SB 818 C578 ENT Issued July 10, 1912. eS DEPARTMENT OF ACKRICUL TURE, BUREAU OF ENTOMOLOGY—CIRCULAR No. 152, L. O. HOWARD, Entomologist and Chief of Bureau. THE RICE WATER-WEEVIL AND METHODS FOR ITS CONTROL. BY E. S. TUCKER, Entomological Assistant. WASHINGTON : GOVERNMENT PRINTING OFFICE: 1912 22a bb BUREAU OF ENTOMOLOGY. L. O. Howarp, Entomologist and Chief of Bureau. Cc. L. Maruatr, Lintomologist and Acting Chief in Absence of Chief. R. S. Crirton, Haeccutive Assistant. W. F. Tastet, Chief Clerk. F. H. Cuirrenven, in charge of truck crop and stored product insect investigations. A. D. HopxKins, in charge of forest insect investigations. W. D. Hunter, in charge of southern field crop insect investigations. I’. M. WEBSTER, in charge of cereal and forage insect investigations. A. L. QUAINTANCE, in charge of deciduous fruit insect investigations, i. F. Puiuirs, in charge of bee culture, DD. M. Rogers, in charge of preventing spread of moths, ficld work. Ro.xta P. Curriz, in charge of editorial work. MABEL CoLcorD, in charge of library. SOUTHERN T1IELD Crop INSEcT INVESTIGATIONS. W. D. Hunter, in charge. W. D. Pierce, G. D. Smiru, J. D. MircHeLtt, Harry PinKkus, B. R. Coan, R. W. MorRELAND, engaged in cotton-boll weevil investigations, FI. C. Bisuopp, A. H. JENNINGS, H. P. Woop, W. V. KiNG, engaged in tick investi- gations. A. C. MorGan, G. A. RUNNER, S. E. Crump, D. C. PARMAN, engaged in tobacco insect investigations. T. E. Hottoway, HE. R. BArBer, engaged in sugar cane insect investigations, EH. A. McGrecor, W. A. THOMAS, engaged in red spider and other cotton insect investigations. J. L. WEBB, engaged in rice insect investigations, R. A. Cootey, D. L. VAN DINE, A. F’. Conrapi, C. C. KRumMBHAAR, collaborators. II CIRCULAR No, 152. Issued July 10, 1912. United States Department of Agriculture, BUREAU OF ENTOMOLOGY. L. O. HOWARD, Entomologist and Chief of Bureau. THE RICE WATER-WEEVIL AND METHODS FOR ITS CONTROL. (Lissorhoptrus simpler Say.) By EH. 8S. TucKEr, Entomological Assistant. ECONOMIC IMPORTANCE. The most serious insect enemy of growing rice in the Southern States is the rice water-weevil (Lissorhoptrus simplex Say) (fig. 1). When in its larval stage, the insect is known to rice growers as the “rice root-maggot.” The larve feed on the roots of rice plants, and the adult weevils cause some harm by feeding on rice leaves. Owing to the extensive growing of rice in sections of Louisiana, Texas, and Arkansas within recent years, the weevil has found very favorable conditions in the rice fields for its multiplication in propor- tion to the increase of the acreage and to the number of years in which rice has been grown in any section. The development of definite rice-growing areas in these States has naturally resulted in particular centers of high infestation by the weevil. Rice growing has consequently been attended by great damage to the crops on account of the insect’s attacks. The amount of loss that is occasioned by the attacks is difficult to estimate, as the reduction of yield has been variously reckoned in different localities. Since all fields are not affected alike and differ- ent portions or spots of a field are apt to suffer the severest injuries, although the plants seldom fail outright, the growers differ much in their opinions of the extent of damage which they sustain, but all agree in the declaration that it is considerable. General statements of the shortage of production include a report by a grower at Beau- mont, Tex., who placed his loss as low as 1 per cent; but the attacks in some fields at Stuttgart, Ark., have been severe enough to cut down the yield as much as 75 per cent. 9, THE RICE WATER-WEBEVIL. Fic, 1.—The rice water-weevil (Lissorhoptrus simplex) : a, Rice plant showing injuries; b, larval scars on section of root; ¢, section of rootlet showing feeding scars; d, water line; e, é, €, roots severed by larve ; f, injured leaf; f’, enlarged section of injured leaf; g, adult beetle, dorsal view, much enlarged; h, antenna of beetle, more enlarged; i, larva, side view, much enlarged; j, enlarged segment of larva, lateral view; k, dorsal structure of larva. (Original.) THE RICE WATER-WEEVIL. 8 The recent work of the bureau on the rice water-weevil was begun in 1910 by Mr. C. E. Hood, working under the direction of Mr. D. L. Van Dine. The present writer began work on the problem in 1911. In this circular many notes made by Mr. Hood are incorporated. The object of this paper is to give as much practical information as is now available about the weevil and measures for its control in order that rice growers may make proper efforts in fighting the pest and secure larger crops. The cooperative facilities afforded by the Agricultural Experiment Station of Louisiana, through Prof, W. R. Dodson, director, in providing accommodations at the State Rice Station, Crowley, La., and allowing free use of the unpublished notes comprising a preliminary investigation of the rice water-weevil by Mr. Wilmon Newell, in 1909, deserve grateful acknowledgment. HISTORICAL ACCOUNT AND DISTRIBUTION. The weevil was originally described in 1831 as Bagous simplex by Thomas Say. It and another species of weevil were given the generic name of Lissorhoptrus by Dr. J. L. LeConte in 1876. Le- Conte and Horn have stated that the weevil commonly inhabits swampy places throughout the eastern part of the United States. Its northern range extends into the Lower Peninsula of Michigan, according to Hubbard and Schwarz, and Dury has recorded the spe- cies as being taken near Cincinnati, Ohio. It is also reported from New Jersey, Maryland, and the District of Columbia. Mr. E. A. Schwarz has concluded “ that the genus Lissorhoptrus occurs all along the Atlantic coast (including the Gulf of Mexico), recurs along the Great Lakes, and is occasionally found inland.” As an injurious insect, the species first attracted the attention of rice farmers along the Savannah River in Georgia and South Caro- lina. In 1881 Dr. L. O. Howard visited a rice plantation known as “ Proctor’s,” and owned by Col. John Screven, on the South Carolina side of the river, a short distance below Savannah, Ga., for the pur- pose of studying the insects affecting rice crops. An account of his observations, including notes on the rice water-weevil, was published in the report of the United States Commissioner of Agriculture for 1881 and 1882. But little advance has been made in further knowl- edge of rice-crop insects up to the present investigation. DESCRIPTIONS OF STAGES. The adult——The mature insect is a small, dark-gray weevil (fig. 1,7). The technical description by Mr. E. A. Schwarz in the account above mentioned is here quoted: Lissorhoptrus simpler—tImago: Average length from tip of thorax, 3 mm. Oblong-oval, covered with large, dirt-colored scales, but usually entirely en- 4 THE RICE WATER-WEEVIL. veloped in an argillaceous coating, which renders scales and sculpture irrecog- nizable. Rostrum stout, as long as head and thorax, subcylindrical, densely rugosely punctulate, neither sulcate nor carinate; head densely punctulate. Thorax as long as wide, constricted anteriorly, lateral lobes well developed, sides moderately rounded, base truncate, a finely impressed median line, sur- face densely rugosely punctate, sides at middle with a shallow transverse im- pression. . Elytra much wider at base than thorax and about twice as long; humeri oblique, strongly declivous at apex, punctate-striate, interstices wide, subconyex, 3d and 5th more prominent at declivity than the rest. Prosternum flattened, transversely impressed in front of coxze; abdomen coarsely punctate. Tibiz somewhat curved, armed with a strong terminal hook; tarsi narrow, third joint not emarginate; claws slender, approximate. Very little difference exists between the sexes. The females usually have a slightly larger body than the males, and are often more dis- tinctly marked with a black area on the back. The marks of colora- tion, however, show more plainly on live moistened specimens in the field than on dry examples either alive or dead. According to Mr. W. D. Pierce, a secondary sexual character is presented by the con- figuration of the scrobe on the beak. He has determined that the scrobe of the female is slightly curved, but in the male it is practi- cally straight. These fine distinctions are difficult to make out with certainty on account of the natural curvature of the beak. The pupa.—No example of the pupa fit for description has yet been obtained, as it is very soft and any slight pressure or touch that is ex- erted in attempting to remove one from the mud crushes or distorts it. The egg—All attempts to secure deposited eggs have afforded only partial results. For purposes of description dependence must at present be placed upon the appearance of eggs obtained by dissection of gravid female weevils. Mr. Wilmon Newell, in presenting a de- scription based upon such observations, has stated that the egg is pure white, cylindrical and slightly curved in form, and has a length about five times the diameter. It is barely visible to the naked eye. LIFE HISTORY. SEMIAQUATIC HABITS. Water is an element in which the weevil delights. It swims readily on or beneath the surface, and it feeds, rests, and mates almost as fre- quently in the water as above it. To determine how long the adults can live under water, Mr. C. E. Hood conducted a test in which one weevil died after passing the first 24 hours of submersion, but two did not die until after being kept submerged for fully 96 hours. The weevil does not carry a bubble of air for breathing purposes when it _goes below the surface, although tiny globules of air are apt to adhere to parts of the body. Without water, the insect can not breed. The eggs are probably deposited on roots under water or in mud, and the THE RICE WATER-WEEVIL. 5 larva, and doubtless also the pupa, require a bed of saturated earth in which to live. Wet conditions of soil with suitable vegetation appear to be necessary for the development of all the stages. FOCD PLANTS. The semiaquatic life of the insect demands that its proper food plants be adapted for growing in moist situations or entirely in water. The adult weevil itself is not disposed to feed on any plant unless the roots are at least partially covered with water or soft mud. In South Carolina Dr. Howard observed weevils feeding on “ Sagit- taria, Scirpus, Cyperus, Nymphea, and Nuphar ”—plants commonly known as arrowhead, bulrush, galingale, water lily, and spatter-dock. Besides these, he reported wild rice (Zizania aquatica) as well as cultivated rice (Oryza sativa). One specimen has been collected as a visitor on Baptisia at Victoria, Tex. All positive records of addi- tional food plants refer entirely to grasses and they are the result of observations that were mostly made in Louisiana. Mr. Hood has re- ported some of the Louisiana grasses by the common names of “ bull grass” and “nigger’s wool,” which grew at Crowley. “Hurrah grass” was recorded by Mr. D. L. Van Dine at Matagorda, Tex. Adult weevils fed on the leaves of these undetermined grasses and the larve were found on the roots of the first, which was identified by the writer as a Paspalum and was said to have been introduced into the country. “ Bull grass” is a very common term in the section and refers to several species of grasses. The occurrence of weevils on Walter’s swale grass (Paspalum membranaceum) was first observed by Mr. Newell at Lake Arthur, La. While similar observations have been made by the writer at Crowley, La., and Pine Bluff, Ark., the finding of larve on the roots of the grass at Crowley presented complete evidence of the true host relationship of the plant. This fact, however, may have been dis- covered by Mr. Newell two years previously at the same place where he found larve infesting the roots of a stocky Paspalum, which he was inclined to regard as another species. Also during the season of 1911, at Crowley, La., the writer found two other species of grass which attracted the weevils from the nearest rice plants. One of these was Bermuda grass (Capriola dactylon). It grew on a levee in a rice field which had become partly overflowed with the flood water. As an attempt had been made to grow it on the land previous to the rice crop, its occurrence under flooded conditions was exceptional, and no larve were found attack- ing the roots. It can not be considered as a proper host plant. In the other case, a bunch of “ water crab grass,” undoubtedly a species of Syntherisma, was making a desperate struggle for existence 6 THE RICE WATER-WEEVIL. 4 within a flooded rice field. Having evidently started into growth before the field became irrigated, this crab grass was able to live in a depth of about 6 inches of water. Not only were the leaves severely fed upon by weevils, but the roots were attacked by larve. APPEARANCE OF ADULTS IN RICE FIELDS. Since the growing of rice offers special inducements for the breeding of the weevil, due to the attraction of the plants and the wet condi- tions which they demand for growth, rice has become the favorite food plant of the insect. Directly after the rice fields are flooded the weevils appear and commence feeding on the leaves of the young plants. In southern Louisiana, where much of the water is supplied by canals, the irrigation of rice fields usually begins in the first week of May, but the time of turning on water in different fields is often later, the flooding sometimes not being done until in July to accord with late planting. Where water is pumped onto the fields, a steady flow must be maintained for several days before any large area of land can be inundated.- The flooding of fields in Arkansas is not generally effected earlier than the middle of June. By following the application of water in every field the weevils gather most numerously on plants that stand in the depressions and lower portions having the deepest flood. Mr. Hood has counted as many as 18 weevils on a stool and 12 on a single plant. An average of at least 1 weevil to every 5 or 6 plants in one field has been reckoned by Mr. Newell. Some inclination to avoid direct sunlight during days of hot weather is shown by the weevils, as they seem to prefer positions in the shade of the plants and under the surface of the water. | They are rather sluggish except when swimming and are disposed to feign death if taken in the hand. They show no inclination to fly during the day and even refuse to expand the wings on being tossed into the air. Passage between separate plants is accomplished in the daytime by swimming. That they can fly for long distances, however. is clearly proven by their attraction to artificial lights at night. This propensity will be more fully discussed with reference to methods of control. Invasion of fields must therefore be con- summated at night. NATURE OF ATTACKS BY ADULTS. Rice is attacked in the same manner as other similar host plants and the effects of the feeding by the adults are soon manifested by the appearance of scars on the leaves. (Fig. 1,7.) In the act of feed- ing, the weevil braces its body firmly on the upper side of a leaf, and moving slowly forward in a longitudinal direction either up or down the blade, it chews out the epidermis and produces a scar, leaving i THE RICE WATER-WEEVIL. 7 the underside uneaten. These scars are very narrow, being in fact no wider than the spread of the mandibles, but they vary in length from a small fraction of an inch to more than 2 inches, depending on the time in which the insect engages in feeding. When the thin underside dries within the scar, it splits and forms an open groove throughout the injured space. The leaves suffer no serious ill effects from being fed upon unless the scars become numerous enough to cause wilting and dying. Adults prefer tender young plants rather than the coarser strong growth. MATING AND OVIPOSITION. Throughout the period in which the weevils remain in evidence, mating takes place on nearly all occasions when a male and female happen to meet, and this usually occurs on a leaf. The gravid females crawl down the stems of the plants and evidently deposit their eggs singly in a puncture that is first gnawed in a root. Mr. Newell has mentioned that he has seen adult weevils which he be- lheved to be females make punctures on the stems below the water line. Mr. Hood and the writer have watched the operations of females when ethey apparently undertook to oviposit on rice roots within glass tubes. Each weevil thus observed deliberately sought out a place on a root and ate into it for about a minute. Then she reversed her body, gripped tightly, and pressed the tip of the abdo- men over the hole which she had eaten out. Mr. Hood has recorded that he saw the ovipositor in the form of a brown tubular organ in- serted into the hole. In this case the weevil remained in position without any apparent movement for 50 seconds before the ovipositor was withdrawn. The writer has not been able to see the ovipositor extended nor to detect an egg with certainty. The weevil may climb up above the water after each operation and rest for a long or short period, or continue her actions among the roots for a while. One weevil stayed among the roots for 45 minutes. The device that was designed and used by the writer for observing the method of oviposition by the weevils is illustrated in figure 2. In its construction a long lamp chimney was placed upright in a saucer and cemented at the base with plaster of Paris. A wire sup- port with the top bent into a loop of the proper size for steadying a closed-bottom glass tube, one with an inch diameter being used to hold the roots of a young rice plant in water, was first placed in the center of the saucer. The lower end of the support was also bent in a spiral to secure firmness after being set in the plaster. By means of a string tied to the upper part of the tube, it could be lowered through the top of the chimney into a standing position within the wire loop and also remoyed to permit close inspection of roots and insects inside of it whenever desired. 40996°—Cir. 152—12 » 8 THE RICE WATER-WEEVIL. NATURE OF ATTACKS BY LARV i. Mr. Hood has stated that the larve are first found in the rice fields from one to three weeks after the turning on of the water, the | Bes eee ey j Ben es Mie tem and observing the rice water-weevil: a, Glass lamp chimney; b, vessel containing 2.—Lamp-chimney cage for rearing plaster of Paris; c, glass tube; d, wire support; e, rice plant; f, string lift; g, gauze; h, rubber band; i, j, beetles feed- ing. (Original.) time of their inception varying with the weather. Hot weather accelerates their development. The young larve, which have doubtless hatched from eggs laid in the roots, begin to feed on them, and in course of time as the larve increase in size they devour or sever large portions of the root system. They have been known to eat holes in large rice roots and burrow into them. Mr. W. D. Pierce, at Beaumont, Tex., in 1904, found vigorous larve consuming the entire in- terior of the roots. Figure 1, c, gives a representation of six feeding holes made at a distance not more than one-fourth of an inch apart as Mr. Hood viewed them. The common methods of attack result in a pruning of the roots, after which the severed portions rot and the remaining parts are further marred with feeding scars. At this stage the hold of the plant upon the soil is greatly weakened and it can be pulled from the ground with ease. In some instances on rec- ord the root systems were en- tirely destroyed and the rice plants floated in the water. The injuries done by the larvee first cause the leaves of the rice plants to turn a pale yellow and droop, the lower blades often resting on the water. With severe attacks some of the leaves may die. These effects in the fields become most pronounced on plants growing in depressions and low portions of the land into which the water first flowed and where it THE RICE WATER-WEEVIL. 9 stands deepest. As previously mentioned, such places are most attractive to the adults. Where the adults occur most numerously the larve must be expected to follow in great number. In conse- quence the severity of the larval infestations is shown by a yellow cast of the leaves extending in broad streaks along dead furrows, while spots and areas of yellowish plants also become visibly ap- parent within the hollows and sinks of the land. These signs of injury have appeared in fields after 20 days of flooding, but ordi- narily the larve do not become numerous enough to cause much damage until the water has stood for at least a month. If many of the roots are cut off from a plant (fig. 1, e), its growth is stunted, but as the growing rice plant possesses a strong vital power new roots are put out to replace the ones destroyed, and on the cessa- tion of attacks the injured plant revives, or is said to “ recover,” and makes a belated growth, usually resulting in late heading. Much of the unequal growth of the plants in the fields, as well as the irreg- ular maturity of heads, is accountable to the detrimental effects of the larval attacks. Harvesting must necessarily be delayed until all the heads are ripe, thus involving the risk of loss to the normal yield from storms or other causes. Furthermore, the attacks on the roots of tender young plants pre- vent proper stooling or production of stems. In comparison with normal plants, often less than half as many stems grow from a stool that has suffered damage. Shortage of heads is therefore caused by the failure of badly injured plants to produce a full quota of stems. The fact that the larve are largely responsible for a great deficiency of yield in this respect will impress a comprehension of the amount of loss caused by the insect. DEVELOPMENT OF STAGES. The length of time required for the development of the weevil from a freshly laid egg has been estimated by Mr. Hood to be about 10 weeks. Judging from the first occurrence of larvee in fields after 1 to 3 weeks of flooding, a period not to exceed 10 days would probably be ample time for an egg to hatch subsequent to deposition. Development is hastened with the advance of hot weather when the water and soil become warm. Usually not until about six or seven weeks after flooding do many of the larve attain full growth and appear ready for pupation, although pupe have been found in a field that at the time had been irrigated for only five weeks. In prepara- tion for the pupal stage the larva forms a cell in the mud among the roots or at the tip of one, and Mr. Hood has asserted that the pupa passes two or three weeks before it matures and the emergence of the adult takes place. 10 THE RICE WATER-WEBEVIL. With the aim of working out the details of development of the larval and pupal stages, a number of larvee were placed on the roots of young rice plants, each of which was set in water within a glass tube, the tubes being simply stood in a holder. Attempts to carry through the development of pup from larve when subjected to con- stant exposure to light proved only partially successful, but better progress, although still lacking completeness, was made after shield- ing the tubes from light and supplying a small amount of earth with the roots and water. SEASONAL HISTORY AND GENERATIONS. Adults as well as partially and full grown larvae, and also without doubt the pupz, occur in many fields up to the time of draining for harvest. With late crops in the coast region, however, and in the fields of Arkansas on account of the difference of the season in that State, the number of weevils in all these stages diminishes about the time when the plants begin to head in the latter part of August. Weevils found in fields after the drawing off of water to permit harvesting are apt to be freshly emerged individuals of a new gen- eration. From a collection of infested roots obtained by Mr. Pierce at Beaumont, Tex., June 28, 1904, adults emerged as early as July 2 following. In case such early emerged weevils breed at once, they have a chance to produce a second generation in a season, provided they find late flooded fields or suitable water holes. At Stuttgart, Ark., on September 12, Mr. Hood found roots of rice infested by a few larve which he regarded as representatives of a second genera- tion. The last larva found by the writer during his stay at Crow- ley, La., was taken September 25. While the weevils that emerge in July possibly lay eggs for a second generation, the species is prin- cipally propagated in one yearly generation. In the spring, before many of the rice fields were flooded, Mr. Hood collected adults on grasses and red rice growing in ditches and other places containing water. Since the weevils have not been known to breed in such places until the soil and water become sufficiently warm, at which time the flooding of rice fields is well under way, the deduc- tion is made that low temperatures up to this time exert a restrictive influence upon breeding. Examination of roots of red rice and other plants growing in a constantly flooded ditch at Crowley, La., on October 3, failed to dis- close any evidences of infestation at the time. These results show conclusively that the weevil does not breed at this time of year even in most favorable situations. Not only were the adults absent, but the lack of feeding scars on the leaves denoted that they had not visited there for some time. THE RICE WATER-WEEVIL. ie} The fact that adults live throughout the greater part of the season has been demonstrated several times. In an experiment with speci- mens collected at Mackay, Tex., April 5, 1904, Mr. W. W. Yothers succeeded in keeping the weevils alive by furnishing grass for food until after the middle of July. Weevils confined on rice plants by Mr. Hood at Crowley, La., July 18, lived later than the middle of September, and the writer has made a corresponding record cover- ing a period from July 11 to September 21. The common absence if not scarcity of fresh signs of feeding by adults late in the season or at the time when the new generation of weevils is expected to emerge throws much doubt on the question of their taking any food then. At least they do not remain long on the plants, and the few feeding scars that may appear to have originated at the time are likely produced by lingering adults of the old gen- eration.