SR eo! See es eu: COMER YS i son : Le Ree eKth Sy Sees oe oN oy Oe OS te ee, Sues aie a Pa Fo’ cone aa @, ce Historic, archived document Do not assume content reflects current scientific knowledge, policies, or practices. ER BR ACRAY OF THE U. S. Department of Agriculture Class Aaa ¥ CIRCULAR NO. 66. United States Department of Agriculture, BUREAU OF ENTOMOLOGY, L. O. HOWARD, Entomologist. THE JOINT-WORM. (fsosoma triticc Fitch. ) By F. M. WEBSTER, In Charge of Cereal and Forage Crop Insect Investigations. Since the first known serious outbreak of this insect, which occurred in the wheat fields about Charlottesville and Gordonsville, Va., during the years 1848 to 1854, it has been reported at irregular intervals and in widely separated localities. While it is known to occur sparingly over most of the wheat-growing sections of both the United States and Canada, and probably does more damage than has generally been placed to its credit, its reappearance in the wheat fields of Indiana, Michigan, Ohio, Pennsylvania, West Virginia, Virginia, Maryland, and i) WR \ Ra 5, aN Sa Fig. 1.—Isosoma vritici Fitch: Adult of the joint-worm, much enlarged (from Howard). Kansas in 1904, and in still greater numbers in 1905, serves to bring it again to notice. In 1904 some fields of wheat in eastern Ohio were so badly damaged that they were not harvested, and the present year a serious outbreak in northeastern Indiana has so discouraged some farmers that they are questioning the advisability of putting in a crop of wheat at all. In southwest Virginia the pest has been even more injurious in 1905 than it was the previous year. DESCRIPTION OF THE PEST. The fully developed insect, somewhat resembling a small winged black ant, is clearly shown, enlarged, in figure 1, its natural size being indicated by a line at the right. The color is black, with joints of legs Saray and feet yellow. The young or grub is whitish, with brown jaws, the length being about the same as that of the adult, and the form much like that shown in figure 2, which represents the larva of a nearly related species. LIFE HISTORY. The insect may be found throughout the year in its various stages of development in wheat stems. It lives over winter as a larva or grub in cells formed in the stems prior to the ripening of the grain, the adult emerging therefrom in April or May, according to latitude, or some time after the young grain has thrown up stems and several joints have become ex- posed. The femal,,. using her slender, pointed ovipositor, places her eggs in the re. 2.—Isosoma grande straws. The Riley: Larva of the xe wheat-straw worm—e, exact pOSsl- antenna: /, jaw; lineat t ] on -a:s = right indicates natural length (after Riley). sumed is shown in figure 3, photographed from life by Mr. G. I. Reeves. lic. 3.—Female Isosoma in act of depositing egg in The eges hatch and the young stem—about life size (original). grubs, forming cells, feed in the walls of the stem, reaching their maximum growth by the time the straw becomes fully hardened and ripe. Wintering in the larval state, they pass a short pupal stage and emerge as adults in the spring. EFFECT ON THE STRAW. This is exceedingly variable. Sometimes a distortion of the straw occurs like that illustrated in figure 4; at other times the straw is bent or twisted in almost every conceivable shape; again there will be no 3 enlargement of the straw whatever ; or there may be large galls or ex- crescences, as it were, bursting out of the base of the sheath at one side, some of these abnormal growths hav- -ing pseudo-rootlets extending down- ward from their lower extremity. Sometimes the straw will make about normal growth and the hardened sec- tions will be restricted to an inch or thereabouts just above the lower joints; and, again, the growth will not exceed 3 or 4 inches, often not heading at all, or with aborted head and with the straw galled or hardened to the base of the head. In some cases there is no outward indication whatever of attack, the affected part being wholly inclosed in the sheath, and when this last is removed the presence of the cells is indicated only by a slight discoloration, and _ fre- quently by a few small, more or less irregular, elevated ridges. In threshing the grain the hardened portions of the straw, as shown in figure 5, break up into pieces of from half an inch to an inch or more in length, many of which do not go over with the straw and chaff, but remain with the grain. The presence of these bits of broken straw remaining in the grain is frequently the first evidence the farmer has seen of the presence of the pest in his fields. Mullers and elevator men note them also, and in sections where the pest has committed serious depredations several bushels of these hardened bits of straw are found after each day’s cleaning of the grain. EFFECTS ON THE KERNEL. The wheat heads from infested stems are foreshortened, and the number of kernels thereby necessarily Fie, 4,—One effect of the joint-worm in wheat . Straw (after Webster). = reduced in both size and number, and in case of severe attack they become shrunken. NATURAL ENEMIES. Natural enemies are quite numerous, and most of them have the advantage of being double-brooded, whereas the joint-worm has but one annual generation. Probably the most efficient enemy of this species is a small, slender, four-winged fly, with a somewhat brilliant metallic-colored body and yellow legs. This has a very slight resemblance to an Isosoma, and, indeed, was described as Isosoma allynii, now known as Eupelmus allynii French. A somewhat similar insect with metallic body and yel- low abdomen, Stictonotus isosomatis Riley, is very efficient in destroying the larve in the straw. Homoporus (Semiotellus) chalcidi- phagus Walsh and Riley and beyond a doubt other chalcidoids are also instrumental in holding the pest in check. These are all small four-winged flies, and a number of undescribed forms have recently been dis- covered. The larva of a small, slender, black and yellow carabid beetle (Leptotrachelus dor- salis Fab.) crawls up, descends into the stubble, and devours the Isosoma larve, but -unfortunately its taste seems to be too ob- tuse to allow it to confine itself strictly to Pe ee dia et ed, Sue Tsosoma, and as a consequence it devours maining with the grain after Parasites as. well as host. A mite, Pedven- threshing (original). loides (Hetoropus) ventricosus Newp., is also an enemy, gaining access to the larve precisely as does the beetle larva previously mentioned. PREVENTIVE MEASURES. There are no known remedies, but there are several preventive meas- ures that are not impracticable and are reasonably efficient. In the midst of the outbreak in Virginia, previously mentioned, a ‘* Joint Worm Convention’’ was held at Warrenton, in that State, to devise means for controlling this pest. This body recommended a better system of farming, the use of guano and other fertilizers to pro- mote arapid growth and an early ripening of the grain, and the burning of the stubble, all of which are as advisable to-day as they were at that time. The most serious ravages are observed on thin or impoverished soils, especially along the margins of the fields infested. Anything, then, that tends to add vigor to the young growing grain will constitute a preventive measure. Burning the stubble, where this is practicable, 5 ee, is, of course, most efficacious, but over the larger portion of the terri- tory ravaged by this pest it is customary to seed with grass after wheat, and under this condition burning over the stubble field is impossible. Such fields should be raked over with an ordinary hay rake, and the loosened stubble removed and burned before the adults have emerged in the spring. If, however, the grain is cut low at harvest, and the straw passed through the stables as bedding for stock during the winter, thus becoming saturated by liquids and more or less thoroughly composted, the treatment would seem sufficient to destroy the Isosoma larvee, so that few, if any, would develop adults the following spring. In case of bedding for horses, it seems quite probable that if any larvee survived at all the heat from the decomposing manure would develop them prematurely. However, there has been no experimentation along these lines, and according to a recent press bulletin! by Prof. R. H. Pettit, of the Michigan Agricultural College, serious injuries have fol- lowed the year after application and plowing under of barnyard manure in the fall before the wheat was sown. In this case the manure would necessarily be fresh and the bedding of straw of the same season’s growth, otherwise the adults would have already emerged. This would be a proposition quite different from that of allowing the stable manure to accumulate during the winter and applying it in the spring elsewhere than to the wheat fields, or even of applying it to wheat fields before plowing, months after the larve surviving the effects of the stable had developed and escaped. The one might destroy all or nearly all larvee in the straw, and the survivors would emerge about the stables or in the barnyard; while the other method, simply to take the straw with the living larve present from an old field, move it through the stable, cart it out on a new field, and plow it under, is one that the farmer should evidently be careful to avoid. Rotation of crops is advantageous, because it necessitates the migra- tion of adults from one field to another, and if this is done in stormy weather or during high winds, many of the migrants will be killed or blown astray. It is easily seen that where infested straw is applied to a new field prior to sowing to wheat, this migration of adults would not be made necessary. The sowing of early ripening varieties is also beneficial. Mich. Agri. Col. Exp. Sta., Press Bul. No. 15—The Wheat Joint Worm. Approved: JAMES WILSON, Secretary of Agriculture. WasHineton, D. C., October 20, 1905. O Ns oe , a aye ; Ceres Wieey 4 nee ay * We Rane Re Ra ve x oe SA a ee a a NN \ oo ae tp PLT ‘ \ . o Ly BERS Pee Ay Ny; 3, By SOS SAEED ONE S _. 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