Ci cular No. 93, Revisld. United States Department of Agriftflfrire, BUREAU OK ENTOMOLOGY L. O. HOWARD, Entonvl ■ ut Bu ■f\ ■ THE8PRING GRAIN-APHIS OB NO-t \ l.l.I.I) -i.U\ I -:\ III (J i i,j,t< i ,i graminum Bond. > Bj F. M. Wi Ban r, /»/ *'/,.; cat and Forage-Plant //'-■■/ Investigate Th ■ early history in America of the spring grain aphis (figs, l I . which has come i«» !>e generally known a- the "green bug," \\ ;i- pub- lished in Circular No. s "> of 1 1 1 i — Bureau, and need not be reproduced Dg grain minum i here. Suffice it to say that it is an imported species, long known to be destructive to growing grain in Europe, but not known in this country prior to i^-_>. and not as a destructive insect until 1890. The litera- ture relating to tlii-. the third and perhaps most destructive outbreak of tin- pest, i- so misleading that 1 1 * i — publication seems necessary in order to prevent misapprehension among farmers, and to afford them all possible helpful information in advance of future similar out- breaks. MSTRJB1 HON IN I Hi: I MUD STATES. Tin- bisect i> usually common, ami i- found from New Mexico, Colorado, and Montana to the Atlantic coast, approximately cover- he area south of latitude II , excepting Si ■ York, Se and New England, ami east of longitude 105°. Within tin- territory :t- area of destructive abundance, as well as ti - at- tack during* any year, will lie regulated by two factors: First, the 84843 Clr.! -1 presence of young growing wheat, oats, barley, or rye; and. second, weather conditions favoring its rapid increase and unfavorable for the development of its natural enemies. It will breed freely in the fields from an altitude of less than 20 feet above sea level on the At- Fig. 2. — The spring grain-aphis or "green bug" (Toxoptera graminum): a, Wingless female; '/, larva : <■, pupa. Much enlarged. (From Pergande.) lantic coast to an elevation of nearly 8,000 feet in Xew Mexico, and from eastern Washington, southern Montana, northwestern Minne- sota, southern Wisconsin, northern Ohio, and southern Pennsylvania southward to extreme southern South Carolina, southern Texas, and In: •". — The spring grain-aphis or " grecu bug" (Toxoptera graminum) : ". Winged uii- granl : b, antenna of same. ". Much enlarged : h. highly magnified. I From Pi rgande.) Xew Mexico. Yet. with normal weather conditions during the first four or five months of the year, these facts signify absolutely nothing. for this insect will not be abundant enough to attract any attention by its injuries. [Cir. 93] 3 -, ,,| i:, in i imn 01 n Mi'iKMi RE i BTB1 I HVE 01 rBREAKS. This insect, aa with other closelj allied species of aphides, repro duces m two ways, A.s cool weather approaches in autumn there occur in greater or less numbers both males and females, the latter depositing eggs 1 3ee fig. I), and it is in the egg state onl} that, under ,„ rnm l weather conditions as to temperature, the "green bug " p the winter, and from these eggs il originates in thespring. Bui from spring to fall there are neither eggs nor males; all are females, and these give birth to living young in a series of generations. \\ ith the normal cold of early winter these females gradually disappear and the winter eggs remain; but if the winter temperature is mild, and the temperature of the following spring abnormally cold, the summer met hod of reproduction continues throughout the winter and during spring. Endeed, it is not improbable that males and egg-laying fe males may be found in spring, especially in the South. Ti le orreen bug " will breed freely in - log grain-aphis iminum i : Egg-laying f, -111:1 greatly enlaj - ' """"" enl temperatures ranging from above 100 to below 16 F. As the young mature in eieht days and themselves begin to give birth to young, it will be seen that an exceptionally mild winter foll< wed !>v an abnormally cold spring offers tln> lir-t possible conditions for the asive increase of the pest, which would ordinarily begin breeding only in spring, and from the eggs. With excessive reproduction and the destruction or aging of it- food plant-. this inseel develops a corresponding abundance of winged migrating females, which are the means of the spread northward or outward from original centers. The "green bug" in normal .war- that is, when it- breeding be- gins in spring i- effectively held in check by it- natural enemies, and notably by a minute, black, wasplike insect, Lygiphlebus tritic't Ashm. (see Bg. 5) that deposits eggs singly in the "green bugs," the grubs hatching from the eggs feeding internally on the bug and de- stroying it (see Bg. ''•>. Other natural enemies are the larvse of cer- tain predaceous flies, and the larva and aduks of lady-beetles. The little wasplike parasite first mentioned, however, is the one that keeps the "green bug" in control in normal year-, and in year- when the latter i- mo-t abundant finally overcomes it. a- was the case in 1907 in Kansas, North Carolina, and other States in the more northern pari of the range of the pest. [Or. 93] Unfortunately this parasitic wasp — as with the other beneficial insects — is active only while the temperature is above 56 I\. or at least 10 above that at which the "green bug" breed- freelv: and Fig. 5. — Lysiphlebua tritici, principal parasite of the spring grain-aphis: Adult female and antenna of male, greatly enlarged. Egg of Lysiphlebus tritici at right, highly mag- nified. (Original, i herein is the whole secret of the irregular disastrous outbreaks of the "green bug" in grain fields. As accounting for the outbreak in the year 1907, the" "green bug" had had a whole winter and the following late spring in which to breed and multiply unmolested, and it accomplished its principal damage, as in Texas and southern Oklahoma, before the weather was warm enough for the para- site to increase sufficiently to overcome it. As further illustrative of the important bearing of weather conditions, it is found that in the case of the three important outbreaks of this insect, namely, for the years 1890, 1901. and 1907. the temperature for the first five months of each of these years, including the latter part of winter and spring, was above the normal for the winter months and below the normal for the spring months; in other words, warm winters and cold, late springs. The little parasitic wasp which is so useful in the control of this pest is native to this country, widely distributed, and every year does its work with the " green bug" and with other aphides. It is always [Cir.93] Fig. 0. — Wingless female of " green bug." eontaiuing larva of the parasite Ly- SzphlebUS ti:!'.:i Mile I eii^ larged. (Original.) present in grain fields, as shown \>\ its appearance everj year, to win- on these pests whenever the weather conditions make il breeding and multiplication possible, and its rate of breeding is so rapid i there being o general ion a I i everj ten days) thai with a week or two of favorable weather il gains control over it- host insects and destroys them. rooo PLANTS. The spring grain-aphis is essentially a leaf-infesting insect, rarely being found on the stem. While preferring « « : 1 1 — . it w ill readilj attack wheat, rye, and barley, and ma\ often be l I on the underside of the lower leaves of corn. Corn excepted, its effecl on the l«;i \ <•- of grain, when present in large numbers, i- to cause the infested leaves to change to a red color, which seems to be \ery characteristic of ;optera and does not follow attack- of other species of aphides on these grains. The insect has also been found breeding upon ;i considerable number of grasses, any one of which may constitute its alternating food plant upon which it may survive the summer in different portions of the United States. It has been found breeding freely upon marsh foxtail (Alopecurus geniculatus) in Oklahoma by Mr. W. J. Phillip-, and by Mr. ('. N. Ainslie in Kansas; on yron occidentalism also in Oklahoma, by Mr. Phillip-, and by Mi E. < >. (i. Kelly and Prof. C. P. Gillette in Colorado. Slender wheat-grass (Agropyron tenerum) was found moderately infested by Mr. Ainslie at Las Vegas, X. Mex. The species was found breed- ing upon Bromus at Washington, D. ('.. and also upon Porter's chess (Bromus porteri) at Las Vegas, X. Mex., and on an undetermined species of Bromus at Mesilla Park, X. Mex., all by Mr. Ainslie. The writer observed it \er\ abundantly on orchard grass (Dactylis glomerate) in Indiana in 1890, and again excessively abundant in a Small i-olated meadow of this grass near Midlothian. Ya.. in April. 1907. This meadow was located in a region ncl adapted to the grow- ing of grain, and there was no held of growing wheal or oats within ."> miles. Mr. Kelly found it in Montana, inhabiting marsh spike- grass {Distichlis spicata) in such abundance as to l>e damaging this grass, which in that part of the country i- known commonly as ••-alt grass.* 1 It was found inhabiting -lender wild rye (Elymvs iatus) at Las Vegas, X. Mex., by Mr. Ainslie. Mr. Phillip- found it attacking little barley (Hordevm ptisillum) at Beloit, Kan-., and Kingfisher, Okla., while the writer found this to be of frequent occurrence throughout Kan-a-. Mr. Kelly observed it abundant on squirrel-tail grass (Hordeum fubatum) in Montana, while Mr. Ainslie found it moderately abundant on Tfordeum ca • near Cimarron. X. Mex Wherever Kentucky blue-grass (Poa pratensis) grows, the insect will probably be found breeding upon it through- ICir asj out the entire summer. In fact, this has been actually observed to occur in the city of Washington. Mr. Phillips has observed the same thing in Indiana, and throughout the northern sections of the country where the Toxoptera occur- it is more likely to he found on this plant during summer than upon grain, excepting, perhaps, during seasons of excessive abundance. Mr. Ainslie also found it moderately abundant on beard-grass (Polyp&gon monspeliensis) about Albuquerque, X. Mex. It has been found breeding on yellow foxtail or pigeon-grass (Iseophorus glaucus) by Mr. Phillips at Richmond, Ind.. and on green stipa {Stipa viridula) at Las Vega-. X. Mex.. by Mr. Ainslie. In the latter case the grass was heavily infested. As one or more of these grasses will be found to occur in almost every portion of the United State-, it would appear that the nonoccurrence of Toxoptera in any considerable section of coun- try can not be due to a lack of uncultivated food plants. Of food plants other than grasses we have only the one observation made by Mr. Phillips at Kingfisher. Okla., April 23. 1007. where a species of ragweed growing up in a badly damaged wheat field was quite heavily infested with Toxoptera, at the time breeding freely on this plant. The outbreak on the grounds of the Department of Agriculture was notable in some respects, in that the continued close cutting of the blue grass supplied a continual fresh, tender growth as food for the "green hug." thus preventing the development and escape of winged females: and especially is it notable in view of the total lack of Lysiphlebus tritici, the most important of the natural enemies of this aphis. The only natural enemy found in this case feeding upon the ; ' green bug " was the diminutive black and yellow lady-beetle (Hyperaspis undulata Say), not previously known in connection with this pest. When this outbreak became known to Mr. E. M. Byrnes, superin- tendent of Experimental Garden- and Grounds, he at once had the entire infested block sprayed with a solution of one-half gill of rose- leaf nicotine to each gallon of weak soapsuds. The application was, however, ineffective. Pour days later a strip through this plat was thoroughlv 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 notably less on this area than where the application of manure solution was not mad?. A series of experiments was then undertaken under the writer's direction by Mr. E. O. G*Kelly, as follow-: Tobacco dust wa- applied at rates of one-fourth, one-half, and 1 pound to each 100 square feet, but after over a week had elapsed • [Cir. 93] from the 'hue of application no effect was i" be observed and n<» dead insects were found. Kerosene emulsion was applied ai s and 10 per cent strength . There was pract icall] no difference in the effecl of these two strengths, and ;ii the pnd of nine days n<> " 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 o pound to ■_' pounds of soap to each 5 gallons of water, were applied to similar areas. In this case the stronger solution injured the grass slightly, 1 >i 1 1 not permanently; in the case of the lesser strengths there was no injury whatever. The .effect on the " green bug " was tin- mimic in every case. They were not only literally exterminated over reas treated, but the applications seemed to protect from a rein testation. Tn case of even the weakest solution an examination, five da] after the application was made, revealed the "green bugs" in myriads and In >eding freely on the untreated space, while but 8 inches away and on the treated area living bugs were scarcely to be found, though the dead were to be observed almost as abundantly as were the living on the space untreated. It musl I" 1 remembered, however, that these experiments were carried out in grass kept closely cropped by frequent use of the lawn mower, and the results obtained in no way reflect upon similar experiments carried out \<\ Messrs. Ainslie and Phillips in the grain fields of Oklahoma. invasion of 1907. \ 1 letter appreciation of the interrelation of the "green bug" and its principal parasitic enemy can be conveyed by giving a chrono- logical statement of our investigations of the very disastrous inva- sion of the " green bug" during the winter and spring of L907. The first rumors of injuries by this pesl came to us early in Janu- ary from east-central Texas, where the "green bugs" were reported to Mr. W. 1>. Hunter, in charge of cotton boll weevil investigations of this Bureau, a^ attacking fall oats. During this month in Texas, east of a line drawn from near Gainesville through Abilene and San Antonio to Galveston, the temperature was 9 above the normal. Within this area was a smaller one. the boundaries of which may be indicated by a line drawn from Texarkana to Fori Worth, Waco, and Joaquin. Over this latter area the temperature for the same month was 12 above the normal, and within this area the pesl began its work of desl met ion. Also, judging from data received later, the pest began to breed rapidly in fall-sown oats in southern South Carolina, where the tem- perature was from C> to 9 ab >ve the normal. 83] 8 During February all over the region west of the Mississippi River and the Great Lakes the temperature was above the normal, and in the Carolinas it was only slightly below. During this month much damage seems to have been done in Texas, and there is every probability that the pest was breeding freely in the Carolinas, though it had not yet been reported from the latter State". Up to this time the outbreak in Texas was being investigated by Mr. E. C. Sanborn, an agent of this Bureau detailed to the Texas Agricultural Experiment Station. The first report of the insect outside of Texas was under date of March u. from Mr. ('. TT. Drake, of Summers, Ark., who reported that "a -mall green hug" had destroyed the wheat in spots in the fields in hi- locality. This lettur. received March 11. led to the prompt dispatching of Mr. C. X. Ainslie for the West, with full instructions to investigate the out- break thoroughly, to experiment with mea>ures for destroying the insects in the fields, especially over the >pot- where they seemed to !>.• most abundant, and to determine what could be accomplished in checking the ravage- of the pest by the early introduction of natural enemies into the infested fields. Arrangement- were perfected with Mi - . W. D. Hunter to ship to Arkansas living parasites (LysiphJebus tritici), which were then abundant in Texas, and the -ame train l>. which Mr. Ainslie reached Summers brought several hoxes of the parasites. These parasites were promptly placed in the infested fields and liberated March IS. But Mr. Ainslie found that both the lady heetles and the little wasplike parasites (Lysiphlebus tritici) were already present at Summer- and near-by points in greater num- bers than could pos>ibly have been introduced. The latter were simply everywhere, running about over the young grain plants and placing their eggs in the bodies of the " green bug-." Clearly the importation of parasite- would be useless under these conditions, and Mr. Ainslie. hoping to find a more favorable field for the introduction of parasite- or direct experimental work with rem- edies, proceeded, on March 23, for various points in Oklahoma. At Chandler and Guthrie, March 23 to 2.">. the pest was very abundant, but the conditions at these points were again even less favorable than in Arkansas for the introduction of parasites. For example, on one blade containing about 150 of the "green bugs " Mr. Ainslie counted 25 that were parasitized. lie then proceeded to Kingfisher (March 26) and here found the parasites apparently less plentiful than at the other points visited, which were to the eastward. Arrangements had been made with Mr. Hunter to furnish parasites from Texas fields when these were .called for. and in response to a telegraphic request he dispatched a quantity of material collected by his a.ssi.-tants in Texas and in southern Oklahoma. When this was [Cir. 93] 9 received and the para ite* liberated in the infested fields, native para sites were already issuing in great numbers. In other words, the parasite was already beginning unaided it- active work of control. I'»\ March 27 the "green bugs" developed winged adults in greal numbers, and these seemed to drift northward. Mr. Ain-lie was instructed to look for m region t<> the northward where the " green bug" was just starting, and he made his firsl stop, March 30, ;ii Wellington, Sumner County, Kans., and found the con ditions there such a- to oiler n favorable field for experimentation w ith parasites. By April 1 the fields about Wellington were generally, though sparsely, infested with the "green bug," represented in many cases l>\ winged females thai had seemingly migrated to these fields and were giving birth to their young. Lad} beetles were common, bul none of the Lysiphlebus was observed. After a couple of days spent in the vieinitv of Wellington, Mr. Am-lie returned to Kingfisher to Becure parasites for introduction into southern Kansas, l>ut in the meantime severe weather, accompanied by beavj frosts, had pre- vailed, and the parasites formerly abundant at Kingfisher had I ome exceedingly scarce. \>\ the 5th, however, he began again to find \er\ many parasitized "green bugs," and by the 7th the parasites themselves began to appear again. A bushel of wheat plant-, now nearly covered with parasitized "green bugs," was collected at King- fisher and taken to Wellington April 9. At tin- time fully 12 per cent of the "green bugs" at Wellington were already parasitized, while on the li'th Mr. Ain-lie counted as many a- 11 parasitized in- dividual- on a single blade of wheat. About the middle of March an appeal came to this Bureau from the Texas drain Dealers' Ajssociation, through their secretary, Mr. II. B. Dorsey, at Fori Worth, to investigate the "green bug." In response to tin- appeal Mr. W. .1. Phillip-, of the Bureau staff, was dispatched to Fort Worth, arriving on the 27th. Several days -pent in examining Held- in the vicinity of Fort Worth demonstrated that the "green bug" had totally destroyed the grain in that vicinity and disappeared, and there was no opportunity for experimental work. He then went, by instruction, to Iloliart. Okla.. and later relieved Mr. Ain-lie at Kingfisher, and. in response to a telegram from Mr. Ainslie, -cut an amount of parasitized wheat from Kingfisher to Wellington equal to or larger than the first shipment. All of the material which Mr. Ain-lie took with him from Okla- homa and that supplied him by Mr. Phillips was placed in a single wheat field near Wellington. It i- safely estimated, from count- of average wheat Made-, that upward of two and one-half million- of parasites were thus liberated in a single wheat Held on April '.'. and mm:: Cir 93 09 .: 10 by this time many were already there. This introduction of para- sites was carried out in order to give a decisive test as to whether it was possible to aid in protecting fields in this manner along the ad- vance line of invasion. The weather was still cold, and if the artifi- cial introduction of parasites would, with the return of warmer weather, hasten the control of the "green bug,'' the introduction of such huge numbers would clearly demonstrate this fact. And if such introduction on a large scale proved favorable, it would show reasonable ground for the more general introduction of parasites in lesser numbers. There was a minor introduction of Lysiphlebus started at McPher- son, Kans., April 18, though this parasite was already" found in the fields in that vicinity at that time. The weather during the whole of April was generally cold with, ae on May 4, an occasional storm that is known to have killed many of the parasites, and though there were brief periods of warm weather during which the parasites would increase rapidly, the Lysiphlebus did not finally overcome the "green bug" in southern Kansas until about the middle of May. As will be observed, this experiment was made under weather con- ditions almost uniformly unfavorable to the parasite and favorable to the development of the "green bug." There is no reason for supposing that the weather would affect the introduced parasites differently from those already present when the introduction was made. Mr. Ainslie remained in the vicinity of Wellington, and more briefly at McPherson and Sterling, for the purpose of watching these experiments, and he was, moreover, in direct communication with Mr. Phillips in northern Oklahoma : and the two were therefore able to keep under their observation a wide range of country, thus eliminating the possibility of oversight or misconception on the part of either that might otherwise have occurred. It was during this period of generally cold weather in late April and early May. interspersed by shorter periods of weather favor- able to the parasites, that the latter increased generally throughout Kansas and, judging from reports, also in Missouri and Colorado. It wanted only the more extended warm spell that came soon after to enable them to get the upper hand and subdue the pest, as they did throughout the southern Atlantic coast section earlier in the season. The field in which the two and a half million Lysiphlebus were introduced and liberated on April did not, at the time of the over- coming of the pest in this and the adjacent country in May. indicate any benefit whatever above other fields, near or remote, where no [Cir. it::] 11 artificial introductions had been made. The resull of the minor experiment at McPhereon was, as reported by Mr. Kuan-, no more fa\ t >r:i 1 >l t*. I >i i i-i i iir the lasi two weeks of April ;i greal many small lol of parasite:' were distributed over the southern and central countii Kansas by Mr. S. J. Hunter, of the Kansas State University. The artificial sending out <>f these parasites bj Mr. Hunter and the test of distributing an enormous quantity in ;i single field, described above, were legitimate experiments, Imt the evidence showed \>-v\ conclusively that they resulted in no benefit whatever. In other words, as noted above, the parasites were already infesting 12 per cciii of iIk "green bugs" at Wellington, Kan-.. April 9, when the artificial introduction was made, and •"•" t" 75 \»i cent m King- fisher, Okla., at the same date, and 1 1 n\ were only waiting for weather conditions i<> make it possible for them to do their work. .In-i as soon as the favorable weather arrived the parasites bred enor- mously and quickly overcame the " green bug." In no case was there I field of the hundreds examined in southern Kansas where the para natively present did not outnumber by many thousands or hun- dreds of thousands any number that could have been introduced artificially, at a time when weather conditions had become such that tin- liberations could have had any hen. 'lit. A- shown by the careful investigations t' introducing para ite . while 1 1 1<- other was kept as a check. The Gelds were so widelj separated thai the introductions could nol have spread from one field to the other. Sis areas of i square yard each, selected for i In' examinations in dif ferent parts of each field, were gone over b) Mr. Phillips and two of Professor Popenoe's assistants. Examinations of both of these fields, made on Ma\ 17 and I s . showed that the field in which the p:i i:i ~ i t < ■- Bent from Wellington bj Mr. AJnslie were to be Liberated contained approximately fifty millions of the unparasitized "green bugs'' :m per cent being there found, by similar counts, to be parasitized. On May I s parasites from L2 packages, each containing about half ■ bushel of wheat plants, were liberated in one of these fields. N«>w. ■ count similar to thai made before the parasites were introduced was made on .May 23, and this showed thai the percentage of para- sitism in the field in which the experiment was carried out had in creased only to •">. I per cent, while in the field in which no parasites had been liberated it was L9.3 per cent. On Ma\ 27 a similar count Was made, when the percentage of parasitism in the field where the introduction was made «;h 27.1 per cent, while in the check field it was ">■_'.'> per cent. Clearly, under weather conditions favorable for their development, an introduction of these parasites to the extent of million-, carried oul under field conditions, did not indicate enough efficiency to afford any encouragemenl for the use of this measure in the protection of the grain fields of the fanner in case of future attack. With all the artificial introductions of this parasite that were made in the grain field- of Kansas and adjacent States and Territories, there i- no probability that a single bushel of grain was saved therebj or that the United State- harvested one bushel more of grain than it would have harvested had no introduction- <<( parasites been made or attempted. In substantiation of thi- statement it is interesting to note the history of the "green bug' 1 during 1907 throughout North and South Carolina, upward of a thousand mile- from where an\ introduction of parasites had been attempted, excepting two that the writer himself conducted. A considerable amount of ma- terial was -cut from Winston Salem. X. C., «'ti April 20, to B point ■ few miles west of Richmond, Va.. where it was introduced into a small meadow of orchard grass, with no grain field within •"> mile-. [Clr.SS] 14 I Jut even here the effect was uncertain, as the writer had found the parasite present in tliis locality before the introduction was made. In the other case a larger consignment was sent from the same local- ity in North Carolina to Sumter, S. C, to be placed in a field of oats that the writer visited in company with the owner on the 16th of April, when parasites were found in considerable numbers. In this case the owner of the field, writing under date of June 18 and report- ing on the outcome of the experiment, said: I am sorry that the information to lie derived from our experiments with the parasites is so indefinite. It just happened that other conditions probably over- came the aphis before the parasites had time to multiply sufficiently t<> get in their work. About the time that your box was received weather conditions changed somewhat from cool to warmer weather and the Ihilts seemed to dis- appear very rapidly. From the day the bugs disappeared, the oats, the only grain grown, began to improve, and while they will not make a full crop by any means, they are much better than we anticipated when you were here. This is. as the writer personally observed, also the history of the disappearance of the pest in western North Carolina, where both fall wheat and fall oats are grown and where no parasites were intro- duced, but where they were literally swarming on April 20. From all of this it would seem that throughout the greater areas over which this insect becomes injurious it has so far been impos- sible to assist the work in any way. We have apparently been wholly unable to aid the parasites in getting the upper hand. They accom- plished their work earlier in the Carolinas than in the West, but reference to the records of the Weather Bureau will show that the weather conditions as regards temperature were precisely such as to bring this about. The only possibility of accomplishing anything by the artificial use of natural enemies of the "green bug" seems to be in Texas and South Carolina, where the pest get- it- -tart earliest, making its ap- pearance in the fields in spot- of greater or less area in the fall or early winter. If these incipient outbreak- can be stamped out by farm methods, as indicated further on. or by the encouragement of parasites, or if they can be so weakened as to prevent the " green bug " from developing in* such enormous numbers, it will serve to protect the grain crop- not only of these two State-, but of all those to the northward over which the pest ravages in seasons favorable for its development. The Texas Agricultural Experiment Station is con- templating an experiment whereby they hope, by the artificial intro- duction at the proper time of a large number of the natural enemies of the " green bug " into these spots of early infestation, to forestall a future outbreak. If this can be accomplished it will prove of great benefit to the farmers. Whatever the outcome may be, the experi- ment seems worth trying. [Cir L5 DEVELOPMENT \ \i> I \ I 1 i I \ LYSIPHLEBUS 1 1:1 I n I. Although there are seyeral natural enemies of the "green bug," including one recently described l»\ Dr. L. O. Howard aa Aphelinua nigrituH, \ ft ;ill of them seem to be of little importance as compared with the one minute parasitic species, Lysiphlebus tiit',,1. It is this species, or what we are at present terming as snch, that normally holds Toxoptern in check in this country, and so long as it- develop men! and activity arc not obstructed bj adverse meteorological condi- tions it will probably continue to control it. Indeed, so important is this insect and so powerful is it- influence that in i short space of from ten days to two weeks it can overcome a most serious outbreak of Toxoptera, and thus save from destruction vast areas of growing grain. The species winters over in the field in the body of its host. In many cases these parasites, having been prevented from emerging the previous fall In the advenl of cold weather, hibernate as nearly developed or fully developed adult-, ready to emerge when the tem- perature rises to about 56 F. and remain- there for a sufficient length of time. This is clearly shown by the fact that Mr. E. < ). (>. Kelly found hibernating adult- at Leavenworth, Kan-., on November 13. In <»ne lot of 50 dead, parasitized Toxoptera that had been washed or rubbed from the leaves of the young grain and taken from the mud about the wheat plant- on February 28, after the winter was practically over. Mr. Kelh found 17 containing full-grown larvae of the parasite, 12 containing pupa' of a light color, and 21 containing dark-colored pupa', the latter evidently ready to develop promptly with the advent of warm weather. Mi. Kelly, on the same date, also secured a large number of Toxoptera in various stages of development that were hibernating in wheat fields near Leavenworth, Kan-. The weather had been such a- to preclude the possibility that these had been recently parasitized. Yet some of them soon began to -how the yellowish color characteristic of Toxoptera parasitized by Lysiphle- bus, and adult- were afterwards reared from them. This -how- con- clusively that the Lysiphlebus parasites hibernate in advanced -t.i_ of development in the bodies of their host, which they have killed the previous autumn, and also as larvae in those passing the winter from half to fully grown. The female Lysiphlebus i- even more prolific than the female Toxoptera. Mr. Phillip- has found female- which had upward of MX) eggs iii their ovaries, and Mr. Kelly has reared in some cas 206 individuals from a single mother Lysiphlebus. The eggs are lemon-shaped and white. When excessively abundant this parasite will thrust it- ovipositor into old and young aphides of both sexes, including the sexual female even though previously parasitized; and Mi. Phillip- has observed that it will even ovipo-it in the dead bodies [fir. 93] 16 of those that have been killed by fungous attack. When its numbers are not so great it shows more discrimination and seems to prefer half-grown individuals for oviposit ion. This species of Lysiphlebus is parthenogenetic, as was first ob- served by Mr. Phillips at Richmond, Lad., and afterwards more fully elucidated by Messrs. E". (). (i. Kelly and T. D. Urbahns at Welling- ton. Kans. The experimental breedings by Mr. Phillips in ]!»07 indicated that the offspring of virgin female Lysiphlebus were nearly always exclusively males. Tn a series of upward of 80 breeding experiments carried on indoors, in 1908, by Kelly and Urbahns, only 48 gave results of an}' kind. In only four of these were females pro- duced, the other- giving exclusively males. In the 4 exceptional ca-''- the females remained virgin, and all finally gave birth to males alone. 2 with the first generation. 1 with the >econd, and 1 with the third. The mode of procedure was as follows: Starting with a mated female, the females from among her off- spring were isolated, even before emergence. On their appearance these were given Toxoptera reared under cover to preclude parasit- ism; the few females from among the second generation were again isolated in the same manner, the females in all cases being kept un- mated. It was thus found possible to breed a limited number of females parthenogenetically to and including the third generation. Beyond this all offspring were males, this seemingly being the limit. Just why such a large percentage of these experiments should have proved abortive is not clear. The conditions under which they were carried out were of course unnatural but much more protected from the adverse elements of the open field. The e parasitize Toxoptera and adult- secured. This experimenl also was repeated several times. Female individuals of Lysiphlebus were taken from the corn leaf- aphis (Aphis maid is Fitch) in the field and the adull parasites per- mitted to parasitize Toxoptera, from which finally tin- adults emerged. This experiment was repeated several times. Female specimens Lysiphlebus were taken from the cotton or melon aphis (Ap l>'i'i ( Hov. ) from New Mexico and given Toxoptera as a host, the adult parasites develop- ing successfully there- from. Female specimens of Lysiphlebus were taken from A/>Ii>- tin hi in the field and given Toxoptera as a ' , , . i • Much • ".' i red (Oris Inal. • nosl . their onspnng transferred to .1. maidi-radiris, and the next generation transferred hack t<> Toxoptera. Female individual- of Lysiphlebus were taken from I. setaria in the held and allowed to parasitize Toxoptera, their offspring transferred to . I . s< tai ia . the next general ion to Toxoptera, and the following generation to .1. brassicce, from which adults were secured. In many cases those breedings were reversed. The only failure were in attempting to transfer Lysiphlebus issuing from Toxoptera to Chaitophorus and in transferring Lysiphlebus issuing from Toxoptera to Macrosiphum rudbekiat. These experiment- were reversed with the same results. The female goes about, if in grain fields, among the plant-, and when she finds an aphis she quickly throw- her abdomen underneath her body and between her legs and with a springlike motion thrusts her ovipositor int i the body of the aphis (fig. s >. leaving therein a [Cir 18 tiny egg. This egg hatches into a larva in a few days, and the usual position in the body of the "green bug" of the larva up to the time it becomes full-grown is shown in fig. 6, page 4. Up to this time it has fed within the body of the "green bug"' without reaching any of the vital parts, but preventing to a greater or less degree the giving of birth to young. This is an important fact, for, as the parasite seems to prefer partly grown young, it begins to check the increase of the pest before the death of the " green bug" takes place. Mr. Phillips has found that females parasitized at this period of their development do not reproduce for more than a very few da vs. After about six days the larva of the parasite reaches full growth and becomes more active, working its way about within the still living body of its host, which now dies a seemingly terrible death. The motions of the parasitic larva within cause the skin of the "green bug*' to become rotund in shape, as shown in fig. 9; the skin also becomes darker and hardens. Within four days (the life cycle in warm weather occupying about ten day-) the adult Lysiphlebus emerges through a round hole in the dried skin of the " green bug." as shown also in fig. 0. In fields that have been destroyed the leave- become almost covered by their brown bodies, as shown in fig. 7. As stated, many of the " green bugs " are stung by the Lysiphlebus while quite young, and if these develop to winged adults, as the}' do at times in myriads and drift away to distant fields, they carry the parasite with them in their bodies. One of these parasitized winged females is shown in fig. 10. The very act of migration of the " green bug." therefore, brings the parasite, and there is no need of artificial introduction, for if the center from which the " green bug " is migrating has the para- sites, as it always doe-, the latter are of necessity carried by their hosts, and. furthermore, the adult parasites fly with the latter with favoring winds. During strong winds the Lysiphlebus does not use its wings, but crawls about over the plants and probably does not become scattered by gales. But in warm, comparatively still weather the writer has observed both winged " green bugs " and parasites crawling about on the windows of railway coaches many miles away from seriously infested fields of grain. [Cir. 93] Fig. 0. — Dead " green bugs," showing hole from which the matured parasite of Lysiph- lebus trilici emerges. The top figure shows the lid still attached, hut pushed back; the bottom figure shows the parasite emerging. Enlarged. (Original, i 19 EXPERIMENTS IN DESTROYING " liREEN HIT.9 OVER SMALL AREAS. On leaving Washington both Mr. Ainslie and Mr. 1'hillip- were instructed i'> pi ace themselves in the position of ;i farmer whose grain fields were beginning t<> show the presence of the "green bug 11 by small deadening spots, and to leave nothing undone or untried that would seem to afford relief and save the crop. Mr. Ainslie instituted some experiments in the use of a brush drag immers, Ark., and Mr. Phillips carried ou( similar experiments ;.t Hobart, Okla., but in neither case was the measure sufficiently ive to warrant its recommendation. Experiments in rolling infested fields with heavy farm rollers were conducted by 1 »« »t 1 » of these agents, l>m ii was invariably found that this measure was only effective on smooth lands. When the seeding is done with a grain drill, as most of ii is, the plant- gro^ up in the bottoms of slight furrows, and the roller comes I green in contact with the ridges only. lca\ ing the young plant- and their inhabitants almosl wholly untouched. This measure, also, is therefore of little practical value. Mr. Ainslie tried dusting with lime and also with sulphur, bul both substances were ineffective. Both Mr. Ainslie and Mr.Phil lips carried out a series of care fill experiment- in spraying with kerosene emulsion and with whale-oil soapsuds. From these experiments it was found possible to destroy 50 per cent or more of the "green bugs" at an expense of about si per acre. This treatment, of course, is intended for use only where, a- seems to he more usual to the southward, the outbreaks of the pest originate in spots in the field-. Mr. Ainslie also tried covering some of these -pot- with straw and burning it. thus destroying, <^' pourse, both grain and "green bugs." This, too. gave encouraging results, and probably would prove effect- ive if applied earlier in the Season, when the pe-t first begins to appear and the infested -pot- are small. At Hooker. Okla.. Mr. Phillip- tried th» efficiency of plowing these -pot- under, and a- the field in which he was working was isolated and the "green bugs" did not make their way in from without, he was able t<> -how conclusively that such outbreaks, under certain condition-, may he -topped. 20 In summing up these field experiments, then, it is found that these spots may be treated successfully either by plowing under and har- rowing and rolling the surface of the ground, by spreading straw over them and burning, or by treating with a 10 per cent solution of kerosene emulsion. Except in the southernmost regions infested by this pest, however, the greatest difficulty does not arise from these i-olated colonies, which seem to extend outward day after day. hut from the fact that, after their food supply lias become either largely destroyed or the grain too old and tough for them to feed upon, immense swarms of winged adults are produced, and these drift, in general, northward with the advance of the season and infest the grain fields of entire sections of the country much earlier and more completely than would he possihle from the scanty stock natively present. This habit is also seen in the behavior of the pest in its original home in Europe. It may therefore prove that the country north of the Red River may he more or less protected if the pest can be early overcome in northern Texa-. Agricultural methods of control. The fact that the " green bug " in the South originates in spots in the grain iields has been alluded to, and also that from these fields come the vast swarms of winged females that develop and drift over the country, dispersing themselves in uninfected fields. Early sown fields or fields overgrown with volunteer grain seem especially to invite early attack in the more southern localities. "Where these im- mense swarms settle down in a section of country, even the best field- ed' grain may succumb to their attacks. But usually, outside of an extremely limited area, there is a noticeable difference in intensity of attack as between different fields. In Oklahoma and northward, fields that have been late sown or that were pastured during the winter suffered worst and were the first to be destroyed. It has been fre- quently noticed that a field of grain may be totally destroyed, while an adjoining field, though seriously injured, will frequently pmduce a partial crop. An investigation of the history of these fields has invariably shown that the result in the latter case is due to fertile soil. proper cultivation, and seeding at the proper time. It seems to have been almost universally true, outside of the limited area of total destruction, that the best farmed fields have suffered the least. This does not apply alone to wheat, as the writer observed a field of oat- near Hutchinson, Kans., that gave promise of a fair yield, where almost the entire crop would otherwise have been destroyed. The owner of this field, who had been obliged to plow up other field- where the cultural methods had been the same, expressed his opinion [Cir.93] 21 thai ili>' reason the one field escaped the attack <<\ the " green bug i" -i i« -I i mi extent \\:i- that it had been for man} years in alfalfa, only crop, and that ruin, h. en taken from it since alfalfa had b ''ii turned under. He stated that the " gre n bug" was ;ii one time n- abundant in this field as in the ones which he had been obliged to plow under, but that in the one case the plants had withstood the attack better and were in better condition when the "green bugs" were overcome by the parasites, and thus able to start growth anew and \ ield to the oti ner a fair percentage <>f n crop. [n extreme western Kansas a field of 10 acres of oats lying adji to an irrigating ditch, but which had not been irrigated, showed very forcibly the effect of irrigation. Along this irrigation ditch wa ragged border of vigorously growing oats from 10 to 30 or 10 feet in width where the "green bug" had seemingly done no injury. B yond this, where the moisture from the irrigating 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 not until spring; the former was uninjured by "green bugs.'' while the latter was killed. While late sowing in Texas will prob- ably lessen attach in the fall, it i- doubtful if this can be recom- mended north of the Red River. November-sown wheat wa- cer- tainly less affected than others in North Carolina. THE PRE8EN1 " GHEES BUG " -III \ I !"\ IN rill: -"l I ill i:\ -I \ 1 1 -. m w 1. 1909. The situation over the country with reference to a future invasion of this pest, though not alarming, i- sufficiently serious to rendei a word of warning exceedingly appropriate. In widely separated localities from Western North Carolina to eastern New Mexico the insect ha- become sufficiently abundant during March and April to work considerable injury locally. This -how- thai the p<-t ha- re- covered from the severe reverse given it by it- natural enemies in 1907, and that a repetition of the mild winter of 1908 9 and the present cold, backward spring will be almost certain to precipitat more of less disastrous invasion. Of course no one know- what I winter of L909 In and the spring of L910 will be, hut it -tan.!- the grain growers in hand throughout the country south of Virgi Kentucky. Missouri, and Kansas to destroy, a- far a- p all volunteer Grain coming up in the held- during the coming autumn: and where fall oat- are sown, a- i- generally the case throughout I Country, the sowing should he delayed a- late a- possible. The-.' two measures have a tendency t" prevent the pest from becomii oughly established in the grain fields during the autumn months, and H'ir. ;>:;j 22 arc the only measures that can be taken that will have a tendency to ward off an impending invasion. We have found that where serious damage has been done to fields of »rain in late winter and spring- such fields had become seriously infested during the preceding autumn. The carrying out of these measures in the southern portion of the country has a tendency to protect the grain fields farther north, for we have had additional illustration of the fact that winged individuals are. during the spring months, being almost continuously carried northward by the wind. It is somewhat a question as to whether the spring-sown oat- far- ther north would suffer to a less degree if there were no invasion in the South in fields of fall-sown grain, both of oats and wheat. "While it is not possible for an insect to make its way or be carried by the wind from Texas to northern Kansas. Missouri, southern Illi- nois. Indiana, and Ohio, nevertheless continuous breedings to the southward certainly do influence the numbers over this last-mentioned territory. If the farmers of the country, instead of being carried away by the highly colored new-paper reports of the effect of the introduc- tion of a few parasites in their fields, will seek to evade the pest by the destruction of volunteer grain in the fall and late sowing in the extreme South and turn their attention to better farm methods, in- cluding not only cultural methods but by all means rotation of crop-, watching for and stamping out the pest when it first appears in the South in the fall and winter, they will in all probability suffer far les> from destruction of their ci'ops when the next invasion of this pest occurs. Approved : James "Wilson, Secretary of Agricultun . Washington, D. C, April 27, 1909. [Cir. 93] O UNIVERSITY OF FLORIDA 3 1262 09216 4465