Historic, archived document Do not assume content reflects current scientific knowledge, policies, or practices Bulletin No. 16. New Series. U.S. DEPARTMENT OF AGRICULTURE; DIVISION- OF ENTOMB >LOGY. THE HESSIAN FLY IX THE UNITED STATES. I'EKTAKKD UNDER THK DIRECTION OF THE ENTOMOLOGIST, By HERBERT 0SBOBN, Prof e*8or of Zoology and Entomology, Iowa Agricultural College, Ame*, Toica. WASHINGTON: GOVERN mi«:n T pbikting office. 1808. DIVISION OF ENTOMOLOGY. Entomologist: L. O. Howard. Assist. Entomologists: C. L. Marlatt, Th. Pergande, F. H. Chittenden, Frank Benton. Investigators : E. A. Schwarz, H. G. Hubbard, D. W. Coquillett. Assistants: R. S. Clifton, Nathan Banks, F. C. Pratt, Aug. Busck, Otto Heidemann. Artist: Miss L. Sullivan. Bui. No. 16, New Series, Div. of Entomology, Dept. of Agriculture. Frontispiece. •* 1? Vi S ^Q ^i%* \ - ^- s^i?^ **Sf\ " iP^ ^>>7«?r^^^t?sV V r A a L \//2/6. °o — t ? y^ <4-^— - -" ' - • . — I- ' sa °%<^\\j* \\ \^^^^^y^yy^yy^ \ <°Y^k\i MiMMMLsX I^tl hJ? Ife \"° — -K 1 1 at rv J % 6 8 Mr? /~\p 7 M Smm} A. In r 1 i / ■* i- W//J///////' A_ Ik P 1 V i } ! 'vWh / i / ' i ^ ( § ■~-rv -i r \ i / i\ | r //Tv / — "* ) 1 / ! / 0 r~vr~4w-_ ) ~T/l 'Tr i /^ 1 "vizier fa T^~S^a=-y / / """ ■—* *\ — ji \j J 1 mi % / ( i\ \ — y / L / 55/ N-r / / ' / / / )•' \ / 7 "~'e*i:~— — Js y / / ' V/ " — + — °s r » "9 i» m ■g % Bulletin No. 16, New Series. U. S. DEPARTMENT OE AGRICULTURE, DIVISION OF ENTOMOLOGY THE HESSIAN FLY IX THE EXITED STATES. PREPARED UNDER THE DIRECTION OF THE ENTOMOLOGIST, By HERBERT OSBORN, Prof essor of Zoology and Entomology, Iowa Agricultural College, Ames, Iowa. WASHINGTON: GOVERNMENT PRINTING OFFICE, 18 9 8. LETTER OF TRANSMITTAL. r. S. Department of Agriculture. Division of Entomology, Washington, 1). C. September 1, 1- -. Sir: In the letter of introduction to Bulletin Xo. 15. New Series. I mentioned tbe fact that the chinch bug was one of the most dangerous of the destructive insects of North America, and that the necessity for a complete and timely bulletin for distribution by this Department was emphasized by the almost daily demand for information. The same condition of affairs exists regarding the Hessian fly, and the accompany- ing manuscript, which has been prepared by Herbert O shorn, entomol- ogist of the Agricultural Experiment Station at Ames, Iowa, and pro- fessor of entomology in the Iowa State Agricultural College, has been prepared by your direction and under the writer's supervision, to fill the want. I recommend its publication as Bulletin Xo. 1<>. New Series. Respectfully. L. O. Howard, Hon. James Wilson, Entomologist. Secretary of Agriculture CONTEXTS. Paere Introduction 7 Importance and early history 7 Original habitat of Hessian fly 9 Distribution 10 Means of distribution 11 Outbreaks in spring- wheat regions in Northwestern States 13 Description and life history 14 Development 17 Annual generations 18 Food plants 25 Effect upon the plants 27 Natural enemies of the Hessian lly 27 Primary parasites 28 Merisus destructor 31 Bteotomns subapterus 32 Pteronialns pallipes 33 Eupelmus allynii 31 Platygaster herrickii .'. 35 Polygnotns hiemalis 35 Lygocerns triticum 36 Secondary parasites 36 Tetrastichus productus 36 Tetrastichus ca rinatus : 37 Utilization of parasites 37 Introduction of Entedon epigonus 38 Other natural enemies 41 Nematode worms 41 Thrips 11 Remedies 41 Burning the stubble Ii' The plowing under of stubble 43 Destruction of volunteer wheat 43 Planting of decoy strips 43 Early or late sowing of tall wheat II Intermittent wheat culture 45 Pasturing with sheep 4"> Rolling 4t! Mowing LG Selection of resistant varieties <>f wheat 46 Use of insecticides IT Combination of remedial measures 48 Bibliography L8 Explanation of plates 58 B ILLUSTRATIONS Page. Map showing distribution of Hessian fly in America Frontispiece. Plate I. Wheat plant showing injuries by Hessian fly; also stages in devel- opment of the insect 58 II. Different views of Hessian fly at different stages; also parts enlarged 58 Fig. 1. Cecidomyia destructor; genitalia 15 2. Merisus destructor 31 3. Bteotomus subapterus 32 4. Eupelmus allynii, male 34 5. Eupelmus allynii, female 34 6. Platygaster herrickii 35 7. Tetrastichus productus 37 8. Entedon epigonus 40 6 THE HESSIAN FLY IN THE UNITED STATES. INTRODUCTION. It is now seventeen years since any comprehensive treatise on the Hessian fly in America has been published. In the meantime so many important facts have been learned concerning the life history, food habits, and parasitic enemies of this important pest that such a treatise is urgently demanded. While the main object in such a review is the bringing together of these recent contributions with the important deductions with regard to treatment which follow, the fact that the elaborate essays by Drs. Fitch and Packard, so exhaustive for their time, are inaccessible to a great majority of farmers and even to many students, is a sufficient reason to present the details known concerning this insect. In the following presentation the attempt has been to condense this information into as compact form as possible and to devote the greater part of the space to the questions having most practical importance and to facts giving the essential basis for remedial measures. In pre- paring the work the writer has been indebted to the exhaustive papers by Fitch (30)* and Packard (90) and, for recent contributions, particu- larly to the important papers by Forbes (34-39), Webster (137), Linde- mann (60), and MarchaJ (71). A list of the more important articles referring to this insect is given at the end of the paper, and will indicate the literature available, and avoid the necessity of too frequent references in the text. I am indebted to Dr. L. O. Howard for many notes and to Profs. S. A. Forbes and F. M. Webster for material. IMPORTANCE AND EARLY HISTORY. The Hessian fly probably ranks next to the chinch bug as a farm pest in the United States, and its ravages in other countries have long been known and appreciated. While its first scientific description was by Thomas Say in 1817, it had been for many years recognized as a pest in wheat and had received in this country the popular name of Hessian flyin the belief that it had been introduced by Hessian soldiers during the war of the Revolution. This belief, as we shall see later, seems to * The numbers after authors" names correspond to numbers in a bibliographical list which is appended. 7 8 THE HESSIAN FLY IN THE UNITED STATES. have been well founded, for while absolute proof of introduction at that particular time and place is wanting, the evidence all goes to show that the insect was introduced from Europe at very nearly that period, and it evidently must have been brought in straw used for packing or baling. Dr. Fitch gives an exhaustive summary of the early appearances and spread of the insect from the point where first observed. These indi- cate a spread from Long Island into adjacent territory at a rate approxi- mating 20 miles each year, and Packard has compiled a detailed table showing the time of appearance of the pest in each of the States where it is known to occur. The first scientific description by Say (117) in 1817 is rather exceptional, especially for the scientific descriptions of that time, in that it contains a description of the larvre as well as of the adult forms, some details of life history, and remarks on its economic importance. This shows clearly how fully its injuries must have been appreciated at the time, a recognition which was emphasized in its spe- cific name, destructor. Say's description and account must, however, have had limited pub- licity, for years later there appeared in no less prominent a journal than Silliman's American Journal of Science an article by a Dr. Muse which purported to give a true account of the pest, but which contains many serious errors, the insect being referred to the Aphides, and the author evidently unaware of the more careful description and reference of Say. The article, however, contains some important details of life history and emphasizes the importance of destroying volunteer wheat in stack yards as a measure of control. Dr. Fitch's elaborate monograph appeared in 1847 and the articles by Dr. Packard in 1878 and 1880. At about this time, between the years 1878 and 1887, there occurred a somewhat lengthy discussion between Dr. H. A. Hagen (16-47) and Prof. C. V. Eiley (108-109) as to whether this pest is of native or for- eign origin, but no economic question was involved and it is unneces- sary to discuss their papers here. During the years 1887 to 1890 Professor Forbes, State entomologist of Illinois, devoted much of the effort of his office to a study of this pest, and many interesting and valuable facts were gathered concern- ing the life-history limits, especially the midsummer condition of the insect. The important point was determined that there may be three or even four broods in a year, dependent upon climatic or food conditions. Prof. F. M. Webster has contributed a number of observations pub- lished in experiment station bulletins of Ohio and Indiana and in Insect Life. In other countries the insect has received of late years considerable attention. On its appearance in England it was studied by Miss Ormerod (84-85) and by Messrs. Enoch (25-26) and Whitehead (140). In 1887 Prof. K. Lindemann (60), of Moscow, made a careful study ORIGINAL HABITAT. 9 of its distribution, injuries, and habits in Russia, determining particu- larly the variations of brood in different parts of the country, the effect of climate, and of limiting its food plants to wheat, rye. and barley. An important recent contribution has been made by Dr. Paul Mar- chal (71), whose conclusions we shall have frequent occasion to use. He has determined that there may be as high as six broods per year; that the insect is greatly influenced by climatic conditions, has sepa- rated a distinct species affecting' oats, and added greatly to our knowl- edge of the parasites. In 1897 Prof. W. M. Schoyen,* the official entomologist of Norway, discussed its appearance in that country, pointing out that it was responsible for considerable damage, and showing that it had a wider distribution there than had been generally credited to it. Still later, Dr. M. Paspelow (91), of Moscow, has added further details in determining the life history of the species and its habits in central Russia. ORIGINAL HABITAT OF HESSIAN FLY. Notwithstanding all the effort that has been devoted to determining the original home of the Hessian fly. we are still in the dark as to its exact original habitat and the exact time of its introduction into America. Two difficulties which are well-nigh insurmountable must always obstruct such precise determinations. The earlier accounts, which might be interpreted as applying to this species, are all too vague to permit one to say absolutely that they do so apply, and no distinctive name, common or technical, is available to trace the species prior to 1778. The name •• Hessian fly" was first used for the species after its appear- ance in ]Sew York in 1778. and presumably on the ground that its intro- duction was attributed to the Hessian soldiers, although, as has been suggested by Ilagen. such a name might have been applied simply as a result of the bitter feeling existing against these invaders, and which sought a vent in transferring their name to the detestable pests that were ravaging the wheat fields. The fact that it is con lined so strictly to wheat, rye. and barley, as food plants, should lead as to think that it has been associated with these as food plants from prehistoric times and to look for its source in the locality where these were indigenous. Inasmuch as this is a ques- tion impossible of absolute determination, although authorities gener- ally refer their origin to western Asia, we have still a doubt: but. so far as America is concerned, we ma\ reasonably conclude that as the hosts are introduced plants the Hessian fly is an introduced ins It seems unnecessary here to revive the controversy as to the intro- duction of this species, in view of the exhaustive papers by Professors Hagen and Riley and the evidence by the latter that all supposed Beretning om Skadeinsektei og Plantesygdomme, L896, p. s. Kristiam... - 10 THE HESSIAN FLY IN THE UNITED STATES. references to the Hessian fly before 1776 must in reality have referred to other species. Those interested will find full details in the papers cited in the bibliography. DISTRIBUTION. At present the Hessian fly has a very wide distribution throughout the wheat-growing region of Europe and America. There is evidence of its having existed probably from prehistoric time in the countries of southern Europe adjacent to the Mediterranean Sea, and, as has been stated elsewhere, great probability that it has followed its natural food plant (wheat) from the supposed original habitat of that cereal in west- ern Asia. Its introduction into America has already been mentioned, and we need srate here only those facts concerning its distribution throughout the United States that are of importance in connection with the wheat industry. Its spread in this country from about the year 1776 was for a number of years at a pretty uniform rate of prog- ress until it occupied the wheat-growing district of the eastern United States. Following this, its distribution quite naturally followed the expansion of the wheat district associated with the development and settlement of the Mississippi Valley. Its eastward distribution seems to have been more gradual than the westward, a recent record placing its extreme limit in Maine, at Bangor. Southward it has gone as far as the northern part of South Carolina, and in its extreme southern limit in Texas it reaches nearly to the Gulf. Westward it occurs throughout a considerable part of Kansas, the eastern part of Nebraska, and northward, according to Webster, it has been found in North Dakota, and records furnished by Dr. Howard ])lace it at Clinton, Big- stone County, and Barrett, Grant County, Minn. (See inap, frontispiece.) On the Pacific coast it has been recorded for the territory adjacent to San Francisco by Koebele (55), and Professor Woodworth (141) dis- cusses its occurrence and variations in the wheat fields of the experiment station at Berkeley. An article by Mr. A. Gains (-41), entitled " Potato bug and Hessian fly," in the Oregon Naturalist for January, 1896, would indicate that it has appeared in Oregon, but the article is not at hand for a determination of the locality. Professor Piper, of the Washington Agricultural College, states that the Hessian fly is as yet unknown in Washington, although they are in fear of its introduction. Professor Aldrich, of the University of Idaho, says that it has not appeared in that State. From this distribution it may be concluded that the Hessian fly has practically the same distribution as its food plants except for the northern limit, where conditions seem to interfere with the successful existence of the insect. In Germany the Hessian fly has attracted frequent attention, but it appears to be confined more to the southern provinces and to be less noticed, or at least not often destructive in the north. Liudemann (60) credits it to Silesia, Posen, Pomerania, Bavaria, and Wurtemburg. MEANS OF DISTRIBUTION. 11 Tn Austria-Hungary it is credited to Hungary, Carinthia, I stria, Moravia, Bohemia, " Saehsen Goburg.* In Italy it has been located at Brindisi and Naples. In Russia Lindemann states that it has a very wide distribution. Through his own researches and through numerous correspondents who furnished him material he located it in thirty-six different provinces, as follows: Bessarabia, Vladimir, Vologda, Volhynia, Kursk, Mohilev, Moscow, Nischni Novgorod, Samara, Saratov, Simbursk, Smolensk, Voronesh, territory of Don Cossacks, Eketerinoslav, Kazan, Kaluga. Kiev, Kostroma, territory of Kuban Cossacks, Novgorod, Orel, Penza, Podolia, Poltava, Pskov, Perm, Riazan, Stavropol, Tambov, Toula, Kharkov, Kherson, Tschernigov, Estland, Yaroslav. In Norway Schoyen reports it as occurring at Hole, Kingerike, and points near Ohristiania. In England the Hessian fly first appeared in 1886 in Herefordshire, Essex, and at other points. •In France the Hessian fly lias been particularly destructive in Vendee, as recorded by Marchal (71), and it has also been credited to the province of Isere. Dana recorded its occurrence at Toulon. So far there seems to be no record for Belgium, Holland, Denmark, or Sweden, although there would be good reason to suppose its possible occurrence in these countries, as also in Spain (recorded by Dana in the Island of Minorca) and in Portugal, where no observations seem to have been made. In quite recent years it has been introduced into New Zealand, as recorded in the following note from Insect Life (Vol. I, p. 32): The Hessian fly halfway round lite world — The Hessian fly, Cecidomyia destructor, has reached New Zealand. The March 1888 number of the New Zealand Fanner reports it from four different farms in the Rangitikei district, one of these being at Belle- vue, near Marton, a town 33 miles southeast of Wanganui, in the Statu of Wellington. MEANS OF DISTRIBUTION. The powers of flight possessed by the Hessian fly are sufficient to provide for its ready dispersal over limited areas, and where there are continuous or slightly separated plantings of wheat, rye. or barley no other means of dispersal need be sought. This natural spread was estimated by Fitch to be at the rate of about 20 miles per year in the vicinity of eastern New York, based on its exten- sion from the center on Long Island, where it was first observed and from which it spread in all directions. This rate would seem to be as high as is admissible from purely natural means, as with plants at hand for deposition of eggs there is little tendency on the part of the insect to leave the held where it emerges, especially for the autumn brood. In the local transfer of straw, however, there is opportunity for some fur- ther dispersal which might supplement the flight of the insect in slight degree. 12 THE HESSIAN FLY IN THE UNITED STATES. The only other means of distribution, and the only one which seems a possible basis for its transportation to distant regions, is by the car- riage of straw containing the puparia, or "flaxseeds," as they are called. Under ordinary conditions it is evident that this straw must be transported during the summer-resting period of the insect and that puparia retaining their vitality must, in the new location, be brought into proper situations to permit the development of pupa* and the emergence of adults. The winter "flax seeds," being contained within the sheaths of growing plants and below the surface of the ground, could not furnish a means of dispersal, as at that time the only means of distribution would be the shipment of growing plants and their transplanting in a new locality, a process certainly not to be thought of as a probable source of dispersal. With ordinary development of the summer "flax-seeds" there would appear to be little chance of scattering the insect in straw, especially since the great majority of these must be in the stubble remaining in the field where they grew. It has been proved, however, that the puparia may retain their vitality under certain conditions for long periods of time, and certainly those which may be high enough to be taken from the field with the straw would find most favorable conditions for the retardation of their devel- opment so that they might be ready for the completion of their cycle when the straw is scattered on moist ground in some other and possi- bly far-distant locality. The carriage, then, of puparia in straw used for packing and shipped from point to point would seem to be the only means available for the wide dispersion of the insect, and it is to this method that its dispersal is generally credited. The introduction into the United States near Xew York City has as its most probable founda- tion the straw used as bedding by the Hessian troops landed during 1776 and 1777, and while there is lacking positive evidence that the insect existed at the point of their starting or even of embarkation, the source of straw they might have used and scattered after landing may have been in some infested locality, while the argument that the troops arrived at a time of year when the insect could not have been trans- ported disappears when we recognize the possibilities of retardation elsewhere discussed. The recent introduction of the insect into New Zealand is believed to have been due to the scattering of straw used in the packing of merchandise, and while the exact time seems unknown, the certainty that the introduction must have been in some such manner shows how important is the destruction of such packing material in any country where the insect is not present and where grain growing is of any consequence. Careful attention to this point may serve to postpone, at least for some time, the dispersal of the insect in the wheat-growing sections of Oregon, Idaho, Washington, and other points, especially where wheat culture is carried on in isolated districts separated from other wheat regions by extended ranges of mountains or stretches of arid land. OUTBREAKS IN NORTHWEST. 13 OUTBREAKS IN SPRING- WHEAT REGIONS IN NORTHWESTERN STATES. In 1896 there was a considerable outbreak of the Hessian fly in the spring-wheat region of northern Iowa, southern .Minnesota, and prob- ably a part of South Dakota. Professor Lugger (69) in Minnesota and the writer (89) in Iowa called attention to these occurrences in bulletins on the insect outbreaks of the year, and both noted the great abundance of parasites in the material received. The presence of the latter pre- cluded the rearing of adults, but the characteristics of the attack, the distinctive features of the larvae and puparia, and the fact that the typical parasites of the Hessian fly were reared leaves no question as to the species. In the summer of 1897 the writer traveled over a considerable part of northwest Iowa and touched on southwestern Minnesota and eastern South Dakota with a view to examining the extent of injury, nature of the attacks, and so far as possible to study the conditions affecting the Hessian-fly outbreaks in this region. In nearly all the localities visited the injuries of the previous year had not been repeated, or the insect was present in such limited numbers as to cause very little damage and attract no attention from farmers. In a number of the fields in the vicinity of Alta and Storm Lake, in Buena Vista County, there was a small percentage of injury, possibly 1 to 2 per cent, it being possible to find occasional stalks of wheat broken down in the manner characteristic of the Hessian ti}' and with larvae or puparia in the usual position under the leaf sheath. On farms where the year before there had been considerable injury and the crop had, following my suggestion, been early plowed under, there was no trace of Hessian fly even in large fields. In Lyon County farmers stated that there had been injury in 1896, their description of the injury leaving scarcely a doubt as to the author, but no traces of Hessian fly were to be found during my stay in the count}-. I was informed that in the vicinity of Sioux Falls, S. Dak., there were several farms that had suffered the year previous, but here. too, I could find no evidences of the presence of the insect, nor could 1 hear of any injury for the season of 1897. Examinations of fields in the vicinity of Cherokee, and Sioux City. Iowa, and Yankton, S. Dak., resulted in finding no infested fields, nor did I learn of any serious injury from Hessian fly theretofore. A little later in the season (July 30), I received word from Mr. 11. E. Crosby, Alta, Iowa, that he had examined several tields in that vicinity and found but few in which the insect was not present. Without stating definitely the extent of the damage, he leaves me to infer that the amount of injury was about the same as noted at the time I was there. I also received a communication from Mr. M. A. Marley, oi' River Sioux, in Harrison County, close to the Missouri River, contain- ing reports of injuries in the wheat tields at that point and from his description there was evidently a greater amount of damage than in 14 THE HESSIAN FLY IN THE UNITED STATES. the localities farther north. In general, for the territory lying north of 42 J° north latitude west of the Mississippi River, the insect is practi- cally unknown to the majority of the iarniers and no account is taken of it in their calculations on the wheat crop. The conclusion seems warranted that while the Hessian fly may sur- vive in this region in small numbers, and occasionally so multiply as to attract attention in limited localities, that the conditions for its increase are too unfavorable for it to multiply greatly. These conditions would seem to be the general occurrence of a considerable period of dry weather in midsummer and autumn, and absence of food plants, thus forcing the insect to become single brooded. This greatly reduces its power of multiplication, exposes it to destruction by desiccation, or starvation, and the greater activity of parasites. If the insect ever becomes troublesome in this region it would seem a most simple matter to con- trol it by simple adaptation of proper measures, especially the resort to burning the stubble and early plowing under, discussed in detail in the chapter on remedies. From all that could be learned, and from the previous history of the insect in this region, it seems to me fair to conclude that the Hessian fly is not a menace to the wheat industry of this region, as was feared when its extension into this territory was first noted. The natural conditions prevailing in the region, with the ready multiplication of parasites, will serve to keep it in check during ordinary years. If farmers will only recognize the characteristic breaking down of wheat due to its presence, and in years when this is noted proceed to burn the stubble or plow it under and roll, they can prevent its multiplica tion and the possible damage that might follow in the succeeding year. DESCRIPTION AND LIFE HISTORY. The descriptions of the Hessian fly have been quite numerous, and some of them given with considerable accuracy of detail, so that there should be little difficulty in distinguishing the species from related forms. In many cases it is, however, deficient in characters which defi- nitely separate it from the most closely related forms. It is clearly of no little importance to have a positive basis for the separation of the insect from related forms, particularly those which occur in closely related plants, and especially if they agree with it in the character of the puparia. The adult insect (Plates I and II), like other members of the family Cecidoinyidse, to which it belongs, is a small, guat-like, two-winged creature, about half as large as a common mosquito, which it resembles in form. The female is about one-tenth of an inch long (2.5 mm.), of a dark color, the abdomen in freshly issued specimens appearing red, with, black patches or bands of black, and with red bands at the articula- tions, depending upon the amount of distension. DESCRIPTION AND LIFE HISTORY. 15 The head is small, somewhat contracted dorsally, with a row of bris- tles on the posterior. margin; eyes black, antennae long, black, semi- pallid, usually of 17 joints, this number varying in different specimens from 16 to 18; joints rather short, cylindrical, and joined by a very short, small filament, each provided with an irregular whorl of fine hairs. The thorax has two rows of long backwardly curving bristles near the median line, and a patch on either side. The legs are long and delicate, with a dense covering of blackish scales dorsally, the basal joint of the tarsus very short. The wings appear smoky black from scaly covering, but the scales are very narrow, not broad, as those on the body and legs. The halteres are yellowish, with broad blackish scales covering the outer part, the basal part naked, except a narrow border. The abdomen is long, ovate when contracted, but capable of great extension for the terminal segments. The ovipositor (fig. 1, a) is com- pressed, cylindric, very minutely hairy, with an oval lobe at the extremity, which is minutely striate and more densely hairy than the basal portion. The male is smaller, more slender, and appears darker than the female. The antenna' are longer, the joints, more distinct, 17 to 19 in number or 16 to 20 for ex- tremes, and connected by a much longer filament, and the whorl of hairs is much more prominent, the hairs longer, and arranged in a more perfect verticil. The outer claspers (fig. 1, b) are very robust and apparently loosely connected to the abdomen. The basal part is heavy, with numerous strong tubercles and a few scat- tered bristles. The distal part is, when at rest, at nearly right angles with the basal part, narrower, faintly tuberculate, very minutely hairy. and with a strong claw like tooth at end. The inner claspers (fig. 1. c) are broad, oval, minutely hairy, the posterior margin with a row of tine hairs, and toward the apex three or four blunt teeth. Between the claspers is a strong chitinous process, and anterior and dorsal to them two pairs of finely haired, slender, finger-like processes directed dor sally; anterior to these, and forming the posterior border of the abdom inal segment, is a prominent hairy rim, broken at the median line dorsally. The egg is characterized as about one half millimeter long, cylindric, roundingly pointed at the ends, glossy translucent, slightly reddish in color, and becoming deeper red with development. The larva has usually been described without reference to distinct stages, but Marchal (71) has defined three forms, the first ol' which, just issued from the egg, is capable of locomotion and travels from the point «- 6 c Fig. 1. — Cecidomyia destructor: a, ovipositor of fe- male; b, outer claspers of male: c, inner claspers of male (origiual). 16 THE HESSIAN FLY IN THE UNITED STATES. of hatching to the location under the sheath. Its size is slightly larger than the egg from which it hatches, and it presents thirteen segments, of which the first constitutes the head. It is distinguished from the second form principally by the presence of two triangular, fleshy, ear- like appendages, lightly incurved below on each side, and comparable to tentacles; the anterior buccal border is trilobed, and beneath is the mouth in the form of a small triangular opening. The last segment is lightly emarginate posteriorly, and each of the two lobes thus formed carries four setiform papillae. The second larval form, which is fixed to the stalk and is the one usually described by writers, is, when grown, 3 millimeters long by a little less than 1 millimeter wide, of a flattened, cylindrical form, and so transparent that the internal organs are easily seen. There are twelve segments beside the head, which is small and more or less retracted. The anterior end is narrowed and usually somewhat bent. The posterior end tapers, is bluntly rounded, and with two lobes on the posterior segment. The segments are but slightly indicated exter- nally, but are plainly marked by the internal masses of adipose tissue arranged in series along each side, as well as the respiratory organs, the spiracles being plainly visible under the microscope as minute openings in rounded yellowish tubercles (Plate II Be). -The mouth- parts are indistinct (Plate II B&), and the sternal spatule is, until the larva is ready to pass to the next form, either entirely wanting or inconspicuous. The digestive, nervous, tracheary, and adipose systems, which are very plainly visible in the larvae, have been described in particular by Marchal, whose paper should be studied for details in this regard. The third larval form — that inclosed within the puparium — is dis- tinguished especially by the development of the sternal spatule or " breastbone." In other respects there is little difference anatomically from the preceding, but it is a quiescent not a feeding stage. The sternal spatule, which becomes conspicuous at this stage, is a horny structure projecting from between the first and second body segments, and is provided at its anterior extremity with two pointed spurs. The bifurcate form of this spatule is used by Marchal (71) to separate this species from avence, in which there is but one point. The use of this organ, which projects forward under the first segment and rests against its ventral surface, has been a subject of considerable discussion. The explanation which is best supported was proposed by Enock and is sustained by Marchal (71). This is that the spatule is used by the larva to reverse its position in the puparium so that, whereas the larva rests at first with its head downward and toward the roots of the plant, it rests, after turning, with its head upward and toward the upper part of the plant, a position which has obvious advantages when Ave consider the direction in which the pupa and imago must escape. The pupa when first issued from the puparium is white, but acquires DEVELOPMENT. 17 a rosy tint. It presents a very delicate appearance, the pupal being extremely thin. On the front is a prominent pointed chitinous rostrum of a brown color, the function of which is considered to be the cutting of the puparium to permit the exclusion of the papa. Above the origin of the antenme are two horns called by M arena] the cephalic horns and posterior to them two larger, curved, thoracic horns (Plate II C.) which contain, according to Marchal, trunks of the tracheal y system. DEVELOPMENT. The deposition of the eggs has been described with great care by Herrick (50), as follows: The eggs are laid in the long creases or furrows «>f the upper surface of the haves of the young wheat plant. While depositing her eggs, the insert stands with her head toward the point or extremity of the leaf, and ar various distances between the point and where the leaf joins and surrounds the stalk. The number found on a Bingle leaf varies from a single eg^ up to thirty or even more. The egg is about a fiftieth of an inch long, cylindrical, rounded at the ends, glossy and translucent, of a pale-red color, becoming in a few hours irregularly spotted with deeper red. Between its exclusion and its hatching, these red spots are continually changing in number, size, and position; and somtimes nearly all di>appear. A little while before hatching, two lateral rows of opaque white spots, about ten in number, can be M-en in eari- 24 THE HESSIAN FLY IN THE UNITED STATES. mating the damage as high as 25 per cent in some places, and at from 5 to 10 per cent of the entire crop, he says : In Southern States this insect is double brooded and hibernates in the "flaxseed" stage in winter wheat, volunteer wheat, and in other plants, including, possibly, some of the larger grasses. But this is their habit only in the South. Here the insect must lead a different sort of a life, for instead of being double brooded it is single brooded. This could be expected from the conditions prevailing in the greater part of the State, but we have had no proofs thus far. Of all the infested stalks gathered as soon as the injury became visible, not a single Hessian fly has issued, and numerous puparia (the " flaxseed" stage) are still unchanged in the breeding cages. This assuredly seems to indicate that the flies do not issue during the autumn, as they do farther South, but remain in the culm until spring. Another proof, though not a safe one to depend upon, is the fact that no larv* or puparia could be found in the volunteer plants of wheat growing near fields that had been badly infested. The many puparia kept in properly constructed breeding cages gave forth, however, very large numbers of parasites. Three different species were raised, and in such numbers that in some cases nearly all the Hessian flies had been destroyed in the puparia. For all of the material collected in 1897 the failure to produce adults was fully as manifest, and it seems to me that in many cases the retar- dation amounted simply to the death of the insect. Even when not producing parasites the puparia have failed to produce adults, and it would seem that the process of desiccation had gone to the point of destruction before conditions permitted the development of the insect. In many cases the puparia were shriveled and gave evidence of incom- plete development, and I suspect that in many cases the straw had ripened and cut off their nutriment so early as to prevent maturity. This might easily occur if the adults emerged and deposited eggs a little late in spring. The occurrence of a cold, late spring would here favor the retardation of emergence of the adults and allow such maturity of the wheat as to largely prevent development of larva?, and as such conditions are of frequent recurrence in this region there would seem to be in this a natural check on the species that may be sufficient in general to limit the insect to harmless numbers. I have, on the other hand, seen the early maturity of Hessian flies in breeding cages ; as infested wheat sent me by Professor Webster during the past winter produced flies emerging from March 4 to 7, and speci- mens of puparia kept in an office room before being sent to me emerged still earlier. With the amount of evidence that has now accumulated there seems no longer any possibility of questioning the acceleration and retardation of the insect for conditions of latitude and of climatic variation within the same locality. Further, it appears to me that we have sufficient evidence to conclude that the conditions affecting this acceleration or retardation are temperature and moisture, and that with a knowledge of these conditions it should become possible for the intelligent culti- vator to foresee the occurrence or absence of the pest to such an extent as to adapt his agriculture to the avoidance of their injury. The methods for such adaptation naturally fall under the discussion of remedies. PEST OF WHEAT, BYE, BARLEY, ETC. 25 FOOD PLANTS, The question of the food plants of the Hessian fly presents a par- ticularly important one. for the possibility of its survival in a district where its normal food plants are not grown during one or two ye or of its living for one or two broods on grasses, so as to adapt itself better to crop conditions of cereals, all depend on whether it can exist on other than its principal known host plants. From early times the Hessian fly has been recognized as a pest of wheat, rye. and barley, and most of the early literature considered it simply as a pest of these crops. Some years sinee. however, the point was made that it could live on various grass plants, and some observa- tions by careful observers tended to support such a view. The following extracts from reports on this point will show the nature of the testimony submitted: The Hessian fly attacking grasses in California. — According to Lindemann. the He— sian fly has been found upon Phleum pratense and Agropyrnm repens in Russia, but up to the present year it had not heeu recorded as occurring in this country upon any wild grasses. "We are'in position now, however, to add four grasses to the list of its food pbrits in the United States. In 1887 Mr. Koehele sent us from Alameda, CaL, specimens of Elymu8 americanus and of a species of Agrostis which bore pnparia supposed to he those of this insect. The adults were not reared, however, and tin- question remained unsettled. On page 71 of the current volume we published, under the head of "California notes." a letter from Mr. Koehele. in which he mentioned finding Hessian fly pnparia in a grass in the Santa Cruz Mountains. This fact was called in <|".es- tion by Mr. James Fletcher, and we wrote Mr. Koehele for specimens and received from him Bromus ciUatus and a species of Agropyrum. both carrying pnparia. These were very much like the normal pnparia of the Hessian lly. but were smoother and more plump, showing little trace of the longitudinal ridges. Plies were obtained from these, and others also obtained from the grasses were sent on by Mr. Koehele; and. alter comparing these very carefully with specimens from wheat from different parts of the country, we find they are not to be separated, although from the speci- mens first received a variation in the number of the antenna] joints raised some doubts. We find, however, alter the examination of nearly 100 specimens of individ- uals reared from wheat from various sections that the joints of the antennae in the male range from 16 to 20 and in the female from lii to l!'. * On the other hand, we have, aside from all the early history of the pest, a number of positive records which strongly confirm the view that the insect never occurs normally or survives on other plants than wheat, barley, and rye, which arc in closely related genera. In 1890 Professor Forbes undertook to prove experimentally whether the Hessian fly could develop on other plants than its usual hosts, and to this end introduced flies into cages with timothy, redtop [Agrostis vulgaris), bine grass (Poa pratensis .orchard grass Dactylis glomerata . and foxtail (Setaria), in all cases without result, though in some « active adults had every opportunity to deposit eggs. While Professor Forbes gives this result only negative value, it is certain that it gives no support to the idea of a variety of food plants, and. taken with the • Insect Life, Vol, III, p. 306. 26 THE HESSIAN FLY IN THE UNITED STATES. other evidence now available, would seem to favor the conclusion that wheat, rye, and barley are the normal and only food plants of the species. With regard to the identity of the specimens obtained from Elymus in California, Dr. Howard considered there was some doubt, and sub- mitted the material to Mr. Theo. Pergande for critical comparison, the result of which is presented in the following record: 4855. Cecidomyid on Elymus americanus, not the Hessian fly. — Examined and com- pared larvae and imagos of the Cecidomyid from Koebele (4855) with those of Ceei- domyia destructor with the following results : The differences in the imagos of both are very small, though I find in the male of the Hessian fly that the inner pair of claspers are provided, near or close to the apex of the posterior edge, with four or five stout and blunt teeth, and that the large basal piece of the external claspers bears, near the lower external edge, a number of stout, conical, black tubercles. In 4855 the teeth of the inner claspers are wanting, while the whole posterior edge is strongly serrate. The tubercles of the external claspers are rather small, color- less, and difficult to be seen. The hairs of the genital organs and the tubercles from which they arise are also more prominent in the Hessian fly than in 4855. Of the larvse of the Hessian fly we have only such as were taken from {he pupa- riurn. Whether or not these materially differ from those before pupation I am unable to say, though the figure in Packard's Bulletin No. 4 indicates that there are two tubercles at the end of the body, whereas in 4855 this segment bears four large and acutely pointed processes, entirely unlike those of the Hessian fly. These dif- ferences in adult and larvae seem to be of enough importance to consider 4855 to be a different species.* Professor Lindemann, in 1887, believed he had sufficient ground to declare that the Hessian fly develops only in wheat, rye, or barley, never in other grasses, this conclusion being based on extended and careful observations in fields where a variety of grasses occurred. Later (in 188S) he seems to have felt it necessary to revise this opin- ion, and records having larvae sent to him that were found upon tim- othy (Phleum pratense) and Triticam repens, and also on account of the record by Mr. C. H. Whitehead of the occurrence of the puparium on Rolcus lanatus. Marchal, in reviewing this question, suggests that Lindemann has given unnecessary weight to these observations, and that even if com- parisons with larvae or adults showed close similarity, it would still be necessary to prove their identity from biologic criteria. Uis own results convinced him of the close limitation of C. destructor to wheat, rye, and barley, and he separates the species avenae finally on careful experimentation, that proved the inability of destructor to survive on oats or of avenae to live on wheat. There seems strong reason, in view of the evidence produced by Mar- chal and the differences indicated by Pergande, to adopt as final the position taken by Marchal. While precise experimental evidence in * Department record made by Theo. Pergande. NATURAL ENEMIES. 27 each case may be desirable, we have the general fact that throughout an immense territory in the United States where wheat is grown in close proximity to oats, timothy, and other grasses, we have never had a record'Of the Hessian fly's attack upon these crops. In any deductions, therefore, relating to the control of the Hessian fly, it may be considered for all practical purposes that the insect lives only on wheat, rye, or barley, and will not perpetuate itself on other plants. EFFECT UPON THE PLANTS. The attacks of the Hessian fly upon the plants produce very char- acteristic effects, generally so distinctive that the appearance of a field will at once indicate to a practiced eye the presence of the pest. The effects differ with the season, perhaps, more properly, with the stage of growth of the wheat plant at the time of attack. In autumn the eggs are laid upon the early appearing leaves and the passage of the larvae down the sheath carries them down to or below the surface of the ground, often very near to the root itself. Here their presence causes more or less swelling of the base of leaf and culm, scarcely enough to be counted a gall formation, but the immediate effect seems to be a stimulus at the point of attack. Indeed, as Webster has pointed out, the affected plants present a darker green color, which has been recognized by farmers as indicative of Hessian fly attack, this color to be followed later by a brownish and then a yellowish color for the infested tillers. If the plant is attacked early and fails to tiller, the result is death of the whole plant; if tillers have already formed, the larva' may enter but one or part of them, and the others may develop into healthy stalks and furnish the basis for a crop. The attack in spring being made usually after the stalks are well formed, the eggs are placed on the lower leaves, and the larvae, as a rule, will be found just above the first joint. Their presence here so weakens the stalk that it bends over, the upper part of the stalk falling to a horizontal position and at right angles to the base. The appearance of these fallen stalks is particularly characteristic, and an examination will bring to view the larvae or puparia just below the bend and above the lower joint. Rarely the larvae may occur above the second or third joint, and it is stated that sometimes they pass below the ground, as with the autumn brood, and in such case the stalk falls by breaking at the surface of the ground. These tacts have a value not only as a means of distinguishing the Hessian fly from other wheat pests, but it can easily be seen that the position of tin4 larva1 mast be a determining factor in the adoption of certain measures of control. NATURAL ENEMIES OF THE HESSIAN FLY. The importance of the parasites of the Hessian lly is probably hard to overestimate, since to this factor we have doubtless to refer the usual scarcity of the insect. This may be inferred, in part, from 28 THE HESSIAN FLY IN THE UNITED STATES. the fact that Say, in his original description of the Cecidomyia, pre- sented a description of one of the most abundant of the parasites which was already at that time recognized as an efficient agent in the destruc- tion of the pest. It is also shown by the estimate commonly made by the writers who have dealt with the subject that fully nine tenths of the Hessian flies are destroyed by parasites, a circumstance which accounts for the fact that the Hessian fly is seldom abundant or excessively destructive for more than one year at a time in any particular locality. In the speci- mens which were received from different points in Iowa in 1896 I was unable, because of the parasites, to secure a single perfect fly, and I am informed by Dr. Lugger, the State entomologist of Minnesota, that his experience for 1897 was the same as reported in his annual report for 1896. This being the case, there is abundant reason for a careful consider- ation of the various species known to attack it, and the presentation of descriptions whereby they may be recognized should be one of the most serviceable parts of a discussion of the insect. An interesting comparison of the parasites of the insect in Europe and America ha? been made, whereby it has been brought out that there are similar parasites in the two regions, and, furthermore, that in some cases where the species do not appear to be identical the same genera are represented, and that a list of species presenting counter- parts may be arranged for the different regions where the insect occurs. A comparative list adapted from Marchai will be useful to show this point. PRIMARY PARASITES. For America the following species have been recorded : C'HALCTDID.E. Merisus destructor Say. Bcvotomus subapterus Riley. Pteromalus pallipes Forbes. Eupelmus allynii French. Entedon epigonus Walk. (Artificially introduced.) Pkoctotrypid.e. Polygnotns hiemalis Forbes. Platygaster herrickii Packard. As secondary parasites we may record Tetrastich us product it* Riley and Tetraslichvs carinatus Forbes. In Kussia, Lindemann records the following: Chalcidid^e. Merisus intermedins Lindra. Entedon epigonus Walk. (Seiniotellus nigripes Lindm.). Eupelmus karschii Lindni. Euryscapus saltator Lind. (Reared also from g;ills of Tsosoma hordei.) Tetrastiches rileyi Lindm. (Secondary parasite of Merisus.) PROCTOTRYPID.E . Polygnotus minutus Lindin. NATURAL ENEMIES. 29 Tn England, Miss Eleanor A. Ormerod and Mr. Fred Knock have obtained the following parasites: Chalcidid e. McrisiiH destructor Say. Bceotomua subapterua I 'i ley. Aferi8U8 intermedins Lindm. Entedon epigonua Walk. Eupelmu8 karachii Lindm. Eury8capu8 saltator Lindm. Tetrastichua rileyi Liudm. Tetrastichus (2 species). Proctotrypid^e. Pohjynotus minimis Lindm. Platygaster herrickii Packard. Marchal records from Cecidomyia destructor the following as being obtained from Vendee: Chalcidldae. Mersus destructor Say. HoIcwm cecidomyia' Ashmead. Baotomus riifomaeidatus Walk. Eupelmus atropnrpureus Dalm. Proctotrypidae. Polygnotus minutus Lindm. Polygnotus zosini Walk. Trichasis remulits Walk. Before taking up in detail the species of parasites known to infest the insect in America, we may stop to notice the remarkable studies of Marclial upon the early development of some of the parasites as observed by him. The most striking of these relate to the early stages of Tricha- sis remulus, which is said to deposit its eggs in May and June, either in the egg or the very young larva of the Cecidomyia, the larva' of the Platygaster being always encountered in the very young larva of the Ceeidomyia. In some cases where the punctures by the parasite have been too numerous the larvae attacked die and dry up without com- pleting their development. In such cases the parasites are arrested in their development and perish. More often the Oecidomyian larva con- tinues to feed and grow to the time of forming the puparium. The puparia of the attacked larva1 are smaller and paler than those of nor- mal larva', sometimes even of minute size, generally very flat, and always of irregular form. The course of development of the Trichasis has been very fully sum- marized by Howard* in his review of Marehal's paper, and 1 can do no better than reproduce the following extract: According to Marchal the first larval form of T.reinxlus corresponds to the type of the curious oy clops-like larvae studied by GaniD, and which certain authors regard as an adaptive form, while others sec in it an ancestral form. The post-embryonic development, according to Marchal, is as follows: When they are young and motionless and have not issued from the cysts which (Science Vs.. Vol. VII, pp. 246-247.) 30 THE HESSrAN FLY IN THE UNITED STATES. contain them, these larvae are always lodged in the interior of the nervous system of the host larva, and there they bring about alterations and proliferations of a very curious character. The most frequent position is at the posterior of the extremity of the nerve chain, where the cyst of the parasite is formed. This extremity spreads out into an enormous bouquet of club-shaped, giant cells, which alone fills the larger part of the body cavity of the host. The larva of the parasite is lodged in a cyst filed with liquid, the cellular structure of which, with broad, polygonal con- tour, seems to indicate an amniotic envelope in a condition of retrogression. All around this membrane the giant cells are grouped. These exist not only in the immediate neighboihood of the cyst, but all the surrounding region of the nerve chain seems to have undergone the same degeneration and growth of giant cells. The youngest cells are hyaline, and present a fibrinous, longitudinal structure. The oldest cells are filled with fatty globules, and become entirely opaque. The giant cells increase and isolate vesicles, which separate and fall into the body cavity in the form of protoplasmic spherules, which are absolutely characteristic. When one dissects a Cecidomyid larva under the microscope he can be sure, if he sees these spherules floating in the liquid, that there are in the preparation one or more larva? of this parasite. The localization of the larva? of the Trichasis in the nerve chain or in the nerves of the larvae presupposes that the parasite pierces the egg or the young larva upon the median line at the time when the nervous system has not begun to branch and is concentrated in a single ventral band. The mass of giant cells evidently accumulate in themselves the nutritive material necessary to the parasite. They are a kind of internal gall, developed by the presence of the para- site. The Trichasis, in the condition of the cyclops-like larva, waits in its cyst until the tissues which surround it have submitted to the transformations by which it profits later for its food; then, when the host larva, exhausted by its presence, is transformed into a sort of sac filled with giant cells, it issues from its cyst to devour the accumulated material, which, probably, has nutritive qualities nearly identical ■with those of the vitellus. After undergoing successive transformations into three larval forms the adult insect finally issues from the puparium of the host, only one adult finally making its appearance from an individual puparium, although in the cyclops stage four larva? may be present. There seems in this first stage to be a physiological competition between Trichasis larvae, only the oldest surviving to take on- the second stage. An interesting point is that there appear to be definite molts from the first to the second and from the second to the third stage, and that the dead bodies of the cyclops larvae which succumb do not interfere with the devel- opment of the survivor. Another species to which Marchal has given careful study is the Polygnotus minutus Lindni., and which he has localized in the stomach instead of the nervous system. As many as ten or twelve were found grouped together and developing simultaneously, and destined, all or nearly all of them, to complete their development. Quoting again from Howard: The group of young larvae forms a mass situated in the interior of the stomach. It is surrounded by a hyaline and perhaps adventitious membrane. Each para- sitic embryo is also surrounded by a membrane of its own. The larva is elliptical, somewhat attenuated at its posterior extremity, and provided with rather well- devoloped mandibles. They fill the gastric cavity, which is generally distended. The second and third larval forms follows The host is almost entirely devoured and reduced to a cutaneous sac. When ready for pupation they occupy the entire body cavity of the host, the skin being distended and showing by impressions the positions occupied by the contained parasites, thus appearing full of minute NATURAL ENEMIES. 31 These facts have particular interest as showing the effect of the parasite on the tissues of the host, and the most remarkable point perhaps is the formation of the giant cells with Trichasis, indicating a process of gall formation in these tissues analogous to the gall forma- tions produced in plant tissues by the presence of various insect- oi insect Larvae. Merisus destructor Say. (Fig. 2. This species, first characterized by Say as Ceraphron destructor, is doubtless the most universally important of the Hessian fly parasites, as it occurs not only throughout the American territory affected by the Hessian fly. but is known also in England and continental Europe. It has received notice from nearly every writer on the Hessian fly since its first description, and Dr. Riley has given a full statement of its synonymy and a discussion of its relation to subapterus, but no author has given us the knowledge of its early stages or the relation it bears in development to that of its host that is desirable in its practical treat- ment with reference to securing most advantage from its work. Riley says: The eggs of this parasite are with- out much doubt deposited in the half- grown larva- of the Hessian fly early in the spring, and in the more southern portions of the wheat belt there are in all probability two generations, the first issuing from the puparium in April and May and the second issuing all through the summer and fall. Many, judging from my experience in- Fig. -2.--M- istu desi uetor [from Riley). doors, hibernate in the pupal Btage ' within the Cecidomyid puparium and cut their way out the following spring. In the Xorth, however, there seems to be but one annual generation. In Iowa, as we have noted, there is an emergence of adults in early autumn, and either these must be able to deposit eg^ or else live over winter as adults, otherwise they must perish without providing for another generation. Marchal refers to this species certain larva- encountered in the larva- of Cecidoinyia, and characterizes them as glabrous and full, the larva- being very different in appearance from the normal occupants of the puparium. The following detailed description is by Dr. Riley, in Proceedings «>t the U. S. National Museum, volume 8, page 415: Male. — Length (average) 1.98 mm. Qreatesl width of fore wing, 0.62 mm. Antenna- long filiform, strongly pilose : fnniole joints subeqnal in width, decreasing Blightly in length from 1 to ti; joint 1 a little more than twice as long as broad; the olnb is nearly as long as the two preceding joints of the t'nnirle together, ovate, flattened on the sides, and acuminate at tij». The ocelli are lar^e ami prominent. Head and notum densely and rather tinelv punotate, the punctures <'ii the mesoscntellnm and 32 THE HESSIAN FLY IN THE UNITED STATES. metanotum finer than those on the head, pronotum, and mesoscuturn, those on the nietanotuni being deeper; metanotum with an indication of a median carina. The abdomen is oval, convex above, flattened below, glabrous, hut very finely shagreened. The hind tibiae have but one apical spur, and the hind trochanter has two very minute tooth-like projections below. General color black ; antennal scape yellowish, pedicel and flagellum brown to blackish, pedicel often yellowish below; head and thorax with a bluish, green metallic reflection; all coxa? black with metallic reflec- tions ; all femora black or dark brown, with yellowish tips ; all tibiae and tarsi honey- yellow. Wings perfectly hyaline; wing veins very distinct, dark brown in color; spurious veins more distinct than in M. subapterus. Abdomen black with a yellowish spot varying in size above and below at base. Female. — Averages in size a little larger than the male, from which she differs prin- cipally in the antenna?, which are short and have a slight clavate tendency; the funicle joints increase slightly in length from 1 to 6; club short and obliquely acu- minate; scape short, light yellow-brown in color; flagellum brown; club lighter in color than the remainder of the flagelluin; pile very short and fine. Described from 4 males, 10 females. Differs from all other described species of the genus in the combination of the pale scape, hyaline wings, and flattened abdomen. Bccotomus subapterus -Riley. (Fig. 3.) Pteromalus .' fulvipes Forbes. Wingless male. — Length varies from 1.58 to 2.74 mm. Antennae inserted a little below the middle of the face, their bases close together, but still distinctly separated; scape reaching to the ocelli; flagellum short, finely pilose, club oval, acu- minate, flattened laterally; joints of the funicle sub- equal in length, joint 1 a trifle longer than broad, the rest increasing very slightly in width to joint 6, which is as wide as long. Cheeks well rounded; ocelli in a curved line, middle ocellus indistinct; head consider- ably broader than thorax, densely and finely punctate. Pro- and mesonotum with punctation similar to that of the head; metanotum rounded, with somewhat larger and deeper punctures. Abdomen ovate, acumi- nate, not flattened, perfectly glabrous. Color: Head and thorax with a dark-greenish metallic luster; bulla of antenna- black, scape and pedicel honey-yellow; flagellum yellow-brown, often with a darker metallic tinge, especially at the joints, causing the flagellum in Fig. 3,—Bceotomus subapterus some instances, particularly in the smaller individuals, (after Riley). to appear dark; pile whitish; all legs honey-yellow, coxae very slightly metallic at base; tarsi, and some- times distal end of tibiaj, whitish ; abdomen black ; penis (often extruded to a consid- erable length) brown. Female {winged and wingless). — Length varies from 1.8 to 2.8 mm.; average wing expanse, 3.75 mm. Differs from male in the following respects: The antennae are more clavate, the sixth funicle joint slightly broader than long; the flagellum is always black, with a slight metallic tinge, and the pedicel is usually tipped with black at its distal end; the pile is much shorter and finer than in the male. The femora and the tibia? are in general of a darker brown, in which case the knees and the distal third of the tibiae are whitish. The metallic luster of the thorax is more subdued, and the abdomen has the characteristic female notch when seen from the side. The wings are perfectly hyaline, and the veins are onty faintly tinged with yellowish; the spurious veins are very faintly perceptible. NATURAL ENEMIES. 66 Described from many male and female specimens, only three of the latter being winged. All bred from final larva of the Hessian fly collected at Cadet, Mo., by J. G. Barlow, and issuing through tin; coarctate larva shell. Distinguished from other described species by tin- contrasting antenna? in the - and by the ovate abdomen which, when fresh, has no flattened dorsal surface. This species is probably, next to destructor, the most important of the Hessian fly parasites. Indeed, Dr. Riley has stated that t he relative abundance of this and the preceding species is probably a question of latitude or location, and this species has been bred much more com- monly than destructor from infested wheat from Missouri. The winged and wingless individuals are considered as certainly belonging to tin- same species, and the proportion of winged to wingless individuals is said to vary at different seasons of the year. '-Thus, from a lot of puparia of the Hessian fly, received in the summer of 1883 from Mis- souri, there issued 31 wingless males, 28 wingless females, and 3 winged females. Of these about one-third issued from the straw in August. 1883, and the rest, including all the winged individuals, hibernated in the straw and issued in April and May, 18S4."' From this it would appear that we may have much the same retarda- tion of development in the parasite as in the host, and that the appear- ance of adults in autumn or in the following spring may be a matter of conditions. Pteromalus pallipes Forbes. A short, thick species, with the head broader than the thorax, the abdomen ovate and obtuse. Head and thorax bronzed black, thickly set everywhere with punctures of medium size. The occiput and the dorsum of the thorax with a lew scattered appressed hairs. The front of the head is vertically grooved for the long, first joints of the antenna'. Eyes pale red, month-parts brown. The antennse are about as long as the head and the thorax, thirteen jointed, the first joint pale j ellow, second joint dusky, the remaining joints black. The first joint is about equal in length to the lour following, the third short, that and the fourth together shorter than the second and about equal to the fifth, the joints widening from the first to the fifth (except the third, which is not wider than the second), the following joints, to the eleventh, of about equal diameter, thence tape) ing rapidly, the last three not being clearly distinguished. The first joint is nearly smooth, the second somewhat hairy, all the others black pubescent, each with a transverse ring of long appressed yellow bristles. The mesoscutellum is broadly rounded behind, the sides with an irregular excavation, the met ascutellum with an elevated margin and an evident median carina. The sides of the mctathorax are densely clothed with long black hairs. Wings transparent, veins dusky yellowish, the post-costal and stigmal of equal length, about two-thirds as long as the costal. Wing membrane sparsely pubescent, the veins with a row of still', erect black hairs. Patagia dusky yellowish. The legs are pale yellow throughout, except t he coxa-, which are of t he body color. The abdomen is smooth and shining, except the under sides of the three posterior segments, which are pubescent. It is black above and piceous beneath, the i of the segments being somewhat tinged with brown. Length, 2.o nun.; head, 0.95 mm. wide; thorax, 0.7 by 1.06 mm. Long; antennse, 1.23 mm. ; wing, 1 .!» mm. 6086— No, 10 :.S 34 THE HESSIAN FLY IN THE UNITED STATES. Eupelmus allynii French. (Fig. 1.) Professor French, who was the first to describe this species, at first believed it to be a wheat pest, but subsequent study and the observa- tions of Drs. Riley and Forbes have established it as a parasite of the Hessian fly, with a number of other forms. The fact that it lives on other iusects is a point in its favor, as this enables it to survive during years when the Hessian iiy is wanting or very scarce. Professor French's description is as follows: Male. — In this sex the body, wings, and antennae are colored like the females, but the antenna' arc a little more slender at their ends. The head and thorax Fig. l.—Eupeluois allynii, male (after Riley). FIG. 5. — Eupelmu: allynii, female (from Riley). have about the same measurements, but the abdomen is a little shorter, the whole insect being from 0.06 to 0.07 of an inch. The legs have all the femurs yellow, front tibiae yellow, middle and hind tibiae fuscous, except at the apices, which are yellow; feet as in the females. Female. — Average length, 0.10 of an inch. Color of body and antenna1 uniform black, the first with a slight greenish luster. Head about 0.025 of an inch wide, about two-thirds as long; the antennae a little enlarged at the ends, hairy, micro- scopic hairs moderately scattered over the head and thorax. Thorax, as well as head, punctured; wings hyaline, dotted over with microscopic hairs, the thorax in its widest part about the width of the head. Abdomen gradually tapering from near the base, the ovipositor slightly exserted. Color of the legs varies slightly; in five specimens the anterior and posterior legs have the femurs fuscous except at the ends, the tibiae with basal half fuscous, the rest yellow; the terminal joints of tarsi fuscous; the middle pair of legs are yellow throughout except the terminal tarsi. Two specimens have all the femurs fuscous, yellow at the ends. One specimen baa all the femurs pale red and the tibiae fuscous, but this is probably a change from yellow by the poison bottle used in killing. One is marked like the first five, with the yellow replaced by pale red ; another is like the first five, except that the middle tibiae are a little clouded at base. According to the breeding records of Professor Forbes, this species issues during June and July, especially from June 13 to July IS. NATURAL ENEMIES. 35 Platyga&ter herricJcii Pack. Fig, 6. This parasite lias been obtained from the Hessian fly and is counted one of the common species infesting it. It was credited \\ itli punctur- ing the egg and laying its egg within to hatch later and eon same the larva. This was considered as a very improb- able method of attack, as the true egg parasites were known to complete their life cycle within the egg itself. The observations of Mar- chal on Trichasis have, how- ever, shown the probability of such a mode of attack in that species, and so there would seem a possibility of such habit for this. If occurring in the fall and affecting particularly the larva' Jiving in winter wheat, it will be s^en that it operates at a season when the Merisus is most inactive. This is a very minute species, being only l.\ to 1} of a millimeter in length. It is described as black, shining, finely punctate; the antenna; 10-jointed, black; the wings veinless, or with a submargiual vein appearing as a yellowish streak. Pack (after Ri Polygnotus hiemalis Forbes. Plalygaster hiemalis Forbes, Psyche, vol, .">. p. 39 (1888.) Male and female. — Length, 0.80 to 1.40 mm. Black, polished; head about two and one-half times as wide as long anterio-posteriorly, the vertex posteriorly only faintly aciculated, the face smooth, polished. Antenna' 10-jointed, brown black, the fiagel- Inm twice as long as. the scape ; pedicel as long as and much stouter than the first two funicular joints; first funicular joint small, not longer than thick, yellowish basally; second larger and a little longer than the third; club 5-jointed, the joints. except the last, a little longer than wide, the last cone-shaped, one-half longei than the preceding. In the male the second funicular joint is thickened, curved, and as long as the pedicel, the latter whitish or yellowish at the tin: the funicular joint small, contracted at base; club 6-jointed, villose, the joints oblong, slightly pedicel- late, the first, the shortest, narrowed basally, the last ovate, not quite twice ;i> lone, as the penultimate. Thorax ovoid, polished, the mesonotal furrows delicate hut dis- tinct posteriorly ; in the male almost obliterated, the middle lobe projecting slightly upon the scntellum. Scutellum very high, transverse, convex. Metapleura Bubseri- ceous. Togul.e rufo-piceous. 'Wings hyaline, pubescent. Legs dark brown to piceous, trochanters, tips of anterior femora and tibiie, base of middle and posterior tibi«e, and all tarsi, brownish yellow or honey J ellou , sometimes the posterior femora black. Abdomeu in the female about as Long as the head and thorax together; in male shorter ; in hot li sexes the petiole and the foveohe ;it base of the second segment striated. 36 THE HESSIAN FLY IN THE UNITED STATES. Habitat. — Western States. This species seems to have been first reared by Dr. Riley from specimens of the Hessian fly (Cecidomyia destructor Say) August 16, 1876, received from Blair, Nebr. It has, however, since been bred from the same fly by various persons in the Western States. Professor Forbes reared it in 1888 at Champaign, 111. ; Professor Cook, of the Agricultural College of Michigan, in 1890, and Professor Webster, at Laporte, Intl., in 1889. I know of no specimens reared in the Eastern States. Can it be a species moving eastward? (Ashmead.) Lygoccrus triticum Taylor. Ceraphron triticum Taylor, Am. Agric. 1860, p. 300, f. 1 ; Cress. Syn. Hym., p. 248. Lygocerus triticum Taylor, Ashmead, N. Am. Proctotrypida?, p. 110. This fly does not correspond with the above (Ceraphron destructor Say), therefore 1 have named it triticum, from the botanical name of wheat. It is not of such a shining black as Mr. Say's fly, but is rather rusty in appearance, from a few hairs scattered over its body. In some specimens, when very fresh, the legs have a bright tinge of yellow. The antenna? (&, fig. 2) are termed setigerous (having the basal joint large) and the last four globular, the intermediate one furnished with four long bristles resembling plumes. This is a very sure mark for distinguishing this family according to European classification. The eyes are large in proportion, the palpi 3-jointed. The fore wings have submarginal cells, with a faint nervure ran ning to apex. The under wings have a long nervure running through and two smaller ones descending to the inferior region; these are so very slight that you can only see their existence by a deep shade of the wings in a strong light, but are evi- dently nervures, indistinct as they are. The ovipositor is retractile and tubular. The fly deposits her eggs in the pupa of the Hessian fly. (Taylor.) Unknown to me, and the above description is copied from the American Agricul- turist. Miss Taylor further informs us that "this fly can be found in every wheat field throughout the country, from spring to autumn." Her description is very imperfect, and her figure of the male antenna strongly recalls the branched antenna of an Eulophus. (Ashmead.) The above reference, quoted from Ashmead's "Proctotrypidse," gives all that appears to be known concerning- this species. SECONDARY PARASITES. Aside from the parasites attacking the Hessian fly directly, there are species which attack their parasites and are called secondary parasites. These, of coarse, by reducing the numbers of the primary parasites, operate to the disadvantage of the cultivator. Two species have been described in this country, both in the genus Tetrastichus. Tetrastichus productus Riley. (Fig. 7.) Male. — Average length, 1.5 mm. ; wing expanse, 2.6 mm. ; greatest width of the fore wing, 0.5 mm. Scape somewhat broadened below, inserted near the middle of the face in a deep groove, and reaches nearly to the ocelli. Elagellum long, flat- tened, hairy, each joint except club with a whorl of long, slender hairs at base. Funicle joints twice as long as wide. Head considerably shrunken after death. Head, pronotum, and mesonotum smooth and shining; metanotum, pro, meso, and meta pleura, and all coxre above finely punctate. Submarginal vein of the fore wing with a single stout superior bristle behind its middle; marginal vein three times as NATI/IWI. ENEMIES. 37 long as stigmata] ; post-marginal wanting. Median impressed line of meeosternnm very distinct; inetanotal carina distinct, rather short. Abdomen narrow , coinpi laterally, snhacuruinate. General color shiny black, with slight metallic reflections; flagellum, brown; all trochanters, distal end of all femora, all tibiae, and tarsi honey yellow; wing veins, brown, very distinct. Female. — Length (average). 2.1 mm. ; wing expanse, 3.2 mm.: greatest width of fore wing, 0.55 mm. Scape slender, pedicel ovoid, ring joint- very -mall: flagellnm rather short, but slightly compressed: club ovate; funicle joints snbeqnal in size, joint 3 rather shorter than 1 and 2, its length exceeding its width but tdigbtly. Abdomen narrow, flattened dorso- ventrally, prolonged to an acute ^ c« tip. Described from six males and seven females. Tetrastiches car inatus Forbes. A slender, smooth, dark steel-blue species, 2 mm. in length, with pale legs. 4- jointed tarsi and 8-jointed antennae. The head is very short, not wider than the somewhat slender thorax, impunctured. as are also the thorax and the abdomen. Eyes large, dark red, broadly elliptical, occupying the whole longitudinal diameter of the head and even encroaching upon its posterior surface. Front broadly bisulcate for the reception of the scapes of the antenna1. Antennae short, 8-jointed, joints very distinct, except those of the ovate club (three in num- ber), which are very closely compacted. Second joint shorter than the third, which is longer than the fourth and fifth, these being subequal. First and second joints of the club nearly equal, thicker than the preceding. Flagellum of the antenna- pale, provided with a few erect, black hairs and long appressed yellow ones. Prothorax is very short: the mesoscutum very long, narrowing posteriorly, where it is broadly truncate against the scutellum. regularly convex, minutely carinate longitudinally on the middle line : parapsidal grooves complete. Scutellum vaulted, with two longitudinal carinae. Abdomen of the female pointed, ovate, broadest in front of the middle, somewhat flattened above. Legs rather long, pale yellow; fore tarsi dusky, middle and hind tarsi dusky at tip; all the tarsi 1-jointed, first joint of front and middle tarsi shorter or do longer than the second, that of hind tarsi longest of all. The entire surface is very sparsely provided with coarse, yellowish hairs, longest and most numerous at the tip of the abdomen. Costal vein very stout, provided with unusually long hairs: stigma] vein short: postcoital nearly obsolete; do trace of median or snbmedian. This species was bred in our breeding cages from the made at Anna, Jnue 24. (Forbes.) Tetraslichus productus (from Riley). collections UTILIZATION 01 PARASITES. It may seem hardly necessary to devote so much attention to the parasites of an insect if it is not possible to so use them as to secure some practical control of the pest. That this fan be done by the proper recognition of the time of emergence of the parasites seems at 38 THE HESSIAN FLY IN THE UNITED STATES. least extremely probable, although there is yet too little evidence as to the issuing of parasites at times when the development of the host is retarded to warrant positive assertions. That the parasites do in some seasons issue with much less moisture than is necessary for the development of the host seems almost certain, and there is sufficient basis in this to delay the burning of stubble during dry summers until the parasites have had time to issue. There is another direction, however, in which the parasites may be employed, which is of interest more particularly to localities that have been recently invaded or where the parasites are not present. We have already seen that the regions where the Hessian fly is most widely distributed contain a goodly list of parasites, and such as would appear to occupy about the same position with reference to the host. We may easily conceive, however, of the introduction of the Hessian fly into a new territory, such as isolated wheat districts in Oregon or Washington, without the parasites accompanying them. In such cases there would be very evident advantage in the prompt introduction of parasitized pnparia and the setting free of the para- sites so they might establish themselves. Another direction for effort is the introduction of species not found in one country but which are common in another. Thus the introduction into this country of spe- cies common in Europe but not found here would add to the effective agents in control by whatever portion of the history of the species might be exposed to the attack of this species not open to the parasites already* present; and that the different parasites work at different times or in different ways is hardly to be doubted. Introduction of Entedon epigonus. One of the most promising efforts at introduction of the parasites occurring on the Hessian fly in the Old World was made in 1891, by Dr. 0. V. Riley, who received pupae parasitized with Untedon epigonus (Semiotellus nigripes) of Russia from Mr. Fred Enock, of England. These were distributed to Trof. S. A. Forbes, in Illinois; Prof. A. J. Cook, in Michigan, and Prof. F. M. Webster, in Indiana. The report of results given by Professor Forbes is worthy of reproduction. I am not aware that any reports of the other introductions have been pub- lished. Professor Forbes's report, taken from Insect Life, Vol. IV (p. 179), is as follows: According- to my promise I submit the following account of a recent experiment, begun at your instance and with material furnished by you, for the transfer of a European parasite of the Hessian fly to the United States. In accordance with arrangements made by telegraph, I received from you May 6 a package of Hessian fly puparia, said to have been parasitized by the European species Semiotellus nigripes, and with this package a letter from you asking me to take charge of and liberate the parasites in an inclosure of infested wheat, with an idea of introducing the species. A second package came two days later, accompanied by a letter of advice from your assistant, Mr. Howard. NATURAL ENEMIES. ' 39 I had growing at the time under gauze, but otherwise in the open air, ;i small plot of badly infested wheat. 21 by 3 feet, in very fortunate condition for the experiment. This wheat had been transplanted March 26 from a field near Roodhouse, in Morgan County, for use in making observations on the life-history of the Hessian fly, and contained when transferred large numbers of the insect in the hibernating pupa- rium. Male and female adults had begun to appear in the inclosnre by April 1, and these transformations continued to May 13, the greater number of them occurring about April 20, when, for a few days, more than twenty adults could lie counted in the cage at a time, not to mention others doubtless concealed in the wheat. The first lot of foreign parasites was exposed in this cage May 7. and the second lot May 11, both packages containing Living adults when opened. At the time of the fust introduction eighteen of the wheat stalks were examined, and fifteen young larvae of the Hessian fly Mere found upon them, and all the con- ditions were thus favorable to the success of the experiment. Four days after the introduction of the parasitized foreign material five freshly emerged specimens of SemiotcUus nigripes were noticed in the cage, and others appeared May 13, June 29 and 30, and July 1, 3, 9, and 14. On the date last mentioned the wheat in tin was overhauled and the puparia were removed and divided into three lots; one to be kept at the office for regular observation of the transformations, one to be taken into southern Illinois and distributed through fields of stubble containing Hessian fly puparia, and a third to be sent, in accordance with your letter of July, to Mr. James Fletcher, Dominion entomologist. Ottawa, Canada. The parasitized puparia received from Washington were all spent by this time, or, perhaps, some time before. Removed from the cage July 18 they were kept until October 7 without the appearance of another parasite insect. Parasites of the new generation continued to emerge from the lot kept for observation until Augue the exact dates being July 16, 18, 21. 23, 21. 27. 31, and August 1. 6, 10. 12, 10. 20, 23, 2.".. and 2!'. Most of these were released in a field of moderately infested wheat stubble on the experimental farm of the agricultural experiment station at Champaign, begin- ning with 4 specimens July 22, and adding 13 on August LIS on August 6,23 on August 10, 15 on August 12, and 1 on August 20; 77 adults in all having been thus released at this place. In the meantime measures had been taken to introduce the parasites on a larger scale in southern Illinois, faking with me about two-thirds of the material obtained from our breeding-cage experiment — the parasitized puparia still in the straws — I traversed several counties from Central ia south to Union County, and thence to St. Louis and Jacksonville, stopping at intervals, but finding no satisfactory situa- tion until I reached Scott County, July 17. On the farm of Messrs. Edward and Frederick Vantyle a held was found 3 miles northeast of Roodhouse, the yield of which has been reduced by the Hessian fly from about 30 to ."•"> bushels to the aire to 15. It was the only field in the immediate neighborhood which had be damaged, and in this one the fly had not been noticed the year before. There was, consequently, little probability of excessive native parasitism of the succeeding brood, and it seemed likely that the fly would occur there this tall in volunteer grain and Later in the regular sowing. The owners agreed to leave unplowed a piece of stubble, on which my specimens were scattered, while the remainder of the field was to be plowed for wheat within a few days. The fact that specimens of the Semiotellua continued to emerge from the (heck lot retained at Champaign for some weeks after this distribution is evidence that a considerable number of the parasites must ha\ e gone abroad in Scot t County. Indeed, forty or fifty of them, which had completed their transformation en route, escaped from the box when it was opened in the field. It will be seen from the foregoing narrative that we succeeded completely in breed ing a generation of the foreign parasite in our plots of wheat infested b\ the lies- 40 THE HESSIAN ELY IN THE UNITED STATES. sian fly, and that these bred insects were successfully distributed to fields infested by the fly at two places m Illinois — in Champaign and Scott counties, respectively. It should be said, in conclusion, that the latter part of the summer was exceed- ingly dry throughout central Illinois, and that as a consequence but little volunteer grain grew in either of the above localities, and that neither in this nor in the early sown wheat was there any considerable amount of Hessian-fly attack — circumstances which are to some extent unfavorable to rapid success of the experiment for the intro- duction of this parasite. The Vantyle farm was visited by my assistant, Mr. Marten, September 24. at which time the plowed portion of the field was being drilled to wheat. Along the margins of this plowed ground, near the plot which had been left in stubble, was a scanty growth of volunteer wheat, in which, after considerable search, four nearly full-grown larvaj of the Hessian fly and one fresh puparium were found. Little other volunteer wheat was seen in the neighborhood. A brief search of the stubble remaining showed only parasitized puparia from which parasites had already escaped. The Champaign County plot was examined September 30, when one hundred and Fig. -Entedon ejAgonns (from Howard, in Insect Life). twenty plants of volunteer wheat grown in the experimental stubble field were over- hauled. In these plants two larvae and seven puparia of the Hessian fly were found. October 5, from forty-three plants eight puparia and two nearly full-grown larvae were taken. As the period of the emergence of the imported Semiotellus was substan- tially the same as that of the native 8. destructor, the two coming out side by side in our breeding cages, it seems practically certain that the imported parasite must have had as fair a chance for propagation in the field as its native congener. We will of course keep careful watch of these localities next year, and will notify you of any observations then made bearing on the reappearance and the spread of this imported enemy of the Hessian fly. The results of the introduction in the vicinity of Washington are recorded by Dr. Howard in Insect Life, Vol. VII, page 414, as follows: In the last number of Insect Life (p. 356) we published a figure of Entedon epi- gonus (fig. 8), the principal European parasite of the Hessian fly, and mentioned the attempts which Professor Riley had made in 1891 to introduce the species into the wheat fields of this country. One of the last acts performed by Professor Riley before leaving this office in May, 1894, was to send a batch of parasitized puparia of REMEDIES. 41 the Hessian fly,, just received from Mr. Fred Knock, of London, to the farm of Mr. G. Morgan Eldredge, at Cecilton, Md. During May, l*!ir>, wishing to ascertain whether or not this attempt had been successful, Ave sent Mr. William II. Ashmead to Cecilton to make careful observations. He found that the parasitized puparia had been placed upon the ground at the borders of a field which appeared to he rather badly affected by the Hessian fly. The crop was harvested and the land plowed at the end of August and planted in winter oats, which at the time of Mr. Ashmead*s visit were from 4 to 6 incheshigh. After harvest the wheat straw was stacked in the immediate vicinity of the place where the parasitized pnparia were deposited, and a small quantity of winter wheat was sowed (during August), so that the Hessian lly might find an early place for oviposit ion, giving the parasites a good chance. Mr. Ashmead swept volunteer wheat in the immediate vicinity of the straw stack, and also swept the adjoining field, at that time in winter wheat. He was in the field but a single ossible. Thrips. — Both Mr. B. D. Walsh and Mr. Theo. Pergande have ex- pressed the opinion that the Cecidomyia may be attacked by thrips. but so far as I am aware no demonstration of such attack has been made. Their remarks on this subject have been republished in volume I of Insect Life, pages 138 and 139. REMEDIES. While investigations of recent years can hardly be said to have added any absolutely new methods of treatment, it is evident that more precise knowledge of the life history and especially of the variations in time of appearance and number of broods does enable us to state with much greater confidence the conditions under which certain meas- ures are available. Knowing the conditions affecting acceleration and retardation of development, it becomes possible to specify the appro- priate occasion on which to resort to burning, plowing under, delay of seeding, etc., and it will be our effort in the following discussion of remedies, most of them of long recognition, to so state the conditions under which each maybe most effective that the cultivator himself, without having to call in a professional entomologist to examine the field, may act intelligently. 42 THE HESSIAN FLY IN THE UNITED STATES. In fact, we Lave the authority of Professor Webster for the statement that the Hessian fly need be no longer a source of loss under a proper system of agriculture. That the farmer, however, be best prepared to contend with the insect involves for him a thorough knowledge of the conditions favoring or obstructing the action of the insect, and to this end he should be jwrticularly familiar with the conditions of accelera- tion or retardation of development as affecting the time of appearance of the various broods. Probably the most important measures available with our present knowledge are those directed against the insect in its summer resting period or the early issuing flies of late summer and early autumn. BURNING THE STUBBLE. This remedy has been one of the standard measures from very early times, and while objection has been raised to it on account of the fact that the parasites will be destroyed along with the Hessian fly, it may be considered as one of the most generally applicable. To be effective, the burning must be performed before the flies have had an opportu- nity to emerge, but in this respect there is little danger of being too tardy unless unusual moisture accelerates the emergence of the flies. Postponement until the parasites have had an opportunity to emerge would, in fact, be an advantage, and, during dry weather in July and August, the firing may be postponed. In some cases the burning is made more effective by cutting the wheat pretty high, so as to leave a larger amount of stubble, thus insuring a more rapid spread of the fire. It has the further advantage of leaving with the stubble any chance " flaxseeds" which may occur higher up on the stalk than the usual position. An objection to burning, which has been suggested by Lindemann, and is supported by Marchal, is that under a given climate it may be that at the time of harvest a considerable part of the puparia will have already matured and the flies issued, so that those destroyed will be simply an insignificant part that have been delayed in their develop- ment, and their destruction, while useful, would be so in but a slight degree. The determination of the condition of the "flaxseeds" would be difficult except by examination by an expert entomologist, and treatment with reference to this point is rather impracticable. So far as the American wheat grower is concerned, it would seem unwise to use this objection, as the benefit in general from burning infested stub- ble is so great that other considerations maybe overlooked. The main point is to determine the time of movement, and this in general should be as soon after harvest as the conditions of the season are likely to cause the emergence of flies. Along with the burning of the stubble we may call attention to the desirability of burning chaff and screenings after threshing, as Miss Ormerod has pointed out that many puparia are to be found in these REMEDIES. 43 materials. While probably loss useful in this country where the straw- is of less value and is not cut so close to the ground, the fact that we have here a possible source of danger is sufficient reason to take the small trouble necessary to guard against it. THE PLOWING UNDER OF STUBBLE. Xext to burning, and available when burning is impracticable, the plowing under of stubble is perhaps most important. To be most effect- ive the stubble should be turned to the depth of several inches and the field rolled, so as to compact the earth and prevent the issuing of the flies which may develop from the puparia in the ground. The time of plowing depends upon the condition of the season, and here the con- ditions which suggest plowing in ordinary farm practice are those which best apply to the destruction of the insect. If the season be dry. the necessity for plowing does not exist, as the great majority of the insects will remain in the dormant condition, and those which hatch will fail to find food plants upon which to deposit eggs upon which the larvae can feed. With the occurrence of rains, which put the ground in suitable condition for plowing, there is probability of an early emergence of flies, and further, of the springiug up of volunteer wheat to furnish their progeny with necessary food. In this connection it may be mentioned that where the crop is so seriously infested that it is not considered worth harvesting, it may pay to plow it under as early as possible, roll thoroughly, and plant to corn or other late crops. This method was adopted with excellent results by some farmers in the spring- wheat region of northern Iowa. DESTRUCTION or VOLUNTEER WHEAT. It is evident that if all the food supply for insects during late sum- mer and early autumn is destroyed, the flies emerging during this period will be unable to deposit eggs or their larva1 to develop. The volun- teer wheat around stacks or through the fields, if present in any quan- tity, should be plowed under so that this source of food supply ma\ be cut off. PLANTING OK DECOTJ STRIPS. Many authors recommend the planting of narrow strips of wheat in the field as decoys, but the plan has apparently been little used by farmers. This is perhaps because it entails extra labor and expense and presents only possible advantages. Professor Webster considers that while it is hardly possible to entrap the major part of the fall brood of larva1, it is certainly possible to entice to these plats the strag- glers and interlopers, which have been known to be capable of consid- erable injury. While the pest can not be exterminated in this way, its power to commit serious injury may be considerably weakened. Vol linteer wheat would apparently serve the same purpose if appearing 44 THE HESSIAN FLY IN THE UNITED STATES. early enough to attract the flies, and should in any case be plowed under as deeply as practicable. The proper time for sowing decoys will vary with the latitude. According to Webster, for northern Indiana they should be sown during the latter part of August, and in the southern part of the State not later than the first week in September. To the north and south of this he does not undertake to give dates, but it would depend upon the date of appearance of the fall brood of flies, the wheat being planted early enough to attract the flies at the time of their emergence. A decoy crop should be destroyed within four weeks at the utmost, and turned under so deeply that any insects maturing would be unable to escape. EARLY OR LATE SOWING OF FALL WHEAT. In winter- wheat regions the time of sowing in autumn is, with refer- ence to the Hessian fly, a very important item. Early-sown wheat will naturally be exposed to the deposition of eggs by flies issuing in the autumn, but, on the other hand, if the plants have got well started and thrown out numerous tillers there is much less danger of their complete destruction, and if the flies should not be numerous a considerable gain may result. The principal objection to this view would seem to be that the multiplication of the insect is encouraged and there would be a strong probability of more serious attack the following spring. Early sowing may be practiced if desired, especially on a small scale, and then if it is found that the crop is considerably infested it may be plowed under the same as a decoy crop and the field resown later. Late sowing of fall wheat has been one of the principal resources against the Hessian fly, and the writings of most of the leading ento- mologists have agreed in a strong recommendation of this policy. Packard quotes numerous writers in support of this general plan, and it appears to be very generally adopted by farmers. To be successful the sowing should be late enough so that the plants do not appear above ground until after the bulk of the Hessian flies have issued and died. It has been shown, however, that the flies may emerge quite late in the season and deposit eggs even after frosts are common. Marchal remarks that in Vendee the wheat sown after October 20 has been completely free from injury. In the practical use of this remedy it becomes essential for the farmers of any given latitude to determine the time of appearance for the bulk of the autumn brood of flies and to time the late sowing accordingly. This will be a progressive date from north to south. Webster says: If farmers in the extreme northern part of Indiana and in southern Michigan can sow their wheat with safety about the 12th to 15th of September (and we have dem- onstrated that the fall brood emerges largely prior to the 15th), and farmers in the extreme southern part of Indiana delay sowing until after the first days of October, there must be a general system of retardation which, if understood, may be used to advantage throughout the intervening territory. Starting in southern Michigan on the 12th or 15th of September and passing 4 REMEDIES. 45 degrees south to the vicinity of Evansville, IimI., we .should expert about t In- same condition of the Hessian fly during the first week of October; that is, if we pass the danger line about the second week of September in southern Michigan, we should expect to encounter it again in southern Indiana in the first <>r second week of October. A considerable correspondence and my own experiments indicate that this is easily true. Evidently there will be considerable seasonal variation, so that these dates must be taken subject to slight changes in either direction, but it may be assumed that the earlier or later appearance of the brood will depend upon the character of the season in moisture and warmth, so that if the weather remains unusually dry and hot the fall planting should be proportionately delayed, while if conditions favor an early emergence a crop may be planted somewhat earlier. Taking the lati- tudes mentioned as a guide, the farmers of the winter wheat belt through Illinois, Missouri, southern Iowa, Nebraska, and Kansas can determine pretty accurately as to the proper time for seeding. INTERMITTENT WHEAT CULTURE. While the Hessian fly is a winged insect and capable of traveling to some distance, the fact appears to be that it prefers to deposit its eggs in the immediate vicinity of the place of its emergence. This is con- sidered especially true of the adults from the spring brood, which are supposed to select the tillers in the field where they emerge rather than to scatter to adjacent fields. The interruption of wheat culture, therefore, for one or two seasons, even if adopted on a single farm, will have an appreciable effect in preventing injury to the crop in after years. A suitable rotation, even as applied to a single field, is counted as serviceable in the reduction of Hessian fly injury. It communities can adopt a uniform system of rotation or alternation of wheat crops with crops that are not capable of supporting the Hessian fly they should secure almost perfect immunity from tins pest. In fact, tins seems to me to be practicably accomplished throughout a large part of the State of Iowa, where wheat is grown as an occasional crop and tin' Hessian fly has been practically unknown since the early settlement of the State. PASTURING Willi SHEEP. One of the methods suggested in the early history of the Hessian fly problem was that of pasturing the winter wheat for the purpose of destroying the larva'. The first published account of the insect states that by feeding thecrop very close in winter and spring, if the land is rich it will again spring up and the worms do not much injure the second growth. If practiced at the right time it is possible that the eggs might be nipped off and devoured with the leaves, but if it is remembered that the eggs usually hatch within four days alter deposi- tion, that the plants at this time would furnish rather limited pasturage, aud that the larva' soon after hatching make their way down to the 46 THE HESSIAN FLY IN THE UNITED STATES. surface of the ground or below it, it will be seen that there is little basis for favorable results in this method. If the flies are noted as depositing freely at a particular time, and sheep or other stock are turned in at once in sufficient numbers to graze the crop pretty closely, a considerable redaction of larva4 might result. The method, however, iuvolves pretty close observation on the part of the fanner to deter- mine the fact of deposition. ROLLING. The suggestion that the passing of a heavy roller over the ground will serve to crash the eggs has been commented on by Fitch. He suggests tbat it may be successful, particularly on fields that are so smooth and free from stones that almost every plant will receive a firm pressure by the operation. Necessarily the method must be applied immediately after deposition of eggs, and Fitch suggests that some plan of brushing the leaves would be still more effective by dislodging the eggs and preventing the larvae from following their usual course into the sheath of the young plant. Of this method Fitch says: Mr. Goodhue, of Lancaster, Wis., in a communication in the fifth volume of the Prairie Farmer, suggests that the larva} concealed within the hase of the leaves may be destroyed by mowing the wheat and feeding it to the stock. We deem this proposal a valuable one for exterminating the second or spring brood from a wheat field. In those cases where the worms are discovered in the month of May to be fearfully numerous at the joints of the young stalks, there can be little doubt but that on smooth ground the scythe may be so used as to take off almost every spear below where the larva) lodged; and that thus a second growth of stalks will be produced, quite free from these depredators. The following facts lead me to believe that on a fertile soil wheat may be thus mowed with little if any eventual injury to the crop. Portions of a field of my own, the past season, grew so rank that, deeming that it would become lodged and mildewed, by way of experiment a space in it was mowed down after the plants were two feet in height, and another after the heads had begun to put forth. Though not so early in ripening, the appearance of these two patches at harvest proved, so far as a single experiment could do, that wheat might be mowed at the former period without any diminution of its productiveness, while at the latter both the straw and heads would be of a more slender and feeble growth. There would seem to be few occasions where this method could be used, and I am confident that in the majority of the Western States it would be entirely impracticable, as the presence of the fly is not mani- fest early enough in the season to permit of its adoption. SELECTION OF RESISTANT VARIETIES OF WHEAT. From early times there has been a recognition of the fact that cer- tain varieties of wheat were much less subject to injury than others. Considerable literature has accumulated concerning these ." fly-proof" varieties. The varieties possessing these qualities are such as have coarse and siliceous stems, enabling them to stand and not break over REMEDIES. Vi from the presence of the fly. Varieties which tend to develop ondary shoots or '-tillers" are also considered preferable daring g sons when the Hessian fly is prevalent. Of such varieties a consider- able list lias accumulated, many of which are doubtless obsolete at the present time. The Underbill variety is stated to have been the favor- ite for nearly a century. The Mediterranean wheat has been held in high repute in the Middle States, as also the Red Cap and Red -May. The Olawson receives strong commendation from various sources, and Professor Cook speaks of it as a favorite variety in Michigan. The Spelter, China, aud White Flint are mentioned by Fitch, but do not seem to have remained in favor. Prof. C. W. Woodwortb improved the opportunity of the occurre of the Hessian fly in the experimental plats of the University of Cali- fornia to note the effects upon different varieties, and made a list including something like a hundred and twenty different varieties. He tabulates his result for the three years 1S80. 1887, and 1889, and summarizes his conclusions as follows. Volo and Washington Glass are the only varieties that have remained free from the Hessian fly. The latter, however, never yields well with as. Several other varieties have a very good record. Especially free from the fly are the following: Bearded Wheat from Missoyeu, Forelle, Palestine, Polish, Blue Grass, Common March. Diamond, Egyptian Imported. The following varieties have had more or less fly, but never in abundance : Bearded Macaroni, Big Long-bearded Club, Egyptian, Genoese Winter, Greek Atlanti, Hun- ter's White, Imported Circassian, Nicaragua. Nonette Lausanne. Red Club, Russian Red Bearded, White Club. He further makes a comparison of early and late varieties, and of 100 early varieties only 45 were badly infested, against 07 of the late, an advantage for the early varieties of over HO per cent. This question seems not to have received as much attention in Europe as in America, but Miss Orraerod has named the Square Head, the White-chaff Bed, Golden Drop, and Ivivett's Red as resistant varieties, while in France Marchal cites M. de Biguet, professor of agriculture, as recommending the Bordean wheat as a resistant variety. I si. OF INSECTICIDES. There seems to be scarcely any reason io expect success from the use of direct remedies in the form of insecticides, but some efforts have been made in this direction, and attempts to destroy the larva' with lime, soot, salt, etc., have been made. None oi' these, however, seems to us to have sufficient merit to deserve extended notice. Aside from the expense and labor of their employment, there is little reason to believe that they will accomplish as much as the more simple methods of farm practice. The same may be said with still greater emphasis concerning all suggestions as to treatment of the seed wheat, since there is no possible connection between the seed wheat and the infesta- tion of the held. 48 THE HESSIAN FLY IN THE UNITED STATES. COMBINATION OF REMEDIAL MEASURES. A little thought concerning the measures which have been discussed above, with a recognition of the life-history facts upon which they are based, will suggest that the best practical results will be obtained not by reliance upon any one method, but by an intelligent adaptation of two or more, according to the conditions prevailing for the season. These will constitute a practice which can be modified for each year as the conditions will indicate. With the harvesting of the grain, there is open the policy of burning the stubble or plowing it under or allowing it to stand for the exclusion of parasites. If the weather is very dry, it will be best to defer burn- ing, to allow the issuance of as many parasites as possible, but if burn- ing is to be adopted at all, it should be done before fall rains set in or the field has grown up to weeds. If rains occur early, burning will be best; and in any case the stubble should be plowed under and rolled as soon as there is any appearance of a volunteer growth of wheat. The chaff from threshing should be burned and the screenings burned or fed to stock as early as possible, and care should be taken during autumn to plow under and roll the volunteer wheat that springs up in the stackyard. If winter wheat is to be planted, strips of decoy wheat may be put in to be plowed under at the end of three or four weeks, and finally the crop planted at as late a date as practicable, according to dates given in the paragraph on late planting. This practice can be duly combined with the selection of resisting varieties of wheat and the application of fertilizers. It will be observed that the modifications are based primarily on the weather — whether dry or moist, a condition apparent to everyone, and that the suggestion amounts to postponement of burning or plowing if dry, or the early adoption of one or both if wet. BIBLIOGRAPHY. The following list of papers on the Hessian fly includes, it is believed, all of importance that have appeared in America and such of the foreign works as have an importance to the American student. Of the Ameri- can literature, a long list of articles in agricultural papers have been excluded as unnecessary in such a list, although the earlier articles of this character are well covered. Those appearing in recent time have been largely a restatement of well-known facts, without any contribu- tion to a knowledge of the insect. Any who may care to trace this class of articles further will find full references in the Bibliography of North American Economic Entomology, jmblished by the Division of Entomology, United States Department of Agriculture. (1) Ackerly, Samuel. Au account of the wheat insect in America, or the Tipula vaginalis tritici, commonly called the Hessian fly. <(Amer. Mo. Mag. and Crit. Rev., August, 1817, vol. 1, pp. 275-279, 3 figs. BIBLIOGRAPHY 4!> (2) Bacon, W. D. Season of 1816. . p, 28, pi. 1. (20) Curtis, John. Farm insects. < London, I860, p.2 Includes account of the Hessian tly. «;i)S(;_y(). 16 4 50 THE HESSIAN ELY IN THE UNITED STATES. (21) Delafield, J. Insects in a general view and agricultural survey of the county of Seneca, nyia destructor. (23) Devereaux, W. L. Errors in Hessian fly literature. September, 1885. (24) Doran, E. W. Report on the Economic Entomology of Tennessee. hy ; name and synonyms; figures larva, pupa, and imagos, and normal and injured wheat plants. (29) Fitch, A. Insects injurious to vegetation. No. 5. The Hessian fly — contin- ued. <1. c, January, 1847, vol. 5, pp. 1-27. ull. No. 40. Ky. Agric Exp. Sta., March, 1892, pp. 1-51, tigs. 28; also in 5th Ann. Rpt., 1894, pp. 43-88. Treats of the Hessian fly and several other insects. (43) Gaylord, W. A treatise on insects injurious to field crops, fruit orchards. vegetable gardens, and domestic animals; with a description of each and the best methods of destroying them or preventing the ir ravages. <_Trans. N. Y. State Agric. Soc, 1843, vol. 3, pp. 127-174, plates 3. See New Engl. Farmer, 1845, vol. 23, pp. 314, 315. (44) Glover, Townexd. Insects injurious and beneficial to vegetation. ull. No. 128. N. Car. Auric. Exp. Sta., July, 1896, pp. 148-155. A few notes on Hessian fly and other insects. (76) McMillan, Conway. Twenty-two common insects of Nebraska. ull. Agric. Exper. Station of Nebraska. 6 February, 1888, vol. 1, No. 2, pp. 33-133. Separate. (77) Meade, R. H. Cecidomyia destructor Say. The Hessian tly. ^Entomologist, July, 1887, vol.20, pp. 170-173. (78) Morhis, Margaretta Hare. Observations on the development of the Hessian fly. .> tera in relation to other orders of* insects, with maps and illustrations Washington: 1883 (6 March, 1881), pp. 11+347 + 12 + 92,18 figs.,4 maps. (Includes No. 90.) (100) Riley, C. V. Wheat insects. .. pp. 150-161; "wheat injured in Nebraska in 1876 by Cecidomyia destructor and Meromyza am* i ieana; r-.r. ages of larva, description of imago and means against the latter: occurrence of Disonycha flaviventris in Nebraska. (101) Riley, C. V. The Hessian fly. , December, 189.3. pp. 146-157, 4 figs. (Also in 24th Ann. Kept. Ent. Soc. Ont., p. 88. (139) Weed, F. M. The Hessian fly.