9Y. IT; Circular No. 1 17. Issued February 25, L910 United States Department of Agriculture, BUREAU OF ENTOMOLOGY. L. O. HOWARD. Entomologis THE WESTERN <: i ( \ jit, a s occidt uli By I'. /;; Cha ' I cut unit (■KO. I. Kl Sin citil l"n ill \in nl IXTRODVCTIOX. ■;i — tem saw fly [Ve\ u, The western gra — tem sawfly {C'eplu Marlatt), which has caused much alarm ami irot-a li wheal growers of S'orth Dakota during the season of 1909, is not by any means a ne'w insect, although this is it- first appearance in the Fn I. Western Brass-stem snwflj [Cephun occidentalism: u. Larva; 6, female sawfly; isa stem showing work c, Rnlarged ; and has since been reported at intervals as feeding upon grasses and occa sionally upon wheal in Canada and the United States. For the pur pose of affording farmers all available information relative to the 2204H \... 1 i t" It) 2 pest this circular has been prepared. The account of the habits and seasonal history of the insect, list of food plants, and description of both larva and adult represent the work of the many observers men- tioned in the paragraph on history and distribution, as do also the clos- ing statements as to natural cheek- upon it- increase, and preventive treatment. HISTORY AND DISTRIBUTION. The first observation on this insect was made by Mr. Albert Koebele." an agent of this office, who found the larvae burrowing in grass stems in California in 1890, and who reared the adult-. From these and others which had been collected in Montana and Nevada the species was described by Riley and Marlatt, who said: "The eco- nomic importance of this species arises from the fact that it may be expected at any time to abandon its natural food plant in favor of the small grains, on winch it can doubtless successfully develop. Such changes in the food habits of our native insects are constantly occurring to the great detriment of our agriculture, as i- illustrated by the attack of the Nematus and Dolerus species on wheat, these insects normally affecting wild grasses." The fulfillment of this prophetic suggestion was not long delayed. In 1896 the late Dr. James Fletcher.'' entomologist to the Dominion of Canada, reported that he had found the adults, which he be- lieved were those of Cephus pygmceus L., the European species, at Indian Head. Northwest Territories [Saskatchewan | . and that Mr. John Wenman, of Souris, Manitoba, had sent in wheat straw- con taining larvae. Mr. Wenman wrote that the damage resulting from this attack was not appreciable. In 1902 Doctor Fletcher' found the larva' numerous in grasses in the Northwest. In L905, 1906, and 1907 the junior author observed the work of the larvae in grasses throughout the northwestern United States, and in 1906 found them damaging wheat at Kulm. X. Dak. In his report for the year l'.MIs Doctor Fletcher again referred to tins insect, stating that in the pre- vious autumn it had appeared in central Manitoba and the south eastern part of Saskatchewan in much more serious number- than at any previous time. " The broken straws which resulted from its attacks were seen in many fields and occasioned some alarm." Mr. Norman ( 'riddle ''--a farmer and careful observer of insects, of Aweme, Manitoba, and the inventor of the grasshopper poison which bears his name — recognized the insect a- Cephus occidentalism and wrote Doctor Fletcher at the end of the season that the species had increased Insert Life. Vol. III. |>. 71. 1S90. ''Ann. Rep. Exp. Farms Canada f. 1896, pp. 229 230. 1897. <•■ Letter. ''Ann. Rep. Exp. Farms Canada f. 1907 S, pp. mi 192, 1909. ICir. 1171 3 considerably during the last year or two and had turned its attention in wheal and rye. In 1908 the authors found it in grasses in the Willamette Vallej in Oregon. In 1909 Prof. II. B. Penhallow, of New York City, writing from Sherwood. X. Dak., stated that it was damaging from '> to 25 per cent of the wheat in man) fields in i he Souris Valley, and Mi'. R. VV. Sharpe, of Fargo, X. Dak.. reported similar depredations in the Red River Valley. Larva' or adults have been found in Manitoba, the Dakota-. Nebraska, Kansas (probably), Saskatchewan, Montana, Wyoming, Colorado, Oregon. \c\ ada. and Call fornia. II VBITS VXD SEASOM \l. HISTORY. In Manitoba, according in Mr. Criddle," the eggs are laid singlj by the female sawfly i fig. 1. b) upon a stem of grass or wheat, not far from the head, between June 20 and the second week id' July. ••The larva' (fig. 1. a) soon hatch and begin to eat down inside the stem, usually reaching the ground toward the end of August, at which time they mature." They then cut a horizontal ring on the interior of the stem near (he surface of the ground so a- nearly to sever it. after which the\ close the cavity below smoothly with a plug id' castings and -pin a thin, silken, cylindrical cocoon below the plug (fig. 1. i i. The -tem usually breaks oil' neatly at the engraved ring during the autumn, hut may remain in position until winter and possibly longer. "In these retreats," to quote again from Mr. Crid die. "the larvae pass the winter and remain in an active condition unchanged until May of the following year, when they turn to pupa?. and emerge a- perfect sawflies toward tin' end id' dune, the date vary ing somewhat with the season." The adults were taken by Doctor Fletcher,' duly 5, on the flowers of tumbling mustard. The injured stem appears discolored between the first and third joint- and the larva may he seen through the translucent wall of the ?tem when' ii is eaten thinnest. In the case of wheal, the stalk often bends at this point, an inch or two below a joint rather than above a- in He— ian fly injury, and the head fall- to the ground shortly before harvest. Dr. d. II. Comstock' found that the European corn -awtlv. an allied species, did not affect I he size of the head or of the kernels, but it is well known that grasses have the heads blighted by our species, and Professor I'enhallovv writes that the head- id' wheat are shrunken Owing In the diver-ion id' sap at this critical time. If this l»e generally true, the damage to the crop i- much greater than ha- been estimated from the number of fallen head-. Mi-, ('riddle" "Ann. Rep. Exp. Farms Ca inula f. 1907 8, pp. 191 192. 1909. i. Rep. Exp. Farms Canada t'. 1896, pp. 229 230, 1897 i:nl. ll. Cornell Univ. Agr. Exp. Sta., N'ovember, IS89. I 171 states that in a field of wheat at Awenie, .Manitoba. 75 per cent of the infested stems collapsed before harvest, but we observed a field at Kulm, X. Dak., to have only 6 per cent of the injured straws broken. The native grasses do not collapse when attacked by this insect and it is possible that some stiff-stemmed wheats may stand up better than other varieties. This is an advantage to the fanner in preventing total loss of the affected heads, but a disadvantage if it prevents him from detecting the cause and extent of a serious shrinkage of the kernels. The damage has been confined heretofore to the edges of fields bordered by grass lands or roadsides. Mr. Criddle" states that 50 per cent of the stand is infested for a distance of 100 feet into the fields, and that the damage is apparent to a lesser extent throughout the crop. Pie also states that the insect seeks wheat only when it fails to find enough flowering stem- of grasses in which to deposit its eggs. Recent reports from North Dakota indicate that the injury may be more general than heretofore and suggest that the insect has probably adapted its habits to conform to the farm methods of thai region so that it no longer depends upon native grasses 1 nit breed- throughout the fields, at once distributing the damage more evenh and increasing its capacity for harm. A pest which can take advan- tage of wild food plants and yet be independent of them is far more dangerous than one which can feed only upon wheat or one which requires both wheat and a native grass. FOOD PLANTS. This sawlly is a native insect which has learned to attack wheat and. according to Mr. Criddle, rye also, since these have taken the place of its native food plants — quack grass and wheat grass ( Agropyron i. brome grass (Bromus), rye grass (Elymus), and timothy (Phleum). It was especially abundant in Agropyron along railroad embank ments in North Dakota in 1905 and 1906, so that in many clumps of this grass onedialf of the heads were prematurely whitened. DESCRIPTION. The larva (fig. 1. a) is about three-fifths of an inch long and one- eighth as wide, slightly Larger near the head, and tapering toward the tail, which ends in a small, blunt, upturned, brown tubercle. The body is yellowish white: the head, a spot on the back of the neck, rings on the palpi, the tips of the paired cerci. and the setae on the last segment, are pale yellow: the margin of the cheeks and of the antenna! segments, a faint streak on each cheek through the eye. the mandibles, the stigmata, and the median anal tubercle, are mahogany " Loc. cit. [Clr. 117] .) brown; the mandibles shade to black ;il the t i f » — and ;ii the hii the eyes are black. The adult (fig. 1. I>) is a black, shining, four-winged saw fly, about one-third of an inch long, spotted and banded with yellow. The original description" is as follows: The ;uliili insect agrees almost exactly with Ci pint* iii/ymtrux in colont coming much '-loser to it in tliis respect than to any other American species, but is in every way more slender and graceful and would never be mistaken for the European species. The head is narrower in proportion to the body aud is more globular when viewed from the side. Viewed frou uarrows more pos teriorlj from the eyes than iii/iiiikiiis. * * * The species may be characterized as follows: 2 Black; basal joints of the maxillary palpi, large spol on mandibles, two spots beneath anterior wings, membranous regions of thorax, small spot on lower posterior edge of dorsum of first segment, larger one on second segment, band, dentate on basal margin, on apical half of dorsum of third, fifth, and sixth segments, and more or less of the lower and apical margin of the re maining segments, lemon yellow. Legs black, slender: spot on posterior coxa- above, upper side and tip of femora, yellow; tibiae and tarsi reddish yellow except tips of posterior tibia 1 and their tarsi, which are brownish; last joint and .laws of middle and an- terior tarsi also brownish. Antenna' 20 i'| jointed, longer than head and thorax, slender to joint T. beyond which the articles are shorter and thickened Wings slightly smoky: veins brown except costal and margin of stigma. which are yellowish: a small infuscated spot at base of discoidal vein: second recurrent vein joins the third submarginal cell near the base of the cell; cross veins of lanceolate cell slightly curved and oblique. Abdomen not much longer than bead and thorax, strongly compressed laterally. Lengt h. '.» I 1 nun. Exp. al., 16 19 mm. $ smaller and more slender than the 9: abdomen less c pressed; antenna' 18 21 jointed. Coloration as in ? except a large spot on the clypens. one jnsl below the eyes in front, the entire pectal region of the thorax, and the posterior margin of the third, fifth, and remaining ventral segments, which are lemon \ ellow. The miller side of the coxa?, trochanters, and femora, including the apex of the latter above, are lemon yellow; the tibia- and tarsi are as in the case of the $. In some specimens the femora are entirely yellow or with a narrow black line on the anterior pair above, and the yellow band on the third ventral seg- ment is occasionally obsolete. Length, s nun. Exp. al., 15 IT nmi. Habitat: Santa Clara County and Santa i 'in/ Mountains, California, Sevada, and Montana. Described from 2-t females and II males, of which 'S* specimens from Cali- fornia were bred bj Mr. Koebele, and 1.". from Nevada and Montana were collected. Insect Life, Vol. IV. pp. 177 17s. I Sill. [Cir. 1 171 NATURAL CHECKS. Mr. ('riddle found thai many of the broken stem? of infested whcai had bent in such a way as to crush and kill the larva which was working at the point where the stem collapsed. Since the stem- of grasses do not break under the attack, this is a danger which the in- sect has incurred by changing to a new food plant. This form of accident materially reduces the number of individuals which may reach maturity and deposit eggs in the wheat, since from 6 to 7.~> per cent of the infested stems break near the point where the larva is working, shortly before the larva reti'eats toward the roots to pre- pare for hibernation. Parasites were reared by the junior author from larvae collected at Minot, X. Dak., belonging to an undescribed specie- of the Chalcidid tribe Entedonini. PREVENTIVE MEAS1 R] S. Mr. Criddle tried burning the stubble in the autumn with the aid of straw scattered over it, but found thai the larva' were not much damaged thereby. A remedy which suggests itself and has been practiced to some extent is the plowing down of all stubble, either in autumn or before June 15, at which time the adults may lie expected to emerge and deposit eggs. Grass growing near the edges of fields should be mowed early in July, while the larvae are small, to prevenl them from maturing and attacking the crop of the following year. Approved : James Wilson. St - /■' tary <>i . I griculturi . Washington, I). C, December 24, 1909. [Clr. 117] o Digitized by the Internet Archive in 2013 http://archive.org/details/wstemOOunit «ii|ig«