- irv Circular No. 66, Revised Edition. I I oited States Department of Agriculture, BUKKAU OF BNTOMOLO Entomologiiit and Cli J0INT-W01 i !i< h i I M WSBBTl i: m! Forage Plant l since the first known Berious outbreak of the joint-worm (Isosoma tritici Pitch), which occurred in the wheal fields about Charlottesville and Gordonsville, Va., during the years 1848 to 1854, this insecl has been reported ;it irregular in ten alsand from* idely separated localities. While it i- known to occur sparingly over most of the wheat-growing sections of both the United State- and Canada, and probably _• 7 1 s Cir. Bl 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, in its various stages of devel- opment, throughout the year. It lives through the 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, 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 eggs in the • ■ stems. The exact posi- tion assum- ed is shown in figure 3, from a photograph from life by Mr. G. I. Reeves. The eggs Fig. 3.— Female Isosoma In act of depositing egg in hatch and the young grubs, stem. About lite size (author's illustration). f ormmg ( . e jj. s feed ill the Avails of the stem, reaching their maximum growth by the time the straw becomes fully . udened 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. [Or. LO] Fig. 2.— Isoxoma grnndc Larva of the wheat- straw worm; r, anten- na; /. jaw. Line at right indicates natural length. (After Riley.) 8 Mr. Phillips of thifl Bureau has, during two successive years, found thai "unfertilized females \\ ill deposil ami thai these eggs \\ ill hatch out larvie which develop to adull insects. It is pr< ibable, how ever, thai these adults w ill be round to be ■l\ 01 till males. iiiii i o\ i hi s 1 1; \\v. The effecl on the straw of the work of the joint- worm is exceedingly vari- able. Sometimes .1 distortion occurs like thai illustrated in figure I ; a1 other times the straw i-> benl or twisted iu almosl even conceivable shape; again, there will be no enlarge- ment of the straw whatever; orthere nun be large galls or excrescences, as it were, bursting oul of the base of tlu« -heath at one side, some of these abnormal growths having pseudo- rootlets extending downward from their lower extremity. Sometimes the straw will make about normal grow th and the hardened sections will be restricted to an inch or there- abouts just above the lower joints; and, again, the growth \\ ill nol exceed :; or f inches, often nol heading at all, or with aborted head and with the straw galled or hardened to the base of the head. In some oases there is no outward indication of at- t.-u k whatever, the affected pari be- ing \\ holly inclosed in the sheath, and when thislasl is removed the presence of the cells i- 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 5, break up into pieces of from halt an inch to an inch or more [dr. 06] in length, many of which do no! 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 OX 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 aureovirid'ts Crawford, and the other, smaller, darker colored, and slender, also somewhat resembling an Isosoma, is Eupelrnus allynii French. The writer reared also another species in Ohio, Websterellus tritici Ashm., which has similar habits. A somewhat similar insect with metal- lic body and yellow abdomen, Stictonotus isosomatis Riley, is very efficient in destroy- ing the larva 1 in the straw. Homoporus (Semiotdlus) chalcidijihagus 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 small, slender, black and yellow carabid beetle (Lepto- trachelus dorsalis Fab.) crawls up, descends into the stubble, and de- vours the Isosoma larvae, 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 (Hetoro'pus) ventricosus Newp., is also an enemy, gaining access to the larvae precisely as does the beetle larva previously mentioned. [Cir. 66] Fig. 5.— Bits of hardened straw re maining with the grain after thrash ing. (Author's illustration.) I-Kl \ I \ I l\ I mi \-i 1:1 There are no known remedies for the joint-worm, but there are several preventive measures t lmt are not impracticable and are reasonably efficient . In the nudsl of tin- outbreak in Virginia, previoualj mentioned, a 'Joint-worm Convention" was held at Warrenton, in that State, to devise means for controlling tlii- pest. ' I " 1 1 i — bod} recommended a better system of farming, the use of guano and other fertilizers to pro- mote a rapid grow th and an earl) ripening of the grain, and the burning of the si iil>l>l»\ nil of \\ 1 1 irli arc as n<\\ isable tt)-tla\ as thej were at thai time. The nu>--t serious ia\ ages are observed on thin <>i- impoverished soils, especially along the margins of the fields infested. Anything, then, that tends to add vigor to the young grow inu r grain will constitute a |>iv\ entive measure. Burning t In- st ubble, \\ here i his i- pract icable, is, of course, most efficacious, but over the larger portion of the terri- torj ravaged by this pesl it is customary to seed with grass after wheat, and under this condition burning over the Btubble 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. It', however, the grain is cul low at harvest, and the straw passed through the stables as bedding for Btock during the winter, tlm> becoming saturated by liquids and more or less thoroughly composted, the treatment would seem sufficient to destroy the [sosoma larva? so thai few, if any. would develop adults tht" following spring. In case t>f bedding for horses, it seem- quite probable thai if an\ larvae at all survived the thrashing machine, the heat from the decomposing manure would develop them prematurely. However, there has been nn experimentation exactly along these lines, and according to a press bulletin by Prof. K. II. IVttit, 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 t»f straw t>f 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 t he winter ami applying it in the spring elsewhere than to the wheat fields, <>r even of applying it to wheat fields before plowing, months after the larva surviving the effects of the stable had developed and escaped. The one might destroy all or nearly all larva' in the straw, ami the survivors would emerge about the .-tables or in the barn van I : while the other met hot I. -imply to take the straw with the living larvae present from an old field, mov< ■■ Mi.-li. A. ip. S P l">. The Wheat Joint-Worm. through the stable, cart it out on a new field, and plow it under, is one that the fanner 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 street- a pile of bricks to be used in the erection of a building. These bricks were stamped "MftS- sillon, Ohio,'' and were packed in straw which the chief contractor stated came with the bricks from Ohio. This straw contained larvae 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 grain 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- f/, '.* ,« i |\ Vl 71! ing machines, has shown that almost all of the larvae 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- tions of stubble from fields in the vicinity of these ele- vators. So far as we have gone into the investigation everything indicates that the danger from these broken bits of hardened straw, or even from t he st ra w 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 larva' deftly eaten away, and the joint-worms missing. In no case was the entire gall gnawed aw ay, but just enough of the walls immediately over the larva to make pos- sible the removal of t he latter (fig. 6). While we have not been able to get definite information as to the identity of this decidedly beneficial animal, suspicion seems to point to the short-tail shrew (Blariita' [Cir. 1.'.] Fig. 0.— Wheat straws injured by the joint-worm (Isosoma tritici), from which the joint-worms have been removed by some beneficial animal, perhaps the short -tail shrew (Blarina breiicauda). (Author's illus- tration.) icauda) as the species to which credil Bhould be given, and prob- a l,|, muc h of the work is done while the grain is in shock. Rotation of nop-, is advantageous, because il necessitates the migration of adults from one field to another, and if this takes place in stormy weather or during high winds, manj of the migrants will be killed or blown astray. Il is easily Been thai where infested strav is applied to a aev. field prior to Bowing to wheat, this migration of adults would not be made oecessarj . The Bowing of early ripening varii ties is also beneficial. Approved : .1 Lit ES WlLS< )\ . Secretary of Agriculture. Washington, D. C, July 16, 1908. |CU O UNIVERSITY OF FLORIDA 3 1262 09216 4507