* Historic, archived document Do not assume content reflects current scientific knowledge, policies, or practices, U. S. DEPARTMENT OF AGRICULTURE, BUREAU OF ENTOMOLOGY— BULLETIN No. 110. L. O. HOWARD, Entomologist and Chief of Bureau. THE SPRING GRAIN-APHIS OR "GREEN BUG" BY F. M. WEBSTER, In Charge of Cereal and Forage Insect Investigations, AND W. J. PHILLIPS, Entomological Assistant. Issued September 6, 1912. WASHINGTON: GOVERNMENT PRINTING OFFICE. 1912. BUREAU OF ENTOMOLOGY. L. 0. Howard, Entomologist and Chief of Bureau. C L. Marlatt, Entomologist and Acting Chief in Absence of Chief. R. S. Clifton, Executive Assistant. W. F. Tastet, Chief Clerk. F. H. Chittenden, in charge of truck crop and stored product insect investigations. A. D. Hopkins, in charge of forest insect investigations. W. D. Hunter, in charge of southern field crop insect investigations. F. M. Webster, in charge of cereal and forage insect investigations. A. L. Quaintance, in charge of deciduous fruit insect investigations. E. F. Phillips, in charge of bee culture. D. M. Rogers, in charge of preventing spread of moths, field work. Rolla P. Currie, in charge of editorial work. Mabel Colcord, in charge of library. Cereal and Forage Insect Investigations. F. M. Webster, in charge. Geo. I. Reeves, W. J. Phillips, C N. Ainslie, E. 0. G. Kelly, T. D. Urbahns, Harry S. Smith, Geo. G. Ainslie, J. A. Hyslop, W. R. Walton, J. T. Monell, J. J. Davis, T. H. Parks, R. A. Vickery, V. L. Wildermuth, E. G. Smyth, Herbert T. Osborn, Philip Luginbill, C. W. Creel, E J. Vosler, R. N. Wil- son, Vernon King, entomological assistants. Nettie S. Klopfer, Ellen Dashiell, preparators. Miriam Welles Reeves, collaborator. 2 » LETTER OF TRANSMITTAL. U. S. Department of Agriculture, Bureau of Entomology, Washington, D. C, December 28, 1911. Sir: I have the honor to transmit herewith for publication the manuscript of a bulletin on the spring grain-aphis, popularly known as the ''green bug," by F. M. Webster and W. J. Phillips, of this bureau. The investigations upon which this bulletin are chiefly based began under a special appropriation made by Congress in the spring of 1907. These investigations have been continued without inter- ruption up to and including 1911. PreHminary reports upon the work were published in Circulars Nos. 85 and 93. The present report, however, is a complete record of the entire investigation, including many aspects of the problem not before touched upon in any publication relating to this group of insects. I recommend the publication of this manuscript as Bulletin No 110 of the Bureau of Entomology. Respectfully, L. O. Howard, Entomologist and Chief of Bureau. Hon. James Wilson, Secretary of Agriculture. CONTENTS. Page. Introduction 11 Earliest observations on the insect in America 13 Early records in Europe 16 Known distribution in the Eastern Hemisphere 16 Known distribution in the Western Hemisphere 18 The outbreak of 1890 19 The outbreak of 1901 21 The outbreak of 1903 21 The outbreak of 1907 27 Losses from depredations in 1907 39 The situation in 1911 40 Food plants 41 Character of attack 44 Viviparous development 44 In the South 44 In the North 49 Rearing methods 51 Stem mothers 58 Description of the different instars 58 Description of the summer forms 59 Molting 61 Number of molts 61 Birth of young 63 Number of generations per year 63 Age at which females begin reproducing 70 Reproductive period 71 Longevity 72 Fecundity of viviparous female 73 Fecundity of wingless vs. winged females 75 Average number of young produced daily 76 Sexual forms 76 Descriptions 77 Molting 78 Oviparous development 78 Age at which females begin oviposition 78 Place of oviposition 79 Period of oviposition 79 Length of life of the sexes 80 Fecundity of oviparous forms 81 Aberrant individuals 81 Influence of winds on diffusion 81 Influence of temperature on diffusion 88 5 Page. Embryology 94 Methods and material 95 General description of the egg 95 Observations 97 Summary of embryological development 102 Natural enemies 103 Internal or true parasites 104 Aphidius testaceipes Cress 104 Description and identity 104 Life history 105 Oviposition 105 Length of period from egg to adult 106 Effect of parasitism by Aphidius upon development of host. . 106 Effect of parasitism by Aphidius upon fecundity of host 107 Movement of larva within the host and manner of attaching it to the plant 109 Fecundity 113 Parthenogensis 114 Hosts of Aphidius testaceipes 115 Hibernation 117 Influence of winds in the dispersion of Aphidius testaceipes 118 Temperature influences of Aphidius 119 Effects of wet weather on the diffusion of Aphidius 121 Other species of Aphidius 122 Aphelinus. 122 Notes on life history and habits of Aphelinus 124 Secondary parasites 125 Megorismus sp 125 Aphidencyrtus aphidiphagus Ashm 126 Pachyneuron sp 127 Allotria sp 128 Predaceous enemies 128 Lady-beetles 128 Syrphid flies 129 Lacewing flies 132 Cecidomyiidae 133 Birds 135 Miscellaneous enemies of Toxoptera 135 Ants and their relation to Toxoptera 136 Remedial and preventive measures 136 Field experiments 136 Cultural methods 139 Artificial introduction of parasites 142 Literature consulted .' 144 Index ? '145, ILLUSTRATIONS Page. Plate I. Fig. i. — Wheat field totally destroyed by the spring grain-aphis ( Toxoptera graminum). Fig. 2. — Circular spot in wheat field where growing grain has been destroyed by the spring grain-aphis 32 II. Fig. 1. — Stand on which experiments were carried out in rearing the spring grain-aphis. Fig. 2. — Area on grounds of the United States Department of Agriculture, at Washington, D. C, where the spring grain-aphis usually occurs on bluegrass in excessive abundance during summer 36 III. Development of the embryo in the egg of Toxoptera graminum. Fig. 1. — Longitudinal section showing the blastoderm partly formed. Fig. 2. — Longitudinal section showing the thickening of the blastoderm about the ovarian yolk previous to invagination. Fig. 3. — Longitudinal section representing the germ band at the beginning of invagination folding inward about the ovarian yolk. Fig. 3a. — Section of the blastoderm. Fig. 4. — Longitudinal sec- tion of a more advanced stage of invagination, the germ band having almost closed over the ovarian yolk 100 IV. Development of the embryo in the egg of Toxoptera graminum. Fig. 1. — Longitudinal section representing the somewhat cone- shaped germ band ready to release itself from the surface of the egg. Fig. 2. — Sagittal section representing the tubular germ band com- pletely submerged within the yolk. Fig. 3. — Transverse section of the germ band. Fig. 4. — Sagittal section showing the germ band folding and differentiating into amnion and germ band proper .... 100 V. Development of the embryo in the egg of Toxoptera graminum. Fig. ] . — Sagittal section showing the germ band differentiated into three layers and folded almost upon itself. Fig. 2. — Surface view of Plate VI, figure 1. Fig. 3.— Surface view of Plate VI, figure 2. . 100 VI. Development of the embryo in the egg of Toxoptera graminum. Fig. 1. — Sagittal section of the embryo, showing the segmentation. Fig. 2. — Sagittal section showing a much more advanced stage of growth than that of figure 1 100 VII. Development of the embryo in the egg of Toxoptera graminum. Fig. 1. — Sagittal section showing the embryo in position to escape from the center of the egg. Fig. 2. — Sagittal section showing the embryo at the surface of the egg. Fig. 3. — Sagittal section, later stage of development. Fig. 4. — Sagittal section; dorsal organ im- mersed within the body cavity where it has begun to disintegrate. VIII. A lady-beetle enemy of the spring grain-aphis. Pupae of Hippodamia convergens attached to stem of cowpea and wheat straws in a field where the spring grain-aphis had been excessively abundant 128 IX. Fig. 1. — Brush drag used by the junior author in experiments and also by farmers in destroying the spring grain-aphis in the fields at Hobart, Okla. Fig. 2. — Roller used in experiments by the junior author and by farmers in experiments in destroying the spring grain-aphis in Oklahoma 136 7 8 THE SPRING GRAIN-APHIS OR TEXT FIGURES. Pag-e. Fig. 1. The spring grain-aphis {Toxoptera graminum): Winged and wingless viviparous females and young on wheat plant 12 2. Map showing the locality from which the spring grain-aphis was re- ceived in 1882 and the two additional localities where it is probable that it also occurred in injurious numbers in that year; also the two localities where it was found in 1884 14 3. Map showing the distribution of the spring grain-aphis in both the east- ern and the western hemispheres 17 4. Map showing the known distribution of the spring grain-aphis in the United States and Canada 19 5. Maps showing areas covered by outbreaks of the spring grain-aphis dur- ing the years 1890, 1901, 1903, and 1907 20 6. The spring grain-aphis : Male and antenna 45 7. The spring grain-aphis: Winged viviparous female and antenna 46 8. The spring grain-aphis : Wingless viviparous female 47 9 . The spring grain-aphis : Oviparous female showing eggs within the abdo- men 50 10. The spring grain-aphis: Hind tibia of oviparous female 50 11. The spring grain-aphis: Eggs 51 12. The spring grain-aphis : Young, first instar 59 13. The spring grain-aphis: Young, second instar 59 14. The spring grain-aphis: Pupa of winged viviparous female 60 15. The spring grain-aphis: Shrunken and nearly spent oviparous female.. 79 16. The spring grain-aphis: Aberrant female with both eggs and embryos in abdomen showing through the body wall 80 17. The spring-grain-aphis: Aberrant female pupa which produced young. 81 18. The spring grain-aphis: Shell of egg after young stem-mother has emerged 103 19. Aphidius testaceipes, principal parasite of the spring grain-aphis: Adult female, antenna of male, egg ±04 20. Aphidius testaceipes ovipositing in the body of the spring grain-aphis... 105 21. Position of larva of Aphidius testaceipes in the body of wingless adult female of the spring grain-aphis, from 11 a. m. to 12.32^ p. m 110 22. Position of larva of Aphidius testaceipes in the body of the spring grain- aphis at the beginning of the change to a yellowish color Ill 23. Full-grown larva of Aphidius testaceipes taken from body of the spring grain-aphis as shown in figure 21 Ill 24. Larva of Aphidius testaceipes spinning its cocoon in the dead body of the spring grain-aphis 112 25. Larva of Aphidius testaceipes working its way prematurely from the body of the spring grain-aphis 112 26. Full-grown larva of Aphidius testaceipes 112 27. Pupa of Aphidius testaceipes immediately after pupation 113 28. Dead "green bugs " ( Toxoptera graminum) showing exit holes of Aphidi- us testaceipes 113 29. The spring grain-aphis: Winged female parasitized by Aphidius testa- ceipes 118 30. Aphelinus mali: Adult and stigmal club 122 31. Aphelinus nigritus: Adult and stigmal club 123 32. Aphelinus semiflavus: Adult and stigmal club 124 33. The spring grain-aphis: Dried remains from which adult Aphelinus nigritus has emerged 124 34. Megorismus sp. : Male, female abdomen 126 ILLUSTRATIONS. 9 Page. Fig. 35. Aphidencyrtus aphidiphagus: Adult 127 36. Pachyneuron sp. : Adult 127 37. Allotria sp. : Male, female antenna 128 38. The convergent lady-beetle (Hippodamia convergens) : Adult, larva, pupa 129 39. The nine-spotted lady-beetle (Coccinella 9-notata): Adult 129 40. The nine-spotted lady-beetle (Coccinella 9-notatd): Full-grown larva. 129 41. The spotted lady-beetle (Megilla maculata): Adult, larva, pupa 130 42. A South African lady-beetle, Adalia flavomaculata 130 43. Syrphus americanus: Adult female and details of male 131 44. Eupeodes volucris: Adult female and details of male 131 45. Sphxrophoria cylindrical Adult female and details of male 132 46. The golden-eyed lacewing fly (Chrysopa oculata) : Adult and details, eggs, larvae, cocoon 133 47. Aphidoletes sp., a cecidomyiid fly enemy of the spring grain-aphis 134 48. Aphidoletes sp., a cecidomyiid larva which attacks the spring grain- aphis 135 DIAGRAMS. Diagram I. Maps of the United States east of the Rocky Mountains, showing normal temperature and departure therefrom for the critical period December, 1881, to May, 1882 15 II. Maps of the United States east of the Rocky Mountains, showing normal temperature and departure therefrom for the critical period December, 1889, to May, 1890 21 III. Maps of the United States east of the Rocky Mountains, showing normal temperature and departure therefrom for the critical period December, 1900, to May, 1901 25 IV. Maps of the United States east of the Rocky Mountains, showing normal temperature and departure therefrom for the critical period December, 1902, to May, 1903 26 V. Maps of the United States east of the Rocky Mountains, showing normal temperature and departure therefrom for the critical period December, 1906, to May, 1907 28 THE SPRING GRAIN-APHIS OR "GREEN BUG." INTRODUCTION. Investigations of the spring grain-aphis, or "green bug" (Toxop- tera graminum Rond.) (fig. 1), in America were first begun by the senior author in the year 1884, at Oxford, Ind., where the insect was accidentally introduced with, or had in some obscure way gained access to wheat plants which had been transplanted from the open to rearing cages standing out of doors on a blue-grass lawn (June 6) and used in carrying out investigations on the greater wheat straw- worm (Isosoma grande Riley). At that time the insect gave no indi- cation of its present economic importance and for this reason was not then given special attention. In 1890, when the pest really first gave evidence of its capabilities as a grain destroyer over a wide range of country, the senior author again took up its study, gaining considerable additional knowledge of its habits and of the influences of temperature and season upon its abundance. (See Diagrams I-V.) The less serious outbreak of 1901 was not investigated and our information relative to it is derived chiefly from correspondence of the bureau for that year. The incipient outbreak of 1903 was reported from Texas by Prof. E. D. Sanderson, at that time State entomologist, and from South Carolina by correspondents of the bureau. The last and most disastrous outbreak of all, that of 1907, was investigated not only by both of the authors, but by Mr. C. N. Ainslie, who began his work on the species at Summers, Ark., on March 18, continuing the investigation almost uninterruptedly through the summer, working over the country from central Okla- homa northward to Canada, and returning to Washington in Sep- tember. The junior author spent April, May, and a portion of June in Oklahoma and Kansas in field investigations, returning to Richmond, Ind., where he was at that time located and where he took up a systematic study of the insect, its habits, and develop- ment— a study which has been continued up to the time of prepara- tion of this manuscript for publication. Messrs. E. O. G. Kelly and T. D. Urbahns spent much time in a study of the parasites; indeed/ most of the assistants in cereal and forage insect investigations have 11 12 contributed more or less to our knowledge of the pest and its natural enemies, and throughout the following pages credit has been given // m V / T** ■T" •<&&*■> - Fig. 1. — The spring grain aphis ( Toxoptera graminum): Wheat plant showing winged and wingless viviparous females with their young clustered on the leaves, and a few parasitized individuals on lower leaves. About natural size. (Original.) each individual where possible to do so. For a critical, technical study of the parasites of the species, credit should be given Mr. J. C. Crawford, assistant curator, Division of Insects, U. S. National L EARLIEST OBSERVATIONS IN AMERICA. 13 Museum, and Mr. H. L. Viereck, expert, Bureau of Entomology, who are specialists in the parasitic Hymenoptera. During the winter of 1907-8 Congress provided the sum of $10,000 for carrying on these investigations; otherwise this work would have been impossible. EARLIEST OBSERVATIONS ON THE INSECT IN AMERICA. The first examples of Toxoptera graminum to be found in America and identified as such were probably collected with the oats plants which they were destroying by Mr. H. S. Alexander, of Culpeper, Va., on June 15, 1SS2. A letter in the files of the Bureau of Ento- mology, written on the above date and addressed to Hon. George B. Loring, then Commissioner of Agriculture, stated that he, Mr. Alexander, was sending by that evening's mail specimens of an insect which had almost entirely destroyed the oats crop in his neighbor- hood. But he very evidently neglected to indicate on or within the package the name and address of the sender. Under date of June 17, 1882, the records of the old Division of Entomology show, how- ever, that a package of oats or wheat plants — exactly which could not be determined by the person making the examination — were received on that date, badly infested by what was determined as Toxoptera graminum. As there was nothing on or within the package to indicate the source from which the material came, the locality has since remained in obscurity. Upon a recent examination of the old letter files, the communication of Mr. Alexander was found and a reply thereto by Dr. Riley, dated July 7, 1SS2, stating that the communication had been received from Mr. Alexander, but that the specimens referred to by him had not arrived. As the Division of Entomology did not have these specimens before them when Mr. Alexander's letter was received, or did not connect these specimens with his letter it was assumed that the species was the well known SiphonopJiora avense- Fab., a name at that time applied to what is now called Macrosipltum granaria Buckt. Evidently the connection between the letter and package was never investigated, as the insects in the package proved to be Toxoptera, It is significant that of the eight communications received at the Department of Agri- culture about that time, from various points in Virginia and including also one from Maryland, all relating to the wheat louse, this one from Mr. Alexander is the only one not shown to have been accompanied by specimens, and also it was the only communication in which reference was made to the destruction of oats, all of the other letters alluding to insects found infesting wheat or rye, which were probably M. granaria Buckt. Without a doubt, therefore, the letter of Mr. Alexander refers to the package received June 17, 1SS2, without 14 THE SPRING GRAIN-APHIS OR ' ' GREEN BUG. ' ' name or address of the sender. A correspondent of the "Country Gentleman," writing over the initials G. C, from Chrisman, Eock- ingham County, Va., about 50 miles west of Culpeper, under date of June 16, 1882, makes this statement: Wheat looking well and promising, but there is a little green bug on it that may injure it. This same little green fellow is ruining the oats in this neighborhood, and has already destroyed them entirely in many localities.1 It is not at all surprising that Toxoptera and Macrosiphum should have been confused at that time, as the former species was yet unknown in the country and its presence could only be determined from winged individuals. In all of the succeeding out- breaks of Toxoptera it has been more or less difficult to separate the wingless individuals of these two species definitely from each other, even experts having been often at fault where there were only im- mature individuals upon which to base a separa- tion. In this connection Mr. B. F. White, writing from Mebane, N. C, Jan- uary 28, 1890, complain- ing of damage at that time to oats in his locality by Toxoptera, specimens of which accompanied his communication, stated that the same insect appeared in 1882, in May. So, then, it seems quite likely that, while the discovery was first made at Culpeper, Va., the insect occurred over a considerable area of country in Virginia, extending southward into northern North Carolina (see fig. 2; Diagram I, p. 15). From the foregoing it would appear that at this early date there was a more or less destructive outbreak of this pest in the southern Atlantic States. That the species was confined to this area, how- ever, is hardly possible, and indeed it is not beyond possibility that damage to oats may have extended much farther westward, though we have been unable to find definite proof to that effect. The all- important temperature influences are also indicated. Fig. 2.— Map showing the locality from which the spring grain-aphis was received in 1882 and the two additional localities where it is probable that it also occurred in inju- rious numbers in that year; also the two localities where it was found in 1884. ( Original. ) Cultivator and Country Gentleman, vol. 47, p. 498, June 22, 1882. EARLIEST OBSERVATIONS IN AMERICA. 15 On June 7, 1884, Mr. Albert Koebele found this species infesting wheat plants at Cabin John Bridge, situated in Maryland a few miles above Washington, and about July 1 of the same year the senior T.LTST_^ V If &'' }- [ j ~~j I V S4.B 3SJ | <'-"'•■' . 1 ?**o **J i 44.V 'Y^T'"y'\ *-§-;- r-Xis" / 46 4 «? 46J50,-'.-— *^?v / . fsEii \ svS 1 1 l'-^N^ V»Vde.CE.M BER, 1661. V \ • i — ^, \ jjx ~r- .4 r^y ^ -/"S. -* ' J r f- Lrfi \k. V S [ ( S- Y ,j ! «> \nn I *s.o I ** 67 *\ A . N 70.6 J \ 7 APRIL.,IS8£. \ \ttS 26 7 , si o ; ^ *._^ *v' y-'_^ - Diagram I. — Maps of the United States east of the Rocky Mountains, showing normal temperature, upper line, and departure therefrom, lower line (+, above normal, and, — , below), for the critical period December, 1881, to May, 1882; above normal ( + ) in winter and below normal (— ) in spring being favorable for outbreak of spring grain-aphis. (Original.) author found it in one of his rearing cages, placed out of doors at Oxford, Ind. (see fig. 2). In the latter instance the species showed a preference for wheat plants over those of rye, and in September it 16 was common in the fields on volunteer wheat plants in the same locality and also about La Fayette, Ind. In some fields it was ob- served breeding on the young growing wheat throughout the autumn and early winter up to December 13. On the 30th of December it was still to be found alive in the fields, though not in great abundance. EARLY RECORDS IN EUROPE. The first exact knowledge we have of this insect is its occurrence in excessive abundance about Parma, Italy, in 1847. Five years later, in 1852, Rondani, who described the species during this year, wrote to Prof. Bertoloni under date of June 14, also from Parma, relative to the insect as follows: We have in our city an innumerable number of insects of a species of the Aphis genus, of Linnaeus, of the order of Hemiptera. Sometimes and in certain places the number of these insects flying in clouds in the air has been so great as to render them troublesome to people, entering the nose, eyes, and even the mouth, when one can not think how to protect oneself from them. Elsewhere in this letter Rondani stated that he had never been able to find it on any but graminaceous plants, where it nestled on the leaves. In commenting on this letter of Rondani, Prof. Bertoloni took occasion to say that " innumerable specimens of the Aphis graminum Rondani are seen in the streets of the city of Bologna, and these have several times entered my nose and eyes when passing rapidly along the canal of Reno." KNOWN DISTRIBUTION IN THE EASTERN HEMISPHERE. Besides these occurrences in Italy and Hungary (see fig. 3), in 1884 Dr. G. Horvath records an attack on oats in central Hungary, which took place in June, 1883, and 10 years later, in 1894, Prof. Carl Sajo records a second outbreak among growing oats, also in Hungary. Schouteden, in 1906, records the species from Belgium, but gives no further data except that it affects the Graminacese. Under date of October 7, 1907, Mr. H. Neethling, chief of the horticultural and biological division, department of agriculture, Bloemfontein, Orange River Colony, South Africa, in a letter ad- dressed to the United States Department of Agriculture, stated that the wheat aphis was one of the greatest scourges with which the farmers of his colony had to contend, nearly the whole crop having been destroyed by it for several consecutive seasons. Again, under date of September 28, 1908, the same gentleman stated that the pest had been particularly active that season, it being estimated that more than 50 per cent of the entire wheat crop of the colony had been destroyed by its ravages. This latter communication was accompanied by specimens of Toxoptera graminum as well as a small DISTRIBUTION. 17 26675°— Bull. 110—12 18 THE SPRING GRAIN-APHIS OE ' ' GREEN BUG." hymenopterous parasite, Aphidius sp., and larvae and adults of a coccinellid, Adalia favomaculata De G., both of which were observed destroying the aphidids. Under date of October 1, 1910, 'Sir. C. P. v. d. Merwl, assistant biologist of the same department, stated that another outbreak of the pest had taken place that spring and con- siderable damage had been done. In this communication the state- ment was made that the writer had personal knowledge of the occurrence of the species during the past 20 years, and that farmers had stated that they had always known of its occurrence in that country. It had, however, become seriouslv destructive during: recent years and at that time farmers were being forced to give up growing wheat extensively on account of its ravages. In the Agricultural Journal of India x 'Sir. H. Maxwell-Lefroy, government entomologist of British India, stated that the wheat aphis (Toxoptera graminum) seeks shelter in the depths of the grass roots; hi different ways insects adapt themselves, but these had probably done it gradually, moving in from cooler to hotter areas step by step. From the illustration of this insect accompanying this statement and from specimens later submitted by Mr. Maxwell- Lefroy, it has been found impossible to determine the species involved as Toxoptera graminum. On November 25, 1910, Mr. William Sewall, of Xjoro, British East Africa, called at the office of this bureau to complain of the ravages of a green louse or fly which attacked and destroyed wheat on his farm in the above-named locality, situated almost directly on the equator hi a prairie-like country at an elevation of 7,000 feet above sea level. A communication was received from Mr. Sewall bearing date of August 22, 1911, accompanied by specimens, in which he stated that the ravages now extend over an area of 700 acres. He also stated that his neighbor, Lord Delamere, who had not been troubled previously, experienced severe losses over an area of about 4,000 acres. The specimens accompanying Mr. SewalTs letter have been determined as Toxoptera graminum by Mr. J. T. Monell. With these records of the known and probable distribution of Toxoptera graminum, it does not seem improbable that if the minute insects of the family Aphididae were carefully studied this species would be found generally diffused throughout the temperate and tropical regions of the world. KNOWN DXSTPJBUTION IN THE WESTERN HEMISPHERE. With reference to the distribution of tins insect in the Western Hemisphere (see fig. 4) , it can be said that it has only been studied in the L'nited States. Its occurrence in western Canada is well established. On the south it is known along the Mexican border from the Gulf of i "Imported insect pests." Agricultural Journal of India, vol. 3, part 3, pp. 243-244, July, 1908. THE OUTBKEAK OF 1890. 19 Mexico almost to the Pacific Ocean. It has not actually been found in Mexico and no one has searched for it there. Wheat in Mexico is said to have been injured by a " green louse, " and it is reasonable to suppose that the insect may occur far to the southward of its present known range of distribution. Its entire absence from eastern Canada and northeastern United States, except in eastern Massachusetts near Boston, where it seems to have been found by Mr. Paul Hayhurst in September, 1908, will be noted. THE OUTBREAK OF 1890. (Fig. 5, p. 20; Diagram II, p. 21.) Up to the year 1890 in this country the very destructive nature of this insect had not yet become apparent ; hence it had not received the close attention that, as we now understand, it justly deserves. 7>v L W <-—__• •/ \ : • •• v -•> / • — 1 ! •I \ ,j -j • •; • V* -t— ->— -• \; i * T"— • ■=■—«• • • L*-S- J ♦ • — 1> V. I— « -> • v , 1 I "— i "*-* ^ Yig. 4. — Map showing the known distribution of the spring grain-aphis in the United States and Canada. (Original.) While the senior author was and had been engaged in grain-insect investigations in Indiana during the six years following its discovery by him at Oxford, the species was not looked upon as one of those deserving especial attention: therefore from 1884 to 1889 no notes were made upon it, and no references to it are to be found in the correspondence of the Division of Entomology. Mr. J. T. Monell, now of tins bureau, however, has specimens in his collection from Illinois, taken in 1886. During Xovember and December, 1889, the insect was again observed in such abundance in fields of young wheat about Lafayette, Ind., as to attract the attention of the senior author, who found it repeatedly on young wheat in the fields during the entire winter. The influences of mild or high temperatures during winter, especially 20 in the South, and low temperatures during spring months were carefully observed and set forth in a report published later.1 As early as the middle of January, 1890, it was reported by Mr. P. C. Xewkirk as killing the young wheat about Jalapa, Tenn., and on the 26th of the same month Mr. B. F. White, of Mebane, X. C, reported it as ruining both wheat and oats in his neighborhood. Mr. J. L. Fooks, writing on the same date from Era, Tex., stated that the insect had played sad havoc with the wheat in his neighborhood, while April 7 Mr. D. J. Eddleman, Denton, Tex., complained of the pest destroying the wheat. Writing in 1901 Mr. H. K. Jones, Valley View, Tex., stated that the insect appeared there about 10 years pre- Fig. 5.— Maps showing areas covered by outbreaks of the spring grain-aphis during the years 1890, 1901, 1903, and 1907. (Original.) vious and killed about all the wheat in the county. From this and other correspondence, accompanied by specimens, it seems that wheat in Cooke, Grayson, Collins, Denton, and Wilbarger counties, Tex., was more or less damaged by this pest.2 Xo reports are at hand showing injuries to wheat or oats in what was at that time Oklahoma and Indian Territories, for the reason that little of either of these grains was at that time grown. But we now know that grains were not essential to its presence in that country. In Missouri the situation was more acute and strongly indicates that the pest was present in southeastern Kansas and northern Arkansas. According to Mr. Monell's notes, the pest completely i Insect Life, vol. 4, pp.. 245-248, 1892; Bui. 22, Div. Ent., IT. S. Dept. Agr., pp. 64-70, 1890; Yearbook U.S. Dept. Agr. for 1907, pp. 239-241. J Insect Life, vol. 3, p. 75. THE OUTBREAK OF 1890. 21 destroyed a field of 60 acres of oats belonging to Hon. Roland Hazard at Mine Le Motte, situated about 100 miles south of St. Louis, Mo., Diagkam II.— Maps of the United States east of the Rocky Mountains, showing normal temperature, upper line, and departure therefrom, lower line (+, above normal, and — , below normal), for the critical period December, 1889, to May, 1890; above normal ( + ) in winter and below normal (— ) in spring being favorable for outbreak of spring grain-aphis. (Original.) the observations being made June 10, 1890. In Missouri the situa- tion appears to have been pretty clearly set forth by Colman's Rural World, then the leading agricultural paper of the Southwest. In the 22 THE SPEIXG GEAIX-APHIS OE issue of that publication for June 12. 1890, the following statement is made: The oat crop in the vicinity of St. Louis and probably extending a hundred miles in even' direction is being completely destroyed this season by an aphis, commonly called, we believe, the Texas louse. The oat fields look brown and bare, this little green insect sucking the juices and sapping the vitality of the plant. It increases with amazing rapidity, fully as rapidly, we judge, as the hop louse, swarming in even- direction and earning destruction in its path. The only thing they seem to feed upon is the oat. In the issue of the same publication for June 19, a week later, the following statement is made: The oat crop this season will be almost a total failure in St. Louis County. Hundreds of acres have been totally destroyed by the aphis, or plant louse, the depredations of which have been so widespread and effective that only a very small per cent of the crop will mature. Hundreds of farmers have despaired of the crop entirely, and have plowed up their oat fields and planted corn instead. The Weather Crop Bulletin of the Missouri State Board of Agri- culture for the week ending July 4. 1890, gives the following estimates of the oats crop throughout the State. Northeastern Missouri, 63 per cent; northwestern Missouri, 70 per cent; southeastern Missouri, 25 per cent; central Missouri, 30 per cent; southwestern Missouri, 54 per cent. As another writer describes it. the damage was most serious south of a line drawn diagonally across the State from the northeast to the southwest corner. The statement made in Colman's Rural "World to the effect that the oats crop within a radius of a hundred miles of St. Louis had been completely destroyed by the oats aphis or "Texas louse " would include within this radius territory nearly half way across southern Illinois. Mr. B. F. Johnson, of Champaign, 111., an agricultural writer, who appears to have traveled over the country quite extensively and observed the situation closely, writing to the Country Gentleman under date of June 24, sized up the situation as follows: For some weeks after it was seen above ground, the oat crop looked well and promised well, and this continued to the first or about that date in June. Since then oats have been going behind hand, with the threat now over them that all the crop has been more or less seriously reduced in yield and a considerable portion will be lost. In fact, the oat aphis, after ruining the oat crop south, has appeared on the black soil in force and nothing less than many and heavy rains will arrest his progress. As before reported, the dry weather in May favored a light growth of straw, as in 18S7, and hopes were entertained that long heads of sound grain would result. Such would have been the case had not the aphis appeared and sucked a part of the life-blood of the plants. The present appearance of a majority of oat fields — the acreage on the black soil coun- ties is an enormous one — is rather uneven as to growth, color, and measure of develop- ment, a part of which is owing to the greater or less fertility of the soil, but chiefly to the depredations of the aphis, that takes the weakest plants growing on the thinnest land. In the issue of August 14 of the same publication, Mr. John M. Staid, of Adams County, 111., states that in western Illinois the only THE OUTBREAK OF 1890. 23 cause of the failure of the oats crop recognized was the green louse. Directly upon this point his statements were as follows: We never had a better prospect for oats until the green louse began its work. Some fields were not attacked by the louse, though it infested surrounding fields. From the fields not attacked by it there was a splendid yield of oats; while, of course, the other fields yield scarcely anything. In every township there were a few fields that were not attacked by the green louse and that made a good yield. The fact that those fields not attacked by the green louse invariably made a good yield, while those that were attacked made a poor yield, is proof that in this part of the State, at least, the green louse was the prime cause of the failure. This feature of the apparent immunity of some fields from attack while others adjacent were destroyed has since been observed again and again, especially along the borders of a serious invasion, which was precisely the stuation in western Illinois at the time indicated by Mr. Stahl. In Indiana the senior author investigated the outbreak personally, and while the pest was present as far north as Lafayette, there was little if any damage from its attacks north of Indianapolis. In the neighborhood of Franklin on June 25 many fields were badly damaged, but the injury was much more severe to the southward and at New Harmony, Ind., on June 11, the oats crop was ruined. The same was to be said of the country across the Wabash Kiver in Illinois. While both Toxoptera and Siphonophora were present in most cases the former largely outnumbered the latter and there was no difficulty in properly crediting the destruction to Toxoptera. The occurrence of this insect in southern Ohio was greatly obscured owing to the fact that it was, as elsewhere, confused with MacrosipTium granaria Buct. Clarence M. Weed, writing for the Ohio Farmer (see issue of July 12, 1890), states that in Ohio the grain plant louse had been reported from Pickaway, Clermont, Butler, and Franklin coun- ties. It seems, however, that in Clermont County, according to Mr. Ed. C. Ely, the plant lice were at work as early as May 30. In a later issue of the same paper, July 19, 1890, Hon. Abner L. Frazer, of Clermont County, Ohio, stated that the aphidids were very numerous in his fields on June 9. While it is impossible to say with absolute certainty that all damage was due to Toxoptera, nevertheless Waldo F. Brown, writing from Butler County1 on June 19, says: Oats are in a critical condition. The leaves have turned red. It has not the appearance of rust, looking more like the firing of a plant in dry weather, and I should not wonder if the crop proved a total failure. In both Illinois and ^Missouri the aphidid causing the damage was termed the " Texas louse," and wherever a technical name for it was used at all it was called SipTionopTiora avenes Fabr. Because Toxoptera was at that time but little known, and owing to the i Country Gentleman, June 26, 1890, p. 506. 24 extreme difficulty in separating its young and its wingless adults from those of other species, it would seem that more or less damage to the oats crop might be with justice accredited to Toxoptera in Butler, Miami, and Clermont counties in extreme southern Ohio. THE OUTBREAK OF 1901. (Fig. 5, p. 20; Diagram III, p. 25.) The outbreak of 1901 was less extensive than that of 1890. Little damage was reported south of Waco, Tex., but from this point northward wheat was more or less injured^ and oats were destroyed to the northward into what was at that time Oklahoma and Indian Territories. The farthest point to northeast at which damage was reported, with specimens of the depredator, was Saratoga, in extreme southwestern Missouri. The specimens accompanying correspond- ence from Texas and Oklahoma gave ample proof of the identity of the destroyer, which in Texas alone ruined grain to the extent of several million dollars. In central Texas the ravages of the pest began to attract attention early in March, while the report from Missouri came under date of April 30. It will be noticed that the direction taken by this invasion followed very closely that of 1890 (see fig. 5), beginning, however, farther south in Texas, not extending so far to the northeast, and dying out, as it were, earlier in the season. These phenomena will be explained farther on under meteorological influences. THE OUTBREAK OF 1903. (Fig. 5, p. 20; Diagram IV, p. 26.) As foreshadowing the impending outbreak of 1903, as early as November 26, 1902, Mr. J. F. Ordman, writing from Windthorst, Tex., complained to this bureau of the ravages of the green louse, stating that it had destroyed several small areas in his wheat field and that it was reported generally prevalent in his neighborhood. This outbreak was, however, an incipient one and resulted in little injury, the seriously infested areas being confined to northern Texas, exclusive of the " Panhandle," with possibly the country in the then Oklahoma and Indian Territories bordering the Red River, and in South Carolina. While the outbreak was thus limited in area, the natural enemies of the pest in the West evidently fell far short of completely subjugating it. In March, 1904, Prof. E. D. Sanderson and Mr. E. C. Sanborn found it in Grayson County, Tex., sufficiently abundant to work serious injury in the fields of young wheat and oats, in some cases the destruction of the growing grain THE OUTBREAK OF 1903. 25 being complete. The same gentlemen reported the pest present in limited numbers during the spring of 1904 in Collin, Hunt, and ^ 24.0 • -V.s J" °t% £r -J"37.0 3*4/ 1 \ 4|.o\ -4.9 \ \ r U ■ 1 — ~^r 1 — ! J -a^ — j— XJ V -Y i V 24.5 <267 \-4.8 1-3.2 , 502. 31.. : \ °-9 -i-« ! 52. 0 >£ 15.0 : •,-2-'3 V* ^FEBRUARY, 1901. V i i ryk$^f\& i- — 4 ~ v— \i __^> ; ._ 1 "Sets ;&o>» \ 625 .-3.0 -4.8 » * APRIL, I90I. Diagram HI.— Map of the United States east of the Rocky Mountains, showing normal temperature, upper line, and departure therefrom, lower line (+, above normal, and — , below), for the critical period December, 1900, to May, 1901; above normal ( + ) in winter and below normal (— ) in spring being favorable for outbreak of spring grain-aphis. (Original.) Travis counties. This year, however, the parasites evidently did more effective service, as at Whitewright, Grayson County, Tex., on March 10, 1904, Mr. Sanborn found that 60 per cent of the Toxoptera 26 in some oats fields were parasitized. The junior author spent some time in northern Texas during November and December, 1904, Diagram IV. — Map of the United States east of the Rocky Mountains, showing normal temperature, upper line, and departure therefrom, lower line (+, above normal, and — , below), for the critical period December, 1902, to May, 19C3; above normal (+) in winter and below normal (— ) in spring being favorable for outbreak of spring gram-aphis. (Original.) investigating insects in the fields of wheat and oats without finding the pest. He was not looking for this species particularly, and it was doubtless still present in very limited numbers. 27 THE OUTBREAK OF 1907. (Fig. 5, p. 20; Diagram V, p. 28.) The outbreak of 1907 was by far the most serious and widespread that has occurred in the United States up to the present time. Start- ing in east-central Texas, the invasion swept northward and east- ward, covering a somewhat fan-shaped area, through Oklahoma, Kansas, northwestern Arkansas, Missouri, and across Illinois to within 60 miles of Chicago. Though possibly not doing so much damage in the Ohio Valley as in 1890, it extended westward through Oklahoma and Kansas into southeastern Colorado. While not especially injurious to oats and not at all to wheat in the States of Nebraska, Iowa, Minnesota or the Dakotas, the late Dr. James Fletcher states that in Canada it actually did some damage in Sas- katchewan. Less damage was probably done in Indiana and Ohio than in 1890, though the ravaged area in general followed the ground covered by the previous outbreaks; in this latter case the northeastern terminus of the seriously ravaged area appeared to be confined more closely to the upper Mississippi River and Illinois River valleys than to that of the Ohio River, thus sweeping more broadly to the northward. On the Atlantic coast fall oats were destroyed or badly injured in South Carolina, and both wheat and oats in western North Carolina. In Virginia, Kentucky, and Tennessee neither grain was, as a rule, seriously damaged. The areas shown in figure 5 indicate all injury, even though slight, in occasional and widely separated fields. In the valleys of the upper Missouri River and the Red River of the North there was little or no injury, and it seems doubtful if the pest occurred in that section prior to this outbreak. Forebodings of trouble from this pest came as early as November and December, 1906. According to copies of Mr. Sanborn's notes, as placed at our disposal by Prof. A. F. Conradi, the species was sent to the Texas experiment station from Howe, Grayson County, Tex., where it occurred on oats, as early as November 14, 1906, and one day earlier from Allen, Collin County, of the same State, where it was present in great numbers attacking volunteer oats plants. On December 22, 1906, it was sufficiently abundant about Piano, Collin County, Tex., to destroy oats in patches in the fields, its natural enemies at the time being in a dormant condition because the tem- perature had not reached and remained at a degree that would render them active. During January and February, 1907, these conditions continued, the Toxoptera breeding and spreading unre- strained by its enemies, so that the area over which it was becoming destructive continually increased. Rumors of injuries by this pest came to us early in January, 1907, from east-central Texas, where the " green bugs" were reported to Mr. W. D. Hunter, in charge of cotton boll weevil investigations of 28 this bureau, as attacking fall oats. During this month in Texas east of a line drawn from near Gainesville through Abilene and San Diagram V.— Map of the United States east of the Rocky Mountains, showing normal temperature, upper line, and departure therefrom, lower line (+, above normal, and — , below), for the critical period December, 1906, to May, 1907; above normal (+) in winter and below normal (— ) in spring being favorable for outbreak of spring grain-aphis. (Original.) Antonio to Galveston the temperature was 9° F., above the normal. Within this area was a smaller one, the boundaries of which may be indicated by a line drawn from Texarkana to Fort Worth, Waco, and THE OUTBREAK OF 1907. 29 Joaquin. Over this latter area the temperature for the same month was 12° F. above the normal, and within this latter area the pest first began its work of destruction. For reasons to be explained later in their proper place, the spread of the pest was much more rapid to the north and northeast from north- central Texas than it was in the opposite direction. In March the pest was found generally present about San Antonio, Kerrville, Menardville, and New Braunfels, of that State, but because of the small acreage of grain grown in that section the damage was not serious. Indeed, the same may be said of the country west of a line drawn from western Wilbarger County to the Brazos Kiver at Round Timber, Baylor County, and west of the Brazos to and except about Waco. East and north of this the damage ranged from serious to total ruin. As early as March 6 it was also reported to the bureau as destroying wheat in the vicinity of Summers, northwestern Arkansas. This was probably due to local causes, uninfluenced by invasions of swarms of winged viviparous females that were being continually swept from off the more disastrously affected country to the southwest and drifting toward the northeast. Mr. C. N. Ainslie was instructed to proceed from Washington, D. C, to this part of the country, where he arrived on March 16. On March 15 the Texas Grain Dealers' Association, through its secretary, Mr. H. B. Dorsey, made an appeal to the chief of this bureau for aid in devising means for destroying the pest and curtailing or preventing its ravages. In response to this appeal the junior author was dispatched to Fort Worth, Tex., arriving there on March 26. The situation here was found to be most serious. Hundreds of acres of both wheat and oats had been wiped out of existence; in many cases fields were observed where it was impossible to find a living plant, and as a rule numbers of such fields were being plowed and prepared for other crops. Plate I, figure 1, shows a field entirely destroyed. The weather at this time was hot and dry and Toxoptera appeared to have been entirely overcome by its natural enemies. On March 25, 1907, a telegram was received from the Roosevelt Grain Elevator Co., of Hobart, Okla., reporting serious attacks from Toxoptera and appealing to the Secretary of xlgriculture for assist- ance. The junior author was at once instructed to proceed to Hobart, where he arrived April 1, remaining until April 5. This point ap- peared to be on the western border of serious injuries by the pest, and the situation was therefore not so grave as in Texas. From the junior author's observations it appeared that much of the damage that was being done was caused by insects which had drifted into the fields and not from individuals originating therein. This was evi- denced by the fact that in wheat fields where a part had been sown 30 THE SPRING GRAIN-APHIS OR " GREEN BUG," early and the remainder later in the season the latest sown was very much more seriously damaged than that sown earlier. About the only portions of the early-sown part of the field to suffer serious injury were on the poorest soil. In short, the Toxoptera was found to be working its greatest damage in late sown or pastured wheat fields and among the young oats. Natural enemies were busily at work and apparently fast overcoming the pest. In the meantime Mr. Ainslie had found the pest destroying wheat in spots in the wheat fields about Fayetteville and Summers, Ark., March 16 to 20, as well as at Chandler, Okla., March 24, and at Guth- rie, Okla., on March 25. Near the latter place large circles were observed in the otherwise green fields of wheat. In the center of these circles the red soil was exposed by reason of the killing of the wheat plants, and these exposed circular areas were bordered by a band or girdle of yellow half-dead wheat plants, where the Toxoptera were most abundant. (See PL I, fig. 2.) In another field in this vicinity there was a stack of oats straw of the previous year, and from this stack a dead area extended at least 100 feet to the south. This area was nearly circular, with the stack almost in the center of the circumference. Xear and surrounding the stack was an area of dead volunteer oats, and beyond this a stretch of bare ground indicated where wheat had once stood. From people occupying a house near by something was learned of the previous history of this straw stack from which Mr. Ainslie determined that volunteer oats had sprung up after thrashing in 1906; these oats turned brown soon after, causing some wonder among farmers, and during the winter the plants died. The trouble spread to the wheat adjoining and here the wheat plants died early in the spring. There was here seemingly a repetition of the conditions in the fields about Summers, Ark., where Toxoptera infesting volunteer oats extended its destruction from these to the wheat near by. On March 26, between Guthrie and Kingfisher, Okla., Mr. Ainslie observed that the dead spots in the wheat fields were a striking feature of the landscape, for in the sunshine the bright green of the young grain made a striking contrast with the yellow-rimmed red circles where the Toxoptera had destroyed the wheat. Occasionally a field was free from these areas, but more of them were frightfully spotted in this manner. A field of wheat that was pastured more closely than most grain fields lay in the edge of Kingfisher and showed the attack of the Toxoptera worse than in adjoining grain. On March 27, at Kingfisher, Toxoptera was flying by the millions, the air being full of the migrants, and farmers who drove to town were covered on the windward side to their annoyance. The aphides seemed for the most part to fly low, but the wind hurried them at such a rapid rate that they might easily have been invisible when higher in the air. On the THE OUTBREAK OF 1907. 31 following day large numbers of Toxoptera were on the wing, always moving north. In a field of oats, sown in February, the plants had hitherto been very thrifty, but at this time in a great many of the drill rows the plants were about dead for a space of 8 or 10 feet, and in case of later sown fields the plants were all fast dying under the attack. There was becoming gradually apparent a fact of consider- able importance regarding the relative number of winged forms in the fields. In oats fields where the food was succulent and good it was difficult to find a single pupa, while in older and less succulent wheat, perhaps within a yard of the oats, pupss would form 75 or 80 per cent of the population of the blades. This was afterwards verified repeatedly by observation and by actual counting; indeed, through- out the entire spring this fact seemed to be substantiated. From March 31 to April 3 Mr. Ainslie carefully examined fields of wheat and oats in the vicinity of Wellington, Kans. He found wheat fields invariably evenly infested with Toxoptera though nowhere in any great numbers. Many of these were winged adults, indicating that they were migrants, and the young about them clearly evidenced a recent invasion. No dead areas were observed in the fields north of Pond Creek, Okla., but between Kingfisher and this point the circular dead spots were plainly in evidence. These dead areas, (PI. I, fig. 2), from their regularity in the field, plainly indicated the rows of oats shocks of the fall previous and were clearly to be seen where the oats had been shocked and allowed to stand through a period of wet weather. This generally produced a vigorous growth of volunteer oats when the shocks were finally stacked or removed, and in this young grain the Toxoptera seem to have had an early start. In some cases it was easily possible to observe these spots all over a field, although the volunteer oats were rarely entirely killed — perhaps only changed to a reddish color. The infestation seemed to be more marked in the wheat in the vicinity of these spots, and later the Toxoptera swarmed about these places. It may be noted that these observations of Mr. Ainslie in north- western Arkansas, southern Kansas, and northern Oklahoma were made upon the same dates as those of the junior author about Fort Worth, Tex., and at Hobart in southern Oklahoma, thus covering a latitude of nearly 400 miles. Mr. Ainslie returned to Kingfisher, Okla., April 3, and was joined there by the junior author on the 8th of the same month, where a number of experiments were carried out in the field, the results of which are given in the proper place. By- the 8th of the month para- sitized Toxoptera was found excessively abundant in the fields, in evidence of which a case was noted where a section of a leaf of wheat 1J inches in length carried 43 brown, parasitized individuals. Mr. Ainslie left Kingfisher, Okla., for Wellington, Kans., on the following 32 day, taking with him more than a bushel of these wheat plants with the parasitized Toxoptera thereon and on the 11th this material was put out in a field near Wellington where the Toxoptera was the most plentiful, in order to determine if it was possible to increase the limited numbers of parasites at the time observable in the fields so as to expedite the work of the latter in overcoming the pest. This was the first artificial introduction of Aphidius into Kansas, six days after which Prof. S. J. Hunter began distributing parasites. The following day a second lot of material sent from Kingfisher by the junior author, some of it carrying as many as 100 parasitized Toxoptera to a single blade of wheat, was distributed in a wheat field, also near Wellington, by Mr. Ainslie, some of it being placed in bunches to protect it from the weather and the remainder scattered over the ground among the growing wheat. The Aphidius already observed in the fields on the 11th appeared to be on the increase, as many as 11 parasitized individuals being observed on a single growing leaf, though but few of the adult parasites were observed abroad in the fields. On April 18 parasites were sent to McPherson and on May 18 to Manhattan, Aphidius being present in the fields at the time of introduction. These introductions will be taken up in detail farther on in this bulletin. On April 12 a letter was received from Mr. J. A. Akers, at Hooker, Beaver County, Okla., stating that the ' 'green bug" was destroying his wheat. The junior author, being notified of the outbreak, pro- ceeded there, arriving on April 24, and found that Mr. Akers's field was the only one in that locality that had been injured, and, in fact, it was outside the zone of destructive infestation in this State. This field comprised 52 acres, over a portion of which oats had been sown the previous year, while cowpeas had been grown upon another and much smaller part. Volunteer oats were plentiful over the first mentioned area. One of the infested spots was located among the wheat and volunteer oats, while the second spot was in the area pre- viously devoted to cowpeas. There were no other injured spots in the whole field, although an occasional Toxoptera could be found here and there over the field, which was also true of other fields in this vicinity. It is a significant fact that young plants of Agropyron occidentale Scrib. were found growing in both of these spots and they were as badly infested as the wheat plants. A few parasitized Toxoptera were found, but the parasites were apparently developing slowly on account of cold weather. The junior author went to Indiana the latter part of the first week in May, but was recalled to Kansas and reached Manhattan on thel8th, where he was met by the senior author, and a final experiment for the artificial introduction of parasites was here planned and begun at this time, the results of which are given farther on in the proper place. Bui. 1 1 0, Bureau of Entomology, U. S. Dept. of Agricultur Plate I. *-*t -* •> SSSri. wt- ^^^r^^~m&^^,^ ^kt Fig. 1.— Wheat Field Totally Destroyed by the Spring Grain-Aphis (Toxoptera graminum). Contrast with uninjured portion of field shown in figure 2. ( Original. ) Fig. 2.— Circular Spot in Wheat Field where Growing Grain has been Destroyed by the Spring Grain-Aphis. The growing grain on these circular areas is as completely destroyed as in the field shown in figure 1. Increasing in size and number, the spots come to include whole fields. (Original.) THE OUTBREAK OF 1907. 33 From here the junior author made a trip into northwestern and north- eastern Kansas and south-central Nebraska to determine the north- ern limit of destructive infestation. The following places were visited: Solomon, Dickinson County, Kans. ; Beloit, Mitchell County, Kans. ; Lenora, Norton County, Kans. ; and Kearney, Buffalo County, Nebr. The infestation at all of these places was very slight and no damage was done. At two places only, Solomon and Beloit, were parasites found. The senior author in the meantime proceeded to Great Bend, Barton County; Dodge City, Ford County; Garden City, Finney County; and Syracuse, Hamilton County — all in Kansas. The object of this trip was to see how far Toxoptera had spread to the westward. It was found at all of the above points, doing consid- erable injury; at Syracuse an unirrigated field of oats of 10 acres was found bordering an irrigation ditch. Along this ditch was a ragged border from 10 to 30 or 40 feet in width of vigorously growing oats where the "green bug" had apparently done no injury, while beyond this border, where the moisture from the ditch had not penetrated, the loss was total. In another case in the same locality, a part of the wheat in an unirrigated field came up in the fall and the rest not until the following spring; the former was uninjured by "green bugs/' while the latter was killed. From Syracuse the senior author proceeded to Wellington, Kans., to join Mr. Ainslie. In a letter dated June 5, 1907, Prof. C. P. Gillette states that he made a trip into the Arkansas valley early in the spring and found Toxoptera doing very serious injury to wheat fields; to such an extent was this the case that he advised some of the farmers to plow up some of their fields and plant other crops. Following this trip there was a heavy snowstorm and the "green bugs" were greatly diminished in numbers, though at the date of his writing (June 5) Toxoptera was abundant in the fields. On July 9 Prof. Gillette sent us badly parasitized Toxoptera on blue grass from Fort Collins, Colo., with the statement that the " green bug" had largely disappeared from the grain fields in that locality. Mr. Ainslie remained in the vicinity of Wellington, Kans., from the last week of April to the 21st of May, at which date he was joined by the senior author and went south to Kingfisher, Okla. The condi- tions found there were serious in the extreme, most of the grain fields being bare and many had been plowed and displaced by other crops. Between Wellington, Kans., and Kingfisher, Okla., a strip of country was encountered by them about 30 miles in width, beginning above Medford, Okla., with Pond Creek about midway between, and extending almost to Kremlin, Okla., over which the injury from Toxoptera was not nearly so great as in the country both to the 26675°— Bull. 110—12 3 34 THE SPRING GRAIN-APHIS OR north and south. This area was investigated by Mr. Ainslie on the 23d of May. There was plenty of evidence of Toxoptera attack. Some fields were killed outright and others badly spotted, but a number of fields were little injured. No particular reason could be assigned for this condition of the fields, and this area, with a few interruptions, extended on to the west indefinitely. This belt extend- ing across the wheat-growing section of Oklahoma was evidently observed by Mr. Sanborn, who stated in his notes, copies of which were furnished by Prof, Conradi, under date of March 29, 1907, " Northern boundary of parasitized infestation is between Kingfisher and Enid." Again, under date of March 30, "Pondcreek, Okla. Doing great damage, in large spots, here. There lies a peculiar fea- ture between this and Kingfisher. At these two points the infestation was about equal. Enid has no damage yet." Mr. Ainslie now started northward to trace Toxoptera to its most northerly point in the United States and to learn to what extent its parasite occurred with it, stopping at the following places: Kingman, Kingman County, Kans.; Hutchinson, Reno County, Kans.; Sterling, Rice County, Kans.; Scott, Scott County, Kans.; Great Bend, Barton County, Kans.; Oakley, Logan County, Kans.; Colby, Thomas County, Kans.; Goodland, Sherman County, Kans.; Manhattan, Riley County, Kans. ; Lincoln, Lancaster County, Nebr. ; Plainview, Pierce County, Nebr.; Dixon, Dixon County, Nebr.; Sheldon, O'Brien County, Iowa; Mason City, Cerro Gordo County, Iowa; Dodge Center, Dodge County, Minn. ; Rochester, Olmsted County, Minn. ; Brookings, Brookings County, S. Dak.; Aberdeen, Brown County, S. Dak.; Fargo, Cass County, N. Dak.; East Grand Forks, Polk County, Minn.; Hallock, Kitson County, Minn.; Grafton and Park River, Walsh County, N. Dak.; Larimore, Grand Forks County, N. Dak.; and Casselton, Cass County, N. Dak. He reached the last-mentioned place on August 5, after which he returned to Washington, D. C. Except at Kingman, Hutchinson, Sterling, Great Bend, and Man- hattan, Kans., Mr. Ainslie found but little damage resulting from Toxoptera, the most striking feature being the fact that parasites were found associated with Toxoptera at each point visited with the following exceptions: Goodland, Kans., very few Toxoptera in this immediate vicinity; Lincoln, Nebr., no Toxoptera found; Brookings, S. Dak., 2 to 3 Toxoptera only seen; Aberdeen, S. Dak., no Toxoptera found; Fergus Falls, Minn., only 1 Toxoptera observed here. The significant feature of this is that no parasites were introduced artifi- cially at any of these points outside of Kansas. From statements made by Prof. J. M. Stedman, who was professor of entomology at the University of Missouri at this time, it appears that Toxoptera was swept over the border from Oklahoma and Kansas into southwestern Missouri. Prof. Stedman states that there were from six to eight counties in the southwestern corner that were very THE OUTBREAK OF 1907. 35 badly infested; outside of these counties the infestation was slight. He received very few if any reports of its occurrence north of the Missouri River. It probably occurred in the northern part of the State also, as the bureau received a report, with specimens, of injury to oats at Weaver, Lee County, Iowa, and Mr. C. N. Ainslie found it occurring in small numbers at several points in northwestern Iowa. From reports received by this bureau it seems that Toxoptera was very abundant in northern Illinois, confining its injuries chiefly to oats. Mr. Edgar McGee, of Sciota, McDonough County, 111., sent us specimens July 5 which proved to be Toxoptera, and in a letter dated July 29 he stated that it was very widespread, that his and adjoining counties were badly infested, and that some fields of oats were so seri- ously injured that the owners had plowed them under and planted other crops. The yield in that locality, from Mr. McGee's report, seems to have been greatly reduced. At Sandwich, Dekalb County, 111., there was apparently consider- able damage to oats; no specimens were received; the injury in all probability was, however, due to Toxoptera. To quote from a letter from Mr. Clark Graves, bearing date of July 12: I have today mailed to you, under separate cover, a fair sample of the oats of this vicinity, and I think from general appearances that the crop will be shortened half on account of the green bug. The bugs have now disappeared, and it would seem that the late oats have suffered considerably more than the early ones. There were no specimens of plant-lice in this material from Mr. Graves. A report, with specimens, was received from Manteno, Kankakee County, 111., which stated that that section had suffered considerably from " green-bug" attack. We have only one record of serious injury from Indiana in 1907 that can without doubt be attributed to Toxoptera. This was in a small field of oats just outside the limits of Indianapolis. The junior author examined this field and found that over an acre had been seri- ously affected, part of it being entirely destroyed. The " green bug" disappeared from the oats before the latter headed out, probably overcome by Aphidius and other enemies. This infestation appar- ently originated from rank bluegrass growing along one side of the field. Later in the season, when the oats had been harvested, Tox- optera could be found along this margin on the bluegrass, where the sexes appeared and eggs were produced. Toxoptera was found at other points in Indiana, but only in small numbers. Mr. T. H. Parks, of this bureau, states that in the latter part of June, 1907, the oats on his father's farm in Pickaway County, Ohio, were badly damaged by aphides. He states that parts of some fields in the neighborhood were scarcely worth cutting. Aphides were very abundant on the plants and parasitized aphides were very plentiful also. The oats plants that were badly infested turned brown, and 36 THE SPRING GEAIN-APHIS OR before they were ready to head out the aphidids disappeared. This was probably due to the presence of the parasites. Wheat was not attacked or injured by these aphides. Mr. Parks did not have any of this material identified, and we can not say absolutely that this was Toxoptera graminum Rond., but the character of the attack, the sudden disappearance of the aphidids, and the fact that they did not disturb wheat coincide with our observations on this insect in this latitude and to us clearly point to Toxoptera as the originator of the trouble. Part of the trouble referred to in letters cited in Bulletin 210 of the Ohio Agricultural Experiment Station was, in all probability, due to "green-bug" attack, since from our own observations on this species in northern latitudes a part of this injury appears to be characteristic of Toxoptera. North and South Carolina also suffered somewhat from the depre- dations of this insect in 1907. The senior author made a trip into this section, reaching Sumter, S. C, April 17, 1907. He found that all fields of oats, the only grain sown, were more or less affected; here and there brown areas occurred, showing the characteristic work of Toxoptera. This condition was noticeable from Sumter, S. C, to Charlotte, N. C, indicating that the infestation was general. Both Macrosiphum granaria Buckt. and Toxoptera graminum Rond. were present, but the latter was by far the more numerous. There were very few parasites or coccinellids in evidence. In a letter dated June 18 Mr. E. C. Haynsworth, of Sumter, stated that soon after the senior author's visit in April the weather became warmer and Toxop- tera disappeared very rapidly. In some parts of North Carolina the injury was quite serious. Mr. Franklin Sherman, jr., of the North Carolina Department of Agricul- ture, has kindly placed his notes on this outbreak at our disposal. He stated that the worst area of infestation centered about Winston- Salem, in Forsyth County, N. C, although some injury was also inflicted in Guilford, Davie, and Rowan counties in the same State, some fields being almost totally destroyed. Parasites were present, though not in sufficient numbers to hold Toxoptera in check. The senior author went directly from Sumter, S. C, to Winston- Salem, N. C, reaching the latter place April 19, where he was met by Mr. Sherman, and they went over the ground together. A number of fields were examined, ranging from slightly infested to totally destroyed. In some fields of wheat, where there had been quantities of volunteer oats, the infestation was more severe. Parasites were present in great abundance in some fields, but they did not appear to have checked the pest in time to save all of the fields. The senior author thus summarizes this outbreak: From a study of the entire neighborhood it seems quite evident that the outbreak of Toxoptera in the vicinity of Winston-Salem was primarily due to the presence of Bui. 11 0, Bureau of Entomology, U. S. Dept. of Agriculture. Plate II. Fig. 1.— Stand on which Rearing Experiments were Carried Out in Rearing the Spring Grain-Aphis. (Original.) Fig. 2.— Area on Grounds of the United States Department of Agriculture, at Washington, D. C., where the Spring Grain-Aphis Usually Occurs on Bluegrass in Excessive Abundance During Summer. The area infested is indicated by (Original.) THE OUTBREAK OF 1907. 37 fields of fall oats and more or less volunteer grain in other fields, all of which consti- tuted breeding grounds for the pest during the preceding autumn, and from which winged individuals migrated and established new colonies in other fields; these, owing to influence of weather on the development of parasites, caused the most of the injury in wheat. We received a letter with specimens from Mr. L. M. Smith, Mr. Sherman's assistant, at Newport, Carteret County, N. C, stating that he found a small field of oats in the outskirts of town that was con- siderably damaged by Toxoptera. This county is on the coast and Newport has an elevation of 19 feet. From this it seems that in all probability Toxoptera covered the entire State. The senior author also found Toxoptera in destructive abundance at Midlothian, Chesterfield County, Va., in a small meadow of orchard grass. Mr. J. L. Phillips, the State entomologist, reported a slight outbreak at Cloverdale, Botetourt County, Va., in rye, and stated that considerable damage had been done in some parts of the field. One undetermined Aphidius was found at Midlothian, while none was reported from Cloverdale. There was an outbreak of Toxoptera in the bluegrass lawns north of the buildings of the Department of Agriculture at Washington, D. C, in July, 1907. The infested area (see PI. II, fig. 2) was appar- ently confined to the space of about an acre, where it was excessively abundant; outside of this area practically no Toxoptera could be found. This offered a good opportunity to test spray materials and a number of experiments of this kind were carried on. Dr. Howard, personally, found Aphidius present in this infested area though in very limited numbers. In all probability this was Aphidius avenaphis Fitch, as we have since found this species in this exact locality but at no time have we found A. testaceipes Cress., which, until Mr. Viereck revised this group, had been considered to be Lysiphlebus tritici Ashm. We did not, in 1907, find any species of Aphidius present and did not know that Dr. Howard had done* so, as he soon after sailed for Europe and at the time Circular 93 of this bureau was published the statement as to its nonoccurrence was not called to his attention in time to be corrected and he did not inform us of his find, supposing that we knew of it already. Mr. Kelly, how- ever, found Allotria sp. present there in 1907, and we have since found this to be a parasite of Aphidius, which may account for the fact that the latter was present in such limited numbers. In 1908 Aphidius avenaphis was quite plentiful there, although specimens were not preserved, while Allotria sp. was found sparingly on the grounds else- where in the vicinity. As Toxoptera attracted no attention in this area on the grounds of the Department of Agriculture in 1909 we have no records for that year. In 1910 Toxoptera was again injuri- ously abundant on the same area and no Aphidius could be found, while Allotria sp. was still in evidence. It seems possible that condi- 38 tions were unfavorable for the rapid increase of Allotria in 1908, which conditions would prove favorable for Aphidius and also unfavorable for its host, the Toxoptera. This infested area on the department grounds in Washington has proved to be of considerable interest, as the fluctuations of Toxoptera there, as well as those of its parasite Aphidius and the secondary parasite Allotria, must coincide with what is going on in similar places over the country, thus forming small secluded breeding areas where Toxoptera survives throughout the summer, more especially in the South. The area in question is a depression covered chiefly by bluegrass, occupying perhaps half an acre, surrounded on all sides except the south by shade trees (See PL II, fig. 2.) It is rather more moist and therefore cooler in summer than other portions of the grounds and in common with the rest is kept closely mown. An underground steam pipe which affords heat for a large number of greenhouses extends along the southern and eastern margins ; the ground above this pipe is always much warmer than the surrounding area during winter, the snow disappearing first and the grass in that location starting much earlier in spring. So far we have not found that these latter conditions have any influence in enabling the Toxoptera to breed viviparously during the winter. Even when the Toxoptera was excessively abundant here none could be found in the bluegrass-covered grounds only a few yards away, except in 1910, when it was quite numerous about the Washington Monument some four blocks away. Because of its isolation — there are no grain fields within miles on the Maryland side of the Potomac River and the department experiment farm at Arlington, Va., has the only grain for miles on the west side of the river — and because these last had never suffered from Toxoptera attack, this area became of too much importance as a convenient held of observation and experi- mentation to make an attempt at experimenting with the importation of great numbers of Aphidius desirable. There is every reason for believing that it is in similar favorable localities that Toxoptera passes the summer months in the southwestern portion of the country, where, as observations have shown, it is not able to withstand the high temperatures of the open fields. Toxoptera has been studied throughout the summer in the South- west with much difficulty, and not at all satisfactorily for the reason that we have been unable to keep it under continuous observation in the open fields. Except in cases of local outbreaks here and there over the country there has been no serious injury to grain crops by the " green bug" since 1907. Many additional localities for the species have been added since then, however, and it now appears to cover almost the entire United States, excepting perhaps New York and the New England States. (See fig. 4, p. 19.) THE OUTBBEAK OF 1907. 39 LOSSES FROM DEPREDATIONS IX 1907. It is impossible to arrive at the actual monetary loss occasioned by this fearful outbreak, as no data have been collected with this special end in view, either by the State or National governments. Several points must be considered in making such an estimate. Large areas planted to wheat and oats were abandoned, part being planted to other crops and the remainder left lying idle. Much money that was entirely lost was expended in seed, fertilizers, pre- paring the seed bed and planting; of course all of the fertilizer would not be lost where another crop followed. The greatest source of loss came through partial or actual destruction of the young wheat, thus greatly reducing the yield. The Bureau of Statistics of the Department of Agriculture kindly compiled the following table for us, which will shed some light on the amount of loss probably attributable to the " green bug." Table I. — Losses from depredations by the spring grain-aphis in 1907 in Kansas, Oklahoma, and Texas. KANSAS. Winter wheat. Oats. Acreage planted in fall of preceding year (pre- liminary). Per cent aban- doned. Acreage harvested (revised). Yield per acre. Total pro- duction. Acreage. Yield per acre. Total pro- duction. 1905 5,645,000 5,702,000 5,930,000 5,930.000 6,173,000 6,195,000 6.3 10.0 4.8 2.5 4.5 35.0 5,290,000 5,132,000 5,645,000 6, 108, 000 5,895,000 4,300.000 Bush. 13.9 15.3 11.3 12.8 14.5 14.2 Busheh. 73,527,000 78,517,000 63,788,000 78,182,000 85.478,000 61, 060, 000 858,000 1,050.000 1,092,000 994. 000 964.000 1.400.000 Bash. 27.1 23.6 15.0 22.0 28.2 33.3 Bushels. 23.248,000 1906 24,780,000 1907 16,380.000 1908 21,868,000 1909 27,185,000 1910 46, 620, 000 73,425,000 26, 680, 000 OKLAHOMA. 1905: Ind. T Okla 286, 000 1,493,000 249, 000 1,403,000 216,000 1,235,000 1,379,000 1,241,000 1,604,000 5.5 3.9 3.2 5.0 28.0 35.0 2.3 6.5 3.0 270, 000 1,435,000 241,000 1,333,000 10.0 8.2 12.0 14.0 2,703,000 11,764,000 2,890.000 18,664,000 202,000 294,000 218, 000 350, 0C0 36.0 33.0 34.2 34.4 7,258.000 9, 717, 000 1906: Ind. T Okla 1907: Ind T 7, 447, 000 12,040,000 Okla 959,000 1,347,000 1,225,000 1,556,000 9.0 11.6 12.8 16.3 8,631,000 15,625,000 15,680,000 25,363,000 418, 000 450,000 550, 000 632,000 15.0 25.0 29.0 36.5 6, 270. 000 1908 1909 11,250,000 15,950,000 1910 23,068,000 16,887,000 15, 500, 000 TEXAS. 1905 1,319.000 1,266,000 1,266,000 988,000 929,000 1,295,000 5.3 3.0 70.0 6.5 27.5 3.3 1.249.000 1,228,000 380,000 924,000 555.000 1. 252^009 8.9 11.5 7.4 11.0 9.1 15.0 11,118,000 14,126,000 2.812,000 10,164,000 5,050.000 18, 780, 000 914,000 914,000 500,000 750,000 615,000 695,000 31.4 34.8 19.0 28.9 18.7 35.0 28,713,000 1906 1907 31,823,000 9, 000. 000 1908 1909 21,675,000 11,500,000 1910 24,325,000 10,342,000 21,256,000 40 THE SPRING GRAIN-APHIS OR If we average the 5-year period and calculate the loss on this basis for 1907. it wih be seen that the total crop for Kansas, Oklahoma, and Texas fell about 50,000,000 bushels short of this average — both wheat and oats being considered. Seventy per cent of the Texas wheat acreage was abandoned. This does not represent the loss as it actually occurred in various parts of the States, as some parts of each State were more badly affected than others and the good parts would bring up the yield for the poorer portions. Sumner County. Kans.. is a good illustration of this. It is located in the extreme southern portion of the State and was in the badly infested districts. To quote from a letter from Mr. George H. Hunter, of Wellington, Kans.. dated February 6, 1908: I wish to explain that our crop of winter wheat in Sumner County for the year 1907 amounted to 1.909.574 bushels; this is our latest estimate, while the general average is about four and one-half million bushels for Sumner County, and that would be a safe basis for you to figure on. According to our acreage last year, if it had not been for the green bugs. I think we would have had at least four to four and one-half million bushels of wheat. THE SITUATION IX 1911. The winter and spring of 1910-11 west of the Mississippi River, but not east of it. was such as would tend to bring about another invasion from the pest. Some injury was reported, accompanied by specimens, from Pecos River valley in southeastern Xew Mexico. Mr. J. T. Monell of this bureau, however, visited the locality in April and reported the pest as having disappeared without doing serious injury. The material received was almost universally para- sitized by Aphidius testaceipes Cress., winch probably overcame the Toxoptera before its occurrence reached the magnitude of an invasion. There was also a limited incipient outbreak in eastern Oklahoma, which was investigated by Mr. Kelly. Here. too. the parasites apparently gained supremacy before serious injury was done, except perhaps in a few isolated cases. There is little doubt that the unusual and excessively high tempera- ture for even a mild winter that prevailed throughout the Southwest during a portion of the winter months was sufficient to revive the parasites as well as to aid their host, and thus bring about conditions that enabled the parasites to prevent the aphidids from increasing in numbers to a point where they were beyond their control. 41 FOOD PLANTS. This insect has a very wide range of host plants and can on that account find fresh food at any season of the year. In this way it is enabled to perpetuate itself over vast areas of country and under almost every variety of climate. Rondani, who first described the species in 1852, gives the following list of host plants: Oats (Avena sativa); wheat (Triticum vulgare); spelt ( Triticum spelta) ; Arrhenatherum elatius (Avena elatior) ; couch grass ( Triticum repens) ; Hordeum murinum; Lolium perenne; Capri- 61a (Cynodon) dactylon; soft chess (Bromus Jiordeaceus) (mollis); and corn (Zea mays). He states also that Toxoptera had been found quite abundant upon the foliage of rice (Oryza sativa) and common barley (Hordeum vulgare). We find no other references to its being found upon rice. In 1863 Passerini adds sorghum (Andropogon sp.) and he also observed it on barley. Macchiati, in 1882, added the following hosts: Dactylis glomerata, Bromus erectus, and B. viUosus (maximus); in 1883 he added Triticum viUosum, Avena fatua, and A. harhata; in 1885, Poa annua. Del Guercio, in 1906, mentions it as occurring upon buckwheat (Fagopyrum esculentum). This is the first and only reference we have found in which it has been accused of infesting plants other than those belonging to the Graminese. Toxoptera was first observed upon wheat and oats in the United States. In 1889 the senior author observed it feeding upon rye and in 1890 he found it plentiful at Lafayette, Ind., upon Dactylis glomerata. In 1907 he found it destructively abundant upon the same grass at Midlothian, Va. This infested field was from 4 to 5 miles from wheat, oats, or rye fields. In Insect Life,1 he states that Toxoptera will live upon the leaves of all lands of grains, including corn, during summer. In 1902 he found Toxoptera feeding upon cheat (Bromus secalinus) and rye grass (Elymus canadensis) at Peotone, 111. The junior author found it quite abundant on volunteer corn plants among oats on April 2, 1907, at Hobart, Okla. A cornfield near a badly infested wheat field was found to be suffering also. Mr. C. N. Ainslie of this bureau, on April 4 of the same year, at Kingfisher, Okla., found a cornfield that was seriously injured by Toxoptera. Farmers in Oklahoma were very much disturbed over the prospect that the corn also would be swept away by the " green bug," but later developments proved that it was not a serious pest to corn. The junior author found Hordeum pusillum and Alopecurus geniculatus badly infested on April 12 at Kingfisher, Okla., and Agropyron occiden- tal was found harboring the pest in large numbers at Hooker, Okla., in May. The senior author, Mr. Ainslie, and Prof. E. A. Popenoe, i Insect life, Div. Ent., U. S. Dept. Agr., vol. 4, p. 245. 42 THE SPRING GRAIN-APHIS OR of Kansas, also found the Hordeum pusillum much infested later in the season. In July there was an outbreak of Toxoptera on blue- grass (Poa pratensis) on the grounds of the United States Department of Agriculture, Washington, D. C. Later in the season the junior author found it on bluegrass in the fields about Richmond, Ind. In the fall of the same year (1907) this was the only plant on which the sexes and eggs could be found. In fact, for Indiana, Illinois, Ohio, and more northern localities bluegrass appears to be the normal host, and the " green bug" is readily found upon it at any time in the year even when it can be found only sparingly upon any other plant. A number of new host plants were added to the list in 1908. Mr. Kelly, of this Bureau, found Toxoptera feeding freely in the fields upon Hordeum jubatum and DistiMis spicata in Montana and upon a species of Andropogon in Colorado. Mr. Ainslie found it breeding freely in the fields upon Hordeum jubatum, H. csespitosum, H. nodosum, Elymus striatus, Agropyron tenerum, Bromus unioloides, B. porteri, Stipa viridula, and Polypogon monspeliensis about Artesia, N. Mex. In one instance Mr. Ainslie found several alfalfa plants (Medicago sativa) with colonies of Toxoptera upon them, as many as 21 speci- mens being observed on a single leaf. This seems very unusual and we have no other records of its occurrence on this plant. Prof. C. P. Gillette, of Fort Collins, Colo., found it infesting Agropyron occidentale, and in 1907 he found it feeding upon bluegrass. During the summer of 1908 Toxoptera was found by the junior author to breed freely upon Dactylis glomerata, Eleusine indica, Eragrostis pilosa, E. megas- tachya, Sporobolus neglectus, Agropyron repens, Elymus virginicus, E. canadensis, and Bromus secalinus, in his rearing cages at Rich- mond, Ind. In 1909 and 1910 a few more plants were added to the fist. Mr. Ainslie found it breeding freely upon Hordeum murinum in Arizona and upon Agropyron occidentale in New Mexico. Mr. Kelly found it breeding freely upon millet (Chsetocloa italica) and upon Japanese millet (Echinocliloa crus-galli) in Kansas. Mr. Harper Dean, jr., then of this bureau, found it feeding upon Stipa leucotricha in Texas. Mr. T. D. Urbahns, of this bureau, found that it bred readily in his cages at Dallas, Tex., upon Bermuda grass (Capriola dactylon), Chxtochloa viridis, Johnson grass (Sorghum lialepense), and upon rice (Oryza sativa). During the summer of 1909 Mr. T. H. Parks, of this bureau, and the junior author observed that Toxoptera bred freely upon Elymus striatus, Juncus tenuis, Poa compressa, Bromus commutatus, B. tec- torum (?), B. inermis, sheep's fescue (Festuca ovina), hard fescue {F. duriuscula), meadow fescue (F. elatior), various-leaved fescue FOOD PLANTS. 43 (F. JieteropJiyUa) , F. rubra, Agropyron occidentals, and Italian rye grass (Lolium multiflorum) , in their rearing cages at Lafayette, Ind. The following is a complete tabulated list of host plants1 to date, in so far as our records show. IN EUROPE. Barley. Corn. Oats. Rice. Wheat. Spelt. Sorghum. Agropyron (Triticum) repens. Avena barbata. Avena elatior=Arrhenatherum elatius. Avena fatua. Bromus erectus. Bromus maximus=B. villosus. Bromus mollis=B. hordeaceus. Capriola (Cynodon) dactylon. Dactylis glomerata. Fagopyrum esculentum. Eordeum murinum. Lolium perenne. Boa annua. Triticum villosum. IN AMERICA. Barley. Corn. Oats. Rice. Rye. Sorghum. Spelt. Wheat. Alfalfa (Medicago sativa). Agropyron occidentale.2 Agropyron repens. Agropyron tenerum.2 A lopecurus 'genicula tus . 2 Cheat {Bromus secalinus).2 Bromus commutatus.2 Bromus inermis.2 Bromus porteri.2 Bromus tectorum (?).2 Bromus unioloides.2 Capriola dactylon. Chsetochloa italica. Chaetochloa viridis.2 Dactylis glomerata. Distichlis spicata.2 Echinochloa crus-galli.2 Eleusine indica.2 Elymus canadensis.2 Elymus striatus.2 Elymus virgin icus . 2 Eragrostis megastachya.2 Eragrostis pilosa.2 Festuca duriuscula.2 Festuca heterop>hylla.2 Festuca ovina.2 Festuca elatior. Festuca rubra.2 Holcus halpensis.2 Eordeum caespitosum.2 Eordeum jubatum.2 Eordeum murinum. Eordeum nodosum.2 Eordeum pusillum.2 Juncus tunuis2 Lolium, multiflorum.2 Poa compressa.2 Poa pratensis.2 Polypogon monspeliensis.2 Sporobolus neglectus.2 Stipa leucotricha.2 Stipa viridula.2 i During 1909 Mr. C P. v. d. Merwl, Bloomfontein, Orange Free State, Africa, wrote us that he had found Toxoptera graminum attacking " Bermuda grass " and their native blue-grass (Andropogon Mrtus). 2 These are host plants not previously recorded. 44 CHARACTER OF ATTACK. The actual effect upon the plant, whether chemical or physiological, is not clearly understood. If a few Toxoptera be placed upon a per- fectly healthy plant, in a few days the tissue in the immediate vicinity of the aphidids will take on a yellowish tinge; if the aphidids remain in one place for a considerable time and increase in numbers, the whole plant gradually turns yellow and dies, the leaves changing to reddish brown. "When the original source of infestation arises from some one or more points within a field, as described elsewhere in this paper, the plants take on a yellowish color in small, almost circular areas, (PL I, fig. 2) and as the Toxoptera increase in numbers the plants in the center die, becoming reddish brown, and the aphidids work outward in every direction from the center, gradually enlarging the spot until it may cover many acres. When a field is infested from without by migrating forms, the aphidids appear to spread evenly over the entire field and the whole gradually turns yellow, and in cases of severe outbreaks a whole field may die simultaneously. (See PL I, fig. 1.) These aphidids are essentially leaf -feeders, rarely if ever being found injuring the heads or fruiting parts of the plant. Toxoptera appears to have a more strildngly disastrous effect upon wheat or oats plants than any of the other common grain aphidids. Seemingly when in no greater numbers than other species the plants will succumb more quickly to the attack of Toxoptera. VIVIPAROUS DEVELOPMENT. Toxoptera graminum, as already shown, has been found to breed over a. wide range of country, and its behavior, under the varying temperatures and climatic conditions prevailing over this vast terri- tory, presents and opens up a broad field for investigation. IN THE SOUTH. In northern latitudes the normal manner of reproduction among the Aphididge is both sexually and asexually. In southern latitudes hese conditions, apparently, do not obtain, as here the normal means of reproduction seems to be asexually, each generation being com- posed entirely of viviparous females. South of about the thirty-fifth parallel, except in high altitudes, it appears that Toxoptera breeds continuously throughout the year without the appearance of the true sexes. April 6, 1906, Mr. George I. Reeves, of this bureau, found the eggs of a plant-louse on wheat at Nashville, Tenn., and Mr. Kelly found males (fig. 6), females, and eggs of Toxoptera at Knoxville, Tenn., in December, 1908. The eggs found by Mr. Reeves may have been those of Toxoptera, but we VIVIPAEOUS DEVELOPMENT IN SOUTH. 45 Fh 46 THE SPRING GRAIN-APHIS OR ' i GREEN BUG. VIVIPAROUS DEVELOPMENT IN SOUTH. 47 can not be sure of the species as they were not reared. Winged and wingless viviparous females (figs. 7, 8) were, however, present at the time the eggs were found, as were also those of both Aphis (Sipho- coryne1) and Macrosiphum. Mr. E. Dwight Sanderson obtained the males and oviparous females of Macro siplium granaria Buckt. in Texas but only artificially in his rearing cages. Mr. R. A. Vickery, of this bureau, found males, females, and eggs of Aphis maidi-radicis Forbes at Salisbury, N. C. These instances mentioned above are probably the most southerly points at which oviparous forms of plant-lice have so far been found in the United States. In the Southern States, wherever there is sufficient food, Toxoptera apparently breeds viviparously throughout the year; for this rea- son the number of generations here, other things being equal, should far exceed that in the Northern States. As a matter of fact, however, the dry, hot, protracted summers of the Southwest are probably disas- trous to the species during the hot months, except perhaps in secluded nooks, where there is a supply of succulent host plants. In northern Texas, as observed by Mr. Urbahns, during June of 1909, Toxoptera rapidly disappeared with the ripening of the grain crops and the approach of hot weather. Winged forms migrated with the breeze early in this month, and wingless forms soon perished from extreme heat and a shortage of green food in the field. Obser- vations clearly showed that it was almost impossible for the " green bug" to live and reproduce in grain fields during the summer. While 1 Probably Siphocoryne avense Fab. The use of the generic name Siphocoryne, as applied to this species, is questionable, and is not at present followed by many, perhaps the major portion, of the students of the Aphididse. According to Schouteden (Ent. Soc. Belgique, vol. 12, p. 217, 1906, Catalogue Aphides de Belgique) it should be Aphis. Some of our best students, however, admit that this particular species, avense, is on the borderland between Siphocoryne and Aphis. Fig. 8. — The spring grain-aphis: Wingless viviparous female, actual size, 2 mm. (Original.) Enlarged; 48 the temperature was above and precipitation below normal, during this particular season, the effect was so evident that there is reason to believe that under normal conditions these aphidids do not live in fields directly exposed to the sun during the summer months. The table on pages 64-69 on daily reproduction, length of reproductive period, and longevity show a decided decrease in all of these for the summer months over those of spring and fall. The facts upon which these figures were based could be secured only by pro- tecting the aphidids from exposure to the hot summer sun. Aphidids exposed without such protection were unable to live through the season, though special care was taken to furnish them with a supply of green food plants.1 Mr. Urbahns secured the following results by removing Toxoptera, together with its green food plants, from a shaded position and sub- jecting it to the temperature of loose, unshaded soil. August 18, with the soil temperature at 145° F. in the sun, 12 Toxoptera on a wheat plant were exposed 30 seconds; 5 fell to the ground dead, 7 remained on the plant dead. Three adults and 4 young on a wheat plant were similarly exposed for 30 seconds, after which time all were dead. One winged and 4 wingless adults on a wheat leaf were exposed for 30 seconds, when they were found to be dead on the plant. Thirteen adult aphidids on wheat plants were exposed for 15 seconds, 5 fell to the ground dead. After 30 seconds exposure the plant was removed to the shade; 6 more were then dead on the plant and 2 were alive between the leaves. Soil temperature 118° F. (shaded by cloud). Nine aphidids on a wheat plant were exposed for 30 seconds, 2 died, and 7 remained alive. A potted wheat plant bearing several hundred aphidids, the temperature being 114° F. in the shade, was removed from the shade for 5 minutes. A large percentage of the aphidids fell to the ground, some survived, but many died. A potted wheat plant bearing several hundred aphidids was kept in the shade where the maximum temperature was 114° F. Next morning many of the aphidids were dead. When the soil temperature was 116° F. shaded by a thin cloud, 3 aphidids on a plant were exposed for 60 seconds, 1 died, and 2 remained alive. August 19, the soil temperature being 128° F. in the sun, 12 aphidids on a young plant were exposed for 30 seconds; 5 fell from the plant and died, while the other 7 were dead on the plant. When the soil temperature was 130° F. in the sun 12 aphidids on a young plant were exposed for 20 seconds. All were then dead. When the soil temperature was 128° F. in the sun 11 aphidids on a plant were exposed for 30 seconds; at the end of this time all were dead — i fell to the ground, and 7 remained on plant. At a soil temperature of 130° F. in the sun 8 aphidids on a plant were exposed for 15 seconds; all were then dead — 3 fell to the ground, and 5 remained on the plant. The results of these experiments prove that Toxoptera can not survive the summer in the open fields in sections of the country where the pest commits its most serious ravages with the greatest 1 Mr. J. T. Monell suggests that this may be due as much or more to the hot, dry air as to the direct rays of the sun. VIVIPAROUS DEVELOPMENT IN NORTH. 49 frequency. They also account for our inability to locate it in such territory during the summer months. A careful search was made at different times for grasses that were actually serving as summer food plants. The only hope of finding such was in well shaded spots along streams, where, from all indications, Toxoptera would be sufficiently protected to live and reproduce throughout the summer. At Piano, Tex., Toxoptera was rapidly disappearing from the fields in early June. By June 14 there was only a limited number of plants which still supported the remaining few of these aphidids and the latter were soon carried away by ants. When confined on green food plants and protected from their enemies by a large frame covered with thin cheesecloth Toxoptera lived until July 3. After this date it was apparently too hot for their existence. Out in the open, where young wheat and oats plants were sustained by frequent watering, they lived until July 15. After this date they apparently could not endure the summer temperature and no more were found. Since no reinfestation appeared up to November 30, it was quite evident that the aphidids had all perished. On June 28 viviparous forms of this species were found rather abundantly in a small field of oats at McAlester, Okla. This field of a few acres in size was on the east slope of a rocky hill. A natural growth of timber surrounded the field and a few trees grew in its midst where rocks make cultivation impossible. Green vegetation was abundant in shaded places and along the creek one-half mile to the east. Conditions of this sort are certainly favorable for Toxoptera to live and reproduce throughout the summer as long as they find the food plants present. While these spots, favorable to Toxoptera, are characteristic of eastern Oklahoma, where, as has been stated, an incipient outbreak of the pest actually occurred in 1911, they are also found along streams in the central part of that State and in northern Texas. As there appears to be no resting or egg stage in the South, whenever there is a warm open winter these'' aphidids become very abundant and threaten the grain crops of this region. IN THE NORTH. Farther north, in the vicinity of Lafayette, Ind., viviparous repro- duction is confined to the months of April, May, June, July, August, September, October, and November. During mild winters, how- ever, the species may breed viviparously throughout the year, as the senior author found it breeding in the open throughout January, Feb- ruary, and March, 1890, notwithstanding the fact that on January 24 the temperature fell as low as + 3° F.; on February 9, to + 6° F., and on March 6 to + 4° F. It appears that a temperature of about 26675°— Bull. 110—12 4 50 THE SPRING GRAIN-APHIS OR GREEN BUG. zero, with no protection, is fatal to Toxoptera, except to the egg, but the fact that it withstood the winter in 1890 can easily be accounted for. That winter was unusually mild throughout, with the excep- tion of the dates mentioned, and if one consults the weather records it Fig. -The spring grain-aphis: Oviparous female, showing eggs within the abdomen, actual size, 2.25 mm. (Original.) Enlarged; will be found that on January 24 there were 3.5 inches of snow, Feb- ruary 9, 3.4 inches, and March 6, 4 inches. The covering of snow in each instance would appear to have been sufficient to protect the Toxoptera, as on December 8, 9, and 10, 1909, at Lafayette, Ind., the temperature fell as low as from — 1° F. to — 4° F. below zero, and plant-lice of all kinds, in the rearing cages out of doors, were killed, while those in a near-by wheat field, covered with several inches of snow, were found to be in good condition on December 13, at which time the cold spell was broken and the ground began to thaw. As a rule, Toxoptera breeds slowly in October and November, at which time the majority become oviparous females (figs. 9, 10) and males (fig. 6). Fig. 10.— The spring grain-aphis: Hind tibia of oviparous female. Greatly enlarged. (Original.) THE SPRING GRAIN-APHIS OR GREEN BUG. 51 REARING METHODS. All of the rearing work, unless otherwise stated in the text, was conducted out of doors under as nearly normal conditions as it was possible for us to secure. The wheat plants on which the Toxop- tera were confined were grown in flowerpots and covered with lantern globes, over the top of which was drawn a very thin fabric commercially known as swiss. The pots were placed on a rearing stand having one side hinged in such a manner that it could be let down in fair weather and closed up in case of gales or severe beating storms. This stand with its contents is illustrated in Plate II, figure 1 . A thermograph was placed in this stand, and thus continuous records of temperature were secured. In the middle of the summer of 1907 two series of investigations were begun and were continued until De- cember to determine the number of generations. In both 1908 and 1909 series of generation studies were begun in spring with the egg (fig. 11) and continued until the egg-laying forms appeared in the fall. In making these observations, the first individuals to hatch from the eggs in the spring were isolated; the first-born from these were in turn isolated, and this process was continued throughout the season until the egg-laying forms ap- peared. The last-born was also kept and the same mode of procedure con- tinued until fall, as was the case in the line of the first-born. All young other than the first-born of the first series and the last-born of the second series were counted each day and destroyed. In this manner, each series being considered, we would arrive at the maxi- mum and minimum number of generations. During these three years a vast amount of data, besides that on the number of generations, was thus accumulated. (See table, pp. 52-57.) Fig. 11.— The spring grain-aphis: Eggs as deposited on leaf: a, Dorsal view; 6, lat- eral view. Greatly enlarged. (Original.) 52 * £3 •na3 mnQjj -P9§ q^iiTN -U93 q^qSig •U0T^J9 -U98 qiii9A9g •UOT^B -J9naS q^xrg -J9H93 'qijr J •noi;BJ9 -TI93 qimoj •uoi^Bja -nag puooag lsjg'-A^u9A\j, •UOp'BJ9n93 q^apjii9AV j, •U0T1'BJ9U92 q^iiag^qSia 'TI0I1'BJ9U93 qiU99JU9A9g q}U9 9 % X T g •U0H'BJ9U93 q^U99^JTJ ,UOi;'BJ9U92 qq.u99;jnoj •UOiaBJ9U93 •noi;,BJ9U93 {% 1 1 3 AY J.. •UOI^13J9U93 q;n9A9ia 'uoi^bj9 -U92 'q;u9x •U0T^'BJ9 -U93 'q^ui^j; -U93 q;q3ja •nopBaa -U93 q'^U9A9g •U0413J9 -U93 'q^xig -J9U93 \%J\3. -U93 q}Jtio & •uot^j9 -U93 piiqj, •uop'Bjg -U93 pU009S -J9U93>SJX1 •amiuiutj^ •nmnnx'BH PS ooooooooooo OOOOOOOOOOOOOOOOOOOOOOqC^KM'-H'-i'OTfiOCOlMOtM ilOOlOtDNN^NNi i (N O y-i CO C-q 00 CO ^s 00 tO>-l 00 O 00 tO < •*NHN'OMOI >t^t^t^t^oocoto-<*< IHNW^'OCONMOsgHNM^iOONOOaOHNM^UJj REARING METHODS. 53 oooooooooo OOOOOCIN ■* ONiO CO o oooooooocxmi-i oo o r--*,-i t- co.-* o i-H i-< « o th o o ih «-h ^oooooooooo ! ! ! OOi-liOOOOOOOOOOM»«NMHHH 10 ■ lOoooooooooooocqeq i-h o 1-1 -* "OOCOOOINHNf3?3rtNHO ..OOOOOOOOOOCO^,-! O CO NOi-H0N00N(DNOMOOTT(IHi0HlNTi.oCNXOWfflO' -U93 XIIUQJj • 0000000©© 'uoi^'BJa ; .' ,' '. ,' ! !,ooo©©ooooo©ooo©oo©ooco o ps hn^o 'UOI}13J9 «3 ! ' lO t>- O niO wH(NM^iflCNMOiO'JiNroTiiiocNooaiOj;Neoj< ^ NUMBER OF GENERATIONS PER YEAR. 65 O CD O oooooooo»o/_N Jz; o c: o o oococc"^ ocoocoown^MtL-iofTti'* c:cOOO!^l'*,-*l'^^^^•*■ • ■ oocccococooooocL-jc^jjNN^tBnio : :-© I MOOONa'*OOOT)iNCL0 05«NN'3"*OHC!C«10Nffil.'5ffiNOmiOC»00«OlOMN!MOH(NCfflmLOCCrJH C!M«cc«NNocxxx«cc-N«ocx^r.«XKc;«a;xxN^r.c:s-r.sr.c:r.;xc; cr. — - cr. cr. s; ~ . c. — - c^ ■ c; ri c-j ri ci 5'i ?i n r"i ?) :•? re 26675°— Bull. 110—12 5 66 THE SPRING GRAIN-APHIS OR GREEN BUG. § S si * o y R, C3 £ g ?- <^> f— : < •S '1 a > Css o iC =0 -uaS ipxis-A^na^x -janag Tpjtj-J4naAVjr, •nopBia -naS tpmbj-Aiua^x •nopura -nag pnip-A^naAvx •nop^ia -U33 pUOOaS-A^naAYX •nope -janaS ^.nj-AinaAvx •nop -■BJana3 q;apuaA\.x •nop -tuauaS tpnaa;anix •nop --GJauag TpnaajnSig; •UOp« -janaS xpuaajnaAag •nop -■BianaS ipnaajxig •noil -t3JauaS Tpnaayjj •nop -eiauaS ipiiaajjno j !!!!!!!! -o •nop -BjauaS tpiiaa:prqx ■nopBianag ipjiaAvx :::::::::::::« i : : : : •nop -BjanaS xpnaAaxg; :::::* I : O O © © O t> t> t~- t- I wNNccoioci'*ffiOWN^a;T'Ncioo'<)'i-i:ar;co' .N vu -c eo CO c Co -< e C I -nag TX).xis--£inaAYx •uotjb -lanag qijg-AinaAvx •noijBia -na§ -qiinbj-A jna^ii 'H0T}B.I9 -nag pipqi-AinaA^x «oooooooo ■iioi;bj3 -nag pnooas-AinaAvx ' ^OOOOOOOOCC^.COCCO. •nOTJB -janag isnj-AinaAvx aoooooooooo^e,^«n«HHn«(,nw««« •UOt). OOOOOOHNM»n«eOW«NNeONNCilO ONNrHHHHOHO -sianag -qiaunaAvx -sianag qmaaianrx . ! ! i ! i ! i i * " " " " i " * " " " -non -ho^-oooos ::::::::::::::::;:;:::•::: -■BianaS mnaaingig; ::::::::::::::::::::::::: •noiis -janag ipyriaainaAag ■hot; -BiauaS qinaaixig * ::::::::::::::::::::::::::::::::::; •nox; :::::::::::;::::::::;:::::::::::::: -Biauag qinaaijrx :::::::::::::::::::::::;::::::::::: •noii ::::::::::::::::::::::::::::::::::: -tuanag q;uaa;mo£ ::::::::;::;;:::::::::::::::::::;:: •non ::::::::::;:::;:::::::::::::::: -■siauag -qiuaaiiTqx :::::::::::::: :::::::::::::::: : -j-j-f •uouBianag qrna-^I •uoii :::;::::::::; ::: ::::::::"::::::::: : : -Bjauag qiuaAa^ :::::::: ? ::::::::::::::::::::::::: : •noii^ianag qmax •noi;Bjanag qimx :::::.:::::::::::::::::;::::::::::: •uoii^ianag t1.1u.gt3; | :::;::::::::::::::::::::::::::::::: •uoiicjauag -qpiaAag •noii^iauag qixrg ! :::;::::::::::::::::::::::::::::::: ::::::::::::::::::::::::::::::::::: •uoiisjanaS qiju ::::::::::::::::::::::::::::::::::: •noi}Bianag qjino 3 •noiiRianaS pnqx •noiiBjanag isjij ::::::::::::::::::::::::::::::::::: 2 ci •nrnuiinij^ rJ^-tLOCNOCCISrlN- ' — ' <-~ C5 Ci — 1— 1— i-^t^ro— I C W D N •# « - a» »o >- ^t^acac S li -0 C C t» l-: r? ^ u: * V T - "C c C C O T O l-5 'tnnaiLJLdj^ •^ c: Si c: or:xxxxr^xxc::r. r-.c - cr 0 ~ t-CN'-cxc: xxxxct^xx 0 «5 "03 ceo sir CD 8 S 3*3 CN C^CNCN O CO i CN ^LOO xoo CN <* « oc C— 1 CN CNCNCS NUMBER OF GENEEATIONS PEE YEAE. 69 OOOOOOOCOt^CO OOOOOOOOOH^HBhtMW^OiOiO'l1 O--HC'lr0) NNNWMCOfMHHHOHOOOOOOOOOO ooooooooooooooooooooooo !Nn«"««MHe,n,f"5!ON<00,SSS2SS 70 THE SPRIKG GRAItf-APHIS OR " GREEK BUG. " Mr. T. D. Urbahns, of this bureau, carried on a series of check experiments at Dallas, Tex., in 1909, starting in March and ending in the fall. (See table, pp. 64-69.) As will be observed, and for reasons explained farther on, he did not obtain the sexes. By these experiments the maximum number of generations was secured as described under rearing methods (p. 51). The maximum number of generations in 1908 among the five series of continuous generations was 21 and, as shown below, occurred in series I of first-born; the mini- mum being 6 in series FF of the series of last-born. The complete series are as follows: Series B, maximum (from first-born), 20 genera- tions; series BB, minimum (from last-born), 9 generations; series C, maximum (from first-born), 18 generations; series CC minimum (from last-born), 8 generations; series F, maximum (from first-born), 16 generations; series FF, minimum (from last-born), 6 generations; series G, maximum (from first-born), 19 generations; series GG, minimum (from last-born), 9 generations; series I, maximum (from first-born), 21 generations; series II, minimum (from last-born), 10 generations. If all of these be added, we will find the average to be 13.6 generations. This will represent the approximate number of generations for the year. In 1909 there were two series reared, A and B, both resulting the same. Series A, maximum (from first-born), 18 generations; series AA, minimum (from last-born), 7 generations; series B, maximum (from first-born), 18 generations; series BB, minimum (from last-born), 7 generations. The average for these two lines would give 12.5 generations, a little lower average than at Richmond, Ind. Mr. Urbahns carried out one series of first-born generation experi- ments at Dallas, Tex., in 1909, from which he obtained only the maximum number of generations. He began March 31 and finished November 3. In this time he reared through 25 generations but did not ascertain the sexes, neither was he successful in finding them in the fields. It appears that the species will vary in the number of generations produced from individuals hatched the same day, and from the off- spring kept under the same conditions throughout the year. This will readily be understood when the amount of individual variation in molting is considered. AGE AT WHICH FEMALES BEGIN REPRODUCING. The age at which females begin reproducing varies greatly between spring and summer and between fall and summer; as between spring and fall the age is very much the same. At Richmond and La Fayette, Ind., Toxoptera begins reproducing at from 5.9 to 16 days between the middle of May and latter part of September. From the time of hatching until the middle of May the period is from 20 to 27 days; REPRODUCTIVE PERIOD. 71 from the latter part of September to and including November the period varies from 12 to 53 days. A case occurred in the autumn of 1907 where it required 53 days for a single individual to reach ma- turity. This individual continued to live up to the 10th of December, when all experiments were closed. The average period from birth to reproduction for the summer months, early spring, and early fall is 9, 22, and 19 days respectively. The average for the entire year, or for the period in which the species breeds, parthenogenetically, for Kichmond and La Fayette, Ind., is 16.6 days. In arriving at these averages, all individuals of the generation experiments for 1907, 1908, and 1909 were considered. Mr. Urbahns found that at Dallas, Tex., the period varied from 7 to 12 days from birth to reproduction, from March to the middle of May; from 6 to 14 days from the middle of May until the last week in September, and from 9 to 11 days from the last week of September to November 3 . The average number of days from birth to reproduction for* each of these periods is 9.6, 7.4, and 9.7 days, respectively. Mr. Urbahns reared a number through December up to the middle of January. During this period the time between birth and reproduc- tion was very much greater, varying from 18 to 25 days, with an average of 20.5 days. The average, beginning with April and con- tinuing until November 3, is 8.9 days. From the foregoing data it will be seen that under favorable conditions Toxoptera breeds much more rapidly in the South than in the North. All of the reproduction experiments upon which these figures are based were carried on out of doors, but the insects were protected from the hot rays of the sun in the summer. REPRODUCTIVE PERIOD. The period of reproduction covers a greater average length of time in spring and fall than during summer, being greatest in the spring, even though the maximum period of reproduction for a single female is practically the same for the three periods. In computing these averages each individual of all the lines of con- tinuous generations was considered, even though they reproduced for a single day only and then died or disappeared from some unknown cause; hence the averages are lower than they would be had these latter individuals not been considered. From this data it will be seen that both the maximum and the average periods are the great- est in the North, where the insect is able to breed continuously in unprotected places throughout the summer. At Richmond and La Fa3^ette, Ind., the maximum period of repro- duction for individuals born from March to the middle of June is 45 days, the minimum 1 day, and the average 18 days; the maximum for individuals born from the middle of June to the middle of August 72 THE SPRING GRAIN-APHIS OR U GREEN BUG. ' ' is 43 days, the minimum 1 day, the average being 12.6 days; the maximum for those born after the middle of August is 45 days and the minumum 5 days, the average being 24 days, while the average for the entire season is 16 days. In Texas the difference between summer, spring, and fall is still more marked, December and January being about the same as the summer months. Mr. Urbahns found that during December and January the maximum reproduction period was 19 days and the minimum 2 days, the average being 8 days; during April and May the maximum was 30 days and the minimum 4 days, the average being 16.8 days; during June, July, and August the maximum was 16 days and the minimum 4 days, the average being 8.4 days; during September, October, and November the maximum was 28 days and the minimum 3 days, the average being 17 days. The average for the entire season was 13.9 days. LONGEVITY. At Richmond and La Fayette, Ind., Toxoptera lives for a much longer period in the spring and fall than in the summer. In fact, in the summer it often survives a shorter time than is required for it to reach maturity in the spring and fall. Those born from the latter part of March to the last week in May live from 15 to 78 days, the average being 43 days; those born from the first week in June to the middle of August live from 9 to 57 days, the average being 24 days; those born from the middle of August on through September live from 12 to 75 days, the average thus being 40 days. The average length of life for the whole viviparous breeding season is 35 days. These averages are not made up from the maxi- mum and minimum alone but every individual in the line of first- born of the continuous generation experiments is considered. Mr. Urbahns found that in Texas the spring grain-aphis lived much longer in spring and fall than in summer. In fact, in the summer it was difficult to keep it alive at all, it being necessary to keep the cages in the shade.1 He also carried on some reproduction experiments in December and January, and in these two months found that it lived from 25 to 39 days, averaging 34 days. In April and May it lived from 13 to 47 days, averaging 35 days; in June, July, and August it lived from 10 to 30 days, averaging 17 days; in September, October, and part of November it lived from 11 to 56 days, averaging 28 days; the average for the season (from March to November) was thus 26 days. In making up these averages only whole numbers are used, frac- tional parts of a day not being considered. Also, all individuals upon which we had complete observations were considered. i Ante, p. 47. ?HE SPRING GRAIN-APHIS OR " GREEN BUG.'' 73 FECUNDITY OF VIVIPAROUS FEMALE. The average person, unfamiliar with the habits of the Aphididse, would scarcely think it possible for such small creatures to become sufficiently numerous to devastate vast areas of grainfields, destroy- ing millions of dollars' worth of property within the space of a few weeks. When one becomes familiar with their powers of reproduc- tion, however, the problem seems very simple. Prof. Huxley * states that the tenth generation alone of a single rose aphis, were all of its members to survive the perils to which they are exposed, would contain more substance than 500,000,000 stout men. Buckton,2 commenting on Prof. Huxley's figures, states that he much underestimates the real quantity of animal matter capable of elaboration from a single aphis in a year, and goes on to say: Basing the calculation, for simplicity, upon the supposition that every aphis lives twenty days, and that at the expiration of that period each aphis shall have pro- duced twenty young and no more, then at the expiration of three hundred days only, the living individuals would be represented by the following figures: Aphides. Days. Aphides. 1 produces in 20 20 = a a produces in 40=202 400 = b b produces in 100=205 3, 200, 000 = c c produces in 200=2010 10, 240, 000, 000, 000 = d d produces in 300=2015=32, 768, 000, 000, 000, 000, 000 = e Again, if 1,000 aphides weigh 1 grain, and 1 man weighs 2,000,000 grains 1 man weighs 2,000,000,000 aphides, ■p •'• 2 000 000 000 =1>638,400,000 men; equal, perhaps, to the population of China seven- fold! To quote further: But a mathematical friend remarks that this calculation even does not express the real rate of increase, since it supposes the progeny of the first aphis to be produced at once, and not to commence producing until the expiration of the first twenty days. To this same friend I am indebted for the annexed calculation. If we suppose the progeny of the first aphis to equal 20 in twenty days, and this progeny to begin producing when five days old 20 young, each of which again on attaining the age of five days begins the propagation of 20 young, and completes also that number in 20 days: Then at Jhe end of 20 days from the commencement of first aphis production * there would be direct issue = 20a At the end of fifth day, progeny a begin to produce, which at the end of first 20 days will altogether equal 154-14+134-12, &C.+2+1 =1206 At the end of tenth day, progeny b begin to produce, which at the end of the first 20 days will altogether equal 10+9+8, &c. +2+1 = 55c- At the end of the fifteenth day, progeny c begin to produce, which at the end of the first 20 days will altogether equal 5+4+3+2+1 = 15c? Total at the end of 20 days equals a+b+c+d =210 The amount, therefore, at the end of 300 days (or 20X15) would not be les3 than the fifteenth power of 210, which is almost impossible to express in figures. There would be room in the world for nothing else but aphides. i Trans. Linn. Soc, vol. 22, p. 215 (part 3, 1858). » Monograph of British Aphides, vol. 1, p. 80. 74 £HE SPRING GRAIN-APHIS OR " GREEN BUG. 91 Toxoptera, in all probability, would not fall far behind these figures and the number might even be greater. Be that as it may, the illustration will suffice to show us that Toxoptera, with such remarkable powers of reproduction, could easily overrun the whole country if not checked in some manner. At Richmond and La Fayette, Ind., the maximum number of young produced in 24 hours was 8 in June, July, and August. The maximum number of young produced by any individual was 93, in the month of July. In Texas Mr. Urbahns found the maximum in 24 hours to be 10 young in May, and the total number of young for one individual reached as high as 84 during the same month. At Richmond and La Fayette, Ind. , considering the progeny from only the individuals of the line of first-born generations, the average num- ber of young for the summer falls below either spring or fall, the spring being in the lead. When both the individuals from the line of first and last born generations are considered, those of the fall average less than those of the spring or summer. In 1908 the evidence was in favor of the line of first-born generations as being more prolific than the individuals of the line of last born. In 1909 the line of last-born generations held its own, especially in the spring and summer, falling behind slightly in the fall. In fact, in each line of generation experi- ments, the last born fall behind in average number of young in the autumn. Also, if an average be taken of the first and last born sepa- rately, the latter will fall behind. Considering each individual of both lines in all generations, both first and last together, the results are as follows: The maximum number of young produced by those born from March to the middle of June is 69, the average number for each individual for this period being 30.3; the maximum for those born from the middle of June until the middle of August is 93 young, the average number for each individual being 25.3; the maximum for those born after the middle of August is 66 young, the average for each individual being 24. The average number of young, including every individual under observation, whether connected with the generation experiments or otherwise, for the entire viviparous breeding season, of the years 1907, 1908, and 1909, beginning the last week in March and continuing until November, both inclusive, is 28.2; there being 216 individuals used to obtain this average. In the generation experiments were a number of individuals that produced from 1 to 10 young and then disappeared, apparently not dying from natural causes. All of these were included, however, in arriving at the final average, as any average obtained by excluding one or more individuals from any cause whatever would be more or less arbitrary, since in nature the mortality, in all probability, would be much greater. All of the rearings were carried on out of doors, FECUNDITY OF WINGLESS VS. WINGED FEMALES. 75 and as the individuals were isolated and protected as much as pos- sible from natural enemies it is probably safe to say that this average is as high as would obtain in the open fields, where they are convenient prey for their enemies. Mr. Urbahns found that in Texas the average number of young produced in the spring and fall was much greater than in the summer. The averages for December and January agree very well with those of the summer period. The maximum number of young produced by a single individual, under observation by Mr. Urbahns, that began reproducing in De- cember and January was 29, the average for this period being 17. 1; the maximum for those that began reproducing in April and May was 84, the average being 58.5 young; the maximum for those that began reproducing in June, July, and August was 39, the average being 17.2 young; the maximum for those individuals that began reproducing after August was 73; the average for the period from March to November is 39.7; the average for the entire number of individuals upon which Mr. Urbahns made observations during 1909, including the rearings during December and January, is 34 young. As will be observed, this is considerably above the average for Indiana. From the foregoing data it will be seen that the spring, in both the North and the South, is the most favorable period for reproduc- tion; in the North the summer period ranks next, the fall coming last, while in the South the summer is so hot that the aphidids can scarcely live at all, the fall ranking next to spring for productiveness. FECUNDITY OF WINGLESS VERSUS WINGED FEMALES. In 1890 the senior author gathered from his observations that the wingless forms were more prolific than the winged. In 1907 the junior author came to the same conclusion. In 1909 Mr. Urbahns, in Texas, observed that the winged forms did not appear to be so prolific as the wingless forms. During the summer of 1909, at La Fayette, Ind., the junior author carried on some experiments with a view of learning, if possible, something definite in regard to this matter. For this purpose 8 nymphs with wing pads and 8 larvae in the fourth stage were selected and each placed in a separate cage, each cage being placed under the same conditions. This experiment began on the 30th of August and all individuals became adult about the same time. The maximum number of young produced by a single winged individual was 44 and the minimum was 10; the maxi- mum number of young produced by a single wingless individual was 61 and the minimum was 4. The total number of young produced by the 8 winged individuals was 224, or an average of 28 young for each individual; the total for the 8 wingless individuals was 274, or 16 THE SPRING GRAIN-APHIS OR " GREEN BUG. JJ an average of 34.25 young to each individual. While too small a number of individuals was taken to make the result conclusive, it plainly indicates that fecundity is greatest among the "wingless individuals. AVERAGE NUMBER OF YOUNG PRODUCED DAILY. By "the average daily number of young produced" is meant the daily average for the reproductive period only of each individual. At Kichmond and La Fayette, Ind., the average number of young produced daily for those born from March to the middle of June is 1.9; the daily average for those born from the middle of June to the middle of August is 1.7; the daily average for those born after the middle of August is 1.2. These figures, of course, include only those individuals in the generation experiments. The average number of young produced daily for the entire year is 1.6. The final average remains the same when all individuals are considered, irrespective of generation experiments. From the above it will be seen that the daily average is greatest in the spring, the summer coming next, and the fall last. This corresponds also to the average total number of young for each indi- vidual for these periods. Mr. Urbahns found that the average number of young produced daily at Dallas, Tex., for those individuals that began reproducing during December and January was 1.5; the daily average for those that began reproducing during April and May was 3.4; the average for those that began reproducing during June, July, and August was 2.1 ; the average for those born after August was 2.5. These averages will be seen to agree proportionately with the average number of young produced by a single individual during these periods, with the exception of the daily average for December and January, which is considerably lower. The average daily number of young for the entire breeding season for which Mr. Urbahns has any data is 2. From the above data it will be seen that the average daily number of young for Texas is far above the average for Indiana. Tins can probably be accounted for from the fact that the reproductive period is much longer in the North and the young are distributed over a longer period. Also the average number of young for each individual is greater in the South. SEXUAL FORMS. The first young of the sexes in Indiana are apparently born the last week in September, the first adults oftentimes appearing as early as the first week of October. The adults can be found from this time on until December, or until they are killed off by extreme cold. The males can easily be distinguished by their small size. The oviparous females (iig. 9) can be readily distinguished without a hand SEXUAL. FORMS. 77 lens by the yellowish areas over the abdomen, due to the fact that the eggs show through the body walls; also, if the males have not been with them, by the manner in which they rest upon the plant, the body being held at an angle of about 45° to the leaf upon which they rest. In assuming this position they hold to the plant only with the two first pairs of legs. Only unmated females rest upon the plant in this manner. The sexes may mate once or many times, although one mating is apparently sufficient to produce fertile eggs. One agamic female may produce all agamic individuals, a com- bination of agamic males and oviparous females, or only true females and males. When only the latter, it seems that the females far outnumber the males. Mr. C. N, Ainslie, in 1908, in Washington, D. C, records a very singular phenomenon. On April 4 of that year he observed males; oviparous females, and eggs of Toxoptera in his cages in the office. A number of eggs were obtained, but none of them would hatch. The source of this material, however, is somewhat obscure. Mr. Kelly had sent in material from Leavenworth, Kans., previous to these finds and this was kept breeding in the office, together with material collected locally. The junior author also found an adult male in his rearing cages in the insectary at Washington during April, 1911. This apparently developed from material that had been kept breed- ing all winter. DESCRIPTIONS. Since in the earlier stages the young can not be distinguished from those of the summer forms, it is unnecessary to go into detail with reference to them. The males may probably be identified in the third instar by their small size; they are much smaller and the abdo- men more pointed, posteriorly, than the summer forms of this stage that later will become winged. Those young that will develop into oviparous females can not be determined with any degree of accuracy until the fourth instar. They are usually a little paler in color, and, instead of embryos, light yellowish ova can be seen, with a hand lens, developing within the body (see fig. 9). The description of the male and female first appeared in the Canadian Entomologist, in an article on " Sexual Forms of Toxoptera graminum, Rond," by Prof. F. L. Washburn.1 His description is as follows: Oviparous female. — Length, 2-2.25 mm.; color, yellowish green, median line of abdomen darker green; head and prothorax somewhat paler than the rest of the body. Eyes black; antennae black, except the two basal joints, and the basal half of the third, which are the same color as the head. Legs yellowish, tibia brownish toward the apex, tarsi black; cornicles greenish, their apex black; cauda greenish. Antennae slender, hardly one-half the length of the body, no circular sensoria. Cornicles slightly tapering, not reaching to the end of the body. Cauda slender, somewhat i Can. Ent., vol. 40, No. 2, February, 1908. 78 constricted above the middle, about two-thirds the length of the cornicles. Tibia of hind leg (fig. 10) swollen and thickly covered with sensoria-like swellings. Lateral tubercles small and single. Winged male. — Expanse of wings about 4.5 mm.; length of body about 1.3 mm. General coloration of the abdomen yellowish green; head brownish-yellow; eyes black; antennae black, except the two basal joints and the proximal half of the third, which are yellowish green. Legs yellow, the femora more or less dusky, the posterior pair darkest; apex of the tibia and tarsi black; cornicles yellowish, with black apex; cauda yellowish. Wings, costa and subcosta yellow; stigma paler, the inner edge of the stigma and the veins black. Antennae long and slender, reaching to or a little beyond the end of the body; third joint with about twenty circular sensoria; fourth with about eighteen; fifth with about nine. Cauda slender, somewhat constricted about the middle, as long as the cornicles. Lateral tubercles small and single. To this description we add the following: Oviparous female. — Measurements of antennal joints (average from eight indi- viduals): I, 0.067 mm.; II, 0.050 mm.; Ill, 0.229 mm.; IV, 0.166 mm.; V, 0.172 mm.; VI, base 0.095 mm.; VI, filament, 0.369 mm.; total length, 1.148 mm. Male (average from six individuals) (fig. 6): 1,0.064 mm.; II, 0.051 mm.; Ill, 0.361 mm.; IV, 0.243 mm.; V, 0.242 mm.; VI, base, 0.107 mm.; VI, filament, 0.407 mm.; total length, 1.475 mm. We find also that the coloration of the oviparous female varies considerably from almost a clay-yellow with a faint tinge of green to a deep green. Individuals are somewhat pruinose also. As they become older the legs and bases of the antennas get darker; each margin of the base of the cauda becomes quite dark. The abdomen of the male varies somewhat in color from deep apple-green to pale green; the thoracic plates, dorsally and ventrally, are of an olive color. MOLTING. As stated on page 62 Mr. Vickery, of this bureau, conducted some experiments at Richmond, Ind., in 1908, to ascertain the number of molts for the sexes. He selected 6 individuals just as they were born and isolated each in cages as heretofore described. Three proved to be males and 3 oviparous females, all of which molted 4 times. Also, at LaFa}^ette, Ind., in 1909, the junior author found that the oviparous forms molted 4 times. OVIPAROUS DEVELOPMENT. AGE AT WHICH FEMALES BEGIN OVIPOSITION. The age at which females begin depositing eggs varies greatly according to weather conditions. From 11 to 41 days are required for them to become adult. If they happen to be born the last week in September or the first week in October the chances are that they will become adult within about 11 days. If they have the misfor- tune to be born the last week in October or during November it may take them over a month to reach maturity; perhaps they would i PERIOD OF OVIPOSITION. 79 not reach maturity at all in case of an early winter. After reaching maturity they will, when accompanied by the male, begin ovipositing in from 3 to 9 days; if the weather is warm, in from 3 to 4 days. The period, then, from birth to oviposition varies from about 14 to 44 or 45 days. Females will, in rare instances only, oviposit without first having been with the male. They will five unfertilized from 31 to 71 days without ovipositing, the abdomen becoming very much distended, and, upon dissection, 6 or more fully developed eggs may be found. In one case a female deposited 2 eggs without having been with a male, but no development occurred within the egg and it shriveled and dried up within a few days. When nearly through ovipositing the female becomes shrunken and misshapen, as shown in figure 15. (Compare with fig. 9.) PLACE OF OVIPOSITION. Throughout the North it ap- pears that bluegrass (Poa pra- tensis) is the most common host plant of Toxoptera, though it occasionally, on account of favor- able weather conditions or the scarcity of natural enemies, be- comes excessively abundant there and escapes to the grains in destructive numbers. Conse- quently it appears that the sexes normally occur on bluegrass. It is also true that they will be bet- ter protected from the extremes of temperature among tall, rank growing bluegrass than they would be on the grains in open, bleak fields. In only a very few instances have we been able to find the sexes upon the growing grains in the fields. It is an easy matter, how- ever, to locate them upon bluegrass in waste places. They appar- ently prefer dead or dying leaves and crawl out near the tip of the leaf, where it has begun to fold, and here deposit their eggs. (See fig. 11.) Several old females have been found at the same time within the curl of a leaf, and as many as 14 eggs have been found upon a single leaf. PERIOD OF OVIPOSITION. Here again, as in the case of viviparous development, varying temperatures are probably the main factor in determining the length of the productive period. Eggs continue to develop within the bodies of the females, apparently, as the embryos do within the Fig. 15.— The spring grain-aphis: Shrunken and nearly spent oviparous female. Enlarged. (Original.) ■ 0 THE SPRING GEAIX-APHIS OB bodies of the viviparous individuals, so long as warm weather con- tinues or until the females become old and die a natural death. The viviparous forms appear to be as susceptible to extreme cold as are the oviparous individuals. From the 14 experiments that were conducted to determine the period of oviposdtioii it was found that it varied from 3 to about 25 days. If. after becoming adult, the female be kept for a week or more and then placed with the male it appears that the reproductive period is shortened. Fig. 16. — The spring grain-aphis: Aberrant female with eggs and embryos in abdomen, showing through the body wall. Enlarged. (Original.) LENGTH OF LIFE OF THE SEXES. The males reach maturity, it seems, as quickly as the oviparous females, but their lives are much shorter. The males live from 8 to 10 clays after becoming adult. The length of life of the oviparous females depends principally upon two factors, namely, weather conditions and the presence of the male. Under favorable weather conditions, and in the presence of the male, they will live from 31 to 6S days. If the male is not present they will sometimes live as long as 88 days. Under these circum- stances they rarely deposit eggs, only one instance, as previously cited, having come under our observation where they did oviposit and then the eggs were not fertile. Their abdomens become greatly distended with eggs, and upon being dissected, as many as six or more full-sized eggs may be found. INFLUENCE OF WINDS ON DIFFUSION. 81 FECUNDITY OF OVIPAROUS FORMS. The oviparous forms are far less prolific than the viviparous. They produce, under favorable circumstances, from 1 to 10 eggs, or an average of 5.4 eggs per individual. This average was made up from observations on 27 individuals. ABERRANT INDIVIDUALS. During our studies of Toxoptera we have found some rather inter- esting abnormalities. In December, 1907,1 while dissecting some individuals in the laboratory, two were found that contained both living embryos and true eggs. In April, 1908, Mr. C. N. Ainslie found the same phenomenon occurring in individuals here in Washington. These latter resembled the wingless viviparous forms externally (see fig. 16). Mr. S. J. Hunter, in " The Green Bug and Its Enemies," finds, besides this form, what he terms "winged intermediate females, re- sembling the winged agamic females in antennal characteristics." Other writers mention the same phenom- enon as occurring among other species of plant-lice, and no doubt these abnor- malities occur much of tener than any of us are aware. At present, however, there appears to be no satisfactory explanation of such occurrences. One single instance came under our observation where a puparium produced 6 young and then died. The cauda of this individual resembled that of an adult insect and the wing-pads were aborted, the abdomen being much broader than that of the normal pupa. (See fig. 17.) INFLUENCE OF WINDS ON DIFFUSION. By referring to the maps (fig. 5) showing the area covered by the different outbreaks of Toxoptera in the United States, west of the Mississippi River, it will be observed that they have all had their origin in central Texas, with a single exception, extending broadly to the north and northeast. This was especially true of two most des- tructive invasions of 1890 and 1907, and was also implied by that of 1901, the case of 1903 having been too incipient. This strongly indicates Fig. 17.— The spring grain-aphis: Aberrant female pupa which produced young. En- larged. (Original.) 1 Proc. Ent. Soc. Wash., vol. 10, pp. 11-13, January. 26675°— Bull. 110—12 6 82 the presence, during each extended invasion, of some important influ- ence that shapes, to a marked degree, the course of these invasions across the country northward and northeastward from the point of their origin in the South. Probably this is due primarily to the direc- tion of the winds during the months between January and June. The degree of influence exerted by the winds in the diffusion of Toxoptera is, however, dependent upon several other factors. In the first place, with wingless individuals alone present, it is clear that no amount of wind of whatever velocity would distribute the species to any considerable degree. Therefore, it is necessary to understand the vital forces that regulate the abundance of winged individuals, which, at the critical period, would probably be almost without exception viviparous females. Field observations have shown, not only among this but among other species of aphidids, that a curtailing of the food supply is a most potent influence in producing the aerial form. Not only has it been observed with Toxoptera that as the food plants lose their vigor, affording less nutrition, the winged individuals become more and more abundant in the fields, but both Mr. Phillips and Mr. Urbahns have been able, by regulating the food supply, to produce these winged individuals, artificially at will, in their rearing cages. In the case of MacrosipJium granariaBuckt.,it has always been noticed that though the heads of wheat be literally swarming with wingless females and young, these young do not perish as the food supply becomes exhausted on account of the ripening of the grain, but develop into winged adults which fly away, leaving only the cast larval and pupal skins on the ripening wheat heads. Therefore, so long as there is an abundant supply of vigorous young grain the percentage of winged adults appearing will be comparatively few. The condition of the food supply, then, is a prime factor in the diffusion of Toxoptera, except when greatly decimated in numbers from excessive parasitism. If the temperature be below the point of activity for the species, it is very clear that the velocity of the wind would have no effect what- ever upon the diffusion of the insect. The conditions necessary, then, for the wind to exert its greatest influence will be a decreasing food supply for the insect under a temperature considerably above that actually necessary for its activity, with numbers not seriously reduced by parasites; under these conditions, many species of aphidids are known to be carried about in immense numbers by the winds. White, in his Natural History of Selborne * has this reference to a migration of small aphidids. As we have remarked above that insects are often conveyed from one country to another in a very unaccountable manner, I shall here mention an emigration of small Aphides, vhich was observed in the village of Selborne no longer ago than August 1, 1785. 1 Natural History and Antiquities of Selborne. By the Rev. Gilbert "White, M. A., London ,1836, pp. 36S-366. INFLUENCE OF WINDS ON DIFFUSION. 83 At about three o'clock in the afternoon of that day, which was very hot, the people of this village were surprised by a shower of Aphides, or smother-flies, which fell in these parts. Those that were walking in the street at that juncture found themselves covered with these insects, which settled also on the hedges and gardens, blackening all the vegetables where they alighted. My annuals were discoloured with them, and the stalks of a bed of onions were quite coated over for six days after. These armies were then, no doubt, in a state of emigration, and shifting their quarters; and might have come, as far as we know, from the great hop plantations of Kent or Sussex, the wind being all that day in the easterly quarter. They were observed at the same time in great clouds about Farnham, and all along the vale from Farnham to Alton. Prof. Karl Sajo calls attention to the fact that many aphidids creep to the crowns of the plant which they infest and then drop them- selves at the proper moment into the boiling current of the storm.1 In the studies made of Toxoptera many instances of this nature have been observed. It will be recalled that Toxoptera graminum appeared in swarms about Parma, Italy, in 1847 and again in 1852. The notes of Mr. C. N. Ainslie, made on Toxoptera in Oklahoma and Kansas, contain very many similar interesting records. At Kingfisher, Okla., under date of March 27, 1907, Mr. Ainslie makes this record. Toxoptera flying to-day by the million. The air was full of the migrants, and farmers who drove to town were covered on the windward side to their annoyance. The aphides seem for the most part to fly low, but the wind hurried them at such a rapid rate that they might easily have been invisible when higher in the air. The following day his field notes contained these significant state- ments: "Large numbers of Toxoptera on the wing to-day, always moving north," and as those who have studied the species will understand, the most interesting statement was that "A heavy thunder shower passed by on the north last night, 30 miles away, and a few drops fell here." In the same locality, under date of April 3, he states that winged individuals of Toxoptera were taking to wing freely, for he had observed many leaving the blades in the fields and taking flight. Again, under date of April 6, "The air is full of ffying Toxoptera to-day, going northeast with a light breeze. They do not fly high, from 2 to 15 feet." (The temperature at Wichita, 30 miles north, was from 42° to 57° F.) At Wellington, Kans., April 24 (with Wichita temperature 45° to 81° F.), he found Toxoptera flying by the million and farmers driving to town had to shelter their eyes from the swarm. On April 29, he records these observations: Yesterday afternoon was warm for awhile (41° to 63° F. at Wichita), light north- west breeze. Toxoptera took wing in immense numbers for 15 or 20 minutes, drift- ing southwest, but soon saw their mistake and the ah' cleared. This is the only instance seen by me when these aphides failed to fly north. The wind did not carry them far this time. A Sunday ball game was in progress when they flew, and I was told that the myriads of aphides interfered with the game; it was like trying to play in a snowstorm. J The Wanderings of Insects. Prometheus, vol. 1, by Prof. Karl Sajo, 84 Under date of May 17, 1907, also at Wellington, Kans., Mr. Ainslie made an interesting record as follows: Yesterday, the 16th, the air was full of Toxoptera rising on wing, but the breeze was light and they had no chance to travel far. If the wind had favored their flight they must have carried parasites with them as guests, by the myriad, for many of them, probably the major part, were parasitized. [The temperature at Wichita ranged from 44° to 82° F.] On the same day the senior author, in company with Prof. E. A. Popenoe, in driving about the country hi the vicinity of Manhattan, Kans., during the afternoon found that they were in the midst of swarms of winged Toxoptera; frequently a number of individuals might be noted crawling about over their hats and coats and to an annoying degree traveling over their faces. Two days later, the senior author observed both winged Toxoptera and Aphidius crawl- ing about on the inside of the windows of a Pullman car in which he was traveling over the Santa Fe, crossing central Kansas. At Piano, Tex., June 4, 1909, Mr. Urbahns learned of a most interesting migration reported to him as having taken place two days before. A farmer, Mr. Foreman, reported to him that "green bugs" were observed flying east, probably coming from out of a very badly infested wheat field, moving with the evening breeze. In this case there was clearly a rapid disappearing of the food supply, precipitating a development to winged adults that were probably forsaking the fields for some other locality affording them a greater abundance of food. It would appear, then, that the influence of winds is more or less dependent upon several other phenomena. With the natural advance of spring from the South, there would be a continually decreasing supply of fresh* tender, succulent food in the South, while to the North this condition would be reversed. Therefore, with winged viviparous females developing with increas- ing abundance along the area of a certain latitude, such winged females as were carried south or backward over an area already ren- dered barren of food would consequently perish. On the other hand, those females that drifted or made their way northward would encounter a continually increasing fresh supply of food; therefore they might be said to follow along with the advance of the spring from the South far into the North, until overtaken b}r their natural enemies. Then, too, south winds are associated with a warm tem- perature and north winds with the reverse, as will be seen from Tables IV- VIII, furnished by the United States Weather Bureau. Another factor that must not be lost sight of is that after about the latitude of southern Kansas and Missouri is reached wheat ceases to be the food plant for Toxoptera in spring, and spring oats takes its place in this respect. INFLUENCE OF WINDS ON DIFFUSION. 85 Still another factor of greatest importance is in the fact that, with a wind from a southern quarter, blowing strongly under a tem- perature sufficient to render Aphidius active, both Toxoptera and parasite would thus be carried on the wing perhaps miles to the northward and scattered over fields not previously seriously infested. The following da}^, or some days after, there might come a north wind with greatly reduced temperature, which, though not sufficiently cold to prevent immediate reproduction on the part of migrant Toxoptera, would yet keep the parasite inactive. That precisely these weather conditions do often occur during years of excessive abundance of Toxoptera is shown b}^ the following tables of the weather (Tables IV-VIII), while the dates thereof show conclu- sively that both Toxoptera and Aphidius were present and active. This last factor will be further discussed under natural enemies. These tables were compiled for us by the Weather Bureau. Table IV. — Maximum and minimum temperatures, with direction and velocity of wind, and character of the day, San Antonio, Tex., 1907. Di- Ve- Di- Ve- Date (1907). Weather. Maxi- mum. Mini- mum. rec- tion of wind . loci- ty of Date (1907). Weather. Maxi- mum. Mini- mum. rec- tion. of wind. loci- ty of wind. wind . Mies Miles per per °F. °F. hour. "F. °F. hour. Feb. 1 Clear SI 63 SE. 11 ' Mar. 3 Clear 80 49 SE. 13 2 Fair 83 49 48 38 N. N. 26 22 4 5 do Fair 82 84 56 64 SE. S. 15 3 Cloudy 16 4 Fair 58 47 43 33 28 34 NE. NE. NE. 20 19 15 6 7 8 do Clear 85 84 82 64 64 66 SE. S. SE. 18 5 do Cloudy -. 15 6 Fair 18 7 Fair 60 68 39 33 N. N. 22 7 9 10 do do 80 80 66 57 S. w. 16 8 Clear 23 9 do 73 38 S. 15 11 do S5 65 SE. 21 10 do 68 42 N. 92 12 do 87 65 s. 21 11 do 72 44 N. 10 13 do 80 70 NE. 17 12 do 74 36 S. 10 14 do 70 47 N. 36 13 do do 78 71 46 50 s. N. 15 24 15 16 Clear 70 76 42 46 NE. SE. 23 14 do 14 15 do 70 40 N. 9 17 do 88 66 SE. 18 16 do 77 44 sw. 11 18 do 88 64 SE. 15 17 do 80 48 SE. 10 19 do 89 62 SE. 15 18 Fair 80 76 79 53 52 44 SW. N. SW. 14 IS 10 20 21 22 ....do do do 89 88 87 63 63 64 SE. SE. SE. 17 19 Clear 24 20 do 20 21 do 80 47 s. 17 23 do 86 66 S. 15 22 Fair 80 52 SE. 19 24 do 88 67 SE. 16 23 Cloudy do 79 62 SE. 15 25 Fair 87 68 SE. 18 24 67 56 NE. 22 26 do 86 68 SE. 20 25 do 66 48 N. 19 27 do 88 69 SE. 17 26 do 68 49 SE. 7 28 do 88 68 SE. 20 27 Fair 81 63 S. 15 29 Cloudy 73 55 N. 26 28 do Clear 80 73 64 52 N. NW. 30 27 30 31 Fair 72 70 55 52 N. N. 14 Mar. 1 Clear 99 2 do 77 43 S. 14 86 THE SPEING GRAIN-APHIS OE ' l GREEN BUG. ' ' Table Y. — Maximum and minimum temperatures, with direction and velocity of wind, and character of the day , Fori Worth, Tex., 1907. Date (1907). Feb. Mar. 1 Weather. Fair. Cloudy do do Fair ....do ....do Clear ....do Fair Clear ....do ....do ....do ....do ....do Fair ....do Clear ....do Fair ....do ....do ....do Cloudy Fair Cloudy do Clear ....do Maxi- mum. Mini- mum Di- rec- tion of wind SW. NW. N. NW. NE. NE. N. S. S. NE. S. SW. SW. N. SW. SW. s. NW. N. s. SW. E. s. NW. NE. SE. SE. NW. NW. SW. Date (1907). Mar. Weather Clear do Fair do do do do Clear Fair do Clear ....do ....do do Fair Clear do do ....do ....do Fair ....do Clear Fair ....do ....do Cloudy Clear ....do Di- Maxi- Mini- rec- tion of mum. mum. wind. °F. °F. 82 49 S. 81 53 SW. 69 53 SW. 82 51 SW. 86 63 SW. 70 53 NE. 78 56 SW. 62 39 N. 81 49 S. 84 66 SW. 78 44 s. 58 38 N. 64 39 SE. 75 46 SW. 83 63 SW. 92 65 SW. 95 64 SW. 88 64 s. 89 63 SW. 87 64 s. 87 65 s. 86 64 s 85 67 SW. 83 67 SW. 83 69 SW. 84 70 s. 73 53 NW. 70 47 NE. 59 49 NE. Ve- loci- ty of wind . Miles per hour. 20 28 22 23 22 17 23 16 35 33 30 20 11 22 24 28 25 24 25 29 25 20 31 31 31 30 14 14 21 Table YI.— Maximum and minimum temperatures, with direction and velocity of wind, and character of the day, Oklahoma City, Ohla., 1907 . Date (1907). Mar. Weather. Maxi- Clear ....do.... ....do.... Cloudy.... ....do.... ....do.... Fair Cloudy.... do Fair Cloudy.... Fan Cloudy.... Fair.* ....do.... ....do.... ....do.... ....do.... ....do.... Clear ....do ....do.... Fair Cloudy.... Fair Cloudy.... do ....do.... Fair ....do.... Cloudy.... Mini- mum. Di- rec- tion of wind N. S. E. S. N. S. N. E. NW. N. S. S. N. N. S. s. s. s. s. s. s. s. s. s. s. s. s. s. w. N. N. Ve- loci- ty of wind. Miles ■per hour. 30 35 23 36 36 38 34 25 47 35 36 30 32 22 25 38 37 35 32 25 32 34 31 35 38 47 38 42 22 31 34 Date (1907). Apr. 1 2 3 4 5 Weather. Fair ....do ....do Cloudy ....do ....do Clear ....do Fair Clear ....do Fair ....do Cloudy do ....do ....do Fair Cloudy do ....do ....do Clear Fair Cloudy Clear.'. Cloudy Fair Cloudy Fair..' Di- Maxi- Mini- rec- tion mum. mum. of wind. °F. °F. 66 38 S. 75 48 S. 8S 58 SW. 68 54 N. 58 42 N. 72 48 SE. 71 47 N. 63 44 N. 79 41 W. 74 43 s. 72 52 N. 58 42 N. 57 33 NE. 61 44 S. 85 49 SE. 64 34 NE. «4 34 SE. 65 41 SE. 52 39 N. 48 36 NE. 51 44 NE. 46 40 N. 69 36 S. 79 52 s. 64 40 N. 66 35 NE. 80 55 S. 77 51 SE. 64 34 N. 50 32 N. Ve- loci- ty of wind. Miles per hour. 34 52 43 36 38 34 24 38 31 26 42 36 22 32 48 38 24 37 26 26 18 22 30 48 42 20 36 36 44 30 INFLUENCE OF WINDS ON DIFFUSION. 87 Table VII. — Maximum and minimum temperatures, with direction and velocity of vind, and character of the day, Wichita, Kans.,from Mar. 20 to May 31, 1907 . Date (1907). Apr. Mar. 20 21 22 23 24 25 26 27 28 29 30 31 1 2 3 4 5 Weather. Clear .....do.... Fair Clear .....do.... do Cloudy.... Fair Cloudy.... Clear Fair do.... Clear Fair Clear Fair do.... Cloudy.... do Clear do.... Fair Clear do.... Fair Cloudy.... Fair.." Cloudy.... Fair." do.... ....do.... Cloudy... do.... do.... Clear do.... Fair , Di- Maxi-Mini- JgJ mum. mum. "~Jr •0f4 .wind I SW. sw. SW. sw. s sw. sw. sw. w. xw. N. NE. s. xw, XE. XE. W. W. X. X. SE. XW. XW. N. SE. N. XE. SE. N. N. XE. X. s sw. sw. XE. Ve- loci- Date ty of (1907;. wind. Weather. Maxi- Mini- mum, mum. Di- rec- tion of wind Ve- loci- ty of wind . Miles per hour. 16 24 24 21 19 24 28 17 30 15 21 17 24 30 24 26 20 15 23 30 23 16 23 26 13 22 18 22 14 25 14 14 9 11 17 34 24 May Apr. 26 27 28 29 30 1 2 3 4 5 Clear Fair Cloudy do Fair Clear Fair Cloudy.... Fair Cloudy.... do ....do.... Fair .....do.... .....do.... Clear do Cloudy.... ....do Fair Clear Fair Cloudy.... Fair Clear Fair Clear Fair Cloudy . . . Fair ....do.... Clear Cloudy.... do ....do.... ....do.... °F. °F. 63 31 1 1 4S 63 41 41 32 49 30 61 31 67 45 51 30 50 23 50 43 51 45 Ol 46 66 50 72 49 79 51 80 52 82 60 79 50 53 37 66 33 82 44 90 60 86 58 71 58 79 50 85 61 8.5 65 86 66 iO 64 82 00 65 48 66 37 54 54 59 69 61 61 65 65 SE. SE. X. X. X. SW. E. X. SE. XE. XW. X. X. SE. XE. SE. S. s N. XW. S. sw. sw. XE. SE. SW. sw. SE. SW. xw. X. X. sw. E. X. X. Miles per hour. 13 19 18 27 16 9 14 27 15 13 15 9 12 9 11 20 35 24 27 22 16 19 12 14 16 24 25 18 17 14 26 14 16 10 13 21 Table VIII. — Maximum and minimum temperatures with direction and velocity of wind, and character of the day, Dodge City, Kans.,from Mar. 20 to May 31, 1907. Date (1907). Weather. Maxi- mum. Mini- mum. Direc- tion of wind. Ve- locity of" wind. Date (1907). Weather. Maxi- mum. Mini- mum. Direc- tion of wind. ve- locity of " wind. Mar 20 Fair °F. 91 94 89 76 86 89 S5 61 74 62 59 55 72 85 73 58 61 67 66 °F. 41 54 43 53 46 46 54 38 44 30 31 34 36 51 49 38 26 39 33 SE. SW. S. xw. s SE. SE. XW. SE. XW. XW. SE. SE. E. XW. X. SE. w. sw. Miles \ per hour. 24 28 28 23 26 30 36 16 35 24 18 16 28 23 22 15 10 25 12 Apr. 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 Fair °F. 63 73 77 64 59 55 68 70 4S 60 51 45 46 48 56 78 76 44 64 °F. 41 40 37 38 35 28 35 39 24 24 32 30 33 28 35 30 36 31 23 NW. XW. SE. XW. XW. E. SE. XW. XE. SE. XW. XE. XE. SE. SE. SE. W. XW. SE. Miles per hour. 23 21 do Clear 16 22 23 do Clear .....do do Fair 27 24 r>4 do "Fair 15 25 Clear 13 26 27 do do do Fair 26 23 28 29 do Clear Cloudy Clear 14 16 30 Cloudy Fair Fair 18 31 Cloudy do" do 10 Apr. 1 9 Clear 9 Fair... 10 3 Cbar Fair 9 4 Cloudy Fair Clear 18 5 .....do Cloudy Fair 24 6 7 do Clear 17 18 88 Table VIII. — Maximum and minimum temperatures with direction and velocity of wind, and character of the day, Dodge City, Kans.,from Mar. 20 to May SI, 1907 — Contd. Date (1907). May Apr. 27 2S 29 30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Weather. Direc- ,Maxi- Mini- ■ tion mum. mum. j of 'wind. Clear Fair Cloudy... Fair ....do... Cloudv... Fair..'.... ....do.... Cloudv... ....do.... ....do.... Fair Clear ....do.... ....do.... ....do.... Fair Clear °F. °F. 81 37 59 32 42 25 45 20 62 37 67 32 33 27 57 27 43 41 50 42 60 40 68 43 71 49 78 45 S4 48 90 60 70 39 55 34 N. N. N. NW. SE. NW. NW. SE. SE. XE. E. N. E. NW. SE. SE. NW. xw. Ye locity of wind. Miles per nour. 16 16 18 7 12 18 20 22 Date (1907). Mav 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 Direc- Ye- Weathpr Maxi- Mini- tion ioeity ier- mum. mum. of of wind. wind. Clear.... do... Fair Cloudy.. Clear.... Fair ....do... Clear.... Fair ....do... Clear. . . . .....do... do... Cloudv.. do... do... Fair F. °F. 67 30 W. 86 42 SE. 92 53 SE. 81 00 NE. 73 50 N. 81 50 SE. 8fi 60 SE. 88 65 SE. 87 64 SE. 78 00 SE. 74 47 W. 62 37 NW. 64 30 SE. 52 42 SE. 58 46 SE. 59 49 N. 67 43 NW. Miles per hour. 10 17 13 10 24 35 33 32 29 41 So 16 28 22 11 24 INFLUENCE OF TEMPERATURE ON DIFFUSION. Directly and indirectly, temperature is responsible for the destruc- tive abundance of Toxoptera graminum in the United States. Di- rectly, because the species will breed throughout the winter months at a temperature under which its natural enemies will remain inac- tive, and besides, it is probably due to this influence that the sexual forms and eggs occur, so far as known, only over the northern por- tion of its range. Our extended investigations have led to the sus- picion that, but for the viviparous reproduction in such overwhelm- ing numbers in the South, during winter end early spring, to drift northward with the season, there would be little if any damage caused by its occurrence in the Xorthern States, where in fairly severe win- ters it probably winters over in the egg stage only. For this reason the authors have thought investigations of the egg and its development of decided economic as well as scientific importance, and the junior author has therefore made a brief study of the em- bryology of the species. The temperatures prevailing over the country where Toxoptera has worked its most serious ravages, and departures from the normal during the season of greatest activity are all given on the tempera- ture diagrams, Xos. I to V (pp. 15, 21, 25, 26, 28) . The upper numbers indicate the normal temperature, the lower the departure therefrom (" + " meaning above and " — " below). Each separate page relates to one of each of the five consecutive outbreaks. From these it will be seen that outbreaks of Toxoptera have succeeded only winters with INFLUENCE OF TEMPERATURE OK DIFFUSION. 89 the temperature in the South above the normal, followed by springs during which the temperature was below the normal. The tem- perature during December, 1902, was below the normal in the South- west. (See Diagram II.) In January, 1903, it was above, but below again in February, and about normal or above in March and April, the result being that only incipient outbreaks occurred in northern Texas and probably South Carolina. (See Diagram II; fig. 5, p. 20.) If the series of temperature maps (Diagrams I-V) be compared with those showing the area covered by each invasion the relation between abnormal temperatures and these invasions will be clearly apparent. These records are those of the United States Weather Bureau and are therefore correct so far as general field temperatures are involved. When it comes to a consideration of the exact effects of temperature and humidity upon the individual Toxoptera, however, the figures will not apply with mathematical exactness, for the reason that to secure this information it is necessary to learn the exact conditions in the midst of the insects themselves at the exact time that such data are being secured. To illustrate, the instruments of the Weather Bureau kept in the shade may indicate a certain tempera- ture, yet in a field perhaps a mile distant on a sunny day, and down among the plants in the midst of the developing insects, there may be several degrees difference in temperature. As will be noted farther on, Mr. Luginbill has found this difference to amount in some cases to several degrees. Besides, it is easy to conceive of other conditions which might have precisely the reverse effect. Further- more, there will be a difference in temperature as between fields with a sandy and a clay soil or between a southern and a northern expo- sure, or with a soil dry on the surface as against a soil with a wet sur- face. It will be observed, therefore, that while the exact tem- perature at which Toxoptera will reproduce, viviparously, is of scientific interest, such information is of minor significance in the field, where it is the more generally prevailing weather conditions, such as are secured by the United States Weather Bureau, over wide areas that become of greatest importance, Mr. K. A. Vickery, on December 4, 1908, at Richmond, Ind., with 5 viviparous females under observation, found that young were produced sparingly at a temperature of 40° F. This was indoors, in a room slightly heated by an oil stove so that the temperature was under control, and frequent readings were made during the day. Under the same conditions numerous young were produced when the temperature reached 45° to 53° F. ' 90 THE SPRING GRAIN-APHIS OB ' l GREEN BUG. ' ' Tabulated, the results of Mr. Vickery's rearings are as follows: Table IX. — Experiments with 5 viviparous females of Toxoptera graminum to determine minimum temperature at which reproduction will take place. Richmond, Ind., December, 1908. Date. Temperature. Number of young produced. Minimum. Maximum. Dec. 3 4 5 6 7 8 9 °F. 40 40 40 40 26 35 39 °F. 45 41 53 45 49 50 50 0 1 6 0 1 7 0 After December 9 the outside temperature increased so that con- trol indoors was not possible. At Dallas, Tex., January 3 to 14, out of doors and under natural conditions, with thermometer within a few feet of the five female Toxoptera 1 to 3 days after maturity, Mr. Urbahns found that young were produced as follows: Table X. — Experiments with 5 viviparous females of Toxoptera graminum to determine minimum, temperature at ivhich reproduction will take place. Dallas, Tex., January, 1908. Temperature. Date. Number of young produced by each individual. Minimum. Maximum. °F. °F. Total. Jan. 3 47 68 1 1 1 1 1 5 4 55 78 3 3 1 5 4 16 5 37 69 3 3 1 2 2 11 6 22 42 0 0 0 0 0 0 7 21 32 0 0 0 0 0 0 8 29 45 0 0 0 0 0 0 9 44 74 4 2 0 3 4 13 10 37 74 4 4 0) 3 5 16 11 14 15 0 0 0 0 0 12 10 22 0 0 0 0 0 13 21 32 0 0 0 0 0 14 Total.. 32 71 0 0 0 0 0 15 13 3 14 16 - 1 -1 Died. INFLUENCE OF TEMPERATURE OX DIFFUSION. 91 Further observations made by Mr. Urbahns on these same dates with eight additional females, the offspring of which were not counted, are of much interest and are given herewith. January 3. Two reproducing. January 4. Four reproducing, 1 pupating. January 5. Five reproducing. January 6. All torpid, seemingly frozen. January 7. All torpid, seemingly frozen. January 8. All torpid, none reproducing. January 9. Seven reproducing, 1 still pupa. January 10. Seven reproducing, 1 still pupa. January 11. All torpid, seemingly frozen. January 12. All torpid, seemingly frozen. January 13. All torpid, seemingly frozen. January 14. Adults and young fallen from the plants and lying on the ground. All except 3 inactive. One female of the first five died on the 10th and nearly all of the others survived but a few days; only one was alive on the 20th. During the spring of 1908 the junior author was engaged in an extensive series of rearing experiments at Richmond, Ind. Both plants and insects were kept out of doors in a small rearing house (see PL II, fig. 1), with a thermograph placed in their midst, so that exact temperature changes were continuously recorded. Plants were grown in flowerpots and over them in each case was placed a lantern globe with the top covered with cheesecloth. Whatever the effect of this inclosure and cover might have been it was evi- dently uniform and, therefore, affected all of the viviparous female Toxoptera on these plants to the same degree. Taking five viviparous females, each a stem mother, colonized separately on single plants, in a precisely similar inclosure, and keep- ing a record of the number and date of young born, we have the fol- lowing tabulated results: Table XI. — Effect of temperature on reproduction of Toxoptera graminum, Richmond, Ind., 1908. Date. Apr. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. Tempera- ture. Mini- Maxi- mum. mum. °F. °F. OD 63 50 70 39 68 33 68 35 74 52 79 60 71 61 74 53 SO 42 67 38 54 36 46 33 47 Number young pro- ; To- dueed by each in- i tal dividual. > No. 3 ! 4 4 5 5 3 2 2 0 0 0 2 0 0 9 6 2 11 0 6 0 ] 6 1 14 1 11 2 15 0 14 1 8 0 2 1 7 0 0 Date. Mav 1. 2. 3. 4. Tempera- ture. Mini-' Maxi- mum, mum. Total.... Total progeny during life Number young pro- duced by each in- dividual. 29 32 60 ! 47 3(3 39 29 To- tal No. 02 Of the five individuals involved in Table XI the two last hatched from the egg March 24, the other three on March 27. This table indicates the influence of high temperatures on reproduction, but also shows that these affect the individual female to varying degrees. The totals for the life of individual females show that all of these were in the vigor of life, not having reached the decline at the time the observations were made. These tabulations are taken from records of regular rearing and reproduction investigations, and were selected wherever there occurred a number of consecutive days with temperatures varying both above and below freezing during each 24 hours. By referring to the continuous rearing by the junior author it will be observed that with favorable conditions a female Toxoptera will produce young every day during the most vigorous portion of her life, the exceptions being toward the close thereof. It would probably be well to mention in this connection some observations of the junior author in regard to the amount of cold that can be endured by Toxoptera. On November 13, 1908, several viviparous females that had been producing young were frozen solidly in a block of ice. They were thawed out after 8 and 24 hours, respectively, and all died. These may have been somewhat weakened by age, however, so on the 14th 2 oviparous females, 1 winged viviparous female, 1 adult viviparous, and 2 individuals that had cast the third molt were frozen in a block of ice and allowed to remain so for 24 hours. About an hour after being thawed out, at a temperature of about 45° F., 1 oviparous female and the winged female turned dark and died, the others keep- ing color, but showing little signs of life. About 3 hours after there were signs of life among the remaining ones; 7 hours after thawing out they were still feeble; 24 hours after thawing out the temperature was raised to 60° F and 1 molted. On the third clay after being thawed out there were 2 young in the cage. Six days later all were dead except the one that was giving birth to }^oung, and her progeny. This will give some idea of the tenacious grip Toxoptera has on life. Attention may properly be called to the fact that unless the utmost caution is employed in the examination of plants for newly-born young there is great likelihood that some of them may be overlooked. Thus they may be born one day under a high temperature but remain undiscovered until later, when the temperature is much lower, and of course be credited to the later date. In the light of all of the observa- tions made by those engaged in these investigations, the minimum temperature under which reproduction begins is about 40° F. Pos- sibly reproduction may occur under some obscure favorable circum- INFLUENCE OF TEMPERATURE ON DIFFUSION. 93 stances at a slightly lower temperature, but these instances are probably too infrequent to become of economic importance. With the eggs in the North the case may be more important, because these, deposited in dead leaves of bluegrass, and sometimes probably buried under several inches of this matted grass, with the living leaves covering this over, the temperature and moisture would both be greater than at several feet above ground without such protection. Mr. Philip Luginbill of this bureau in April, 1911, proved this to be true. He placed a thermometer in just such a position as men- tioned above, in a protected nook where the sun could shine directly on it in the grass and no wind could reach it and found that the temperature was 10° to 12° F. higher than when the thermometer was several feet above the ground and in the shade. The junior author has found that eggs are deposited in just such places, and that hatching takes place in spring at a temperature ranging, as recorded by the thermograph, from 32° to 62° F. It would appear that eggs deposited in a position as mentioned above would hatch sooner than those deposited in places where the temperature would not be so high and the stem mothers from the former would reproduce, the pest becoming more abundant in the spring and making its way from grass to grain earlier and in greater numbers than they would from the cooler locations. This leads us to a very interesting and important point in tem- perature effects on the species. In the South, seemingly south of about latitude 35° to 36° north, it has been impossible to find eggs of this and other species of aphidids in the fields. There is in the perpetua- tion of the species no apparent need of this stage, however, as it is able to continue throughout the entire year reproducing viviparously. In the North this is probably not possible except during very mild winters. The situation is therefore about like this: Gradually as we proceed southward from about latitude 38° the sexual forms and eggs disappear, while to the north of about latitude 36° hibernation is confined more and more to the egg stage, until this becomes ex- clusively the state in which the winter is passed. The practical, economic importance of this is that there is con- siderable doubt relative to the amount of injury the pest would cause north of this belt of country if there were no Toxoptera drifting in from the south. In other words, but for the countless myriads developing south of this belt and sweeping over and beyond it, there would be few if any destructive ravages. If this is the true state of affairs, the oats crop north of this belt is to a certain degree de- pendent upon the success or failure in controlling the pest in Texas, Oklahoma, New Mexico, and South Carolina. Summarizing, then, it would appear from the information we have been able to obtain, and which is given throughout this publication, 94 together with that contained in the various tables and diagrams relating to temperature effects upon this insect: (1) That mild winters are of much more vital importance in Texas than they are in the latitude of southern Kansas and northward, and (2) that the influences of abnormally warm weather, if the temperature rises high enough, have the effect of bringing about activity among the parasites, which has a restraining effect upon the increase of Toxoptera. In the North, where the pest winters over wholly or largely in the egg stage, warm winters are of less importance, while abnormally cool weather during spring and early summer exerts a far greater influ- ence. This fact renders a study of the embryology and temperature effects upon eggs and stem mothers necessary to a full understanding of the entire problem, extending as it does over both North and South. The fact just stated is somewhat peculiar and was unexpectedly revealed by the combined studies of those engaged in the investiga- tion of the insect, and called for a study of the development of the egg, which has been carried on by the junior author with the results given in the following pages. The most important influence of temperature is, of course, upon the development of its principal natural enemy, ApJiidius testaceipes, further discussed in connection with the studies of that insect. EMBRYOLOGY. Although the development of the parthenogenetic egg in Aphididae has received considerable attention from several authors, that of the true egg has received very little study. Hence the junior author has given a limited amount of time to the study of certain important phases in the development of the winter egg, as contrasted with the winter condition of the viviparous insect in the South. Not wishing to duplicate the work of the other writers, who have confined their studies for the most part to the earlier stages of develop- ment, he has begun with the formation of the blastoderm, his main object being to follow the principal stages of development of the embryo through the fall until growth is checked by freezing tempera- tures, to note the time when growth is resumed in spring, and to observe the effect of varying temperatures on development, all of which has to do with the fluctuations of the insect in point of numbers in the North and relates to its economic importance, besides balancing our knowledge of the insect at a corresponding season in the South. Most of these studies were carried out at the University of Illinois under the supervision of Dr. J. W. Folsom. We are deeply indebted both to him and to Dr. W. M. Wheeler of Harvard University for their kindly criticisms and helpful suggestions. EMBRYOLOGY. 95 METHODS AND MATERIAL. The material used in this investigation was collected in the autumn of 1908 at Richmond, Ind., and in 1909 and 1910 at La Fayette, Ind. The eggs were killed and fixed mainly in two solutions that are practi- cally the same. The first was a saturated solution of bichlorid of mercury (corrosive sublimate) in 35 per cent alcohol, 95 volumes, and glacial acetic acid, 5 volumes. The second was a saturated solution of bichlorid of mercury in 50 per cent alcohol, 94 volumes, and glacial acetic acid, 6 volumes. The fixing fluid was raised to a temperature of 75° to 80° C, poured over the living specimens, and allowed to act from 5 to 10 minutes, after which it was replaced by the same solution, cold, for an equal length of time. The specimens were then washed in 70 per cent alcohol, in which they were kept until sectioned. Gibson's fluid was found to be a very good killing and fixing agent also. For sectioning, the following method was employed: The eggs were punctured with a fine needle, dehydrated, and kept 20 to 30 minutes in paraffin of about 54° C. melting point. They were oriented in a watch glass (that had previously been smeared with glycerin) with a hot needle, under a binocular microscope, the bottom of the watch glass being first quickly cooled with a little cold water. The eggs were cut with a Minot-Zimmermann microtome in sections from 8 to 13 /z in thickness, attached to the slide with Mayer's albumen fixative, and stained with Delafield's hematoxylin or by Heidenhain's iron-alum-haematoxylin method. Surface views of the embryo were obtained by dissection. For dissections it was found that the best results were obtained by using material that had been freshly fixed and washed. Grenadier's alcoholic borax-carmine was used for staining in toto. GENERAL DESCRIPTION OF THE EGG. The eggs are broadly elliptical with* a slight reniform tendency. They are 0.70 to 0.78 mm. in length and 0.33 to 0.45 mm. broad. At oviposition the egg is a very pale yellow, changing in a few hours, at a temperature of 50° to 70° F., to a faint greenish color. At this stage there appears an almost circular area of darker green at one pole of the egg; we have termed this the "ovarian yolk," a brief description of which occurs in the following pages. At the end of 24 hours the walls of the egg about the ovarian yolk appear denser and of a deeper green. The germ band is now forming and invaginat- ing. During the next 24 hours this process is completed, the egg becoming a darker green in the meantime. By the third day a rod- shaped body can be seen near the center of the egg. This object is the submerged germ band. By the end of the third day the egg becomes black. 96 THE SFBTSTG GRAIN-APHIS OR "gBEEN BUG.*' Ail these changes can be readily observed with a hand lens by holding the egg up to the light. At low temperatures (below 40° F.) these changes take place slowly. 10 or more days being required for the egg to turn black, if the temperature is near the freezing point. The black coloration is apparently due to a pigment in the shell: the green color, to the developing embryo. At deposition the egg is coated with a viscous substance which hardens in a few days, fixing the egg firmly to the object upon which it rests. T-iere are but two membranous coverings to the ripe egg, the chorion, or shell covering, and the vitelline membrane. The chorion is a rather tough, leathery, homogenous membrane which under a hand lens appears smooth and shining. With a com- pound microscope very faint lines or cracks can be someiimes ob- served on the surface, although usually the surface appears perfectly smooth, with no markings whatever. The vitelline membrane is structureless, colorless, and trans- parent. Under the vitelline membrane is the peripheral layer of protoplasm. This layer is very thin and very finely reticular. It is continuous over the surface of the egg, the cleavage cells lodging in it to form the blastoderm. Internally the egg consists chiefly of a compact mass of yolk granules, supported within the meshes of almost clear protoplasm. The yolk granules are structureless and subspherical in shape and vary greatly in size, ranging from 0.0027 mm. to 0.013 mm. in diameter. At the posterior pole of the egg is a large, dense, almost spherical, granular mass. These granules are 0.0019 mm. in diameter, are almost uniform in size, and the central area apparently takes the stain slightly as though it were a chromatirdike substance. As previously stated, we have termed this mass the ovarian yolk. It is evidently not homologous to the secondary yolk of the parthenogenetic em- bryos. The ovarian yolk is formed approximately at the same time as the formation of the main yolk mass of the egg, while in the case of the parthenogenetic forms of aphidids the secondary yolk enters the egg as the blastoderm is forming. It appears also, from our material, that this oviiriaii yolk is not exactly homologous to the "pole disk" described and observed by Hegner (1908) 3 as we have not- been able to observe that it affects the nuclei in any way. nor have we found any cells which we think correspond to his '"pole cells.'' The function of this granular mass seems to be the nourishment of the developing ovaries, and we have therefore called it ovarian yolk. It is not entirely used up in the early stages of embryonic growth, and remains in close proximity to the developing ovaries throughout the later stages. EMBRYOLOGY. 97 Tannreuther (1907, pp. 631, 632) states that in the species he studied some of the follicular nuclei of the wall of the oviduct which enter the posterior pole of the egg divide several times, the chromatin breaking up into smaller parts and becoming vesicular. These small vesicles then usually unite and form a common spherical mass, though in some cases they remain isolated. In Toxoptera graminum we find no trace of true nuclei within the ovarian yolk (the homologue of Tannreuther's secondary york of the winter egg) until the blastoderm is formed, at which time cells may be found that are apparently migrants from the primary yolk. OBSERVATIONS. For convenience of reference 9 consecutive stages of development are here designated, as follows : Stage 1 (PI. Ill, fig. 1). — Blastoderm just forming, only part of the surface being covered by the cleavage cells. Stage 2 (PI. Ill, figs. 2-4). — This shows early and later stages of invagination of the germ band. The position of the ovarian yolk in relation to the invaginating germ band is shown here. Stage 3 (PI. IV, fig. 1). — The germ band is still adhering to the posterior pole of the egg. Stage 4 (PI. IV, figs. 2, 3). — The germ band is entirely submerged in the yolk, is tubular in form, and uniform in thickness. Stage 5 (PL IV, fig. 4). — During the fifth stage the germ band has differ entiated into the amnion and the germ band proper. Stage 6 (PI. V, fig. 1). — The germ band shows differentiation into layers, and the fundaments of the segments are evident. Stage 7 (PI. V, fig. 2; PL VI, fig. 1).— The fundaments of the ap- pendages have appeared and the invaginations for the stomodaeum and the salivary glands are evident. Stage 8 (PL V, fig. 3; PL VI, fig. 2). — The appendages are much longer, and the invaginations for the stomodaeum and proctodeum are well advanced. The latter is not indicated in Plate V, figure 3, as the last segment curves backward too far. Stage 9 (PL VII, figs. 1, 2, 3, 4).— The illustration of this stage is intended mainly to show the manner in which the embryo reaches the surface and the position of the dorsal organ. In Stage 1 (PL III, fig. 1) the blastoderm is beginning to form. As the cleavage cells become more numerous within the yolk-mass some of them migrate to the surface and lodge within the peripheral layer of protoplasm, where, according to Tannreuther (1907), they divide again, the protoplasm of the nuclei merging with that of the periph- eral layer. The formation of the blastoderm takes place more rapidly in the region of the anterior pole, the posterior being the last covered; 26675°— Bull. 110—12 7 98 the entire layer is then one cell in thickness. The blastoderm, how- ever, does not cover the surface of the ovarian yolk. Not all of these cleavage cells reach the surface; many remain behind, increasing in number within the yolk. These latter cells are indistinguishable from those of the blastoderm. Figs, la and lb represent two of these cells magnified 845 diameters, showing them to be star-shaped masses of protoplasm with a large oval coarsely granular nucleus, more often with a large clear area of nuclear sub- stance around the mass of chromatin granules. At the posterior pole, about the ovarian yolk, the blastoderm be- gins to thicken and to invaginate (Stage 2, PL III, figs. 2-4). This is the beginning of the germ band. At this stage {Stage 2) some of the yolk cells apparently pass into the ovarian yolk. Tannreuther (1907, p. 631) states that the thickening of the blastoderm is caused by the rapid division of the blastoderm cells of this particular part. We find, in addition, that some of tlie cells from the interior of the egg migrate to the posterior pole to assist in this process. Each of the cells of this thickened area is very elongate, and, from a surface view, now has a somewhat polygonal shape, with a large coarsely granular nucleus. The growth of the cells of the germ band carries the ovarian yolk toward the center of the egg (see PI. Ill, fig. 4)- The part of the blastoderm that invaginates first becomes the posterior part of the embryo, and that part that invaginates last becomes the anterior portion. In Stage 3 (PL IV, fig. 1) the germ band is ready to free itself from the blastoderm. The former is now cone-shaped, the base being closed by the ovarian yolk. When the germ band releases itself from the blastoderm, it leaves behind what we have termed the "polar organ:" A cluster of cells embedded within a mass of protoplasm. These cells soon group themselves into a more or less spherical mass, with a less dense vacuolar area at the center (see PL IV, fig. 4). In later stages this central area appears denser and structureless, as though filled with a fluid, and is of a yellow color, not taking the stain, and opening directly upon the surface of the egg. For these reasons we suggest that it may be an organ of excretion. When development ceases in the fall, this body is still present. What was formerly the blastoderm now becomes the serosa. The cells are much more widely spaced now and this wall is much thinner, except at the anterior pole, where the cells are apparently crowded more closely than before. Some of these cells often show large vacuoles on the side toward the yolk. At Stage 4 (PL IV, fig. 2) the germ band is completely submerged in the yolk, has assumed a tubular shape, and is near the center of the egg. The walls are of uniform thickness and composed of a com- , EMBRYOLOGY. 99 pact mass several cells thick, some of "which are vacuolated, and having a coarsely granular nucleus. Figure 3 of Plate IV shows a cross section — slightly oblique, however — of the germ band. The yolk granules of the primary yolk are now more numerous near the embiyo. In Stage 5 (PL TV, fig. 4) the germ band has clearly differentiated into the amnion and the embryo proper; these gradually merge into each other. Tins differentiation apparently takes place by a gradual migration of cells to one side of the germ band. The cells of the amnion at tins time resemble very closely those of the germ band proper. The genu band begins to fold in this stage and its anterior extremity begins to broaden and flatten. The ovarian yolk has de- creased in volume and has assumed a more anterior position in rela- tion to the embryo. The yolk cells in both the primary and ovarian yolk have lost somewhat their amoeboid character, and now consist, each, of a large granular nucleus, with a much thinner area of pro- toplasm about it. The primary yolk granules are smaller and much less numerous than before and are collecting in masses about the yolk cells, with indications here and there of a partition, or wall, forming between them. This stage is reached by the end of the second day, under favorable weather conditions. The "polar organ'' and protoplasm at the posterior pole contain a large central vacuolar area now. In Stage 6 (PL V, fig. 1) the germ band has greatly increased in length, is folded upon itself, and almost forms a loop, the anterior and posterior extremities nearly touching, and both pointing to the posterior pole. A portion of the posterior extremity of the germ band is again folded upon itself. It is now differentiated into three layers, which we take to be, respectively, ectoderm, mesoderm, and ento- derm. The ectoderm and mesoderm consist of a compact mass of columnar cells, two cells thick. The entoderm is much thinner and less compact and forms an almost continuous sheet over the inner sur- face of the germ band. Its cells resemble yolk cells very closely. In this stage fundaments of the body segments appear as slight elevations of the ectodermal surface. The ovarian yolk has assumed a more anterior position in relation to the embryo than in the pre- ceding stage. Between the ovarian yolk mass and the germ band is a group of cells that have apparently separated off from the mesoderm. From this group of cells, in later stages, the generative organs arise. The amnion nowr covers the ventral surface of the embryo and the other surface of the embryo is in contact with the yolk. The amnion is a very thin, delicate membrane, its cells being widely spaced and quite small. The intervening protoplasm between the cells of the serosa has become more constricted and the cells have taken more of an elongated oval shape. The primary yolk has now become defi- 100 THE SPRING GRAIN-APHIS OR nitely segmented into more or less spherical masses, separated by thin walls, each area or mass containing a number of yolk granules and from one to several cells. The polar organ is now almost spher- ical, with a central, pear-shaped area of dense, structureless, non- staining matter of a yellowish color, and an anterior opening. Al- though this evidence is insufficient it possibly indicates that the func- tion of this organ is excretory. The embryo reaches this stage of development about the third day, under favorable conditions of temperature. In Stage 7 (PL VI, fig. 1) the embryo has changed its position so that from a side view it has the form of a reversed figure 6. The portion that in the preceding stage was folded upon itself ventrally has reversed its position and folded back dorsally. The ovarian yolk is now in the region of the first abdominal segments. It is in contact with the embryo, and the group of cells that separated it from the embryo in the preceding stage has assumed almost a spheri- cal form, and a more posterior position, forming the genital organs later on. The three primary regions, cephalic, thoracic, and abdominal, are now sharply marked. Each region is distinctly segmented. The cephalic region has 5 segments indicated, the thoracic 3, and the abdominal 9, the last abdominal being relatively quite large. There are now 15 conical appendages. The antenna} arise from the pos- terior margin of each cephalic lobe. The labrum is between and slight- ly anterior to the antennae. The mandibles are nearer the median plane than the fundaments of the maxillae and the labium. The next three pairs of appendages represent the first, second, and third pairs of legs. Plate V, figure 2, represents a surface view of stage 7, show- ing the embryo straightened out and the position of the appendages. All of these appendages are evaginations of the ectoderm, cross-sec- tions showing an external layer of ectoderm cells and an inner layer of mesoderm cells. The stomodseum (PI. VI, fig. 1) appears now as a simple invagina- tion of the ectoderm, the posterior wall of the labrum forming its anterior wall. The proctodeum has not yet appeared, The salivary glands (PL VI, fig. 1) are represented by a deep, bilobed, ectodermal invagination between the cephalic and thoracic regions. There is now a star-shaped mass of protoplasm about the nucleus of the ovarian yolk cells and the yolk granules are grouped around these cells. The primary yolk is grouped very much as in the preceding stage with the exception that the masses are smaller and do not contain as many nuclei. The polar organ is smaller than formerly, with a smaller number of cells. It still contains a yellowish mass and communicates with the outer surface of the egg. Bui. 1 10, Bureau of Entomology, U. S. Dept. CJP °S9~,oo O,*?ooo oocu0 ~~' ;-c oil! jOOoq 0~> ■"^ in CP m -^S>^ Fig ■PS pp. I ®3a J a Jb % t Fiq. Z PT •"•.-'jj.V/i-v-*'"' cj.c:o.c|. Fiq. 3. o.c). q&. Fig. 4 l^c Fig. ].— Longitudinal s pole. Figures luai previous to invagination. 'Magnified I the ovarian yolk. Magnified l.lfi diam invagination, 1 he genu band having a, '„n00o32ro°oo'^5Oo0V50 ^oo,?0 o ©uOo A> £> ^ Bui. 1 1 0, Bureau of Entomology, U. S. . ,ll ' ' ft '^cPH Fiq.l. . o.q. p> 1 ^;ti u baml ready to release i l'e,K, Ule ovarian M.li, < I,,. kil' I fit- |.o>lfii,a r\ I nanil ;, . MaLnilii.'.l i:,i, ,(ia ha • ll- L' -aaa |.US[eriMl IMIll (I I ,,;, It .Illll'.olk I (:■■■' jj -I -I n! _';:.' i |r[,lr a-nl. .1 b. i 1 1 la- ni ( WN (Original.) Fiq.4. lie siili'siinil (1)0 a:" Bui. 1 10, Bureau of Entomology, U. S. Dept. of Agriculture. Plate V. N'. tot S3. ci- io ro "& U "8: 90E £ J?^ -£ -£ ro (pip 9

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M-o O- pf-ab.rc gt-4hr» Stbb yftmd Jot Ic 1. qc, 5. *e P-M- po FS. Development of the Embryo in the Egg of Toxoptera graminum. g. 1.— Sagittal section of the embrvu showing tin- segmentation. The invagination oMhesalivaiy glainls is now fvi.leni ._ The -Mini!.- :!iapc an| m;u a in ■■' :mH >-! < "^s" o~ < cs l~ — OO o-1 «i cad O "3 1 c3 iO Kind of adult. a hi S= 5 4 z ■4 c -3 O "3 3 CD Oi - > ^ c c ■a c _c c a 5 = •3 a Obi p > c3?c ft c c -2 '5 -3 ft 3^ c € c - rS c Stage when parasitized. Q c f- c ft c - c T3 03 ft S ,3 M 5 o o •3 o -3 C o o a to r pE. ■J IE J j i 11 3K 5 s C t c 1 i 5 "3 ?1 CN r) o OS PARASITE, APHIDIUS TESTACEIPES. 109 Two adult Aphidius issued from those individuals included in the first section of the table and 18 from those in the last section. In this latter section Aphidius began to issue March 30 and the last issued on April 3. Those that issued on the latter date were from those that were adult winged adults when parasitized. All of these experiments were conducted indoors, and those of the last division of Table XII, under a daily temperature ranging from 50° to 80° F. From Table XII it will be seen that Toxoptera that have molted only twice before being parasitized may become winged adults, and in some instances produce young. All of our observations show that individuals that have molted three times and then been parasitized will become adult and produce young, and in case they are wingless they may produce 10 or more. Eleven is the maximum number of young, according to our observations, produced by a single individual after parasitization. MOVEMENT OF LARVA WITHIN THE HOST AND MANNER OF ATTACHING IT TO THE PLANT. Observations were made upon the movements of the larva (fig. 21) within the host by the senior author at Manhattan, Kans., in 1907, and published in the Proceedings of the Entomological Society of Wash- ington.1 It appears that the larva of the parasite, at least until after it attains some growth, moves little if at all within the body of the host, and thus interferes with no vital functions of the Toxoptera. When the larva nears maturity, as shown by the yellowish color of the abdomen of the " green bug," it becomes quite active, making a number of revolutions within the body of its host, at which time the latter seizes the leaf with a rigid death-grip and the last spark of life soon fades. The object of the revolutions is, apparently, to mold the body wall of the aphidid, while it is still plastic, into the most suitable shape for pupation. An idea of how this desired end is accomplished may be obtained by glancing at the accompanying illustrations. Figure 22 shows the normal position of the parasitic larva within the body of the host before the revolutions begin. It was found that a fully developed larva (fig. 23) made three revolutions within the body of the host, always going forward, in the space of 35 minutes. During the next 5 minutes it made another revolution ; a fifth revolution was completed in the next 10 minutes; the sixth during the following 8 minutes; the seventh in the next 9 minutes; the eighth after a space of 4 minutes; the ninth in the following 4 minutes, after which, on account of the opaqueness of the walls of the host, no further count was kept of the revolutions, although several more were known to have been made. Some of these different positions of the larva and i Proc. Ent. Soc. Wash., vol. 9, Nos. 1-4, pp. 110-114, 1907. HO THE SPRING GRAIN-APHIS OR " GREEN BUG." the shapes the body of the Toxoptera assumes are graphically repre- sented in figure 21. At this time, or about one and one-half hours after the observations were begun, the body wall of the "green bug" became quite dark and almost globular in form, and tins shape it afterwards retained. PAKASITE, APHIDIUS TESTACEIPES. Ill Mr. Kelly, of this bureau, later took up the observations at this point, during the fall of 1908, and published the results of his obser- Fig. 22.— Position of larva of Aphidius tcstaceipes in the body of the spring grain-aphis at the beginning of the change to a yellowish color. Much enlarged. (Original.) vations in the Proceedings of the Entomological Society of Wash- ington.1 Mr. Kelly confined some aphidids that were nearly dead from parasite attack on a slide and observed them under the microscope. He found that as the body of the " green bug" takes on a brownish tint, the Aphidius larva within makes a longi- tudinal slit or opening in the ventrum and enlarges it until it is more or less oval in shape, as shown in figure 24. The rigid, firm manner in which Tox- optera grasps the object upon which it is resting at death apparently has the effect of holding it in place while the movements of the parasitic larva are going on within. When the opening is complete the larva begins to spin its cocoon, at the same time ejecting a glutinous fluid that makes the strands adhere to any object Fig. 23.— Full-grown larva of Aphidius testaceipes taken from body of the spring grain-aphis as shown in figure 22. Much enlarged. (Original.) i Proc, Ent. Soc Wash., vol. 11, No. 2, pp. 64-66, 1909. 112 with wnich they come in contact. The body of the aphidid is cemented firmly to the object upon which it finally comes to rest. The inner abdominal walls of the plant-louse are also lined with silk, which firmly adheres to them, and it may be that the silk also acts as a tanning substance for the body of the aphidid, as the latter be- comes leathery and is apparently impervious to water ; the old leathery bodies of the plant- lice may often be found firmly attached to plants after a heavy rain. After the cocoon is completed the larva becomes quiet and in most cases assumes, according to the junior author, a position directly opposite to that which it assumed while feeding and develop- ing. Figure 22 shows a larva feeding, how- ever, in the reversed position; this seems to be unusual, the normal position being as shown in Figure 21, I. The larva oftentimes, on becoming fully developed, is in some way dislodged from the body of the aphidid. This is probably due to some interference while attaching the host to the leaf. These cases are quite numerous in badly infested fields and the larva? appar- ently never become adult. Figure 25 is a graphic illustration of one of these accidents. Mr. Kelly found that the pupal stage lasted from 3 to 4 da}^s. Fig. 24.— Larva oiAphidius tcsta- ceipes spinning its cocoon in the dead body of the spring grain- aphis, showing the slit or open- ing in walls of underside of host insect. Much enlarged. (Original.) Fig. 25.— Larva of A ph idius testaceipcs work- ing its way prematurely from the body of the spring grain-aphis. (From Webster.) Fig. 26.— Full-grown larva of Aphidius testaceipcs: a, Lateral view just prior to pupation; 6, front Anew of head. Greatly enlarged. (Original.) Figure 26 shows the larva just prior to pupation. These observa- tions were made indoors, during the winter, at the ordinary room temperature. It requires from 3 to 5 hours for the Aphidius to PABASITE, APHIDIUS TESTACEIPES. 113 emerge as an adult after the first movements of the pupa begin, and when ready to issue the pupa expands and contracts the abdomen, moving the feet and antennae until these are freed from their gum- like covering. Upon studying the pupae (jig. 27) closely, we find that the prothorax bears two rows of distinct elevations or tubercles, but we have been unable thus far to ascribe any particular function to them and they disappear with the gum-like covering. The junior author finds that the adult gradually works itself about until it gets in a position with its back to the ventrum of the old aphidid shell, when it cuts a circular hole, as described by Mr. Kelly, and crawls out, always with its head pointing toward the head of the old aphidid. Figure 28 represents an old dead body of a " green bug" after the parasite has issued. FECUNDITY. Fig. 27. — Pupa of Aphidius testaceipes immediately after pupation. Much enlarged. (Origi- nal.) From the prompt manner in which Aphidius, under favorable weather conditions, overcomes Toxoptera it will readily be seen that the former must be a very prolific breeder. The average adult female contains from 4 to 450 eggs. These eggs are lemon-shaped (see fig. 19), very pale, and translucent. Messrs. Kelly and Urbahns conducted a number of experiments at Wellington, Kans., in 1908, to determine the number of offspring produced by one individual. They found that one Aphidius would parasitize as many as 206 Toxoptera. In their experiments, however, they used only a few more than 200 Toxoptera to each individual. Mr. Parks, at the same place in 1909, conducted 16 experiments, using from 300 to 500 Toxoptera and he had a maxi- mum, in one case, of 301 aphidids parasitized from one individual Aphidius. His minimum was 3; his next highest number was 33, and his next was 44. Of the sixteen, 12 fell below 100; his average was 94.6. Mr. Parks also conducted experiments at the same time as the above to ascertain what the ef- fects of continuous mating of one male to differ- ent females would have on the offspring. In this experiment 1 male was mated to 12 unfertilized females within a period of two hours, after which each female was placed in a separate cage with about 100 Toxoptera that had not been exposed to Aphidius. 26675°— Bull. 110—12 8 Fig. 28.— Dead "green bugs" (Toxoptera graminum), showing holes from which the matured parasites of A phidius testaceipes emerge. The top figure shows the lid still attached, but pushed back; the bottom figure shows the parasite emerg- ing. Enlarged. (From Webster.) 114 The male refused to mate with any more females after the twelfth. Table XIII shows the results of these observations : Table XIII. — Offspring produced as the result of mating one male Aphidius with 12 females. Female Offspring. Female, cage No. — mated with male from cage No. — Males. Females. 180 180 29 55 181 180 14 33 182 180 21 30 183 180 35 41 184 180 2 8 185 180 0 0 186 180 13 30 187 180 39 25 188 180 1 0 189 180 50 0 190 180 8 9 191 180 26 16 From these data it appears that all of the eggs from the last few females were not fertilized, as Mr. Kelly finds that females predom- inate when the eggs are properly fertilized. Table XIV illustrates this latter point. Table XIV. — Offspring of Aphidius produced from eggs properly fertilized. Offspring. Cage No. — Males. Females. 197 39 67 297 15 20 299 13 33 300 24 40 302 20 34 304 16 50 306 47 12 333 115 15 403 26 41 404 38 93 405 Total . . 26 44 379 429 1 These two females were apparently unfertilized, although they were supposed to have mated, as they give about the same results as some of the unmated females. If these two be eliminated it will be seen that the females are far in excess of the males. PARTHENOGENESIS. In all of the studies of parthenogenesis care was taken to preserve both parents and offspring, the individuals of each family or brood being preserved and kept entirely separate for future systematic studies, which were later carried out by Mr. Viereck. The first record of parthenogenesis of this species was published in the Proceedings of the Entomological Society of Washington,1 by the junior author, whose attention was first called to this phenomenon i Proc. Ent. Soc. Wash., vol. 10, Nos. 1-2, September 15, 1908, pp. 11-13. PARASITE, APHIDIUS TESTACEIPES. 115 during the summer of 1907, while making observations on the life history of the species; hence, a series of experiments was begun in order to learn something definite in regard to it. Seven female Aphidius were selected, just as they issued from their cocoons (being therefore unfertilized), and placed in separate cages with 30 to 40 Toxoptera not previously exposed to parasite attack. All of the parasites began ovipositing at once. After one of the females had apparently parasitized all of the aphidids in her cage she was mated and placed in a second cage with a number of Toxoptera as before. All the offspring from unmated females were males, but the offspring from the single female, after she had mated, comprised 22 females and 4 males. Messrs. Kelly and Urbahns elucidated this phenomenon more fully during the summer of 1908 at Wellington, Kans.1 These experi- ments were conducted as follows : Starting with a mated female, the females from among her off- spring were isolated, even before emergence. On their appearance they were given Toxoptera not previously exposed to parasitic attack. The few females from among this second generation were again isolated in the same manner, the females in all cases being kept unmated. Nearly 100 experiments were conducted in this manner, but only 48 gave results. The offspring of 44 out of the 48 isolated were, all of them, males. Of the 4 remaining females, the offspring of 3 were as follows : 70 males and 3 females; 101 males and 6 females; 67 males and 1 female. In the case of the remaining female, some uncertainty exists as to whether she had been fertilized or not, and, for this reason, a census of her offspring is not here included. Of the three exceptional cases the offspring from one female were not bred any further; from- a second, the offspring became all males in the second generation; the offspring from the third female produced two females in the second generation, all finally becoming males in the third generation. In this manner it will be seen that Messrs. Kelly and Urbahns were able to rear a limited number of females parthenogenetically to the third generation. Beyond this all of the offspring were males. While the conditions under which these experiments were conducted would not obtain under ordinary field conditions where the infestation was great, it could very easily occur where there are very few aphidids present. This apparently abnormal feature, then, would greatly assist the species in tiding over periods of scarcity of plant-lice. HOSTS OP APHIDIUS TESTACEIPES. Since we were able to find Aphidius testaceipes over almost the entire United States, it seemed clear to us that it must have hosts other than Toxoptera graminum. Accordingly Messrs. Kelly and Urbahns con- i Ann. Ent. Soc. Ainer., vol. 2, No. 2, 1909, pp. G7-87. 116 ducted about 200 experiments in order to gain some definite informa- tion on this point. Their mode of procedure was to search out differ- ent species of parasitized aphidids in the fields, rear the adult para- sites, and breed them into Toxoptera graminum; then, if possible, breeding them again into the original host. One attempt, if unsuc- cessful, was not considered sufficient, several trials being made. While conducting these experiments, other species of parasites were found that would breed into Toxoptera also. These will be dealt with in their proper places. In all of these breedings, both parent and offspring were kept separate and preserved for future study. It was found that Aphidius testaceipes would breed interchangeably from Toxoptera into Aphis setaride, Aphis maidis, Aphis middletoni Thos.,1 Aphis gossijpii, and a species of Chaitophorus. This is the same as the list published by the senior author in the Annals of the Ento- mological Society of America,2 with the exception that Chaitophorus is added and Aphis orassicse has been expunged from the list, as it has been learned that the .species of parasite that would interchange with Toxoptera graminum and A. orassicsc is another species of Aphi- dius. Besides the above fist of interchangeable breedings, Aphidius testaceipes has been reared from Aphis oznotherx at Salisbury, N. C, by Mr. R. A. Vickery; from A. medicaginis at Wellington, Kans., by Messrs. Kelly and Urbahns; from A. rumicis at Clemson, S. C, by Mr. G. G. Ainslie; from Macrosiphum viticola at Wellington, Kans., by Mr. Kelly; from M. granaria at Spartanburg, S. C, by Mr. G. G. Ainslie; from Melanoxantherium sp. at Leavenworth, Kans., by Mr. Kelly; from Macrosiphum sp. on black gum (Nyssa sylvatica) at Salisbury, S. C., by Mr. Vickery ; from Aphis avenx, at Salisbury, N. C, by Mr. Vickery; at Leavenworth, Kans., by Mr. Kelly, and at Washington, D. C, by Mr. C. N. Ainslie; and from Aphis medicaginis by Mr. J. T. Monell, at St. Louis, Mo. Aphidius testaceipes has also been reared from several unidentified species of aphidids, as follows: From an aphidid on Ampelopsis sp. by Mr. C. N. Ainslie; from an aphidid on Capsella sp. at Wellington, Kans., by Mr. C. N. Ainslie ; from an aphidid on Kochia scoparia at Rochester, Minn., by Air. C. N. Ainslie ; from an aphidid on locust at Wellington, Kans., by Mr. Kelly; from an aphidid on plum at Salisbury, N. C, by Air. Vickery; from an aphidid on pigweed (Chenopodium album) in Olms tead County, Minn., by Mr. C. N. Ainslie. Further addition to this fist of hosts may be made by citing the hosts of some of the synonyms of Aphidius testaceipes.3 We will deal i Aphis middletoni can not be satisfactorily separated from Aphis maidi-radicis and when found on any other plant except Erigeron it has usually been identified as Aphis maidi-radicis. (See Bui. 85, Bur. Ent., U. S. Dept. Agr., pp. 113-114. Contributions to a Knowledge of the Corn Root-Aphis, by R. A. Vickery .) 2 Ann. Ent. Soc. Amer., vol. 2, No. 2, pp. 67-87, June, 1909. 3 See Proc. U. S. Nat. Mus., vol. 11, pp. 665-S69, 1888. F< PAKASITE, APHIDIUS TESTACEIPES. 11? with these synonyms collectively under A. testaceipes. The hosts then would be as follows: Reared from Macrosiphum cucurbitse by the senior author at Lafayette, Ind.; reared from an aphidid on Eragrostis sp., by Mr. D. W. Coquillett; reared from Macrosiphum sp. on Audibertia stochoides, by Mr. Coquillett, at Los Angeles, Cal. Swept from Eragrostis sp. by the senior author at La Fayette, Ind., October 4, 1885; reared from Myzus sp. on Hosackia glabra by Mr. Coquillett at Los Angeles, Cal.; reared from Myzus ribis (currant aphis) by Prof. A. J. Cook, Lansing, Mich.; reared from Aphis gos- sypii by Prof. G. F. Atkinson, Columbia, S. C; reared from Macro- siplium sp. on Abutilon by Mr. Coquillett at Los Angeles, Cal. ; reared from Aphis avenx by Mr. J. W. Barlow, June 20, 1882, at Cadet, Mo.; reared from Aphis on peach May, 1886, by Mr. Albert Koebele, Fresno County, Cal.; reared from an aphidid on Baccharis viminalis by Mr. Coquillett at Los Angeles, Cal. There are probably many other hosts besides the ones we have mentioned of which as yet we have no knowledge; and when this situation is taken under consideration it is very easy to see that it would be only in rare instances and under peculiar conditions that a locality would be found where Aphidius testaceipes would not be lurking, waiting for favorable weather conditions and abundant supplies of its host aphidids to make its appearance in greater or less numbers. HIBERNATION. Aphidius is capable of withstanding extreme degrees of cold, as witnessed by the fact that Toxoptera parasitized during November, 1907, at Richmond, Ind., did not give up adults until the 27th and 28th of March and the 4th of April following. During February they were in the larval stage within an old dead body of a Toxoptera. Mr. Kelly found that at Leavenworth, Kans., the parasites hiber- nated as larvae and pupae. This was shown by the fact that he found Apliidius testaceipes in the field in this condition on November 13, 1907. From a lot of 50 dead parasitized Toxoptera from the same field, that had been washed or rubbed off the leaves of the young grain and were taken out of the mud about the wheat plants on February 28, after the winter was practically over, Mr. Kelly found that 17 contained full-grown larvae, 12 contained pupae of a light color, and 21 contained pupae of a dark color; the latter apparently were ready to develop promptly with the advent of warm weather. Mr. Kelly collected, on the same date and also from this same field, a number of Toxoptera in various stages of development that were hibernating in the fields and which showed no signs of parasitism; the weather had been such as to preclude the possibility of their having recently been parasitized. I^hese were placed in a warm room and soon showed evidence of parasitism, Aphidius testaceipes being finally reared from them. 118 THE SPRING GEAIN-APHIS OR ' ' GREEN BUG. ' ' The junior author foiuid that at Richmond. Ind., the adult Aphid- ins would Hve for at least two weeks when the temperature was below freezing. The parasites were taken into a warm room several times during these two weeks and they would become active, but when placed out of doors they would soon become numb. These adults were confined, however, so that excessive moisture was excluded, and they may not be able to live for so long a time in the fields unprotected. The fact that Aphidius can dining comparatively cold weather remain for a long period within the body of its host, and the latter give no external visible evidence of its presence, will readily account for the apparent absence of the parasite from any locality for an almost indefinite period: however, when the weather warms up sufficiently for development of the parasite to go on, its presence readily becomes apparent. For these reasons, as well as others that will be men- tioned in then proper places, it is impossible to say. from a cursory examination, that Aphidius is not present. INFLUENCE OF WINDS IX THE DISPERSION OF APHIDIUS TESTACEEPES. As the natural suppression of an outbreak of Toxoptera is more dependent upon the activity of this parasite than of any other of its natural enemies, it is important to learn the extent to which the para- site is able to follow its host in its spread from the South over the country to the northward. Dispersion of Aphidius may be accomplished in two ways — first, as larva? in the bodies of the winged host insect, where it is usually invisible, and. second, by being carried bodily with the winds along with the host . By referring to Table XII on page 10$, it will be observed that a number of cases are there recorded where individuals of Toxoptera graminum which were Fig. 2^.— Winged female of tne spring grain-aphis, \ . f7 parasitized bv Aphidius Usicceipes. Enlarged. parasitized developed tO Winged (Prom Webster.) Mte, ^^ fQJ. ft ^^ Q$ eight or nine days, and during this time gave birth to young, but from their dead bodies Aphidius afterwards issued. The pres- ence of winged parasitized females on the leaves of grain and grasses inhabited by Toxoptera is of common occurrence (see fig. 29). Thus, while it has not been possible to observe the parasitism of individuals and follow out the final dispersion of the same, the evidence tending to show the probability of its general occurrence is so overwhelming that such direct proof does not seem necessary. With the obscurity 119 relative to this matter cleared away, it will be observed that it is entirely possible for great numbers of the adults, or those that are nearly mature, to become parasitized in a southern locality, the latter to develop to winged females under a more or less high temperature, and for both to be carried many miles to the north- ward, and then settle down and begin to reproduce, the Aphidius becoming adult and issuing later from the dead body of its host. In the meantime the offspring of the host Toxoptera would, of course, develop and themselves reproduce, some of them, without doubt, falling victims to the very parasite brought along by their parent. While this may not be the chief factor in the dispersion of this parasite, it probably enables it to follow along with the host insect and become diffused with it, although if low temperatures prevail after the time the migrating female settles in her new home there may be consider- able delay in the issuing of the adult parasite without to any great extent delaying the development and preventing the increase of Toxoptera. With the temperature at a point which enables Aphidius to become active there is no doubt that the parasite follows with the host insect, and, indeed, these parasites are usually found on the wing in the com- pany of their hosts during warm sunny days. With high cold winds, which usually come from the northward and would tend to drive the parasites back over territory to which Toxoptera has already come and from which it has now largely disappeared, the adult Aphidius is observed to nestle down among the infested plants and not to venture abroad. Thus it is that this parasite is doubtless usually present in some form in the grain fields with the Toxoptera, though critical examinations of such fields may fail to reveal them until the temperature reaches a point that enables them to become active. All of this is applicable to the insect in southern territory where no egg stage is yet known to occur. Aphidius occurs all over the coun- try, and we have learned that in the North it winters as fully devel- oped larvae and pupae within the "cocooned" bodies of its hosts, its emergence and activity in spring being controlled by the temperature and its dispersion influenced by the same forces and in much the same manner as in the South. TEMPERATURE INFLUENCES ON APHIDIUS. Probably the whole secret of these disastrous outbreaks of Tox- optera lies in the fact that this parasite is not active in a tempera- ture much below 56° F., while, as has already been shown, the aphis begins to reproduce in a temperature at or slightly below 40° F. — a probable difference of at least 16° F. Therefore the situation in a field of wheat in the South in early spring may be described in this way: There are present many Toxoptera of all ages, with viviparous 120 reproduction continually going on during mild weather. Aphidius may also be present either as invisible undeveloped overwintering larvae within the living bodies of its host, or it may be present as mature larvae or pupae in the dead and dried "cocooned" bodies of the same. Besides this, in the light of recent studies of Aphidius by Mr. Viereck, the same may be true with reference to its occurrence in a considerable number of other common species of aphidids, inhabit- ing a great variety of vegetation, in the same neighborhood, upon which this same species of Aphidius is parasitic. Thus, it is per- fectly clear why, with Toxoptera swarming in the fields, and the parasite present, about 10 days, with the temperature ranging from 40° or 50° to 60° or 70° F., is sufficient to enable the latter summarily to suppress the invasion. The abruptness with which this change is brought about is easily explained by the fact that a parasitized female Toxoptera produces young during only a comparatively few days after being parasitized, although she may survive several days longer, especially if the weather be cool enough to retard the development of the parasite. In the North the situation is usually quite different, as parasites can not begin their work here to any extent until after the eggs have hatched, and the stem mothers and their offspring have appeared in the fields, thereby furnishing host insects. The overwintering of immature Aphidius larvae in the bodies of the host is in the North ordinarily precluded by the absence of living host individuals during severe winters, although mature larvae may winter in the dead bodies of the host as in the South. Stem mothers are probably never present in great numbers and considerable time is therefore neces- sarily required for their offspring to become excessively abundant. For this reason parasitism, over the section where the host insects pass the winter in the egg, begins later, and, at the start, proceeds necessarily much slower than in the South, but on the other hand Aphidius, unless the winter be an exceptional one, must of necessity winter over in the "cocooned" bodies of its numerous hosts, as mature larvae or pupae, and would therefore promptly respond to the warm days of early spring, although delayed somewhat by low temperatures that might not retard the host insects. There is one point in connection with parasitism by Aphidius that must be always kept in view, particularly to the southward, in order that mistakes and misstatements may be avoided regarding its actual occurrence in any particular locality. While the larva is contained within the still living body of its host its presence there is not easily detected. Indeed it is not until the larva becomes nearly full grown that it can be detected even by an expert. Therefore, in the light of what has previously been stated concerning the situa- tion in milder latitudes, there may be millions of living larvae PARASITE, APHIDIUS TESTACEIPES. 121 present for weeks in a field with no visible indication of their presence. Yet only a few warm days are required to bring about their final development, whereupon the presence of the more or less globular, leathery, brown bodies of the parasitized host first begin to attract attention and thus actually reveal the presence of the Aphidius, which has already been established there. An excellent illustration of this is afforded by an occurrence of Toxoptera in eastern North Carolina, observed by Mr. L. M. Smith. In a small field of oats near Newport, wingless viviparous female Toxoptera and young were found in destructive abundance with no indication whatever of the presence of Aphidius. Yet when speci- mens of the pest submitted by Mr. Smith reached Washington, some otf them were beginning to change color from the presence of Aphidius larvse within their abdomens. Again, when Mr. C. N. Ainslie visited Wellington, Kans., April 1, 1907, he observed no trace of the presence of Apliidius, but upon returning to this same locality on April 10 he found them present. Only a few of the Toxoptera had yet become dark brown, but a large number showed the orange color that told the story of their parasitism. Therefore all statements made in previous publications relative to the lack of parasites, or to the extent to which they occurred in any field or locality, must be under- stood as applying only to either the adults or to the browned cocooned bodies of the host insects, and are not in any sense to be considered as indicating the extent to which these host insects were carrying obscured Aphidius larvae about with them in their bodies to develop adults whenever there were a few sufficiently warm days. EFFECTS OF WET WEATHER OX THE DIFFUSION OF APHIDIUS. There is another element affecting the diffusion of this most efficient of natural enemies of Toxoptera, namely, protracted rains. When it is raining the parasite simply will not take wing at all or move about in a way to be affected by winds. This element will not admit of tabulation for the reason that a thunder shower followed by warm, bright sunshine tends to make these, as well as all winged insects, more -active after the storm has passed. Thus, the amount of precipitation really means little, while a slow, drizzling, protracted rain (though the total precipitation may be much less) will keep the parasite in seclusion much more effectively. Hence it is that not only a comparatively high temperature accompanied by winds is essential, but the weather must also be fair and sunny. In British East Africa Toxoptera is worse during seasons when there is much wet weather, and in the Orange Free State outbreaks of the pest seem to be also associated with similar meteorological conditions during spring. 122 THE SPRING GRAIN-APHIS OR " GREEN BUG." Other Species of Aphidius. Aphidius confusus Ashm. has been reared from Toxoptera from different parts of the country, including the Department of Agri- culture grounds in Washington, but to what extent it assisted in overcoming Toxoptera in 1907 is not altogether clear. Its life history is apparently similar to that of A. testaceipes Cress., and its effect upon the aphides is apparently the same. ApJiidius avenapliis Fitch was reared from Toxoptera graminum in the insectary at the Department of Agriculture in Washington, the host insect having been parasitized, under observation, by adult virgin Aphidius reared from Aphis sp. Fig. 30. — Aphelinus mali, a parasite of the spring grain-aphis. Greatly enlarged, much more enlarged. (Original.) Stigmal club, Species of Aphidius, apparently undescribed, were sent to the bureau from Njoro, British East Africa, and the Orange Free State, South Africa, as enemies of Toxoptera graminum in that country. Aphelinus. We have reared three species of Aphelinus from Toxoptera grami- num; Aphelinus mali Hald., A. nigritus How., and A. semijiavus How. Aphelinus mali Hald. (fig. 30) was reared from Toxoptera at Lafayette, Ind., in 1885 by the senior author, by Mr. R. A. Vickery at Richmond, Ind., and from the same species at Clemson, S. C, by Mr. G. G. Ainslie. Messrs. Kelly, Urbahns, and Parks reared it from Aphis seiarix Thos. at Wellington, Kans. Messrs. Kelly and Urbahns also reared it from Schizoneura americana Riley at Wellington. Mr. Vickery reared it from Schizoneura lanigera Haussm. at Richmond, PARASITES, APHELINUS. 123 Ind., and from Colopha eragrostidis Middl. at Mt. Vernon, Ind. Mr. Kelly reared it from Pemphigus fraxinifolii Kiley and from an aphidid taken on Panicum sp. Mr. C. N. Ainslie reared it from Macrosiphum rosse Linn., at Mesilla Park, N. Mex. This species has been previously reared, as stated by Dr. L. 0. Howard x from Scliizoneura lanigera Haussm., Colopha eragrostidis Middl., Aphis orassicsd Linn., Pemphigus fraxinifolii Riley, Aphis monardse OestL, Macrosiphum rosse Linn., Aphis sacchari Zehntn., and Tetraneura colophoidea. Aphelinus nigritus How. (fig. 31) was first reared from Toxoptera at Spartanburg and Clemson, S. C, by Mr. G. G. Ainslie. It was Fig. 31. — ApJielinus nigritus, a parasite of the spring grain-aphis. Greatly enlarged, a, Stigmal club, still more enlarged. (Original.) reared from the same species of aphidid by Mr. C. N. Ainslie at Springer and Mesilla Park, N. Mex., and St. Anthony Park, Minn. Mr. T. H. Parks reared it from Toxoptera at Wellington, Kans., and Messrs. Kelly and Urbahns reared it from Aphis seiarise Thos. at Wellington. Aphelinus semiflavus How. (fig. 32) was first reared from Myzus persicse Sulz. and Chaitophorus timinalis Monell by Prof. C. P. Gil- lette at Fort Collins, Colo., in 1908. It was later reared by Mr. G. G. Ainslie from Toxoptera at St. Anthony Park, Minn., and from a black aphidid on bluegrass (probably Rhopalosiphum pose, Gill.) at Mesilla Park, N. Mex., by C. N. Ainslie. i Ent. News., vol. 19, no. 8, pp. 3G5-366, 1908. 124 NOTES ON LIFE HISTORY AND HABITS OF APHELINUS. Mr. C. N. Ainslie made some observations on Aphelinus nigritus at Mesilla Park, N. Mex., in 1908. He states that when the adult is ready to oviposit it approaches an aphidid very slowly and cautiously, moving or swaying its body slightly from side to side and waving its antennae. When the antennae finally touch the plant-louse it stops, turns suddenly about, moves backward slightly, and then gives the victim a thrust with its hairlike ovipositor. This operation appar- ently causes pain to the aphidid, as she begins to "kick up" her abdomen and there sometimes appears a tiny drop of fluid where the puncture was made.' Fig. 33. — Dried remains of body of the spring grain- aphis from which adult Aphelinus nigritus emerged. Enlarged. (Original.) Fig. 32. — Aphelinus semiflavus, a parasite of the spring grflin-aphis. Greatly enlarged, a, Stigmal club, still more enlarged. (Original.) When the larva of Aphelinus nigritus is fully grown the body of the plant-louse, according to Mr. G. G. Ainslie, turns black and the legs a conspicuous white (fig. 33), while in individuals parasitized by A. mali these appendages are black. The body, however, of so small an aphidid as Toxoptera graminum appears to be but little swollen. Mr. C. N. Ainslie found that under favorable weather conditions A. nigritus developed from egg to adult in from 12 to 13 days. The following diagram will serve to illustrate the different hosts of Aphidius testaceipes, A. avenaphis, A. confusus, Aphelinus malij A. nigritus j and A. semiflavus, which we have shown to attack Toxoptera graminum. This will give some idea of the numerous sources from which an army of parasites may be recruited to oppose any serious invasion of Toxoptera. SECONDARY PARASTTES. 125 'Aphidius. avenaphis. . Macrosiphum granaria Buck. confusus. . testaceipes. Toxoptera graminum . Macrosiphum erigeronensis Thos. .Aphis avenx Fab. Aphis gossypii Glov. Aphis sp. Aphis maidis Fitch. Aphis maidi-radicis Forbes. Aphis medicaginis Koch. Aphis cenotherx Oestl. Aphis rumicis Linn. Aphis setarix Thos. Macrosiphum viticola Thos. Macrosiphum granaria Buckt. Melanoxantherium sp. Macrosiphum sp. on black gum. Myzus ribis Linn, on currant. Myzus sp. on Hosackia glabra. Macrosiphum sp. on Abutilon. Macrosiphum cucurbitx Thos. Aphidid on Ampelopsis sp. Aphidid on Baccharis viminalis. Aphidid on Capsella bursa-pastoris. Aphidid on Eragrostis sp. Aphidid on Kochia sp. Aphidid on locust. Aphidid on peach. Aphidid on pigweed (?). Aphidid on plum. Aphelinus. mail . . .Aphis brassicx Linn. Aphis monardx Oestl. Aphis sacchari (?) Zehntn. Aphis setarix Thos. Colopha eragrostidis Middl. Myzus mahaleb Boyer. Pemphigus fraxinifolii Riley. Macrosiphum rosx Linn. Schizoneura americana Riley. Schizoneura lanigera Haussm. Tetraneura colophoidea (?). nigritus Aphis setarix Thos. semiflavus . .Aphis maidis Fitch. Aphis gossypii (?) Glover. Chaitophorus viminalis Mon. Myzus persicx Sulz. SECOND ARY PARASITES. Megorismus sp. Species of the genus Megorismus, it appears, have been previously considered as primary parasites. Mr. Parks, however, has con- ducted some experiments with a species (fig. 34) at Wellington, Kans., and his results clearly indicate that in this case it is a sec- ondary parasite. In no instance could he rear it from aphidids 126 that had not previously been parasitized; he experienced no diffi- culty, however, in rearing it when the adults were placed in cages with aphidids that were brown, having been killed by some species of Aphidius. It may be that under certain conditions Megorismus sp. is also a primary parasite. Mr. Parks finds that it takes about 30 days in developing from egg to adult in a temperature of about 70° F. indoors. It has been reared in conjunction with ApMdius sp. from Toxoptera graminum and ChaitopTiorus sp. at Wellington, Kans., by Messrs. Kelly and Urbahns; from T. graminum and ApJiis Irassicse in the same locality by Mr. Parks. Mr. Parks also reared it from Macrosi- Fig. 34. — Megorismus sp.r a secondary parasite of the spring grain-aphis: Male, greatly enlarged; female abdomen, more enlarged, at right. (Original.) phum pisi at Washington, D. C. Mr. C. N. Ainslie reared it from Hyalopterus dactylidis in the same locality, and the junior author reared it from Myzus persicx at Lafayette, Ind. Aphidencyrtus aphidiphagus Ashm. The species Apliidencyrtus aphidipJiagus Ashm. (fig. 35) has also been considered a primary parasite, and while we have no direct evidence to disprove this we very strongly suspect that it is in this case a secondary parasite. Like Megorismus, which, we have shown, is sometimes, at least, a secondary parasite, we have reared it only in conjunction with known primary parasites. Mr. G. G. Ainslie could rear it only in connection with Aplidinus sp. from T. graminum at Clemson, S. C, and Mr. C. N. Ainslie reared it from Aphis SECONDARY PARASITES. 127 hrassicse at Mesilla Park, N. Mex., in conjunction with ApTiidius sp. Nothing definite is known of its life history. Paekyneuron sp. A species of Pachyneuron (fig. 36) has been repeatedly reared from Toxoptera graminum and it appears to be generally accepted as a Fig. So.—Aphidencyrtus aphidiphagus , a secondary parasite of the spring grain-aphis. Greatly enlarged. (Original.) secondary parasite. Mr. Kelly has observed it ovipositing in brown parasitized MacrosipTium viticola. Mr. G. G. Ainslie reared it in con- j unction with Apfielinus sp. from Toxoptera and with ApTiidius sp. from Fig. 3d.— Pachyneuron sp., a secondary parasite of the spring grain-aphis. Greatly enlarged. (Original.) Aphis maidis from Clemson, S. C, and from Toxoptera at St. Anthony Park, Minn. Mr. C. N. Ainslie reared it in connection with ApTiidius sp. from ApTiis setarise, A. gossypii, MacrosipTium granaria, and M. erigeronensis and in connection with ApTielinus sp. from Schizo- 128 THE SPRING GRAIN-APHIS OR i GREEN BUG. neura americana. He also reared it from MacrosipTium viticola and Ghaitophorus sp. Pachyneuron sp. appears to be quite generally dis- tributed but little or nothing is known of its life history. Allotria sp. AUotria sp. (fig. 37) is recorded as a secondary parasite. Mr. Parks verified this by careful rearings at Wellington, Kans., in 1909, for he was able to rear it only from parasitized aphidids. The junior author and Messrs. Kelly and Urbahns have observed it ovipositing in parasitized dead aphidids also. Mr. Parks found in his experiments that it developed from egg to adult in about 21 days, under favor- able temperatures. We have reared it only in conjunc- tion with Aphidius. Messrs. Kelly and Urbahns reared it from Aphis gossypii and A. brassier at Wellington, Kans. ; Mr. Parks reared it from Toxoptera from the same local- ity; Messrs. Parks and Kelly also reared it from Tox- optera at Washing- ton, D. C. Mr. C. N. Ainslie reared it from Apliis avense and Eyalopterus dactylidis from the same locality. Mr. Kelly reared it from MacrosipTium viticola from Wellington, Kans., and the junior author reared it from Myzus persicse at Lafayette, Ind. PREDACEOTJS ENEMIES. Lady-beetles. Probably next in importance to the genus Aphidius come the ladybird beetles. These beetles, in both the adult and larval stages, feed upon plant-lice. In 1907 they became very abundant, destroy- ing countless numbers of Toxoptera and greatly assisted Aphidius in subduing the pest. Plate VIII represents the manner in which the pupae are found attached to plants in fields badly infested with Toxoptera; to the left is a 2-inch section of an old cowpea stem; to the right, two short sections of wheat stems. Oftentimes as many as 30 or more pupae could be found within the space of a foot of a single drill row. Adults deposit eggs upon any convenient object. Fig. 37— A llotria sp. , a secondary parasite of the spring grain-aphis. Male , with female antenna at upper right. Greatly enlarged. (Original.) Bui. 1 1 0, Bureau of Entomology, U. S. Dept of Agriculture. & 0J CT Plate VII. bfj sjo to a o w~ "s g°3 •- a; -^ +? be « c3 O «*jp MM h t: c3 a> m 3 S 1 o^ %* bi°2 •r- >.s . bjo^ •2- !>> a! M-J5 S.2 ° id o^ w O 2 cc — ,Q X 03 Z) z It! 2 < c^.S cc 5? ^ - C5 < 03 '.+3 f£ .■■r"d UJ fcXjf — 1 o « i: C5 ^° UJ ai r-flf! X 6 w>° O c3~ h ^O z © £ ft .EH o 03 "3 o a> .. > <8 S^ or CO O o E o |2 ■-d s ° UJ I h u. s^ O -3 no h- LLl O tJ0M S 0. O Si t£— _i +3 ® LU Q .3 -^ M OS5? ■§© 1 72 £-* 23bi Eh ^ r1 '-n -Q-*3 . § 0^> CQ-H ^ c3 >- S-0 !>5„ or +j>,e,^ wO~ M o^x o "K tc'd S m C2 g co -g .^ ~ ^^|S3 ^2 G | .JTc So -H2 2^ . o P^ bX) Ph Bui. 1 10, Bureau of Entomology, U. S. Dept. of Agriculure. Plate VIII. A Lady-Beetle Enemy of the Spring Grain-Aphis. Tupae of Hippodamia convergens attached to stem of cowpea and wheat straws in a field where the spring grain-aphis had been excessively abundant. Enlarged. (Original.) PEEDACEOUS ENEMIES. 129 and, as soon as hatched, the larvae seem possessed of an insatiable appetite, devouring aphidids or even eggs and larvaB of their own species if no plant-lice are at hand. Mr. Kelly has found that an */ Fig. 38. — The convergent lady-beetle (Hippodam id con vergens), an enemy of the spring grain-aphis: a, Adult; b, pupa; c, larva. Enlarged. (From Chittenden.) adult ladybird (Hippodamia convergens) (fig. 38) will devour from 15 to 30 plant-lice in a day. Mr. S. J. Hunter, in ' ' The Green Bug and its Enemies," page 6, states that instances have come under his observa- tion where as many as 100 have been devoured in a single day by an adultlady-beetle. The larvse when nearly grown are probably able even to exceed this record. In one of Mr. Kelly's experi- ments a single beetle deposited as many as 264 eggs, thus showing that this lady- bird is very prolific. When all of these facts are considered it is easy to see that the lady- beetles are rather formida- ble enemies of Toxoptera. Hippodamia convergens appeared to be by far the most abundant ladybird in the Southwest in 1907. Coccinella 9-notata (figs. 39, 40) and Megilla maculata (fig. 41) were also quite abundant. Coccinella abdomi- nalis was present in less abundance. Adalia fiavomac- ulata DeG. (fig. 42), with its larvae, has been sent to the bureau as an enemy of Toxoptera in the Orange Free State, South Africa. Syrphid Flies. All through the Southwest in 1907 syrphids were very abundant and were an important factor in the control of Toxoptera. These insects are beautiful two-winged flies with prominent golden bands across the abdomen. They are always present in mild weather 26675°— Bull. 110—12 9 Fig. 39.— The nine-spotted lad y-beetle {Coccinella 9-notata), an enemy of the spring grain-aphis: Adult. En- larged. (From Chittenden.) Fig. 40.— The nine- spotted lady-bee- tle {Coccinella 9- notata), an enemy of the spring grain- aphis: Larva. En- larged. (From Chittenden.) 130 THE SPRING GRAIN-APHIS OR in grain fields badly infested with plant-lice, and when quite num- erous attract attention by a buzzing noise made while in flight. The predaceous larvae are sluglike and of a dirty grayish or yellowish green color; this is the only stage in which they are destructive to Fig. 41.— The spotted lady-beetle (Megilla maculata), an enemy of the spring grain-aphis: a, Larva; b, empty pupa skin; c, adult. Enlarged. (From Chittenden.) plant-lice. Little is known of the life histories of these insects as very few careful rearings have been made. Syrphus americanus Wied. (fig. 43) and Eupeodes volucris O. S. (fig. 44) were by far the most numerous syrphids in the grain fields in the Southwest in 1 907. A field at Kingfisher, Okla., in April, 1907, literally swarmed with them; 20 or more could be taken with each sweep of an insect net. A curious fact with reference to their occur- rence in such abundance in this field, however, was that Toxoptera was not present there in destruc- tive abundance, while the adjoin- ing field was suffering greatly from their attack, though, curiously enough, the syrphid flies did not appear to be so plentiful there. These two species were present, apparently, over the entire south- western area that suffered greatly from Toxoptera attack in 1907. Syrphus americanus was reared also from Toxoptera material sent in by Air. E. C. Haynsworth from Sumter, S. C. Prof. J. M. Aldrich states in his catalogue of North American Diptera that he reared Eupeodes volucris from Aphis avenx at Moscow, Idaho, Dr. C. V. Riley states, Fig. 42.— A South African lady-beetle, Adaliaflavo- maculata, which with its larva attacks the spring grain-aphis in the Orange Free State, South Africa. Enlarged. (Original.) PBEDACEOUS ENEMIES. 131 in a report of the Department of Agriculture,1 that he reared Syrphus americanus from Macrosiplium granaria. Fig. 43. —Syrphus americanus, whose larva destroys the spring grain-aphis: a, Female fly; b, second abdominal segment of male. Enlarged. (Original.) SpJxxrophoria cylindrica Say (fig. 45) was collected from wheat fields at Hiawatha, Kans., in 1907, by the junior author and was also Fig. 4i.—Eupeodcs volucris, whose larvae were the most abundant and useful in the fields where the spring grain-aphis was most- abundant in the Southwest during the spring of 1907. a, Female fly; b, abdomen of male; c, hypopygium of male. Enlarged. (Original.) reared from Toxoptera material sent in by Mr. Haynsworth from Sumter, S. C, the same year. Mr. G. G. Ainslie reared it from i Report of the Entomologist, U. S. Dept. of Agr. for 1889, p. 351. 132 Toxoptera at Monetta, S. C, in 1908. Dr. Kiley states that he found the larvse feeding on Macrosiphum granaria. Mr. Ainslie took quite a number of Allograpta obliqua Say in the Southwest in 1907, and, though we can not say definitely that it feeds upon Toxoptera, the chances are that it does, as Dr. Riley states that it feeds upon MacrosipJium granaria. Mr. Kelly reared a number of Baccha clavata Fab. from Aphis setarix at Wellington, Kans., in 1908; Mr. R. A. Vickery also reared B. clavata from Aphis maidis at Brownsville, Tex., in 1911 ; Mr. J. J. Fig. 45. — Spliseroplwria cylindrica, a fly reared from larvae attacking the spring grain-aphis in South Caro- lina in 1907: a, Female fly; b, dorsal view of abdomen of male; c, hypopygium of male, lateral view. Enlarged. (Original.) Davis reared this species at Lafayette, Ind., from Aphis medicaginis, also in 1911. This species may in future be found to attack Toxop- tera also. Lace-Wing Flies. The lacewing fly Chrysopa plorabunda Fitch was quite abundant in the grain fields in the Southwest in 1907 and without doubt assisted materially in the destruction of Toxoptera. This is the most common species in this section of the country, where it hiber- nates in the adult stage; thus, whenever the weather becomes suitable it is ready to at once begin oviposition. An allied species is shown in figure 46. The larvae of these insects can move about quite freely and are provided with two long, curved mandibles (see fig. 46) upon which PREDACEOUS ENEMIES. 133 plant-lice or other insects are impaled and held prisoners until they are sucked dry. They are then released and the Chrysopa larvae hunt other victims. Cecidomyiidse. During September of 1909, at Lafayette, Ind., a new predaceous insect enemy to Toxoptera was discovered in the larvae of a little cecidomyiid or two-winged fly, determined tentatively for us as ApMdoletes sp. by Dr. E. P. Felt. It was first observed in one of the stock cages and afterwards it was found to be reproducing in the fields on Myzus persicae. Fig. 46.— The golden-eyed lace-wing fly ( Chrysopa oculata), an enemy of the spring grain-aphis, a, Eggs; b, full-grown larva; c, foot of same; d, larva devouring an insect; e, cocoon; /, adult insect; g, head of same; h, adult, natural size. All enlarged except h. (From Marlatfc.) We have not as yet carefully studied the life history of ApMdoletes sp. The adult fly (fig. 47) is a frail little creature, about the size of the clover-seed midge, pale cream in color, and the abdomen has a pinkish tinge, due to the pink eggs within. The eggs resemble those of the Hessian fly very closely except that they are much smaller. The larvae (fig. 48), which are pinkish in color, descend to the ground when fully matured, and at or near the surface they spin a loose cocoon, to which particles of dirt and trash adhere. In a few days the adults issue. The time required for this little insect to complete the entire life cycle is apparently about 10 to 14 days. The species is not determinable further than the genus for the reason that only the female adults have been secured. 134 This little fellow goes about getting its meals in a very quiet, unobtrusive sort of way. It crawls quietly up among a number of Toxoptera and the first one it touches becomes its victim. It at- taches its mouthparts to some joint of the legs, usually at the artic- ulation of the femur and tibia, and sucks out the juices of the aphidid. With a compound miscroscope the blood can readily be seen flowing in a constant stream, through the limb of the aphidid attacked, into the larva of the cecidomyiid. Rarely is the aphid disturbed and upon close observation the skin of the aphidid will be seen to Fig. 47.— Apliidolctcs sp., cecidomyiid fly whose larvse feed upon the spring grain-aphis. Greatly enlarged. (Original.) gradually shrivel up ; finally nothing but the empty skin remains and the larva crawls away in search of more aphidids, frequently with the old empty aphidid skin adhering to it. The time required to consume the juices of an aphidid varies with the size of the larva and of the aphidid. A larva that is about full grown can dispatch a small aphidid in a few minutes, while from 15 to 30 minutes are required for it to empty a full-grown one. These cecidomyiid larvae have enormous appetites and apparently keep up their work of destruction almost constantly until they become full grown. It is not at all impossible for this insect to become a very im- portant factor in the control of Toxoptera, as the adults are capable of flight and deposit large numbers of eggs. MISCELLANEOUS ENEMIES. 135 Birds. Birds devour immense numbers of the spring grain-aphis. Miss Margaret Morse, of Clark University, has been kind enough to conduct some experiments for us in feeding Toxoptera to quail. She has learned that they are very fond of the aphidids and estimates that about 5,000 individual Toxoptera were eaten by a single quail in one day, preference being shown for those that were unparasitized. Mr. W. L. McAtee, of the Biological Survey of the United States Department of Agriculture, made some special studies of the aphis- eating habits of some of our birds in March- April, 1909, at Winston- Salem, N. C, at the time Toxoptera was so destructive in that vicinity. He states that in a wheat field of about 100 acres there were over 3,000 birds present daily; sometimes the number ran as high as 8,000 to 9,000. So large a number of birds would be found in the fields only during migration, and />--Z^ff even at that time the presence of so many indi- cates that they were attracted to the fields by the abundant food. In so far as could be ascer- tained, about nine-tenths of the birds were feed- ing upon aphidids (including Toxoptera graminum, MacrosipJium granaria, and Aphis avense), some taking as many as 180 at a single meal. These aphidids are" very small, soft-bodied insects and many meals would be required by a bird in a single day to satisfy its hunger. The average number per meal was at least 50, and we may assume that 6 times this number were taken per day. On this basis the number of aphidids de- stroyed by birds on the farm daily during the migration season is 90,000. Below is a partial fist of the species Mr. McAtee found devouring Toxoptera at Winston-Salem. A complete list can not be given at this time, since his studies are not yet finished; many species will undoubtedly be added. Goldfinch (Astragalinus tristis). Vesper sparrow (Po&cetes gramineus). Savanna sparrow (Passerculus sandwichensis savanna). Chipping sparrow (Spizella socialis). Song sparrow (Melospiza melodia). All of these birds occur over the entire South. MISCELLANEOUS ENEMIES OF TOXOPTERA. Under the head of miscellaneous enemies may be considered ene- mies that are of very slight economic importance; those, in other words, that have been observed occasionally attacking Toxoptera. Fig. 4S.— ApMdoletes sp., cecidornyiid larva which attacks the spring grain-aphis, a Larva; b, anterior ex t r e in i t y protruded showing breastbone; c ventral view of poste- rior segment, a, Much enlarged; b, c, greatly enlarged. (Original.) 136 THE SPEIXG GBAIN-APHIS OE ' ' GREEN BT7G. >5 In 1S90 the senior author, at Lafayette, Inch, found that the young of the snowy tree-cricket ((Ecanthus niveus De G.) were very fond of Toxoptera and fed upon them freely. Mr. A. X. Caudell, of this bureau, observed one of the soldier bugs, Reduviolus ferns L., attacking Toxoptera on the grounds of the De- partment of Agriculture at Washington in 190S. During the same year Mr. C. X. Ainslie found a larva of a species of the ladybird genus Scymnus at Mesiha Park, X. Mex., attacking Toxoptera, and he seems to think that numbers are devoured by this insect. In 1909, at Washington, D. C, Mr. R. A. Yickery reared the braconid Lipoltxis piceus Cress, in limited numbers from Toxoptera. The junior author has at times found a fungous disease attacking the aphidids in his rearing cages, but we have never noted this in the fields. ANTS AND THEIR RELATION TO TOXOPTERA. So far as our observations go Toxoptera is not so attractive to ants as are many other species of plant-lice. We have often found various species of ants in attendance on Toxoptera. but the relations did not appear to be mutually beneficial, the ants nearly always gaining the most by such partnerships. At Hooker, Okla., in 1907, the junior author found ant burrows beside plants in an area badly infested with Toxoptera. In this case some burrows were found where the aphidids were slightly below ground on plants in these burrows, the ants being busy about the aphidids, stroking them with their antenna?. Mr. C. X. Ainslie many times observed ants stroking Toxoptera with their antenna?, We have found no instances, however, in which ants care for the eggs of Toxop- tera in winter, and Toxoptera does not appear to excrete so much honeydew as do some other aphidids. This probably accounts for the fact that they are not so popular with the ants as are certain other aphidids. In Texas, during 1909, Mr. T. D. LYbahns found ants busily caring for Toxoptera in Iris rearing cages. He also noted that the ants al- ways attacked the parasite of Toxoptera (ApMdius sp.) whenever they came in contact with it, tearing the larva? out of the old dead bodies of Toxoptera and destroying them. REMEDIAL AND PREVENTIVE MEASURES. With an outbreak of this pest fully established, and the winged adults being carried by the winds and scattered over the fields, there to settle down and reproduce, the difficulties in the way of control are quite insurmountable. FIELD EXPERIMENTS. The brush-drag experiments that were carried out under the direc- tion of the junior author at Hobart, Okla. (see Plate IX, fig. 1), have not, with the trials we have given the brush drag, proved satisfactory, although Mr. Thos. J. Anderson, Government entomologist of British Bui. 11 0, Bureau of Entomology, U. S. Dept. of Agricultur Plate IX. Fig. 1.— Brush Drag Used by the Junior Author in Experiments and also by Farmers in Destroying the Spring Grain-Aphis in the Fields at Hobart, Okla. (Original.) Fig. 2.— Roller Used in Experiments by Junior Author and by Farmers in Destroying the Spring Grain-Aphis in Oklahoma. (Original.) mi REMEDIAL AND PREVENTIVE MEASURES. 137 East Africa, states that it is with them the most effective measure at their command for destro}dng the "green fly" in wheat fields. With us it was used after the aphidid had fully established itself and was literally swarming over the growing grain. Earlier, at the commence- ment of an outbreak, the effect of its use might prove more satisfactory. Similar experiments were carried out with a heavy roller, such as is generally used among farmers for crushing clods in fields and com- pacting the ground. (See PI. IX, fig. 2). In this case the results were even less satisfactory than with the brush drag, because the roller acted only on the clods and other inequalities in the surface of the ground. Where the wheat had been drilled the effect on the Tox- optera was less decisive than where the grain had been sown broad- cast. The wheat plants grow in the narrow furrows or grooves and the insects that were displaced dropped down about the plants and the passing roller struck only the ridges, leaving the insects practically untouched. Where the invasion is not chiefly from outside the field itself, and the pest makes its first appearance in spots, management is less difficult. By plowing under these infested spots and immediately harrowing and rolling them further damage may be effectually pre- vented. The junior author had an opportunity to test this measure in western Oklahoma. Covering these spots with straw, where easily obtainable, and burning, is equally effective, but where this last measure was applied by farmers in Oklahoma in 1907 the fields were so completely overrun from the outside that the good effects were entirely obliterated. As between these two methods of suppression, it must be borne in mind that while the seriously affected spots in a field are very small, a single load of straw will suffice to cover a number of them, prepara- tory to burning, but after these areas become enlarged it is much more practicable to plow them under. Besides the above-mentioned methods of control, experiments were conducted with different kinds of spray materials. In all of our control methods we endeavored to place ourselves in the position of the farmer, and to use such apparatus as could be obtained locally. Accordingly the junior author, upon reaching Hobart, Okla., the first week in April, 1907, prepared to begin some spraying experi- ments. The only spray apparatus that could be found in the town was a knapsack pump. As stated above, since an outbreak of Toxoptera starts in small areas, where the infestation originates within the field, it was thought possible to accomplish something by spraying these areas. As the infestation at Hobart seemed to be quite general, apparently originating from migrations from farther south and east, the small pump was found to be utterly useless. From here the junior author proceeded to Kingfisher, Okla., where there were clearly defined areas of infestation, and, together with 138 Mr. C. N. Ainslie, began experiments with a barrel pump, loaned by a market gardener. One plat was sprayed with 5 per cent kerosene emulsion; another with 10 per cent kerosene emulsion; a third plat with ordinary hard soap, 1 pound to 4 gallons of water; a fourth plat with whale-oil soap, 1 pound to 6 gallons of water. The spraying was done carefully, so as to reach every aphis possible. Upon examination the next day it was found that the 10 per cent emulsion and the hard soap had injured the plants. Not more than 50 per cent of the plant -lice were killed hi any of the experiments. On the loth of April the sprayings were repeated with similar results. All of the aphidids could not be reached, no matter how thoroughly the spraying was done. It was quite evident that unless the ground was almost soaked there would be little or no relief. These spray- ings cost at the rate of about $4 per acre. During the latter part of July it was found that Toxoptera was very abundant on the lawns of the Department of Agriculture at Washington, D. C. This outbreak became known to Mr. E. M. Byrnes, Superintendent of Experimental Gardens and Grounds, who at once had the entire infested block sprayed with a solution of one-half gill of blackleaf tobacco extract to each gallon of weak soapsuds. The application was, however, ineffective. Four days later a strip through this plat was thoroughly saturated with a strong solution of barnyard manure, made by soaking the manure in water. While there was no evidence that this killed any of the "green bugs,'' after nine days the pest was visibly less on this area than where the application of manure solution was not made. A series of experiments was then undertaken under the senior author's direction by Mr. E. O. G. Kelly, as follows: Tobacco dust was applied at rates of one-fourth, one-half, and 1 pound to each 100 square feet, but after over a week had elapsed from the date of application no effect was to be observed and no dead insects were found. Kerosene emulsion was applied at S and 10 per cent strengths, and at the end of nine days no "green bugs" were to be found on the areas so treated. Also there was no perceivable injury to the grass. Whale-oil soap solutions, varying in strength from one-fourth of a pound to 2 pounds of soap to each 5 gallons of water, were applied to similar areas. In this case the stronger solution injured the grass slightly, but not permanently; in the case of the lesser strengths there was no injury to the grass whatever. The effect on the "green bug" was the same in every case. They were not only literally exterminated over the areas treated, but the applications seemed to protect from a reinfestation, in case of even the weakest solution. An examination five days after the application was made revealed the "green bugs" in myriads and breeding freely on the untreated space, while onlv 8 inches away and on the treated area living bugs were REMEDIAL AND PREVENTIVE MEASURES. 139 scarcely to be found, although the dead bugs were to be observed almost as abundantly as were the living on the space untreated. It must be remembered, however, that these experiments were carried out in grass kept closely cropped by frequent use of the lawn mower, and such areas can be sprayed much more effectively than a wheat field, where the ground would have to be literally soaked in order to reach all of the aphidids. In the light of these experiments field spraying seems an impracti- cal measure, even when small areas are involved. Burning or plow- ing would probably be more effective and the recommendations would probably be more readily complied with, as the average farmer does not usually have spray pumps of any description. Lime and sulphur was dusted on the plants in badly infested areas with practically no benefits. CULTURAL METHODS. Examination of a large number of fields infested by Toxoptera, extending over a wide range of country, resulted in securing a con- siderable mass of information that may be included under the head of cultural methods. The senior author visited Sumter, S. C, April 17, 1907, driving over much of the country in that vicinity. All fields of fall-sown oats, the only grain grown, Were infested, there being no perceivable difference in severity of attack between fields following cotton, those following oats, and those on new ground, thus showing that the pest had swept over the country, diffusing itself generally. At Winston-Salem, N. C, April 19-20, where both wheat and fall oats were grown, the ravages of the pest were much more serious, and fall-sown oats were completely ruined. A part of one field that had been in oats the previous year had, that fall, thrown up a heavy growth of volunteer grain, while the remaining portion was free of this growth. Wheat was drilled directly across both these areas on November 15, 1906, the whole field having first been pre- pared by disking, leaving much of this volunteer grain undisturbed. April 20, 1907, when examined by the senior author, the wheat on the part that had been overgrown with volunteer oats the previous fall was totally ruined, while on the clean part the damage was about 50 per cent. In wheat fields generally there was a marked difference in severity of attack as between those seeded before and those sown after about November 1, 1906, the later-sown suffering little while that sown earlier, on ground where there was much volunteer wheat or oats, was seriously damaged. This indicated that the trouble had been aggravated by the volunteer growth at the time of wheat seeding the previous autumn. It was very significant that in late- sown fields on clean ground the injury was comparatively small. In Oklahoma it was observed by both the junior author and Mr. C. N. Ainslie that late-sown and pastured fields were destroyed much 140 more quickly and completely than earlier sown, unpastured fields. But it must be remembered that here the almost universal destruc- tion was caused principally by Toxoptera drifting in from outside sources. One feature of attack by Toxoptera has been especially noticeable throughout most portions of the country seriously ravaged by the pest, particularly where only wingless viviparous females have been found. In such fields the destruction was confined to circular areas which constantly increased in size as the season advanced, so long as meteorological conditions favorable to the increase of the pest pre- vailed; unless, in the meantime, the entire field had become overrun from the swarms drifting in from without. The occurrence of these spots (see Plate I, fig. 2) in the fields, while general, is not universal. For instance, the senior author did not observe them in the fields of fall-sown oats in South Carolina, in April, 1907, but he did find them about Winston-Salem, N. C, a day or two later. At Summers, Ark., Mr. C. N. Ainslie, observed a field of wheat, March 18, 1907, where a rectangular strip at one end had been totally killed out by Toxoptera, and learned from the owner that this area exactly corre- sponded with that of a small patch of oats which the previous year had failed to produce more than a very poor crop and had been plowed under without cutting. In preparing the ground for wheat in the fall of 1906, a volunteer growth of oats was reported to have sprung up on this area after plowing. Again the same observer, a little later in the season, found that the regularity of the occurrence of these spots in rows across a field, in northern Oklahoma, exactly corresponded to the location in this same field the previous summer of oat shocks, which had been allowed to stand out through a period of wet weather; the volunteer grain having sprung up there later in the season and remained growing amongst the young wheat in the fall. In Texas the relation of this volunteer growth in the fields, in autumn and early winter, to the abundance of Toxoptera does not appear to differ materially from what is known to occur elsewhere. When the secretary of the Texas Grain Dealers' Association first appealed to the Government for aid in investigating the pest, particu- lar attention was directed to the possibility that methods might be devised for its control by spraying or otherwise treating the spots in grain fields, for the purpose of checking its ravages before these infested spots had increased in size and before the pest had spread from them over the entire field. Thus it will be seen that primarily infestation is first invited by the volunteer growth starting up in cultivated fields in autumn. If such fields are sown to wheat or oats in the fall, the pest spreads from this earlier growth to the younger and more tender grain. This will of itself suggest several entirely practical cultural methods likely to restrict and prevent the development of the pest in the fields in autumn. REMEDIAL AND PREVENTIVE MEASURES. 141 Crop rotation could scarcely fail of giving beneficial results. The destruction of all volunteer grain springing up in fields from which grain has been removed at thrashing gives promise of the greatest relief . Indeed, if careful attention were given to all fields in autumn, and all of this volunteer growth were destroyed before any grain whatever was sown, it is doubtful if such serious ravages as have occurred in the past could be repeated. This can all be accomplished by close pasturing and careful late plowing, followed as soon as possible by seeding. At Hooker, Okla., the junior author found affected spots both on land that had been devoted to oats the previous year and on land that had previously grown cowpeas. This, as well as some other observa- tions made by other parties, indicates that some of the grasses will have the same effect in inviting attack as volunteer grain growing up in the fields in the fall. It is therefore most urgently recommended, and especially for the South, that all of this volunteer growth of whatever nature be com- pletely lulled out in the fields before seeding the following crop. Not only will this mode of procedure benefit especially the southern grain grower, but in the light of our present knowledge of the pest, it will serve as a protection to the spring oats crop over a large area of country where it is doubtful if serious ravages would occur at all were there not myriads of the pest continually developing to the South and drifting northward in spring with the advance of the season. Following along the same line, attention should be directed to the probability that late seeding may prove a preventive of attack, for the reason that the pest will obviously gain less of a foothold in a late-sown field than it will where there has been an early growth of young grain plants. In other words, there is a likelihood that the pest may break out in spots, as has been several times previously noted, and to this extent late seeding is an advantage. However, this would be a serious disadvantage if the fields should afterward be overrun by hordes of migratory winged viviparous females in spring, yf or in this case the earlier sown and therefore the older and less succu- lent growth would suffer least from their attack. This is shown by the fact that late-sown and winter-pastured fields in Oklahoma suffered most in 1907. It must also be noted that at Winston-Salem, N. C, in April 1, 1907, wheat that had been sown about or a little prior to November 15, on ground free from young growth of volunteer grain, or the grasses, was practically uninfested even though located in the immediate vicinity of other badly infested fields sown earlier on ground more or less foul with young growth. AH of this indicates pretty clearly that if all volunteer growth were eliminated in the fall, and the grain sown late, the pest would not become destructive. Of course the amount of benefit secured will depend upon the uniformity with which this method is carried into effect in any locality. 142 Over the northern part of the country where the insect passes the winter largely or wholly in the egg state, another measure can be applied to great advantage. The junior author has found that blue grass (Poa) is not only a summer food plant, but that it is very largely upon this grass that the eggs are deposited in the fall, and from which the offspring of the stem mothers make their way to the grain fields in spring. He has observed cases where the portion of a grain field bordered by bluegrass was the most seriously affected part of the entire field. If, then, roadsides, fence corners, and other waste lands were closely grazed in fall, winter, or early spring, these eggs would be largely destroyed and the food supply of the stem mother and her progeny cut off. This can always best be done during mild winters on account of a lack of snow. Where close pasturing is not practicable, burning over during the same season will have a similar if not an even more drastic effect. ARTIFICIAL INTRODUCTION OF PARASITES. As ApJiidius testaceipes destroyed such hordes of Toxoptera in apparently very short periods of time, after they had once become established, we thought it possible materially to aid in this destruc- tion by introducing the parasites artifically into localities where they were apparently absent. As Mr. C. N. Ainslie was unable to find any evidence of parasitization in the fields about Wellington, Kans., on April 1, 1907, it was decided to begin operations there. Accord- ingly, on April 9, over a bushel of wheat leaves that were almost covered with parasitized Toxoptera were collected at Kingfisher, Okla. Mr. Ainslie took charge of this material, and on April 10, made a careful survey of the fields about Wellington, Kans., to determine the situation relative to Toxoptera infestation, and on the morning of April 1 1 he scattered a portion of this material in one of the most badly infested fields that could be found in that vicinity, the remain- der being left sheltered by the box lids. At this time he could find parasitized Toxoptera already in the fields, both the dead leathery bodies and those showing the characteristic yellow color. The parasites included in this introduction were roughly estimated at 2,500,000; this number, however, was probably not a "drop in the bucket " to those already in the field. If there were only one or two para- sitized Toxoptera to a leaf, when a whole field is considered 2,500,000 would seem to be a very small number. So far as published records show this was the first artificial introduction of parasites into Kansas. April 12 another lot of parasitized material, sent Mr. Ainslie by the junior author from Kingfisher, which was fully as large as the previous consignment, was introduced into another field 2 miles from the first. All of this material, originally intended for one field, was reported as one experiment by the junior author and appeared as one experiment in Circular 93, since Mr. Ainslie's notes were not on file in the office at the time. We find, however, that Mr. Ainslie, AETIFICIAL INTRODUCTION OF PARASITES. 143 on his own initiative, conducted two separate experiments, thus rendering the results twice as valuable. April 18 a minor introduction of parasites was made at McPherson, Kans., and on April 21 there was another similar one at Sterling, Kans. Parasitized " green bugs" were observed present at each place on these dates. Mr. Ainslie remained in the vicinity of Wellington, and more briefly at McPherson and Sterling, for the purpose of making accurate obser- vations on the effect of these introductions. Two weeks later, on visiting the two fields at Wellington, where the first introduction had been made, Mr. Ainslie found that on account of the cold weather the effect upon the parasites was almost the same as though they had been kept in cold storage. Some of those sheltered by the box lids had issued, but had apparently not ventured far from their shelter and were found in a semitorpid condi- tion capable of little movement. The percentage of parasitism from Aphidius appeared to be the same in all other fields in this locality, irrespective of these introductions, except close about the box lids, where they seemed a little more numerous, the conditions of para- sitization generally being about the same as had existed two weeks previous. The Toxoptera, however, had greatly increased in num- bers, and the fields were now plainly showing the effects of their work. Subsequent examinations of fields at Wellington showed that after the weather warmed up in May the parasites speedily overcame the Toxoptera and that the fields where these artificial introductions were made had suffered as much as any fields in the neighborhood from attack by the "green bug." All of this seems to indicate that no noticeable good resulted from these introductions, which, in the light of our present knowledge, is not at all surprising. The minor experiment at McPherson was also reported upon to us by Mr. W. Knaus, and his report was in accord with our own observations. On May 17 an artificial introduction of parasites was begun at Manhattan, Kans.1 While this experiment bore out our former observations, the results obtained here should not bear as much weight as the earlier introductions, since the Toxoptera was already nearly overcome when the introduction was begun. When one stops to consider the numerous and varied hosts of Aphidius testaceipes, its manner of hibernation, its wide distribution, and the higher temperature required for its development over and above that needed by its host; also the fact that it may readily be transported along with its host as adults, or within the body of the latter, one can readily see the futility of attempting materially to increase its numbers or efficiency by artificial introduction into grain fields. i Cir. 93, Bur. Ent. U. S. Dept. Agr., pp. 10-12, Aug. 22, 1907; Cir. 93, revised, Bur. Ent., U. S. Dept. Agr., pp. 12-13, June 23, 1909. 144 THE SPRING GRAIN-APHIS OR ' ' GREEN BUG. ' ' LITERATURE CONSULTED. Aldrich, J. M. — Catalogue of North American Diptera. Aldrich, J. M. — Cultivator and Country Gentleman, vol. 47. p. 498, June, 1882. Ashmead, Wm. H.— Proc. U. S. Nat. Mus., vol. 11, 1888. Biro, Lajos. — Rovartani Lapok, vol. 2, p. 127, 1885. Buckton, G. B. — British Aphides, vol. 1, p. 80. Buckton, G. B— British Aphides, toI. 3, pp. 135-136. Del Guercio, Giac. — Nuove relazioni ai lavori della R. Stazione di Entom. Agraria di Firenze, ser. 1, no. 2, pp. 144-145, 1900. Hegner, R. W— Biol. Bui., vol. 16, no. 1, pp. 19-26, 1908. Hegner, R. W.— Journ. Morph., vol. 20, pp. 231-296, 1909. Horvath, G. — Rovartani Lapok, vol. 1, p. 143, 1884. Horvath, G. — Fauna Regina Hungarie, vol. 3 (Insecta Hemiptera), p. 60, 1897. Howard, L. O— Ent. News, vol. 19, no. 8, pp. 365-367, 1908. Hunter, S. J. — The green bug and its enemies, Bui. Univ. Ivans., vol. 9, no. 2, 1909. Huxley, T. H.— Trans. Linn. Soc, vol. 22, pt. 3, p. 215, 1858. Kelly, E. O. G.— Proc. Ent. Soc. Wash., vol. 10, nos. 3-4, pp. 163-164, 1908. Kelly, E. O. G.— Proc. Ent. Soc. Wash., vol. 11, pp. 64-66, 1909. Lecaillon, A. — Contribution a 1'etude des premiers phenomenes du developpe- ment embryonnaire chez les insectes, particulierment chez les Coleopteres. Archives D'Anatomie Microscopique, tome 1, 1897. Lecaillon, A. — Recherches sur le developpement embryonnaire de quelques Chrysomelides. Archives D'Anatomie Microscopique, tome 2, 1898. Macchiati, Luigi.— Bol. Soc. Ent. Ital., vol. 14, p. 246, 1882. Manns, Thos. F.— Bui. 210, Ohio Agr. Exp. Sta., 1909. Maxwell-Lefroy, H. — Agricultural Journal of India, vol. 3, pt. 3, pp. 243-244, 1908. Mazzanti, Dr. Dom Luigi. — Nuov. Ann. Sci. Nat. Bologna, ser. 3, vol. 6, pp. 342- 352, 1852. Passerini, Giovanni. — Gli aficli (pamphlet), p. 25, 1860. Pergande, Theo.— Bui. 38, Div. Ent., U. S. Dept. Agr., pp. 7-19, 1902. Phillips, W. J.— Proc. Ent. Soc. Wash., vol. 10, nos. 1-2, pp. 11-13, 1908. Riley, C. V.— Rept. U. S. Dept. Agr. for 1889. Riley, C. V., and Howard, L. O.— Insect Life, vol. 3, pp. 73-76, 1890. Rondani, Camillo. — Nuov. Ann. Sci. Nat. Bologna, ser. 2, vols. 8, 9, 1847. Rondani, Camillo. — Nuov. Ann. Sci. Nat. Bologna, ser. 3, vol. 6 (2), pp. 9-12, 1852. Sajo, Karl. — Zeitschr. f. Pflanzenkrankheiten, vol. 4, p. 4, 1894. Sajo, Karl.— Prometheus, vol. 1, 1889 (1890). Schouteden, H.— Mem. Soc. Ent. Belg., vol. 12, p. 231, 1906. Setterman, G. W.— Colman's Rural World, vol. 53, p. 193, 1890. Stahl, J. M.— Country Gentleman, vol. 55, p. 639, 1890. Tannreuther, G. W. — History of the germ cells and early embryology of certain aphids. Zoologische Jahrbucher, Band 24, Heft 4, 1907. Washburn, F. L.— Can. Ent., vol. 40, pp. 53-54, February, 1908. Washburn, F. L. — Special Report of the State Entomologist of Minnesota, March 1, 1908. Washburn, F. L.— Weather Crop Bui. Mo. State Bd. Agr., 1890. Webster, F. M.— Insect Life, vol. 4, pp. 245-248, 1892. Webster, F. M.— Cir. 93, Bur. Ent., U. S. Dept. Agr., 1907. Webster, F. M.— Cir. 93, revised, Bur. Ent., U. S. Dept. Agr., 1909. Webster, F. M.— Proc. Ent. Soc. Wash., vol. 9, pp. 110-114, 1907. Webster, F. M.— Ann. Ent. Soc. Amer., vol. 2, no. 2, pp. 67-87, 1909, Weed, C. M.— Ohio Farmer, vol. 78, no. 3, p. 33, July 19, 1890. White, Gilbert. — Natural history and antiquities of Selbourne, pp. 365-366, 1836. Will, Ludwig. — Entwicklungsgeschichte der viviparen Aphiden. Zool. Jahrb. Abth. f. Anat, Bd. 3, pp. 201-286, 1888. Witlaczil, Em. — Entwicklungsgeschichte der Aphiden. Zeitschr. f. Wiss. Zool., Bd. 40, 1884. INDEX. Page Abutilon, food plant of Macrosiphum sp 117, 125 Adalia flavomaculata, enemy of spring grain-aphis 18, 129 Agropyron occidentale, food plant of spring grain-aphis in America 32, 41, 42, 43 rcpens, food plant of spring grain-aphis in America 42, 43 Europe 41,43 tenerum, food plant of spring grain-aphis in America 42, 43 Alfalfa. (See Medicago sativa.) Allograpta obliqua, enemy of Macrosiphum granaria 132 probable enemy of spring grain-aphis 132 Allotria sp. , hosts 128 in bluegrass infested by spring grain-aphis at Washington, D.C. . 37 secondary parasite of spring grain-aphis 128 Alopecurus geniculatus, food plant of spring grain-aphis in America 41, 43 Ampelopsis sp. , food plant of aphidid 116, 125 Andropogon hirtus, food plant of Toxoptcra graminum in Africa 43 Andropogon sp. (See Sorghum.) Ants, enemies of Aphidius sp 136 spring grain-aphis 136 Aphelinus mali, hosts 122, 125 parasite of spring grain-aphis 103, 122-123, 125 nigritus, life history and habits, notes 124 parasite of Aphis setarix 125 spring grain-aphis 103, 122, 123, 124, 125 semiflavus, hosts 125 parasite of spring grain-aphis 103 sp. , probable host of Aphidencyrtus aphidiphagus 126 Pachyneuron sp 127 Aphidencyrtus aphidiphagus, hosts ' 126-127 secondary parasite of spring grain-aphis 126-127 Aphidid on Ampelopsis sp., host of Aphidius iestaccipes 116, 125 Baccharis viminalis, host of Aphidius testaceipes. 117, 125 bluegrass, host of Aphelinus semiflavus 123 Capsella sp. , host of Aphidius testaceipes 116 Chenopodium album, host of Aphidius testaceipes 116 Eragrostis sp. ,• host of Aphidius testaceipes 117, 125 Kochia scoparia, host of Aphidius testaceipes 116 sp. , host of Aphidius testaceipes 125 locust, host of Aphidius testaceipes 116, 125 Panicum sp. , host of Aphelinus mali 123 peach, host of Aphidius testaceipes 125 pigweed (?), host of Aphidius testaceipes 125 plum, host of Aphidius testaceipes 116, 125 Aphidius avenaphis, parasite of Macrosiphum (ranaria 125 spring grain-aphis 103, 122 26675°— Bull. 110—12 10 145 146 THE SPRING GRAIN-APHIS OR Page. Aphidius confusus, parasite of Macrosiphum erigeronensis 125 spring grain-aphis 103, 122 sp. , parasite of spring grain-aphis 18 prey of ants 136 probable host of Allotria sp 128 Aphidencyrtus aphidiphagus 126 Megorismus sp 126 Pachyneuron sp 127 testaceipes, artificial introduction against spring grain-aphis, futility. 142-143 description 104-105 dispersion, effect of wet weather thereon 121 influence of winds thereon 118-119 effect of parasitism upon development of host 106-107 fecundity of host 107-109 fecundity 113-114 hibernation 117-118 hosts 115-117, 125 identity 104-105 larva, movement within host and manner of attaching it to plant 109-113 life history 105-118 oviposition 105-106 parasite of spring grain-aphis 40, 103, 104-121 parthenogenesis 114-115 period from egg to adult 106 synonyms 104 temperature influences 119-121 nndescribed species, parasite of Toxoptcra graminum in Africa 122 Aphidoletes sp., enemy of Myzus persicx 133 spring grain-aphis 133-134 Aphis avenae, Allotria sp. a secondary parasite 128 host of Aphidius testaceipes 116, 117, 125 prey of birds 135 Eupeodes volucris 130 brassicx, Allotria sp. a secondary parasite 128 Aphidencyrtus aphidiphagus a secondary parasite 127 host of Aphelinus mali 123, 125 Aphidius other than Aphidius testaceipes 116 Megorismus sp. a secondary parasite 126 currant. (See Myzus rib is.) gossypii, Allotria sp. a secondary parasite 128 host of Aphidius testaceipes 116, 117, 125 Pachyneuron sp. a secondary parasite 127 (?), host of Aphelinus semiflavus 125 graminum= Toxoptera graminum 16 maidi-radieis, host of Aphidius testaceipes 125 males, females, and eggs in North Carolina 47 maidis, host of Aphelinus semiflavus 125 Aphidius testaceipes 116, 125 Pachyneuron sp. a secondary parasite 127 prey of Baccha clavata 132 medicaginis, host of Aphidius testaceipes 116, 125 prey of Baccha clavata 132 INDEX. 147 Page. Aphis middletoni, host of Aphidius testaceipes 116 monardx, host of Aphelirfus mali 123, 125 cenotherx, host of Aphidius testaceipes 116, 125 on peach, host of Aphidius testaceipes 117 rumicis, host of Aphidius testaceipes 116, 125 sacchari (?), host of Aphelinus mali 123, 125 setarise, host of Aphelinus mali 122, 125 nigritus 123, 125 Aphidius testaceipes 116, 125 Pachyneuron sp. , a secondary parasite 127 prey of Baccha clavata 132 sp. , host of Aphidius testaceipes 125 viticola. (See Macrosiphum viticola.) Arrhenatherum elatius, food plant of spring grain-aphis in Europe 41, 43 Astragalinus tristis, enemy of spring grain-aphis 135 Audibertia stochoides, food plant of Macrosiphum sp 117 Avena barbata, food plant of spring grain-aphis in Europe 41, 43 elatior= Arrhenatherum elatius 41, 43 fatua, food plant of spring grain-aphis in Europe 41, 43 sativa. (See Oats.) Baccha clavata, enemy of Aphis maidis 132 medicaginis 132 setarise 132 Baccharis viminalis, food plant of aphidid 117, 125 Barley, food plant of spring grain-aphis in America 43 Europe 41, 43 ' ' Bermuda grass, ' ' food plant of spring grain-aphis in Africa 43 Birds, enemies of Aphis avenx 135 Macrosiphum granaria 135 spring grain-aphis 135 Black gum. (See Nyssa sylvatica.) Bluegrass (see also Poa pratensis). food plant of Rhopalosiphum pox *. 123 African. (See Andropogon hirtus.) Bromus commutatus, food plant of spring grain-aphis in America 42, 43 erectus, food plant of spring grain-aphis in Europe 41, 43 hordcaceus, food plant of spring grain-aphis in Europe 41, 43 inermis, food plant of spring grain-aphis in America 42, 43 maximus= Bromus villosus 41, 43 mollis=Bromus hordeaceus 41, 43 porteri, food plant of spring grain-aphis in America 42, 43 secalinus, food plant of spring grain-aphis in America 41, 42, 43 tectorum (?), food plant of spring grain-aphis in America 42, 43 unioloides, food plant of spring grain-aphis in America 42, 43 villosus, food plant of spring grain-aphis in Europe 41, 43 Brush drag against spring grain-aphis 136-137 Buckwheat. (See Fagopyrum esculentum.) Burning-over infested spots against spring grain-aphis 137 pastures against spring grain-aphis 142 Capriola dactylon, food plant of spring grain-aphis in America 42, 43 Europe 43 Capsella bursa-pastoris, food plant of aphidid 116, 125 Cecidomyiidae, enemies of spring grain-aphis .-,«,...-,. , 133-134 148 THE SPBIXG GRAIN"- APHIS OE Page. Chastochloa italica, food plant of spring grain-aphis in America 42, 43 viridis, food plant of spring grain-aphis in America 42, 43 Chaitophorus sp., host of Aphidius testaceipes 116 Megorism us sp. a secondary parasite 12G Pachyneuron sp. a secondary parasite 128 riminalis, host of Aphelinus semiflavus 123, 125 Cheat. (See Bromus secalinus.) Chenopodium album, food plant of aphidid 116 Chess, soft. (See Bromus hordeaceus.) Chrysopa plorabunda, enemy of spring grain-aphis 132-133 Coccinella abdominalis, enemy of spring grain-aphis 129 9-notata, enemy of spring grain-aphis 129 Colopka eragrostidis, host of Aphclin us mail 123, 125 Corn, food plant of spring grain-aphis in America 41. 43 Europe 41, 43 Couch grass. (See Agropyron repens.) Cricket, snowy tree. (See QLcanthus niveus.) Crop rotation against spring grain-aphis 141 Cultural methods against spring grain-aphis 139-142 Currant, food plant of Myzus ribis 125 Cynodon dactylon. (See Capriola dactylon.) Dactylis glome rata, food plant of spring grain-aphis in America 41, 42, 43 Europe 41, 43 Distichlis splcata, food plant of spring grain-aphis in America 42, 43 Drag. (See Brush drag.) Echinochloa crus-galli, food plant of spring grain-aphis in America 42, 43 Eleusinc indica, food plant of spring grain-aphis in America 42, 43 Elym us canadensis, food plant of spring grain-aphis in America 41, 42, 43 striatus, food plant of spring grain-aphis in America 42, 43 virginicus, food plant of spring grain-aphis in America 42, 43 Eragrostis megastachya, food plant of spring grain-aphis in America 42, 43 pilosa, food plant of spring grain-aphis in America 42, 43 sp., Aphidius testaceipes swept therefrom 117 food plant of aphidid 117, 125 Eupeodes xolucris, enemy of Aphis avenx 130 spring grain-aphis 130 Fagopyrum esculentum , food plant of spring grairf-aphis in Europe 41, 43 Fescue, hard. (See Festuca duriuscula.) meadow. (See Festuca clatior.) sheep's. (See Festuca ovina.) various-leaved. (See Festuca heterophylla.) Festuca duriuscula, food plant of spring grain-aphis 42. 43 clatior, food plant of spring grain-aphis in America 42, 43 heterophylla, food plant of spring grain-aphis in America 43 ovina, food plant of spring grain-aphis in America 42, 43 rubra, food plant of spring grain-aphis in America 43 Fungous disease of spring grain-aphis 136 Grass, Bermuda. (See Capriola dactylon.) blue. (See Poa pratensis.) couch. (See Agropyron repens.) Italian rye. (See Lolium multiflorum.) Johnson. (See Sorghum halepense.) rye. (See Elymus canadensis.) INDEX, 149 Page. Goldfinch. (See Astragalinus tristis.) Grain-aphis, spring (see also Toxoptera graminum) . aberrant individuals 81 age at which females begin reproducing 70-71 ant enemies 136 attack, character 44 bird enemies 135 birth of young 63 confusion with Nacrosiphum, granaria 13, 23 description of different instars 58-59 summer forms 59-61 diffusion, influence of temperature thereon 88-94 winds thereon 81 distribution in the eastern hemisphere 16-18 western hemisphere 18-19 earliest observations in America 13-16 early records in Europe 16 egg, description 95-97 embryology 94-103 observations 97-102 summary 102-103 enemies 103-136 miscellaneous 135-136 fecundity of oviparous forms 81 viviparous female 73-75 wingless versus winged females 75-76 first generation, fifth instar or adult stem mother, descrip- tion 58-59 first instar, description 58 fourth instar, description 58 second instar, description 58 third instar, description 58 food plants 41-43 fungous enemy 136 generations, number 52-57 per year 63-70 literature consulted 144 longevity 72 of sexes 80 losses from depredations in 1907 39-40 methods and material for embryological studies 95 migratory female, description 60 molting 61-62, 78 number of generations per year 63-70 molts 61-62 oviparous development 78-81 female, description 77-78 forms, fecundity 81 oviposition, age begun by females 78-79 period 79-80 place 79 outbreak of 1890 : 19-24 1901 24 150 THE SPRING GRAIN-APHIS OE Page. Grain-aphis, spring, outbreak of 1903 24-26 1907 27-38 parasites, primary or true 104-125 secondary 125-128 predaceous enemies 128-136 preventive and remedial measures 136-143 pupae, measurements of antennal joints 61 rearing methods 51-57 remedial and preventive measures 136-143 remedies, artificial introduction of parasites 142-143 cultural methods 139-142 field experiments 136-139 treatment of affected spots 140, 141 reproduction, age when begun by females 70-71 reproductive period 71-72 sexual forms 76-78 descriptions 77-78 situation in 1911 40 stem mothers 58 summer forms, first instar, description 59 fourth instar, description 59 second instar, description 59 third instar, description 59 viviparous development 44-78 in the North 49-50 South 44-49 female, fecundity 73-75 winged male, description 78 viviparous female, measurements of antennal joints 61 wingless female, description 60, 61 versus winged females, fecundity 75-76 young produced daily, average number 76 Grazing, close, against spring grain-aphis 142 "Green bug. " (See Grain-aphis, spring.) Gum, black. (See Nyssa sylvatica.) Harrowing infested spots against spring grain-aphis 137 Hippodamia convergens, enemy of spring grain-aphis 129 Holcus halpensis, food plant of spring grain-aphis in America 43 Hordeum caespitosum, food plant of spring grain-aphis in America 42, 43 jubatum, food plant of spring grain-aphis in America 42, 43 murinum, food plant of spring grain-aphis in America 42, 43 Europe 41, 43 nodosum, food plant of spring grain-aphis in America 42, 43 pusillum, food plant of spring grain-aphis in America 41, 42, 43 vulgar e. (See Barley.) Hosackia glabra, food plant of Myzus sp 117, 125 Hyalopterus dactylidis, Allotria sp. a secondary parasite 128 Megorismus sp. a secondary parasite 126 Juncus tenuis, food plant of spring grain-aphis in America 42, 43 Kerosene emulsion against spring grain-aphis 138 Kochia scoparia, food plant of aphidid 116 sp., food plant of aphidid 125 INDEX. 151 Fage. Lacewing flies, enemies of spring grain-aphis 132-133 Ladybeetle, convergent. (See Hippodamia convergent.) nine-spotted. (See Coccinella 9-notata.) spotted. (See Megilla maculata.) Lady beetles, enemies of spring grain-aphis 128-129 Lime and sulphur against spring grain-aphis 139 Lipolexis piceus, parasite of spring grain-aphis 136 Locust, food plant of aphidid 116, 125 Lolium multijlorum, food plant of spring grain-aphis in America 43 perenne, food plant of spring grain-aphis in Europe 41. 43 Lysiphlebus abutilaphidis— Aphidius testaceipes 104 baccharaphidis= Aphidius testaceipes 104 basilaris= Aphidius testaceipes 104 citraphis= Aphidius testaceipes 104 coquiUetti {!)= Aphidius testaceipes 104 craufordi= Aphidius testaceipes 104 cucurbitaphidis= Aphidius testaceipes 104 eragrostaphidis= Aphidius testaceipes 104 gossypii= Aphidius testaceipes 104 minutus= Aphidius testaceipes 104 myzi— Aphidius testaceipes 104 persiaphidis= Aphidius testaceipes 104 persicaphidis= Aphidius testaceipes 104 piceiventris= Aphidius testaceipes 104 tritici= Aphidius testaceipes 37, 104 Macrosiphum cucurbitse, host of Aphidius testaceipes 117, 125 erigeronensis, Pachyneuron sp. a secondary parasite 127 granaria, host of Aphidius avenaphis 125 testaceipes 116, 125 in North and South Carolina in 1907 36 males and oviparous females in rearing cages in Texas. . 47 Pachyneuron sp. a secondary parasite 127 prey of Allograpta obliqua 132 birds 135 Sphserophoria cylindrica 131-132 Syrphus ameiicanus 131 spring grain-aphis mistaken therefor 13, 23 pisi, Megorisrnus sp. a secondary parasite 126 rosse, host of Aphelinus mali 123, 125 sp. on Abutilon, host of Aphidius testaceipes 125 black gum (Nyssa sylvatica), host of Aphidius testaceipes. 116, 125 viticola, AUotria sp. a secondary parasite 128 host of Aphidius testaceipes 116, 125 Pachyneuron sp. a secondary parasite 127, 128 Manure against spring grain-aphis 138 Medicago sativa, food plant of spring grain-aphis in America 42, 43 Megilla maculata, enemy of spring grain-aphis 129 Megorismus sp., hosts 125-126 secondary parasite of spring grain-aphis 125-126 Melanoxantherium sp., host of Aphidius testaceipes 116, 125 Melospiza melodia, enemy of spring grain-aphis 135 Millet. (See Chsetochloa italica.) Japanese. (See Echinochloa crus-galli.) 152 Page. Myzus mahaleb, host of Aphelinus mali 125 persicse, Allotria sp. a secondary parasite 128 host of Aphelinus semijlavus 123, 125 Megorismus sp. a secondary parasite 126 prey of Aphidoletes sp 133-134 ribis, host of Aphidius testaceipes 117. 125 sp. on Hosackia glabra, host of Aphidius testaceipes 117, 125 Nyssa sylvatica, food plant of Macrosiphum sp 116 Oats, food plant of spring grain-aphis in America 41, 43 Europe 41, 43 (Ecanthus niveus, enemy of spring grain-aphis 136 Oryza sativa. (See Rice.) Pachyneuron sp. hosts 127-128 probable parasite of Aphelinus sp 1 27 secondary parasite of spring grain-aphis 127-128 Panicum sp. food plant of aphidid ] 23 Parasites of spring grain-aphis, artificial introduction 142-143 Passerculus sandwichensis savanna, enemy of spring grain-aphis 135 Pasturing. (See Grazing.) Peach, food plant of aphidid 125 Pemphigus fraxinifolii, host of Aphelinus mali 123, 125 Pigweed. (See Chenopodium album.) (?), food plant of aphidid 125 Plowing-under infested spots against spring grain-aphis 137 Plum, food plant of aphidid 116, 125 Poa annua, food plant of spring grain-aphis in Europe 41, 43 compressa, food plant of spring grain-aphis in America 42, 43 pratensis (see also Bluegrass). food plant of spring grain-aphis in America 42, 43 Polypogon montspeliensis, food plant of spring grain-aphis in America. 42, 43 Pooecetes gramineus, enemy of spring grain-aphis 135 Quail, enemy of spring grain-aphis 135 Rains, protracted, effects on diffusion of Aphidius testaceipes 121 Reduviolus ferus, enemy of spring grain-aphis 136 Rhopalosiphum pose, probable host of Aphelinus semijlavus 123 Rice, food plant of spring grain-aphis in America 42, 43 Europe 41, 43 Rolling against spring-aphis 137 Rye, food plant of spring grain-aphis in America 41, 43 Schizoneura americana, host of Aphelinus mail 122, 125 Pachyneuron sp. a secondary parasite 128 lanigera, host of Aphelinus mail 122, 123, 125 Scymnus sp., enemy of spring grain-aphis 136 Seeding, late, against spring grain-aphis 141 Siphocoryne avense should probably be called Aphis avense 47 Siphonophora avenx= Macrosiphum granaria 13, 23 sp. on Abutilon, host of Aphidius testaceipes 117 Audibertia stochoides, host of Aphidius testaceipes 117 Soap against spring grain-aphis 138 whale-oil, against spring grain-aphis 138-139 Sorghum, food plant of spring grain-aphis in America 43 Europe 41, 43 halepense, food plant of spring grain-aphis 42 INDEX. 153 Page. Sparrow, chipping. (S.ee Spizella socialis.) savanna. (See Passerculus sandivichensis savanna.) song. (See Melospiza melodia.) vesper. (See Pooecetes gramineus.) " . Spelt, food plant of spring, grain-aphis in America 43 Europe 41, 43 Sphserophoria cylindrica, enemy of Macrosiphum granaria 131-132 spring grain-aphis 131 Spizella socialis, enemy of spring grain-aphis 135 Sporobolus neglectus, food plant of spring grain-aphis in America 42, 43 Spraying experiments against spring grain-aphis 137-139 Stipa leucotricha, food plant of spring grain-aphis in America 42, 43 viridula, food plant of spring grain-aphis in America 42, 43 Sulphur and lime against spring grain-aphis 139 Syrphid flies, enemies of spring grain-aphis 129-133 Syrphus americanus, enemy of Macrosiphum granaria 131 spring grain-aphis 130 Temperature, influence on diffusion of spring grain-aphis 88-94 influences on Aphidius testaceipes 119-121 in relation to development of spring grain-aphis in North 49-50 South 44-49 outbreak of spring grain-aphis in 1907 28-29 Tetraneura colophoidea (?), host of Aphelinus mali 123, 125 "Texas louse," early name for spring grain-aphis 22 Tobacco dust against spring grain-aphis 138 extract against spring grain-aphis 138 Toxoptera graminum (see also Grain-aphis, spring). parasites and their hosts 125 Triticum repens. (See Agropyron repens.) spelta. (See Spelt.) villosum, food plant of spring grain-aphis in Europe 41-43 vulgare. (See Wheat.) Volunteer growth of grain in relation to outbreaks of spring grain-aphis 140, 141 Weather, wet, effect on diffusion of Aphidius testaceipes 121 Wheat, food plant of spring grain-aphis in America 41, 43 Europe 41, 43 Winds, influence on dispersion of Aphidius testaceipes 118-119 spring grain-aphis 81-88 Zea mays. (See Corn.) o