a ? ; Ea SB 9. 80. 818 4 : C578 ited States Department of Agriculture. ENT BUREAU OF ENTOMOLOGY, L. O. HOWARD, Entomologist and Chief of Bureau. THE MELON APHIS. (Aphis gossypii Glov. ) By F. H. Currrenpen, Entomologist in Charge of Breeding Experiments. NATURE OF ATTACK. The melon aphis, or, as it is commonly known, the ‘* melon louse,” injures plants by piercing them with its beak and sapping their vital- ity. It occurs from early spring to late in autumn on melons and other cucurbits of all kinds, and on many other crop plants, and in seasons which favor its increase, notably in summers following springs that are cool and rainy, it frequently develops in enormous numbers and does very serious damage, collecting in masses on the under sur- face of the leaves of plants and causing them to curl, shrivel, and lose color, and interfering with the ultimate development of the fruit. Often it kills plants outright, and destroys whole fields or greatly reduces the yield of fruit. An affected cantaloupe plant is illustrated by figure 1. The melon aphis, like others of its kind, excretes ‘** honey dew,” but this is not so copious as in the case of many species of aphides, for example, certain forms which affect trees. When, however, the aphis under discussion becomes unusually abundant, the honey dew covers the leaves of the affected plants with a thin, sticky coating on which the white cast skins of the aphides adhere, and this attracts attention to injury, as does also the wilting and dying down of the plants. Some persons notice this honey dew, and are unaware of the presence of the insects. They speak of the injury as ‘* honey dew,” and have even applied this name to the insect itself.“ Quite too frequently, by the time the presence of the melon aphis in injurious numbers is noticed, irreparable damage has been accom- plished and the insects have for the most part migrated to other pastures. a Attack by many forms of aphides, especially those which excrete honey dew more copiously, can be readily detected by the presence of insects which feed on the sweet excretion. Among these are flies, wasps, bees, and especially ants. The melon aphis, however, is not an especial favorite with ants, altho some common spe- cies are occasionally found in attendance upon it. The pavement ant ( Tetramorium cespitum L.) is the only species which has thus far been observed by the writer, and neither ant nor aphis appears to be in any way dependent on the other for its exist- ence, contrary to that which is the case with many other aphides, particularly those which have root-feeding forms. 21888—No. 80—O7 DESCRIPTION. The melon aphis is a minute, soft-bodied creature, of variable color, usually of some shade of green or greenish black; in its young and wingless stages, louselike in appearance; and of sluggish habit thru- out its existence. The general appearance of this species in its most commonly observable stages is indicated in figure 2, highly magnified. A brief description of the stages figured will suffice for the present purpose. ~- The egg has been described by Mr. Th. Pergande“ as of regu- larly oval shape and measuring about 0.6"™ in length; yellowish or greenish when first deposited, soon chang- ing to jet black. The larval aphis or nymph (fig. 2,4) when first born or hatched presents no observable characters for com- parative description. It measures less than 0.5™™" and is pale im color, turning later to yellow. The last nymphal stage, corre- sponding to the pupa of other insects, is sufliciently illustrated at ¢ that it requires no verbal description. The apterous or wing less female, which is viviparous (giving Fic. 1.—Cantaloupe leaves showing curling caused by melon aphis; birth to living young), aphides on lower surface. Slightly reduced (original). y is figured at d. Great variation is exhibited in this stage, from pale yellow to very dark green, with black nectaries or honey tubes and pale whitish-yellow legs and antenne. This stage varies in length from 1.5 to 1.8"". The winged female is illustrated at a, which shows a form with pale abdomen. The body is more slender than in the wingless form, the length being «Insect Life. Vol. VII, pp. 309-315, 1895. Technical descriptions are furnished also by Forbes, 12th Rept. St. Ent. Ill. f. 1882 (1883), pp. 83-91. 3 from 1.2 to 1.8"", while the wings expand from 4.5 to 6™™. A darker form of the female is shown in profile at a+, and the antenne, much enlarged, at aa. The male has not as yet been recognized. This is by far the most important and abundant aphis affecting melons and other cucurbits, and is not likely to be confused with any other species occurring habitually on the same class of plants.” It is, indeed, a very important pest, and, taken season after season, the worst aphis occurring in this country. Fic. 2.—Melon aphis (Aphis gossypii): a, winged female; aa, enlarged antenna of same; ab, dark female, side view, sucking juice from surface of leaf; b, young nymph or larva; c, last stage of nymph; d, wingless female. All greatly enlarged (author’s illustration). DISTRIBUTION. The origin of the melon aphis is doubtful, but is probably tropical, since this insect shows a decided preference for plants of a tropical nature, such as the cucurbits, cotton, and orange. Southward the aphis occurs in the West Indies, in Mexico, and in Brazil, and doubt- less elsewhere in South America. It is very generally distributed thruout the United States, but does more injury in the southwest than elsewhere. In Texas, Kansas, and Nebraska it is particularly trouble- some to melons, and in the last two States to cucumbers, which are there extensively grown for pickling. But it may at any time create «The squash aphis ( Nectarophora [Siphonophora] cucurbite Middleton), a much larger species, more uniformly green, and of a much lighter and brighter color, is often found on cucurbits, but seldom in sufficient numbers to cause noticeable damage. + more or less trouble in northern regions, particularly in Virginia, Maryland, Delaware, and New Jersey, where cucurbits are much cul- tivated. Occasionally it is injurious as far north as Minnesota and west to California. It has been collected also in Adelaide, South Australia. INSTANCES OF INJURY. The melon aphis first attracted notice thru its injuries to cotton in 1854, and from that time on it has done more or less damage year by year, and, in view of its rapacity, rapid multiplication, and omnivo- rous habits, will no doubt continue injurious in spite of all that can be done to repress it. Asa melon and cucumber pest it was noticed in Florida and southern Illinois in 1880, and in the next three years caused considerable losses in those States and in Georgia. Soon after- wards it became recognized as a strawberry pest. In later years many other food plants were added to its: known dietary. The years 1892, 1893, and 1898 were unusually bad ‘‘aphis years.” In 1893 information was received from a pickle company of Omaha, Nebr., of severe injury in that State. This company was growing between 30,000 and 50,000 bushels of cucumbers a year, and sey- eral hundred neighboring farmers grew this vegetable for the com- pany. Two-thirds of the crop grown in 1892 was destroyed by the aphis, and in 1893 half of the crop was lost. These injuries made it difficult to induce outside planters to grow for the company. In 1898 this species was extremely troublesome. In order that a good idea of its destructiveness may be had, some reports are cited. In January injury was reported on cucumbers in Florida and in May to strawberries in Delaware, where the insects were described as ‘*taking everything clean.” By June this insect had been very injurious to watermelon in southern Texas, when it destroyed many acres of early vines. Iu July Texas correspondents reported the destruction of 1,000 acres of cantaloupes in one locality, and the out- break assumed such proportions as to cause much newspaper com- ment. One company reported that the ravages of this pest had cost them $20,000, and that agriculturists of that section had sustained irre- trievable loss. In November a Pennsylvania correspondent reported losses to cucumbers grown under glass, and in December this aphis resumed its ravages to cucumbers in Florida. LIST OF FOOD PLANTS. The insect here considered is the most nearly omnivorous of any known species of aphis. The list of plants upon which it has actually been found feeding shows great diversity, and future observations may add many more host plants. It is partial to the plants that have previously been mentioned— melons and other cucurbits, cotton, okra, orange and other citrus 5 fruits, strawberry, and purslane—but it attacks also clover, beans, beets, spinach, tomato, hops, and pear, and several ornamental plants, including hydrangea, begonia, ground ivy (Wepeta glechoma), Aca- lypha, and morning-glory. From its abundance on some of these plants it has received a number of common as well as Latin synonym- ical names, the former including cotton aphis, orange aphis, cucumber louse, and cantaloupe louse.“ It is frequently called also the ‘* black aphis,” especially in its occurrence in greenhouses. Mr. Pergande has found it feeding upon a large number of weeds, among which are shep- herd’s purse, pepper-grass, pigweed (Amaranthus), dock (Rumex), bur- dock (Arctium), dandelion, lambsquarters (Chenopodium), plantain, chickweed, button-weed (Diodia), mallow, dogwood (Cornus), and Jamestown or jimson weed (Datura). Since these aphides are not at all particular as to their food, when they migrate from their favorite plants they start colonies on nearly any plant that chances to be in their line of flight. The writer has seen asparagus and violet attacked, the latter grown in greenhouses. LIFE HISTORY. Attack to cultivated plants begins from early spring till consider- ably later, and is made by winged individuals flying from weeds which serve as alternate food plants. Infestation naturally commences earlier in the South than northward, and may be simultaneous with the appear- ance of the crop above ground. Soon after the plants have developed leaves a few winged aphides can usually be found, and these are the forerunners of myriads to follow. As often as a plant becomes exhausted of its vital juices by the sucking mouth-parts of innumera- ble aphides, winged individuals are developed which migrate to other plants, so that migration in the case of this species is carried on prac- tically thruout the season. Flight from one kind of food plant to another, or from one field to another, is caused also by disturbance from the abundant natural enemies of the insect. The great num- bers of this species sometimes suddenly discovered on melons, cotton, orange, and other plants are often due to enforced migration on account of the death of other food plants in the vicinity, such as might be caused by atmospheric conditions, or by the ravages of the aphides themselves, or of other insects. The removal of the crop on which the insect was at work will produce the same effect. NATURAL ENEMIES. There is perhaps no better example, among insects, of a common and widespread species being held in abeyance and limited to innoxious a@The synonyms include Aphis (Siphonophora) citrifolii Ashm., Aphis citrulli Ashm., Aphis cucumeris Forbes. It is still mentioned in literature as A. ewcumeris. 6 numbers (save in exceptional seasons) by natural enemies than the melon aphis. The usefulness of these natural enemies, of which a large number have been recorded, in subduing the aphides can not be overestimated. Garden and field aphides generally are subject to attack by the same classes of parasitic and predaceous enemies. The number of species of insects known to prey upon the melon aphis is about 35. The list includes many ladybirds or ‘*‘ ladybugs” (Cocci- nellidx),“ which destroy the aphis both as beetles and as larvee; the maggots of certain syrphus-flies (Syrphidze),? which consume large numbers of aphides; aphis lions—the larvee of lace-wing flies, of the families Chrysopide and Hemerobiide.* A number of species of para- sitic insects, chiefly minute forms of Braconide, are also very impor- tant checks on the increase of aphides.“ Many, too, are destroyed by parasitic fungi. The insect enemies of these, as of other aphides, keep their hosts, in many portions of the country and in ordinary seasons, in nearly complete subjection. The parasites, in particular, are most effective in dry, warm weather. In cooler, moist summer weather, especially following the same atmospheric conditions in spring, when vegetables subject to aphis injury are starting growth, these otherwise natural checks are less active, and the aphides, as a result, frequently gain the ascendency. Some of the commonest species of ladybird enemies of this and other aphides are illustrated in figure 3. In the ‘‘aphis year” of 1898 the Scymnus (fig. 3, 4, 7,7) was particularly abundant in and near the District of Columbia on aphis-affected plants. A still more abundant and useful form of this class of insects is the convergent ladybird (ippodamia convergens Guér.), shown in fig. 3, a, 6, c. It is fre- « Hippodamia convergens Guér. and Cycloneda sanguinea L. are prominent enemies, as are also Megilla maculata De G. (fig. 3, d, e) and Coccinella 9-notata Hbst. Other species are Scymnus terminatus Say, S. caudalis Lec., S. cervicalis Muls. (A), Chilocorus bivulnerus Muls., Exochomus constristatus Muls. (H), and Hippodamia 13-punctata L. Syrphus flies include Syrphus americanus Wied., Allograpta obliqua Say, Baccha clavata Fab. (babista Walk.), B. lugens Loew. (H), B. cognata Loew. (H), B. fusei- pennis Say (A), and Lupeodes volucris O. 8. An agromyzid fly, Leucopis nigricornis Egger, also preys on this aphis. Cecidomyiid enemies include certain undetermined species of Contarinia (Diplosis). ¢ Among the lace-wing flies are Chrysopa oculata Say, C. plorabunda Fitch, C. albi- cornis Fitch (A), C. nigricornis Burm. (A), C. lineaticornis Fitch (A), C. attenuata Walk. (A), Micromus posticus Walk., and Hemerobius gossypii Ashm. (A). @ Parasitic braconids include Trioxys testaceipes Cress., Lysiphlebus gossypii Ashm., L. citraphis Ashm., L. cucurbitaphis Ashm., DL. minutus’ Ashm., Lysiphlebus sp., and Pachyneuron sp. A chaleis fly, Stenomesius aphidicola Ashm., has also been reared. The species followed by (H) were observed attacking Aphis gossypii on orange trees in Florida by H. G. Hubbard, those marked (A) by Wm. H. Ashmead on cotton in Mississippi. The others are mostly well known, and have been observed by various persons, as well as by the writer. 7 t quently mistaken for the parent of the aphides. Another very efficient enemy, the nine-spotted Jadybird, is shown in figure 3, 4, ¢. One of the most abundant syrphus-fly enemies is illustrated by J Fic. 3.—a, Adult of convergent ladybird (Hippodamia converge ns); b, pupa of same; ¢, larva of same; d, adult of spotted ladybird (Megilla maculata); é, larva of same; f, adult of nine-spotted ladybird (Coccinella 9-notata); g, larva of same; h, adult of Seymnus terminatus; i, larva of same; j, pupa of same. All enlarged; size indicated by hair line at right (author’s illustrations, j-j original). Of the natural enemies which have been enumerated, ladybirds are particularly valuable, owing principally to the fact that they are active at all seasons, especially at the outset of aphis attack. Parasites are most effective toward the end of the season, when they often reduce 8 > the aphides so that few are left to hibernate and produce other gen- erations of the pest the following year. The value of these natural enemies against aphides is such that entomologists frequently advise the employment of remedies only when the enemies are not present in abundance. The possible utiliza- tion of natural enemies in the field will be considered on pages 15 and 16 of this circular. In tobacco fumigation, which will presently be considered, we have an almost ideal remedy, for the reason that, while aphides are all destroyed, a considerable proportion of the ladybirds and other hardy beneficial insects, which are practically always present on the infested vines, survive this treatment. Fig. 4.—A syrphus-fly (Syrphus ribesii): a, fly; b, lateral view of head; ec, larva or active immature form; d, anal spiracles; e, thoracic spiracle of same. All much enlarged (original). METHODS OF CONTROL. The severe losses occasioned by the melon aphis in its seasons of greatest destructiveness could be largely mitigated and in many cases almost entirely prevented if the employment of methods for its con- trol were begun upon the /nsect’s first appearance. For its successful treatment it is necessary to keep constantly in mind several of the facts that have already been given more in detail. In ordinary sea- sons the species is controlled by the combined operation of natural elements and insect enemies, but at times when the weather is unfa- vorable to the development of these enemies the grower should be on the alert. The presence of the aphides is often not detected until they are numerous, and even then they are not apt to be noticed unless the lower surface of the leaves be examined. All things considered, the most satisfactory way of controlling this insect is by fumigation. As an aid, however, cultural methods are necessary. In the South spraying with kerosene and other emulsions is preferred to the bisulfid of carbon method, and tobacco is now much used, especially in Texas. The encouragement of natural enemies gives promise of success. 9 BISULFID OF CARBON FUMIGATION. This treatment of the melon aphis has been used successfully for some time, and is valuable-in small fields, but less profitable where cucurbit or other crops are grown over large areas. It consists in evaporating bisulfid of carbon under tubs, or similar tight receptacles, such as pails, buckets, or boxes. The chemical is employed at the rate of a dram (about a teaspoonful) to each cubic foot of space; a tablespoonful will serve for ordinary small tubs. This method of treating the plant does not injure it, and if the tub fit tightly to the ground, so as to retain the vapor of the bisultid, all of the aphides which are covered will be killed. This method may be followed sue- cessfully in iarge fields if the grower be careful to watch the vines for the first appearance of the insects, and to treat such hills as require fumigation, removing and destroying plants that are badly affected to prevent the spreading of the insects to others.“ Caution.—In the use of bisulfid of carbon as a fumigant for aphides the usual precaution should be observed not to expose the fumes to fire. The operators must not smoke during this process! As the gas is heavier than air there is no danger, if ordinary care is observed, that the fumes will be inhaled by human beings. HYDROCYANIC-ACID GAS TREATMENT. This gas, as has been demonstrated by Prof. E. D. Sanderson, can be used in the field in much the same manner as the bisulfid of car- bon, with wooden tubs or buckets. It has not, however, been adopted by growers and we do not recommend it. It possesses an advantage over bisulfid of carbon in that the cover used in gassing need not fit closely to the earth. On the other hand, it is deezdedly more danger- ous to human life and must therefore be handled with the greatest care! As a greenhouse insecticide this gas isa perfect remedy for aphides and other small and soft-bodied insects. It is used where tobacco is unsafe; for example, in violet houses, violets being especially subject to ‘‘spot” after fumigation with tobacco. The method of applying hydrocyanic-acid gas is described in Circular No. 37 of this Office. PYAR ETHRUM POWDER. Pyrethrum or buhach insect powder, administered dry with a pow- der bellows to the lower surface of leaves, will kill the insects, altho these sometimes do not appear to be affected at first. A second or third application is sometimes necessary. This is an expensive rem- edy and can not be used with profit on large fields or on plants with large leaves, like squash. «In New Jersey and Colorado many growers simply take out and bury such badly infested plants as are noticed when the hills are turned for cultivation. 10 FUMIGATION WITH TOBACCO PREPARATIONS. Tobacco extracts and fumigating powders have been extensively used for a number of years by florists as fumigants against aphides and other insects occurring in greenhouses, such as white fly, thrips, and other small, delicate, and soft-bodied insects. The extracts con- tain a larger proportion of nicotine than ordinary decoctions prepared by steaming waste stems and powdered tobacco, and are therefore much more effective, which is true also of the powdered forms of nico- tine. A number of these preparations are on the market and are advertised in the principal florists’ journals and in other agricultural periodicals. They are used in various ways, and directions are fur- nished with the packages purchased. The liquid preparations vary in strength from 35 or 40 per cent up to 80 to 85 per cent nicotine. FIELD FUMIGATION WITH TOBACCO. During the years 1904 to 1906 the employment of tobacco or nico- tine preparations in destroying the melon aphis in the field was the subject of experiment in Texas by Messrs C. KE. Sanborn and E. D. Sanderson.” These have stated to the writer that, judging from their experimental use of this method and its practical use by extensive erowers, it bids fair to become the best method of dealing with the melon aphis in its occurrence in the South. The process is in briet the fumigation of a dry preparation under a cloth-covered frame placed over the affected vines. In 1905 and 1906 the writer found that a very short exposure to tobacco fumes killed aphides, when other insects, such as thrips, survived a considerably longer treatment. In practising this method Mr. Sanborn has used apparatus substan- tially as follows: Preparation of the frame and cover.—For vines 2 or 3 feet long he advises a light frame 4 by 6 feet, supported by legs 8 inches in length. Lumber three-fourths inch thick and 2 inches wide is suitable. Strengthen the frames by connecting the ends with acrosspiece. “Two diagonals are also used for strengthening the frame and for conyen- ience in handling, the latter being attached after the cloth cover is in position. The cover is of muslin of a cheap grade (7 or 8 cents a yard) and sufliciently compact to prevent a passage of gas thru its meshes after being oiled. Its size should be about 2 feet wider and 2 feet longer than the frame which it covers. This is sufficient foran S-inch wall and a 4-inch lap to the ground. Dirt is placed about the bottom to keep the gas from escaping there. After the cloth has been cut and sewed into the sizes desired it is satur ated in a vessel of linseed oil whic h fills the pores. It is then a An experiment with tobacco smoke as a ‘remedy for this species was made by Dr. 8. A. Forbes in 1882. The result was not a perfect success, for the reason that a bee smoker was used and the smoke was blown under canvas hay caps coyering the affected plants. ~Nevertheless from 50 to 75 per cent of the aphides were killed by 10 minutes’ exposure. de wrung out, slightly dried, and placed over the frame and held in place by nailing the diagonals to the frame above the cloth. A gallon of linseed oil is sufficient for rendering four covers of the size above specified sufficiently air-tight for this method. The number of frames for use depends upon the degree of infesta- tion and the rapidity of the operators. Ordinarily about 10 frames are sufficient for one man’s attention. Method of application.—The frame is placed over the infested plant. One sheet of the fumigating preparation is torn into from two to four or more equal parts (according to directions on the package or as experience may decide) and each part is put in a tin fruit can under the frame near a corner and then ignited. The cans are perforated at the bottom by driving a large nail in at the side. It is well to usea long taper or fuse for lighting the fumigant, affording the more active beneficial insects time to escape from under the cover before the tobacco fumes are given off. Earth is then heaped on the border of the cloth on the ground to prevent the escape of the smoke. The frame should remain in position ten or fifteen minutes, or longer if preferred. Each operator should have enough frames to handle so that each frame in succession may remain on a Vine during the time mentioned. | In localities where the aphis is most injurious local merchants who deal in insecticides should be informed of the fact and requested to keep a supply of fumigating preparation always in stock. The best time for fumigating is when there is no wind and the vines are damp. In moderately dry weather, however, good results may be obtained. f Caution. —Care should be exercised not to allow the dry fumigant to ignite. It should smolder only. Vines should not be disarranged except where they protrude a few inches beneath the cover. The leaves should not touch the top of the cover. Variations of the fumigating frame.—The frame described above has been used in the fumigation of young plants in southern Texas. The size and make-up of the frames may be altered or improved by the individual grower to adapt them to the size of the vines and the nature of the plant to be fumigated. Farther north than Texas manifestation of injury is not usually observable until the plants have made consid- erably larger growth, and a larger frame, say about a foot high, will be found more desirable for general use. Unbleached cotton of com- pact mesh, at 10 cents a yard, answered as well as the oiled ** muslin” in experiments conducted by the writer, and there is a saving of time in its use. Moreover, it does not collect dirt nor soil the clothing and other objects with which it comes in contact. For the treatment of plants other than cucurbits, such as cabbage affected by the cabbage aphis, eggplant, tomatoes, and other truck Mr. Sanborn advises a hood, using a frame made of two wires bent in a semicircle. Strong barrel hoops may be substituted, and the cover tacked to them at the top where they cross and at the bottom of the 12 hoops. Ornamental plants of low-growing sorts may be fumigated by means of such a hood, while for moderately high plants, such as roses, which are much affected by two common species of aphides, special covers may be constructed. VAPORIZING AND FUMIGATING TOBACCO IN GREENHOUSES. In the vaporization of tobacco—a practise which has been in use since about 1894 and which has largely superseded ordinary dry-tobacco fumigation in many sections—tobacco stems or dried tobacco, in one or another of its various proprietary forms, are placed in a kettle, metal pail, or similar receptacle. A hose is then connected with a steam pipe, the nozzle inserted in the receptacle, and the house to be treated becomes saturated with the vapor of tobacco, with the resulting destruction of aphides and other soft-bodied insects that may be pres- ent, such as thrips or ‘‘ white fly.” Liquid preparations are more generally evaporated over alcohol or other lamps, or are placed upon steam pipes, or hot irons are put into the receptacles. For general greenhouse fumigation, fumigating powders are placed in shallow pans, and a few drops of kerosene are added to facilitate ignition. The dry fumigant is designed to burn slowly, so as to produce a smudge which, when dense, is fatal to aphides. This process of treatment may be applied at any time, by day or over night, and upon its completion the house is ventilated. In some cases the plants are syringed, but this is not necessary with plants like cucumbers.