DLV. INSECTS a ; 66, REVISED EDITION. ; Issued September 21, 1908. C578 ited States Department of Agriculture, ENT . BUREAU OF ENTOMOLOGY, L. 0. HOWARD, Entomologist and Chief of Bureau. THE JOINT-WORM. (Isosoma tritict Fitch.) By F. M. WressTER, In Charge of Cereal and Forage Plant Insect Investigations. Since the first known serious outbreak of the joint-worm (/sosoma tritict Fitch), which occurred in the wheat fields about Charlottesville and Gordonsville, Va., during the years 1848 to 1854, this insect has beenreported atirregular intervals and from 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 attributed to it, its reappear- ance in the wheat fields of Indiana, Michigan, Ohio, Pennsylvania, Sy Fia. 1.—Jsosoma tritici: Adult of the joint-worm. Much enlarged (from Howard). West Virginia, Virginia, Maryland, and 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 in 1905 a serious outbreak in northeastern Indiana so discouraged some farmers that they questioned the advisa- bility of putting in a crop of wheat at all. In southwestern Virginia the pest was even more injurious in 1905 than it was the previous year. The pest was also very destructive in western Ohio and eastern Indiana during the spring of 1908. 52718—Cir. 66—08 2 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 and feet yellow. The larva 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 in wheat stems, inits various stages of devel- opment, throughout the year. It lives through the winter asa larva or grub in cells formed in the stems prior to the ripening of the grain, the adult emerging therefrom in April or May, ac- cording to latitude, or some time after the young grain has thrown up stems and several joints have become ex- posed. The female, us- ing her slen- der, pointed oviposit or, places her eges in the stems. The Fig. 2.—Isosoma grande: exnat; (DOS iacaeen baie tion assum- — na; f, jaw. Line at ed is shown “she ndcatr natura in figure 3, from a photograph from life nuqyes le by Mr. G.I. Reeves. The eggs Fig. 3.—Female Isosoma in act of depositing eggin hatch and the young grubs, stem. About life size (author’s illustration). 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. While there are both males and females among these insects, [Cir. 66] 3 Mr. Phillips of this Bureau has, during two successive years, found that unfertilized females will deposit egos and that these eggs will hatch out larve which develop. to adult insects. It is probable, however, that these adults will be found to be largely or all males. EFFECT ON THE STRAW. The effect on the straw of the work of the joint-worm is exceedingly vari- able. Sometimes a distortion 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 enlarge- ment of the straw whatever; or there may be large galls or excrescences, as it were, bursting out of the base of the sheath at one side, some of these abnormal growths having pseudo- rootlets extending downward from their lower extremity. Sometimes the straw will make about normal growth and the hardened sections will be restricted to an inch or there- abouts 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 of at- | tack whatever, the affected part be- ” ing wholly inclosed in the sheath, and when this last isremoved the presence of the cells is indicated only by a slight discoloration, and frequently by a few small, more or less irregu- lar, elevated ridges. In thrashing the grain the hard- ened portions of the straw, as shown in figure Dy break up into pieces of Fia.4.—One effect of the jnint-wourtnpeheat from half an inch to an inch or more ES Gumerteaeta vite [Cir. 66] 4 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 in the grain is frequently the first evidence the farmer has seen of the occurrence of the pest in his fields. Millers and elevator men note them also, and in sections where the pest has committed serious dep- redations 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 kernels thereby necessarily reduced in both size and number, and in case of severe attack they become shrunken. NATURAL ENEMIES. Natural enemies of the joint-worm are quite numerous, and most of them have the advantage of being double-brooded, whereas the joint-worm has but one generation annually. Among the most efficient of these are two rather common species of insects. One of these, almost as big as the Isosoma itself, with dull metallic thorax and yel- low abdomen and with long ovipositor, is Ditropinotus aureoviridis Crawford, and the other, smaller, darker colored, and slender, also somewhat resembling an Tsosoma, is Eupelmus allynii French. The writer reared also another species in Ohio, Websterellus tritic) Ashm., which has similar habits. A somewhat similar insect with metal- lic body and yellow abdomen, Stictonotus Fig. 5.—Bits of hardened straw re- isosomatis Riley, is very efficient in destroy- cay arate eames i ing the larve in the straw. Homoporus (Semiotellus) chalcidiphagus 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 additional, undescribed forms have been discovered. The larva of a smail, slender, black and yellow carabid beetle (Lepto- trachelus dorsalis Fab.) crawls up, descends into the stubble, and de- vours the Isosoma larve, but unfortunately its sense of taste seems to be too obtuse to allow it to confine itself strictly to Isosoma, and as a consequence it devours parasites as well as host. A mite, Pedicu- loides (Hetoropus) ventricosus Newp., is also an enemy, gaining access to the larvee precisely as does the beetle larva previously mentioned. [Cir. 66] 5 PREVENTIVE MEASURES. There are no known remedies for the joint-worm, but there are several preventive measures 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 a rapid 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 stubbie, where this is practicable, 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 larve so that few, if any, would develop adults the following spring. In case of bedding for horses, it seems quite probable that if any larve at all survived the Figen machine, the heat from the decomposing manure would develop them “cama However, there has been no experimentation exactly along these lines, and according to a press bulletin® by Prof. R. H. Pettit, of the Michigan Agricultural College, serious injuries have followed 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 Hain the larve surviving the effects of the stable had developed and escaped. The one might destroy all or nearly all larve 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 a Mich. Agr. Col. Exp. Sta., Press Bull. No. 15.. “The Wheat Joint- Worms [Cir. 66] 6 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. Exactly in this connection, an assistant, Mr. Charles N. Ainslie, while waiting between trains in the city of St. Louis, Mo., found at the corner of Sixteenth and Locust streets a pile of bricks to be used in the erection of a building. These bricks were stamped ‘‘ Mas- sillon, Ohio,” and were packed in straw which the chief contractor stated came with the bricks from Ohio. This straw contained larvee of this species which later on transformed to adults, but the latter did not emerge from the straw. In the past it has always been thought necessary, as a precautionary measure, to burn the infested bits of hardened straw that break up in thrashing the wheat, many being carried out with the erain instead of going over in the straw. Several experi- ments in rearing adults from large numbers of these broken bits of straw (fig. 5), collected about elevators and thrash- ing machines, has shown that almost all of the larve of both Isosoma and parasites are killed, probably by the concussion of the cylinder of the thrasher. In some cases we have been able to verify these experiments by collec- Fic. 6.—Wheat straws injured by the joint-worm wun of stubble from fields (Isosoma tritici), irom which the joint-worms have IN the vicinity of these ele- been removed by some beneficial animal, perhaps the vators. So far as we have short-tail shrew (Blarina brevicauda). (Author’s illus- . : : tration.) gone into the investigation everything indicates that the danger from these broken bits of hardened straw, or even from the straw itself, is of too little importance to be worth consideration. Prof. R. H. Pettit, of the Michigan Agricultural College, and Mr. W. J. Phillips, of this Bureau, in 1906, found in northern Indiana great numbers of straws affected by the joint-worm, where the enveloping sheath had been torn away, the galls formed by the larvee deftly eaten away, and the joint-worms missing. Inno case was the entire gall gnawed away, but just enough of the walls immediately over the larva to make pos- sible the removal of the latter (fig. 6). While we have not been able to eet definite information as to the identity of this decidedly beneficial animal, suspicion seems to point to the short-tail shrew (blarina (Cir. 66] \\M\ 7 brevicauda) as the species to which credit should be given, and prob- ably much of the work is done while the grain is in shock. Rotation of crops is advantageous, because it necessitates the migration of adults from one field to another, and if this takes place 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. Approved: JAMES WILSON, Secretary of Agriculture. WasuinerTon, D. C., July 16, 1908. [Cir. 66] O 9088 01272 7319