Historic, archived document Do not assume content reflects current scientific knowledge, policies, or practices. “5 f . i Ww 4 | ie | i” | | ¥ cae, "ees : 2 ° ie a ae a- ie rg a ; ba ’ A : 9 | ‘ i | ‘ ' : ‘ . i ’ wz oe. ; | "yy J ; | | ‘ § % 4 ; a ; > +. os ny : “s a a | =. ‘ : ' 7 J “ 4 i fl ‘ t ‘ : 4 i | ‘ rs | Hl j { ? / % . t ; | : ' t ‘ y ‘ | | | b f | P , ; i | ple | | Py, " Be pe tar ti | ° : , : i ; | > ‘ | » 7 | ‘ 4 ; | ; ‘ % > \ ¢ & . yee ‘ ' x : ‘ *) a aie oe fh on, ee : *) U. S. DEPARTMENT OF AGRICULTURE, BUREAU OF ENTOMOLOGY—-BULLETIN NO. 65. L.O. HOWARD, Entomologist and Chief of Bureau THE TOBACCO THRIPS A NEW AND DESTRUCTIVE ENEMY OF SHADE-GROWN TOBACCO. — ie , W. A. HOOKER, oy Special Field Agent. i or weer. * IssvEp Aprit 19, 1907. é 4 sf a al ee aol Oe Mle fe + fhe icra | | hr : a =s =x\ =e =f: = . «. . —— 38s > i> aE *—* — =e a: — = = By ; : mh »| ili WASHINGTON: . GOVERNMENT PRINTING OFFICE. 1907. ee | = ~ les asc aS > Ve bal: a =F ray TFSELINE Se C2 oF iee Re Eis 3 i - a Apes REET eG 2 er ~ a _ E. F. Purures, acting in charge of apiculture. -D. M. Rocers, in charge of gipsy and_brown-tail moth work. A. W. Morri11, engaged in white: fly investigations. E. 8. G. Trrus, in charge of Gipsy. “moti Wdhorutory. C. J. Gruss, engaged in silk investigations. oe en. R. P. Currie, assistant. in. Charge. oR: editoriat “work. of Mane CoLcorD, librarian. : et . j 4 AL of iw Wy a al & ye: t Ai 4 ry Ni ie | i : ar || \ } ~ esis + a Ly, ae CMOS Woke, CUS, Oye ee alee ee | RE Oe ohn es i thy y yt A ie Che eet 3 B fa, ¥ 3 x y Yi A s KS Bi Shee BS i yi meatier Ao tag Bae ne rin take GRA eT Myer ) vu ae t a ee - cal BASS = ont i ‘ \ 4 7 y SFA eid De Ak yaNar Se oe Tarte: vs FA i ay : t a ‘* .7 K ay 3 ? , fe e 5 hg 7 ’ z af ak E ; ee wo fd : ee BUREAU OF A ee \ aie Ts ™ Ly "Yat a We. Roe yi a ry poe ree L. O. How arp, Entomologist and Chief of pied C.. L. MaRLATT, Entomologist land “Acting vy “Chief in absence of Cnier. R. S$. Cuurron, Chief Clerk. EF. H. CHITTENDEN, in charge of breeding—-erperiments. A. D. Horpxins, in charge of forest insect investigations. W. D. Hunter, in charge of cotton boll weevil investigations. M. WEBSTER, in charge of cereal and forage- plaut insect investigations. | . L. QUAINTANCE, in charge of E aeouode. fruit 3 insect ene nied aeane ee U. S. DEPARTMENT OF AGRICULTURE, BUREAU OF ENTOMOLOGY—BULLETIN NO. 66. L.O. HOWARD, Entomologist and Chief of Bureau THE TOBACCO THRIPS, - NEW AND DESTRUCTIVE ENEMY - OF SHADE-GROWN TOBACCO. BY W. A. HOOKER, Special Field Agent. IssvEp Aprit 19, 1907. "fi ion Malin, Ui Pills Pi fin Isla: alto wt i Il . 5 <——— of ‘SAY eo) yA il | Aan il) Ales, We ey os dees See WASHLNGTON: GOVERNMENT PRINTING OFFICE. 1907. LETTER OF TRANSMATAL. U. S. DeparTMENT oF AGRICULTURE, 3UREAU oF ENTOMOLOGY, : Washington, D. C., Janwary 31, 1907. Str: I have the honor to transmit herewith a manuscript by Mr. W. A. Hooker, special field agent in this Bureau, on the tobacco thrips, an insect which has, during the last two or three years, caused great damage to shade-grown tobacco in Florida, Texas, and Georgia. This paper contains a general account of this thrips, and gives recommendations for applying remedial measures, and I rec- ommend its publication as Bulletin No. 65 of the Bureau of Ento- mology. iiespectfully, | L. O. Howarp, Entomologist and Chief of Bureau. Hon. James WIson, Secretary of Agriculture. ENE ENTS: Page. ee aS ee ek rs 2 Se es D Ee eat Se Oe Se a ee D ere Ones mehis Of INjUry. 22 ESOS ak CMe ke ns G LEYS PES ig] 00D | a ee =" 62-438 7 De aE ee ea a 8 EG ee en ll at ipa ee ee. ae oe I ed 8 NN errs ere oe ee ee ee eee Ee oe Se ee ) oh ESA Ee a, cs CR a age Aa EO we ace ee te rere g ee Varo ILy In GT Pleyel = 2 toe * es 10 Paes col-erown nym OF DuIpac. 22° — so ee ae re Ie = 1 EOS a ey eS oe ee eS ee Se oe 10 SEG aa SS OS ales AS Sid ES ee pe es 2 ae ee : 10 LOMO Se 2 ae Se Pe he ee ee <-* a eee 11 eee ne ee hea 2” 2) |. eee 11 SRT enIR et tees See ea tt Gers a) eS Oe 11 NE gee 88 2g SO te er St ere ES 1] Sa TSW TS NESE OS UE bt aR ee ae) eas oa ine Se. Sed =e awe Ai es 11 CL EG SAA) i a ee ey ee eT a id”: a ee SES 12 oo SOREN CS 0 Ne td Se CE Cc Op en Bk ce oie Spee ee 12 Other thrips that may be mistaken for the tobacco thrips___ Tn ae 12 air 2 8 0 FS Se en Bane Megs oy cd al is a ee ee es ee ee eee ae 2 NN Ge 5 el > Se “3 LS sa Sie Se Se ae Ae plbd, Le RR a Rea) BES le PO A 14 rer od Os eee ee a ei Se 14 REE IRIENEN TICNGE ae ee 8s eee, Ae te 2 ee te 14 EE al a NR a De a pc Te 17 SS TESTES a PSE Be a cee Ss 5 IRS a Sere ee a 19 tow TO: moke Kerosene Gmulsion +=.) | 19 " RURESe Ci MNT ECV CHIU SIT 2) See 2 3 ee 19 err Ose Lhe CmnISiGn eo > Sere ey We ad 0S” oe 20 Rar RINT I i aree e eee e e e e e 20 Supplies and Ri peers Pee ee eo a 20 CEI TT Se ia yl oy SR) deg ES a) Sa ee 21 Sr et PerVOmrmieni a fiOns. 5 a 21 IPI tee he | eee ees a ee a ee ed 21 i ee ee ee px. ae COBseCO LUOTIDS-10*1000—G. 8 2 ead es alte 4 ee 22 EE DRESS DS a ESSE SN See et Aa a 22 3 PELUSTR A PTOns PLATES. PLATE I. Fig. 1.—Slat-shade field, showing Iron cowpeas as grown be- tween tobacco crops. Fig. 2.—Leaf of tobacco, showing ‘““white veins,” caused by the tobacco thrips (Euthrips nico- CULTURA FO SS RATE EIN ge Re een Ts II. Fig. 1—Slat-shade tobacco field, showing seed bed. Fig. 2.— Cheesecloth-shade tobacco field. showing seed bed____—~__-___ TEXT FIGURES. Pies i: The tobacco thrips .Cauihrips mcotiane)- adult=_2 os ae 2. Diagram showing total monthly precipitation at Tallahassee, Fla., during April, May, June, and July, 1900-1906, to illustrate rela- tion of rainfall to amount of injury by the tebacco thrips_____-_ rage. THE TOBACCO THRIPS, A NEW AND DESTRUCTIVE ENEMY OF SHADE-GROWN TOBACCO. “ (Ruthrips nicotiane Hinds. ) INTRODUCTION. In accordance with the authorization of the Secretary of Agricul- ture and the instructions of Dr. L. O. Howard, the writer left Wash- ington, D. C., April 14, 1905, to investigate certain injury to shade tobacco at Quincy, Fla. He arrived at Quincy April 16 and spent the following two months in the work. Having reached what seemed to be a satisfactory result, he left there on June 16. June 27 was spent at Palestine, Tex., and June 28 and 29 at Nacogdoches, Tex., in examination of tobacco fields. At Quincy the writer was associated with Mr. W. W. Cobey, tobacco-breeding expert of the Bureau of Plant Industry, from whom valuable advice and suggestions were received. The writer again visited Quincy in October, 1905, and spent two weeks in a further examination. A continuation of the work was planned for 1906, but could not be carried out, although a visit was made at Quincy in November to determine the results obtained where remedial measures had been employed. HISTORY. The first report of thrips injuring tobacco in this country, so far as the writer is aware, was made by Dr. F. H. Chittenden in 1904,° the species concerned being considered as Euthrips tritici Fitch. As will be seen from the following pages, additional material showed that the insect concerned is a new species, Luthrips nicotiane Hinds. A Russian, Lindeman,° first described scientifically in 1888 a species of thrips, Thrips tabaci, which he reported as doing great damage to tobacco in that country. While this same species is gen- erally distributed in our own country and although its list of food plants is large, it is nOt recorded as having attacked tobacco here. Several communications were received by this Bureau during the @Circular No. 68, published February, 1906, gives a brief account of the insect and remedies recommended by the writer. »Yearbook of the U. S. Department of Agriculture for 1904, p. GOS, 1905. ¢Die Schiidlichsten Insekten des Tabak in Bessarabien, Bull. Soc. Imp. Natur., Moscow, pp. 51-65. 1888. See also Targioni-Tozzetti, Animali ed insetti del Tabacco, pp. 222-224, 1891. 6 : THE TOBACCO THRIPS. summer of 1904, with inquiries concerning an injury to shade-grown tobacco in Florida. The insect causing this injury was variously described as “a little parasite,” “a flea,” “an unknown insect,” ete. Not until the winter of 1904 could anything definite be learned. At that time a report was received from Mr. W. W. Cobey, tobacco- breeding expert, of the Bureau of Plant Industry, describing the nature of the injury. It seems that on tobacco grown in the South, and under shade espe- cially, insect enemies of the crop are found at their worst. Of the many insects with which the planter has had to deal in the past, the budworm, requiring two and three applications a week of arsenicals, has been far in the lead in the amount of damage done. It often happens, when a crop is introduced into a new locality, that insects previously unknown, finding in it a desirable food, leave their natural food plant, multiply rapidly through new and more favor- able conditions, and thus become serious pests. This is what has happened to shade-grown tobacco in the South. ,The suckfly (Dicy- phus minimus Uhl.), which first appeared on tobacco in 1888, has made the raising of a second crop of shade-grown tobaceo in Florida unprofitable. The leaf miner or splitworm (fAthorimwa operculella Zell., formerly known as Gelechia solanella Boisd.) also has at- tacked and become injurious to tobacco. And now comes a new pest in this new tobacco thrips, which has threatened to surpass the destructive budworm in actual injury. Injury by the tobacco thrips was first observed in 1902, on tobacco grown in the field on which the first shade was erected in 1896. Since that time the insect seems to have increased rapidly, until, during the summer of 1905, the thrips was found in all shade tobacco fields examined, and the opinion is expressed by several planters that, if allowed to continue its ravages, it is on a fair road to com- pletely check the production of the shade crop. The history of shade-grown tobacco in this country dates back to the vear 1896, when one-fourth of an acre of slat shade was put up at Quincy, Fla. It was found that Sumatra wrapper tobacco grown in this way nearly, if not altogether, equals the quality of the imported article. So successful has been the raising of this tobacco that to-day over 3,000 acres are grown under shade in Florida and the adjoining counties of Georgia, while Texas has a smaller acreage. NATURE AND EXTENT OF INJURY. The injury occasioned by the tobacco thrips is known as “ white vein,’ which, as the term indicates, is due to a white appearance of the veins (see Pl. I, fig. 2). These veins show in the wrapper when manufactured into cigars. The injury is brought about by the re- moval of the sap by the adult thrips in feeding on the upper surface of the leaf. The thrips feed on the space between the veins as well as_ PLATE I. Bul. 65, Bureau of Entomology, U. S. Dept. of Agriculture —SLAT-SHADE FIELD, SHOWING IRON COWPEAS GROWN BETWEEN TOBACCO BiGy elle ) (ORIGINAL. CROPS. BY THE TOBACCO CAUSED (ORIGINAL.) LEAF OF TOBACCO, SHOWING “WHITE VEINS” FIGs 2. THRIPS (EUTHRIPS NICOTIANA). ORIGIN AND DISTRIBUTION. ey! on the veins, but except on the veins themselves the indications of their feeding disappear in the fermentation process. The work of the pest should not be confused with the so-called “white vein ” that sometimes occurs in tobacco grown in the North and which seems to be due to a physiological disorder of the plant. As a result of the thrips’s work, when the crop is affected to any extent, all the white-vein tobacco must be sorted into a grade by itself and sold as such, the expense of grading being thereby largely in- creased. The value of the crop also is greatly reduced, as there is no demand for this grade at present. There seems to be quite a variation in the estimates of the depreciation of tobacco thus affected, one packer estimating the value as decreased from $1.50 to 50 cents, or a loss of $1.20 per pound, while another packer places the decrease at from $1 to 50 cents, or a loss of 50 cents per pound. These seem to be maximum and minimum estimates. For the year 1904 it is estimated that 20 per cent of the crop grown under slat shade was damaged to such an extent by white veins that it was thrown into a grade by itself. The injury for 1905 was decreased to a great extent by the heavy rainfall in the latter part of June andin July. In the crop of tobacco sprayed with emulsion there were practically no white veins to be found, and this was the case in 1906. Early tobacco was especially affected by white veins in 1905, the injury having taken place pre- viously to the rains. One crop of tobacco is estimated by the planter as containing 33 per cent of affected wrappers, practically one-half of which must necessarily be placed in a separate grade. Another crop is estimated as containing 20 per cent of affected wrappers, 10 per cent being placed in a separate grade. The amount of injury will vary from year to year, depending upon the period and amount of rainfall. In the past the greatest damage has been to that particular section near the original shade, but the thrips now seem to be disseminated throughout all the fields of shade tobacco. ORIGIN AND DISTRIBUTION. ~ As soon as possible after reaching Quincy, specimens of the tobacco thrips - were collected and sent to Dr. W. E. Hinds, an authority on this group of insects. He found that they represented a new species and has named and described them.“ _ This insect was taken by the writer at Nacogdoches, Tex., on shade tobacco, as well as at Quincy, Fla. In April adults and larve were taken in large numbers on cocklebur (Yanthium glabratum) growing in the shade fields and in smaller numbers on dewberry, mustard, and 4 _shepherd’s purse blossoms. It has been taken by the writer at Dallas, @ Proc. Biol. Soc. Washington, Vol. XVIII, pp. 197-199, September, 1905. 8 THE TOBACCO THRIPS. Tex., in both winged and wingless forms, on Johnson grass (Sorghum halepense) in March. It would seem, therefore, to be a general feeder and widely distributed through the Southern States. DESCRIPTION. Adult.—Doctor Hinds describes the adult as follows: :; EUTHRIPS NICOTIAN 4 Sp. noy. Average length, 1.05 mm. (0.95 to 1.18 mm.) ; average breadth at middle of abdomen, 0.27 mm. (0.225 to 0.285 mm.). General color of head and thorax light brown or tawny yellow-brown; abdomen dark brown. Head about one and one-half times as wide as long, frequently slightly retracted under ante- rior margin of protho- rax; occiput trans- versely wrinkled, pos- terior margin strongly thickened and darker in color; anterior mar- gin slightly bisinuate, cheeks approximately straight and parallel. HKyes dark red in col- or, not protruding, oc- cupying together fully one-half the width of the front of the head and being one half as long as the head; mar- gins around eyes pale yellow in color; sur- ELE YY Y EELZZHI “MM f Yi? Yj jj Fic. 1.—The tobacco thrips (EHuthrips nicotiane): Adult insect. Much enlarged (author’s illustration). face of eyes finely fac- eted and slightly pi- lose; three ocelli present, well separated, posterior ones contiguous with yellow borders to eyes, pale yellow in color and margined inwardly with pale-orange crescents; one moderately stout dark spine in front of each posterior ocellus; postocular spines weak and inconspicuous. Mouth cone reaching nearly to pos- terior edge of the prosternum, tapering abruptly ; maxillary palpi slender, three- segmented. Antennze inserted slightly below front margin, approximate at base, about two and one-half times as long as the head and approximately equal to breadth of mesothorax; relative length of segments: 4 1 2 2 + 5 6 {i 8 6.2 11.4 13.5 13.6 12.2 16.2 3.0 “4.5 Segment 1 is rounded, three-fourths as long as broad; 2 is as broad as 1; following segments about three-fourths as thick; segments 3 to 6 are con- stricted at bases, becoming more stout successively. Color cof segments 1 and Z uniform light brown; 3 to 5 pale yellow at bases, shading to brown at outer ends, each succeeding segment from 3 to 6 becoming darker in color; 6 to 8 are a'Fhe number of the segment is given above the line and below it the number of spaces covered upon an eye-piece micrometer by an average of the-segments of 10 antenne. Pm, te 7 - a aa i ON a i cari rt ids Ei set Sipe a DESCRIPTION. Y dark brown. Spines upen segments 2 to 5 are of medium size, but not very con- spicuous. Color of head varying from gray-brown to yellow-brown. Prothorax about five-ninths as long as broad and slightly longer than the head; sides rounded, slightly wider at hind than at fore angles; one stout spine at each anterior, and two stouter spines of equal size at each posterior angle; anterior marginal pair of spines about one-half as long as those at front angles; usual row of five spines on each side of hind margin, of which number 4 is equal in strength to those on the front margin. Mesothorax nearly one and one-third times as wide as the prothorax, broadest posteriorly, sides curving outward; mesonotum without conspicuous spines, posterior margin forming an obtuse angle in middle. Metathorax slightly narrower than mesothorax, sides nearly parallel, broader than prothorax at posterior edge; metanotum bears two pairs of spines at front edge, the inner pair being as strong as those at front angles of prothorax. Wings present (probably reduced at some season of year), average length about 0.68 mm., not reaching to the tip of the abdomen, breadth equal to about one-thirteenth of their length; fore wing has two longi- tudinal veins, each bearing stout spines set at regular intervals; fore wings shaded ash gray, hind wings gray only along basal three-fourths of midvein; spines on wing veins dark brown and conspicuous; costa bears 19 to 24 spines; fore vein, 13 to 18; hind vein, 10 to 12; scale, 5; interior of scale, 1; fringe of hairs on costa of fore wing quite heavy, in length exceeding the breadth of the wing. Legs of medium length, lighter than body in color, pale yellow, shaded more or less with’brown on upper side at middle of femora and tibiz; a pair of stout brown spines at inside of tip of each tibia, small brown spines scat- tered along femora and tibiz; spines standing in two rows on inner side of hind tibiz are weak and only about four in each row. Abdomen nearly cylindrical to eighth segment, then tapering abruptly to an acute tip; color uniformly dark brown; a still darker-colored narrow chitinous thickening extends across dorsal side of segments 2 to 8 near anterior edge. Three or four quite stout and rather conspicuous dark-brown spines stand at each side of dorsal plates on 2 to 8; six rather prominent spines stand in a row on posterior edge of ventral plates 2 to 7; terminal spines stout and prominent; tenth segment split open along dorsal median line. Described from 10 females. Male specimens of this species have not been found. Three cotypes (three slides) deposited in the U. S. National Museum. Type No. 8434, U.S.N.M. Three cotypes (three slides) deposited at the Massa- chusetts Agricultural College. Four cotypes (two slides) retained. Habitat—Quincy, Fla.; Nacogdoches, Tex.; Climax, Ga. Wingless females appear in May and seem to predominate by the latter part of that month. This species may be readily distinguished from Luthrips tritici Vitch by its color, which is brown, that of tritici being yellow. Dif- ferences in structure by which the species may be readily separated are found in the postocular spines, those of nécotiane being weak and inconspicuous, while those of ¢ritici are quite prominent. On the wings prominent differences are found in the number of spines on the veins, the costa of nicotiane bearing from 19 to 24, the fore vein 13 to 18, and the hind vein 10 to 12, while in ¢ritici the costa bears from 26 to 28, the fore vein 20 to 22, and the hind vein 15 to 18. Egg.—TYhe eggs are deposited in the tissues of the stem and leaves. Larva, first stage—Length about 0.28 mm.; width of mesothorax 0.11 mm, 24372—No. 65—07 m——2 10 THE TOBACCO THRIPS. * General shape fusiform. Color of posterior part of thorax and entire abdomen pale yellow: elsewhere pearly white. Head quadrate; eyes reddish. Antenne 0.15 mm. in length: distinctly four-segmented: basal segment cylindrical. short: second ovate. slightly shorter than the third: third slightly conical. the apex joining the second; fourth fusiform, widest near the basal fourth, about equal in length to the other three. The fourth segment is distinctly annulated, the second and third indistinctly so; sete are present on all seg- wents. Most numerous on the fourth. Legs translucent white, stout. Abdomen — tapering posteriorly; with ten segments, the first eight nearly equal in length, the ninth twice and tenth three times the length of the preceding. Each abdominal segment with longitudinal rows of setz#, the ninth with two and tenth with four spines that are four times the length of the sete. Larva, second stage-—Length from 0.6 to 1.17 mm.: width of mesothorax from 0.14 to 0.2 mm.:; shape same as in first stage. Color of thorax and abdomen yellowish. with exception of the last abdominal segment. Head quadrate; antennz with four segments, the fourth being more distinctly annulated than in the first stage. Abdomen with the sete increasing in length posteriorly: ninth and tenth segments about equal in length, each less than twice the length of the others. The young nymph or prepupa.—Length, 0.52 to 0.62 mm.: width of meso- thorax, .0.10 to 0.12 mm. Antenne translucent, extending forward, much short- ened and composed of five segments, first two cylindrical and very short, third and fourth globose, fifth tapering to the apex. The last segment of the abdomen is set with four spines by use of which the young nymph seems to protect itself, when approached by another the abdomen being turned upon it. The wing sheaths are very noticeably separated, the upper one extending to the middle of the second segment, the lower one to the middle of the third segment. The legs are translucent white, stout. The full-grown nymph or pupa—Length, 0.68 to 1.22 mm.; width of meso- thorax, 0.15 to 0.20 mm. Shape similar to the adult. Color yellowish: head, antenn:e, wing pads, legs, and caudal segments of the abdomen varying to pearly white. Antenne extending to the middle of the prothorax. Three yellowish ocelli between the eyes, the latter dark red. Wing pads so closely applied as to appear single, extending to the middle of the fifth abdominal segment: length from head to tip of wing pads 0.59 mm. The abdomen is noticeably contracted longitudinally: greatest width, 0.24 mm.:; longest setze, 0.078 mim. HABITS. Feeding —When examinations were first made, April 17, the adult thrips were found feeding in the seed beds on the upper surface of the young tobacco plants, and in the field on the upper surface of the leaves of young cocklebur weeds. In the larval stage they feed on the lower surface of the leaves of tobacco and weeds, but as they become adult seem to prefer the upper surface, a habit which is very favorable for remedial treatment, as they can then be reached much more readily by sprays. To determine the attractiveness of tobacco the experiment was tried of transplanting young tobacco plants into a field that had been prepared ready for transplanting, but in which weeds, consisting of cockleburs and grass, were to be found. In order that thrips might not be accidentally taken from the seed bed on the plants. the latter were dipped in a solution of kerosene emulsion and this washed off with water. Fifteen plants were set in $ LIFE HISTORY. 1] a 2-acre field at intervals of 4 and 8 rods. The day following was rainy and unfavorable to movement of the thrips, but the second fol- lowing day was pleasant. In the afternoon of the second day an examination was made, and four plants were found to have been cov- ered with dirt in the ridging for setting the field. Of the eleven remaining, four plants were found without thrips, five with one each, one with two, and one with three. From this it would seem that the thrips are quite strongly attracted from the weeds in the field to the tobacco. As the thrips commence feeding and breeding on the young plants the lower or sand leaves receive the greatest amount of injury. From the lower leaves they gradually work up the stalks to the leaves above, until at harvesting time they have reached more than half way up. In attacking a leaf they first appear feeding near the tip, and grad- ually work toward the stem. It may be well to note here that the leaves are harvested by picking—called “ priming ”—as they ripen, and that the stalks often reach the slats or cloth 9 feet from the ground. In the early stages of the tobacco the thrips are found on that grown in sun and shade alike, but as the sun tobacco thickens up they seem to leave it and are found in numbers only on the shade- grown tobacco. In a field in which Cuba and Sumatra varieties were grown together the thrips were found to be equally injurious to both. Jumping.—When disturbed, the adults have the habit of jumping. and have thus been mistaken by some for small fleas. This charac- teristic is typical of the genus to which the tobacco thrips belongs. The motion seems to be produced by a combined movement of the wings and abdomen. Flight.—The closely related wheat thrips takes flight readily, but the tobacco thrips apparently does not do so. Notwithstanding all the observations he has made, the writer has as yet failed to see it take wing, and its power of flight must be limited. FOOD PLANTS. The tobacco thrips seems to be a general feeder, as adults were taken in April on blooms of dewberry (Rubus sp.), shepherd’s purse (Bursa bursa-pastoris), and mustard (Brassica sp.). Adults and larvee were taken on oats, wheat, and cocklebur as well as on tobacco. LIFE HISTORY. Methods of study.—In order to determine the life cycle, adult thrips were confined in small wide-mouth vials on parts of tobacco leaves for periods of twelve and twenty-four hours, but repeated attempts failed to induce them to oviposit. The parts of tobacco leaves were thereupon replaced by small bean pods, with the result that oviposition soon took place. Absorbent cotton was used es a stopper for the vial in order to keep the moisture from forming on 19 ~ THE TOBACCO THRIPS. the inside and thus catching the young thrips, which readily succumb when so caught. Life c Veni life cycle of this species is found to be quite short and very similar to that of the closely related wheat thrips, Huthrips tritici. In May and June only twelve or thirteen days are required for its completion. In the tobacco field the eggs appear to be depos- ited in the tissues on the under surface of the leaf. In May and June the incubation period for eggs laid in confinement in young bean pods seems to average about four days. The larve, upon hatching, feed on the under surface of the leaf; during this stage, which lasts seven days, and before changing to pups, they molt twice. When about to pupate the larve crawl to some obscure nook; there they remain inactive, without feeding, during the pupal stage, which lasts two days. The adults, on emerging, have a yellowish color, which in a few hours turns to the normal brown. As adults the thrips crawl to the upper surface of the leaf and commence feeding. Hibernation.—The tobacco thrips appears to hibernate in the adult stage. When the fields were visited, the latter part of October, not a specimen could be found, although another thrips (Chirothrips crassus Hinds), which was taken in large numbers in sheaths of grass found growing in the tobacco fields, was at first mistaken for the tobacco thrips. Mr. W. W. Cobey informed the writer that he had observed the tobacco thrips on the leaves of cocklebur about October 10, previous to a cold spell. Thus it would seem that the thrips goes into hibernation after the first approach of cold weather. OTHER THRIPS THAT MAY BE MISTAKEN FOR THE TOBACCO THRIPS. While the tobacco thrips is the only species commonly found on tobacco, yet a number of other thrips which may be mistaken for this pest are found in the vicinity of the tobacco fields, or even acci- dentally upon the tobacco itself. Among those that may be so mis- taken are the following species: Euthrips tritici Fitch, the “ wheat thrips,” is a species generally distributed throughout the South. It has a wide range of food plants and can be found during a large part of the year in almost any blos- som. In Florida it has been reported as injuring the orange and strawberry by attacking the blossoms. At Quincy, Fla., during the summer of 1905, it was found in large numbers associated with the tobacco thrips in oat fields bordering the tobacco fields. It was also found seriously injuring roses, causing the outer petals to wither before the flowers opened. It may be distinguished from the tobacco thrips by the yellowish color of the adult or winged form, which in the tobacco thrips is dark brown. Thrips tabaci Lind., the “ onion thrips,” has been reported by Prof. A. L. Quaintance as quite abundant in Florida, attacking onions, Be % NATURAL CONTROL. 13 cabbage, and cauliflower. It may be distinguished from the tobacco thrips by its color, which is yellowish. Anthothrips niger Osborn is another species which was very abun- dant at Quincy the summer of 1905. In oats and wheat bordering the tobacco fields it was found breeding in vast numbers with the wheat and tobacco thrips. It was also occasionally taken on tobacco and tomato. It is a strong flyer, and may be further distinguished from the tobacco thrips by its much larger size and black color. A few specimens of £olothrips bicolor Hinds were taken on oats and wheat in the vicinity of tobacco fields. This species may be distinguished by the white or yellowish pigmentation of the first three segments of the abdomen. Chirothrips crassus Hinds was taken in October and November in large numbers in the sheaths of grass growing in tobacco fields. It was at first mistaken for the tobacco pest, because of the similarity in color, but may be easily distinguished, as it does not have the jumping habit of the tobacco thrips. NATURAL CONTROL. ‘ Rains.—Of the natural checks, rain is the most important. It is known that nearly all thrips thrive during warm and dry weather, and that they are washed from their food plants and destroyed in numbers by rain. This is true of the tobacco thrips in that it is washed off by heavy rains, yet unless the rain continues for several days few seem to be destroyed, for at the end of the first or by the second clear day following the writer has found it on the leaves in as large numbers as ever. The influence of rain upon the pest, however, was very noticeable in its effect during the summer of 1905. Up to the latter part of June very little rain had fallen, and the drought was showing its effect on the unirrigated fields. At this time the dry spell was broken and rains were heavy and frequent. The June, 1905, rainfall, which was nearly three times that of the preceding June, yet still below the nor- mal, nearly all fell during the latter part of the month and was fol- lowed by the heavy July rainfall, which was the greatest since 1900, and more than twice that of 1904. Asa result the thrips were kept off the leaves, the plants grew rapidly, and priming was forced into twenty days where it usually takes thirty. The sand leaves were lost in large part because of this rapid ripening and the leaves affected to the greatest extent by white vein were thus eliminated from the crop. As the result of these weather conditions, white veins in the late to- baceo were reduced to a very small percentage. The great amount of injury in 1904 was undoubtedly due to the exceptionally droughty season. This will be shown by the accom- panying chart: (fig. 2) of total monthly precipitation for the last Seven years. That during 1905 and 1906 the injury was so much 14 THE TOBACCO THRIPS. less than in 1904 must have been due to the greater precipitation. As before stated, it is quite evident that the amount of injury by thrips will vary from year to year, depending upon the period and amount of rainfall. The total precipitation in inches at Tallahassee, Fla., during April, May, June, and July of the years 1898-1906 is shown in the following table: Precipitation in inches at Tallahassee. April. May. June. July. re | Length of Year. | Depar- Depar- | | Depar- | Depar- record | Total. ture Font Total. |ture eor| Total. |ture from, Total. |ture from) (years). | normal. | normal. | normal. normal, N898 Nes sees eee 0. 87 —1.89 1.55 —2.65 | 4.49 — 1.25} 10.00 +1.71 14 W899) Sreesanth eee eeees 8 EOS te Seer Pees eans (5 Soeencsaa ISentesee Seace haar cece coose 1900S ace owe ss 4.05 4-1. 05 2.06 —1.60 16.47 +10. 72 10.31 +1. 87 15 LODE sae esc aen ce ete —0. 27 5. 07 +1.59 5. 61 — 0.75 8. 25 +0. 02 16 MOOD. scree sine neler = 0. 84 —1.15 2.86 —0. 62 9.94 + 3.58 9. 83 —2. 40 17 GOB eat rosi sees cae 0.11 —1.88 §. 59 +2. 11 10. 01 + 3.65 7.09 —1.14 18 OA eect eens 1.65 —0.34 1.05 —2.43 1.33 — 5.038 3. 99 —4, 28 8) 10 1 een 3 aie eee eae 0. 92 —1.07 7.99 +4.07 3.50 — 2.86 8. 76 +0. 53 20 GOG ee eee See 0.15 —2.43 Pst Pe +0. 70 5. 17 — 1.23 8.88 --1.00 21 Insects—Specimens of a small bug, 7viphleps insidiosus Say, were found very commonly upon oats, where they seemed to be quite destructive to the thrips. When captured with the thrips by sweep- ing the oats with a net, they were shortly found with a thrips im- paled upon their beaks, sucking out the juices. While this insect may assist in decreasing the tobacco thrips that breed on oats, it has not as yet been found on tobacco. A fungus also was found growing upon dead thrips taken from tobacco in the seed bed; but this may be, and probably is, a form attacking the insect after its natural death. REMEDIES. Remedies may be considered under two heads, namely, cultural methods and insecticide applications. CULTURAL METHODS. It is the practice of many tobacco growers to start the seed bed in the shade-tobacco field (see Pl. IL), and, after the plants are removed, to plant it with the rest of the field. This practice is unquestionably a bad one, not alone from its furnishing a breeding place for the thrips, but also because it becomes a center of infestation for many other pests, particularly flea-beetles. It was noticed during the sum- mer of 1905 that insect pests, and especially flea-beetles, were the most numerous in transplanted seed beds and in that part of the field adjoining the seed bed. It seems advisable, therefore, that the seed bed be located outside and at some distance from the tobacco field. Where it is necessary that the seed bed be located in the field, the thrips can be largely overcome by frequent applications of kerosene emulsion, as hereinafter described. Applications of Paris green also a". Bk CULTURAL METHODS. 15 APRIL | MAY | SUNE | SULY | Fare oesceaaeantd Papier, Fear RE Gar PEAS Ba PRS, RUES I ER ll 190 a : pe TOO ba | ‘oO ili NS : i 8 ON Ss . re | . _-- __-+_-+-__++_- 12,13 errreremaaeat Naar mr NIN PU CP RAGIN Et PEMACCRY ooo 7 ee 16 Hornworm, cultivation as remedy_______~ EE Rg a SE ee OL 16 REEL SIRS RT oS 2S Sha Seah re a 6 fe EE Se Pe ees 2 ee a eee 14 Insecticides, used in experimentation against tobacco thrips ____________ 17-18 Irrigation, overhead, remedy for tobacco thrips_________________________ 16 Johnson grass. (See Sorghum halepense.) fo Kerosene emulsion, remedy for tobacco thrips_____--_--____-____--__-_-_~- 18-21 . Leaf-miner. (See Phthorimaa operculella.) ee Ue CeLve. aseine. wolaeco tating. ——0 =. 2 32 2 18 Molasses, ineffective against tobacco thrips____________________________ 18 nt LOG mene OF Topncce —iripg= 2220 sos ye | m_aikoteen,” acaims? tobacco thrips__-.-_-._-.-.__.-______-_________.__ 20 Oats, food plant of Wolothrips bicolor and Anthothrips niger ~-~-_-_-_-_- 13 : SIC go SE Se Ea Sa a eS 12 CR 6 OS are ee eee 11 rn SO amt On bree tO0GCb.. oo. 12 thrips. (See Thrips tabaci.) eto mlant Of lathring tritici. 2... see 12 a athorimea operculelia, on tobacco. -__-_----.----------2-------_~~-__- 6 aaaiuence.on tobacco thrips... = -- - .-___--_._§ 13-14 S Rose-leaf insecticide, against tobacco thrips________...-...--____-_______ VW “ton io * 24 INDEX. ooses; Tood: plants of Huthrips trier 2a a eee eee ee Rubus sp. (See Dewberry.) ° Ree? tood plant: of teDacco CHE iS ee ee ee ee eee ee ee 16 Shepherd’s: purse, food plantof tobacco thrips.20 ho) tee 8 os Sorghum halepense, food plant of tobacco thrips_______-_-__-_-_§__§ 8 Splitworm. (See Phthorimaa operculella.) Spray, tor tobacco, thrips, no: mijurious eect on) proGguch 2 ol sees 22 Spraying; tor Lobaccomthrips.-cost.= a = ys RA ee 20-21 Strawberry. £000 plant O26 TAPS LANtGts: 3 ae Se Se ee Cee = 12 Suckfiy. (See Dicyphus minimus.) Temperatures, in slat and cheesecloth shade tobacco fields, difference____ 16--17 Thrips tabaci (onion thrips) mistaken for tobacco thrips________________ 12-13 ONELODAEEO. IN RAISSIg eee es Se ee BS ee 5 tobacco.. (See also Huthrips nicotiane. ) Culeural methods: for cOutrol: os tes be ec ee a _.. 14-17 distribution _ ky Bs Mice ERD rol 1 cat <4 1d ah od ET oR AN TSI S Ps 7-8 feeding thabits. 2 s-0 0a 63) ye oe ape te ee ae a (ett Be re eae Een hed RE , = Sun Po See gat LOO SLAIN te ee ee nPop copies 208 2 rece threw Sia i (ee Pa fungus: Ob dead Specimens== 4. - ses ee es eee 14 HIDE Halo 2 eee er Bas pA we ee AE pen elem eRe Sonat des a2 History.as pest. 22286 tf se Ee eR ee ee D-6 injury, Nature-and. extents 2.2 2 a MRR oe ae Del a Sy 6-7 Mmsect, CNEN TY “2-2-9 Leh pee Vie ties Bi ENE 1 Py: 2 ioe uae 14 Ts, insecticides used in experimentation____-_____ ae. 17-18 sMping 2.225 E Sides} hice Ve oa eae in gt eet 11 DL TESCO I Se Tas dae ah ge re a 11-12 methods for stidy_e.3. ot) yk 1 ee ee 11-12 remedies _____ Pr Sy ee Ss 2 oe oi SS ae iene eer eae 14-21 species mistaken fon be UN MEF EE Sy wa SS 12-15 SPA Vin. COS LD: = seat tie ea he SEE Ca a se ae 20-21 wheat. (See Luthrips tritici.) Tobacco decoction, against tobacco thrips_—____________ PETERS Lb en 18 BOSCCE-CNEDUES? HIS SONU nee eh ee eae Re eet oe er Te ee ieee G not a food plant of Thrips tabaci in our country__ ie Re a 5 presence: Of Ant hotnrepS Rigen eo ee ee Fee 13 thrips. (See Thrips, tobacco, and Euthrips nicotiane. ) HOM ALO DLeSeNCe -OL FA MAVOTIE IDS MAGE. ae oe ee Ee ae ees bey Triphieps imsidiosus enemy ot tobacco: thrips=2_ 2" * = ee 14 VEhae-OLk Soap. aeons tobacco ~bhrips ~) 2) 2 ee ae 6-7 Xanthiwn glabratum. (See Cocklebur. ) O a ane