l a rg ed. No. 2. First stage l ar v a . No. 3 . Secon d st ag e larva. No . 4 . Third stage l arva . No . 5. Fourth stag e l arva . No. 6. Margin of advanced lar va, much e nlarged. No . 7. Orifice of fourth stage lar va, much e nl a r ged . No. 8. Pup a, s howing o range-c o ored ar eas, and wax tufts from breathing tubes. No. 9 . A dult whit e fly, with wings fo ld ed up , e m e rging from pupa ski n . No . 10 . F.mpt y pupa case with Tshaped slit .
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Bull e tin 97 G7 the larva , a flattened s cale ; the pupa , plump and eas il y see n ; and the adult winged in se ct. The se stages are nearly alway s fou nd o n the under s urface s of the l eaves. The fo ll owing fact s are taken from Prof. I-I. A . Go ssa rd" s bulletin : 3 T,venty thou s and eggs hav e been estimated on a lar ge o ran ge l eaf. From obse r vation made in th e laborator y, egg -la y in g begin s when the fema l e i s from eighteen to thirty h ours o ld , and from s eventeen to twent yfive eggs are d epos ited . [Th e number of eggs i s doubtle ss g reater.] The l e n g th o f lif e of the female ha s b ee n es timated at fr om thr ee cla y in warm weather, t o thr ee week s in coo l w e ather. and the complete l e n gth of th e lif e cycle from egg to adu l t at from fo rt y to fift y cla ys in s ummer to s ix months in winter. Thi s brief s ummar y of the lif e -hi s tory of th e whitefly applie s . in it s d e tail s, t o th e s pecie s with s mo o th eggs (Ale:yrodes citri) ; but a l so in a general way , a s fa r as i s kn o wn at pre se nt, t o the spec i es with r e ti c ulat ed eggs (Aleyro d e s 11ubifera) . F i g . 12. Eggs and eggs hell s of Al e !f rod 1. , nu b i .f e ra . etted surface and wide opening. Enla r g e d abo ut 9 0 t i mes. TWO SPECIES OF CITRUS WHITEFLY. ( Fig s . 1 , V, 10 , 11 , 1 2 -19. ) Ther e a r e tw o distinct species of th e c itrus whit efly o f Florida , e ach of which ser i o u s l y inf es ts cit ru s tree s . In o rd e r to facilitat e
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6 8 Fl ori d a Agricu lt u r al E x p eri m en t Sta tion referen ce to th e tw o s p ec i es in qu es ti o n , it s h o uld b e s tat e d that the species with th e s m oo th eggs i s Aleyrode s citri , Ril ey and Howard . It i s to thi s spe ci es a l o n e th a t th e c itru s whit e fl y o f F l o rid a h as until r e Fig . U. Eg g s o f Al e y rod, s ci t ri . S mooth s ur fac e . Enl a r ge d ab o ut 90 tim e s . c e ntl y b ee n r efe rr e d . Th e o th e r sp ec i es, with r e ti c ulat e d eg gs , has n o w b ee n n a m e d . Aleyro d e s nu b ifera n. s p. Th e r e ticul a t e d eg g was fi g ured in 1893, b y H. A . Mo r g an , in a s p ec i a l bull e tin o f th e L o ui s i a n a E x p e ri m e nt S t a ti o n . 4 A tt e nti o n wa s fir s t d ir ec t e d t o a n und esc rib e d speci es a b o ut a yea r ago, w h e n so m e eggs of w hit e fl y we r e b e in g exa mi ne d b y m e ans o f a co mp o und m i crosco p e . A d e li ca t e n e t , o r r et i c ul a ti o n , co s istin g of fi ve a nd s i x-s id e d m es h es , a n d w hi c h ca n b e eas il y r emove d. w a s t h e n d e fin i t e l y m ade o u t ( F ig . 1 2). Com p a ri so n o f s p ec im e n s fr o m diff e r e nt l o c a liti es s h owed th a t some eggs we r e a l ways p e rf ec tl y s m oo th ( Fi g . 1 3), w hil e o th e r s a l ways h ad thi s net. Exa min a t io ns of th e fir st sta ge l a r vx of s p ec im e n s h a t c h e d from th e s m oo th eggs, an d fr o m the r e ti c ul a t e d eggs, brou g h t o ut di s tin c t d iff e r ences b e t wee n them ( Fi gs . 1 4 and 1 5) . Fi g . 1 6 s h ows a n o ld e r fi r s t s ta ge l a r va o f th e r e ti c ul a t e d egg t y p e. with a d e li ca t e waxy frin ge a b o ut th e m a r g in . T hi s frin ge va ri es w ith th e age o f .t h e l a rv x, b e in g a b se nt in th e ve r y yo un g, a nd a b o ut a s broad , wh e n full y deve l o p e d , as t h e lat e r a l bri s t l es a r e l o n g . Th e larv a; o f th e fourt!1 s t age ( Fi gs . 1 7 a nd 18) and th e p up a; a l so s h ow di s tincc diff e r e n ces . Diff e r e n ces b e t wee n th e se c o nd a nd thir d s t a g e l a rv a; o f th e two sp e ci es h a v e n o t bee n m a d e o ut. Th e e mpt y pupa ca ses ( Fi g . 11) of the sp e c i es with s m oo th eggs (Ale y r od es c i t ri) a r e firm e r and
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Bull e tin 97 69 remain expanded, with the T-shaped s lit through which the aduit emerged gene r ally wid e open; while the empty pupa cases of the species with r e ti c ulated eggs (Ale-yrodes 11ub-ifera) collapse when the :adults h ave eme r ged . and the edges of the T-shaped slit become more o r l ess fo l ded in wards. Fig. 14. First stage la rva o f Al e yrodes nub fera bef,. re development of Lile waxy fri 11ge. Enlarged about 10 0 times . Fig. 1 5. First stage lan a of .Aley rocles r:ilri . EnlRrged about 100 times. Th e adnlts o f Ale vrodes citri hav e immaculat e wings, while those of Aleyrodes nu.bif era have a smoky-colo red area near the e nd of the wing, easi l y visible in the living insect with the aid of a lens. Fig . 16. First st age lar va nf .,. H e y• odes nubifera, with wn.x: fringe . .En lar ged about 1 O tunes. Fig. 17. Fourt h stage larva of A l eyro d es citri . Photographed b y transmitted light. Enlarged 4,5 times.
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.• 70 Florida Agrirn lt11raJ E.1:pen > m e 11t Station The distinctiv e c haract e rs o f th e eggs and first stage l arv~ can o nl y b e satisfactori l y see n b y th e us e of a compo und microscop e; th e remain i ng c haract e r s ca n b e observed with a goo d hand magnifier. Th e following c hara c t e r s can b e mad e o ut with o ut th e u se of any magnifi e r. The eggs and e mpt y egg s h e lls of Aleyro d es citri ge n e rally appear like a whitish dust o n th e l eaves, and th e t e nd e nc y is for th em to b e co ll ec t d n ea r th e mid-rib ( Figs. 1 and 9), except when th e eggs are very num e r o u s on th e l eaves. Fig. 1 8 . Fo urth stage l a rv a of A!eyrnd e .• niibif~m. Photographed by tra n s mitt e d ligh t . E nl arged about 4 t im es . Th e eggs of Aley rod es n 1 , i b i f e r a ( th e cl o ud y -win ge d whitefly) g e n e rall y h ave the ap p ea ran ce of dark o r black du s t particl es, and th e t e nd e nc y i s for them t o b e di s tribut e d away fr o m th e mid rib and t o wards th e mar g in o f th e l eaf ( Fig. 1 9) . Aleyrodes nub i fera i s a t pr ese nt known to occ ur at th e fo ll ow in g places: Bartow, Bay view, C l ea rw a t e r , Ge n eva , Largo , Ma itl a nd , M im s, Or land o, Ozo n a, Rivervi ew, Suth e rl a nd . Titu svi ll e and W int er Pa rk. U 11til th e p r es e nt t im e, A l e y r o d e s nu.bi f era ha s been o b se rv ed o nl y up on c itru s trees, and both spec i es m ay occ ur together in th e s ame tre e, as a t Ba t ow. Largo, Ma itl a nd , O rl a nd o, Ozo n a, and \tVinter P ark. That the ye ll ow Asc h e r so ni a ap pears to thr i ve o nl y o n Aleyro dcs 1wbifera , and that the whit efrin ge fun g us ha s be e n obse rv ed to b e espec i a ll y effec tiv e against this species of w hit e fl y, wer e r efe rr e d t o in th e accounts _ of th ese fun g i . REF E RE NCES. 1. I\e r ge r , E . W.-Whitefl y Co nditi ons in 1906. Fla. Exp. Sta. B ui. 88, 190 7. 2 . Fawcett, H. S.-F un g i Pa ra s itic up o n A l ey r o des C itri. U niv ers it y of Fl o rida , Special Studies. No. l , 190 8 . 3 . Goss ard , H. A.-'-W hit e fl y. Fla . Ex p . Sta. Bui. 67 , 190 3.
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Bulletin 97 71 4. Morgan , H. A.-T h e O ran ge and Ot h e r Cit ru s Fruits. La. Exp. Sta. Special Bulletin, 1893. 5 . Mo rrill , A. W.-Fumigation for t h e Ci tru s Whitefly. U. S . D ep t. of Agr., Bu r. of E n tomology , Bu i. 7G, 190 8 . 6. Rolfs, P. H ., and Fawcett , H. S.-F un gus Diseases of Sca l e In sects and W hit efly . Fla . Exp. Sta. Bui. 94, 190 8 . 7. W e bber, H. ].-Soot y Mo l d of the O r ange. . S . Dept. of Ag r .. Div. of Veg. Physio l. and Path. , B ul. 1 3, 1 897. F i g. 19. Egg s of whitefly ( Al e yroc/ es nub~f e rn ), s h owi n g distribution on l ea f. x 2.
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