/e^'s- 



€ljt 33ntiirnlist. 



ENTOMOLOGY. 



No. 7— The Wheat Thrips and Three-banded Thrips. 



A leltorfrom David Williams, (luted Gonevn, Wis- 

 consin, July 9tll, says: 



Enclosed I send you specimens of a minute lillle 

 insect that is cnusing some nlarm in this vioinily. 

 Tliey nre found in nil blossoms in great numbers. 

 They first mnde their npponnince nbout the middle of 

 June, or nt least, they wore then first noticed, so farns 

 I have beard, For about two weeks they were found 

 in the blossoms of wheat and of clover, causing num- 

 bers of the blossoms to wither, and in some cases the 

 k«rncl was also attacked. About a fortnight ago we 

 had a very heavy fill of rain, which appeared to de- 

 stroy them ; but within a few days I have noticed 

 their re-appearance in countless numbers. They are 

 very nimble, requiring good eyes and ready fingers to 

 secure them, and I was obliged mainly to my wife for 

 the capture of those which I send you. There are 

 other kinds which I did not succeed in capturing. 



The insects alluded to in the above extract are so 

 minute, that, had only two or three epecimens been 

 sent, I should have been unable to give any definite 

 account of their species. An acknowledgment is due 

 Mrs. Williams for the number of these insects which 

 she inclosed in the quill — a task which the bungling 

 fingers of a man could scarcely have accomplished. 

 Among them I find specimens in all tho singes of their 

 growth, and am honco able to present a history and 

 description of the species, suQiciently exact, I doubt 

 not, to enable it to be recognized hereafter; although 

 it is only from living specimens that such minute ob- 

 jects can be satisfactorily studied, and described witb 

 that precision and fullness which science requires. 



Insects of tho kind to which these belong, may be 

 distinguished from all others by their wings, (see tho 

 accompanying figure, e,) which are long, narrow, and 

 strap-like, and are fringed on both sides with long hairs 

 like eye-lashes. Their mouths are also different from 

 those of all other insects, being nearly intermediate 

 between the htak or bill with which some of the Orders 

 of insects puncture and suck tho (!uid9 on which they 

 subsist, and the jairs with which those of all the other 

 Orders gnaw the substances on which they food. These 

 insects originally formed the genus Thrips, placed by 

 LinnEcus next to the plant-lice, in the Order Hemipte- 

 BA ; but as their wings and the structure of their 

 mouths is so wholly unlike that of any other insects, 

 naturalists of Inte rank them os a distinct Order, which 

 is named Thysanopteba, i. e, fringe-winged. This 

 Order contains the single family Thuipidid*, (cur- 

 rently written Thripidrc by authors, but incorrectly,) 

 which is divided into seven genera by the late Mr. 

 Haliday, whose researches in this group were most 

 extensive. About fifty species of these insects ore 

 known to tho entomologists of Europe. They are all 

 of small siie, more than half of them being only about 

 tho twentieth of an inch in length, or less, and but few 

 slightly exceed tho tenth of an inch; though recently 

 some have been found in Australia which are three 

 times as largo as any which were previously known. 



Most of the species are found in the flowers of dif- 

 ferent plants. They feed upon the juices, and are very 

 injurious, especially in hot-houses, causing small dead 

 spots upon the leaves and flowers wherever they wound 

 them. Some of them also infest melons and cucum- 

 bers. One species is very injurious to the olivo trees 

 in Italy. Another attacks peaches and other fruit to 

 a mieobievous extent. But the species which appear 

 to do the greatest amount of damage is the grain 

 Thrips (T. cerealium.) Our first accounts of this in- 

 sect are from Mr.KinDY,in 1796,(Linnnian Transactions 

 iii, 24C,') who however supposed it to be the Thripi 

 pAysopHS of Linncous, until Mr. Ilaliday showed it tobe 

 distinct from that species. An excellent history of 

 this species is published by Mr. Curtis in his paper 

 on insects affecting the corn-crops, in the Journal of 

 the Royal Agricultural Society, vol VI, p. 499; and fig- 

 ures of the insect and its dissected parts, in the several 

 stages of its growth, from Mr. Haliday's Manuscripts, 



Bro given in the List of Homoplerons Insects in the 

 British Museum, part IV, plates VI, VII and VIII. 

 In the year 1805, one third of tho wheat crop in the 

 province of Piedmont is said to have been destroyed 

 by this seemingly insignificant littlo insect. Mr. Kirby 

 says it is by far the most numerous of any int;ect upon 

 the wheat in England ; he does not think he ever exam- 

 ined an ear of wheat without meeting witb it. lie 

 snys it takes its station in the longitudinal furrow of 

 the seed, in Ibe bottom of which it seems to fix its beak, 

 and probably sucks the milky juice which swells the 

 grain. Thus by depriving the kernel of part, and in 

 some cases perhaps the whole of its moisture, it causes 

 it to shrink up and become what the farmers call 

 " punglod." According to Vossali Eandi, it also gnaws 

 tho young stalks just above the knots, causing the ear 

 to become abortive in consequence of these wounds. 

 It is late sown wheat which is reported to bo chiefly 

 injured by this insect; and enrly sowing is -the only 

 remedy which I find spoken of by those who hare writ- 

 ten upon it. 



Our American species of this order of insects are 

 probably ns numerous as those of Europe, but none of 

 them have been examined and described, except one 

 which occurs in small hollows gnawed in young apples, 

 of which some account is given in my lleport upon the 

 Noxious Insects of New-Vork, just published. I have 

 repeatedly noticed different kinds of these insects up- 

 on growing wheat, but not in such numbers that I sup- 

 posed they were doing any appreciable injury to the 

 crop. The species which I have found most common up- 

 on wheat in my own vicinity, will be found described 

 at the close of this paper. Dr. IIakris has also seen 

 the larva of a Thrips which he supposes to be the T- 

 cerealium. lie merely states that it was orange- 

 colored ; and as the larva of T. cerealium has a black 

 or dusky head and two spots of the same color on the 

 fore part of the thorax, and its antenna: and legs have 

 alternate blackish and whitish rings, it is more proba- 

 ble that his specimens were the same species as those 

 now before me from Wisconsin. Be this' as it may, the 

 oommunicotion from Mr. Williams is important, as 

 making us acquainted with an enemy of the Wheat 

 crop of which we heretofore have had no definite 

 knowledge, and which will undoubtedly at times be 

 quite detrimental in the wheat-growing tlSftricts of our 

 country. 



Although this species, like many others in this Or- 

 der, occurs upon the flowers of different plsnts, it is 

 upon wheat, in all probability, that it will bo often- 

 est noticed, and to which it will prove most injurious. 

 It may therefore appropriately be named the M^'heat 

 Thrips, (r. Iritici.) 



Attached to the surface of the shrivelled flower- 

 leaves in the quill, I find what I doubt not are the eggs 

 of these insects, (see figure, a.) They aro so minute 

 as to be wholly invisible to the naked eye, except when 

 placed upon clean white paper, when they can be mere- 

 ly discerned, appearing like an atom of dark-colored 

 dust. Under the magnifier they are discovered to be 

 of a bright red color, like particles of sealing-wax, 

 and of an oval or almost globular form ; and they are 

 attached to the leaf by a short, thick, crinkled stalk 

 or stem, which is of a dull white color. 



Tho larvcCj (figure, 6,) resemble the perfect insects, 

 except that they are wholly destitute of wings, and 

 aro smaller and softer, with the several segments of 

 the body more equally and distinctly separated from 

 each other by transverse, constricted lines. They are 

 throughout of a bright orange-yellow color, of the 

 same hue as tho worms of tho Wheat-midge, which 

 worms, however, small ns they are, appear like giants 

 when placed by the side of these larvo). Two minute 

 black dots upon the anterior end of the head, are the 

 eyes. Tho legs and antennte are much like those of 

 the perfect insects, except that they are shorter. The 

 two minute joints nt the end of tho antennni, (see fig- 

 ure,./",) can frequently be perceived In the larva state 

 of those organs. 



Buring this state, tho insects of this order are very 



nimble, skipping and throning themselves to a distanca 

 by striking their abdomen suddenly against the sur- 

 face upon which they nro placed. In their pupa state 

 they are much more slow and sluggish in their motions, 

 and become quite active again when they reach their 

 perfect state. The j>upte are like the perfect insects 

 in size and thnpe, except that their wings are short 

 and rudimentary. At first they are merely oval scales, 

 situated upon each side of the two last segments of the 

 thorax. Subsequently they become mure developed, 

 so that they reach to the middle of the abdomen or 

 slightly beyond, but they are still incapable of being 

 used for flying The species under consideration, n hen 

 in its pupa state, is of the same yellow color as when 

 a larva, but the abdomen, at least towards its base, is 

 paler than the thorax. 

 Thepcrfcct insect (figure, c) is but four hundreths 



of nn inch in length Its length is indicated by the short 

 line at d, in tho annexed cut It is thus a fourth 

 smaller than Thrips cerealium, and instead of being 

 black like that species, this retains the yellow color 

 which it has when a la'va, the head ond thorax (which 

 includes the three largo segments next to the head, 

 from each of which a pair of legs arises, as shown in tho 

 figure) being of a deep orange yellow, or like the yolk of 

 an egg, whilst tho abdomen is paler and the legs are 

 whitish yellow. The antenna) (the npienl joints of 

 which are represented more enlarged at./") are whitish, 

 tinged towards their tips with dusky. The fringes of 

 the wings are also dusky. Tho fore legs are shorter 

 but no thicker than the others. All tho details of its 

 structure are so plainly shown in the accompanying 

 figures, that a more particular doscription is unneces- 

 sary. 



Tho species which I have noticed ns the moat com- 

 mon upon wheat in Washington county, New-York, is 

 described in my manuscripts under tho name of tho 

 Three-banded Thrips (Co/£o//iri/)s /rt/uscia<a). It is 

 clearly distinct from the three European species of 

 this genus, though nearly related to the C. Jasciata, 

 Linn. It is nearly double the size of the Wisconsin 

 Wheat Thrips, being seven hundredths of nn inch in 

 length, and is so distinctly marked that with the aid 

 of a magnifier, even preserved specimens can be readi- 

 ly distinguished. It is of a black color, polished and 

 shining, with tho third joint of its antennae white, nnd 

 ita wings black or dark smoky brown with three broad 

 white band.«, whereof one is upon the bnso, another 

 acro.'S the middle, and the third, which is somewhat 

 narrower, upon the tip. The wings show two longitudi- 

 nal veins, but no transverse ones were noticed u on 

 them, nor could I discern any fringe npou either their 

 outer or their inner margin. The fore legs are larger 

 than the others, and the anienno; (see figure, g-.) instead 

 of arising fur apart as in most of the species I have 

 examined, oome out f.-om the front of the head close 

 together, nnd are composed of only five principal joints, 

 of which tho two first are short and a third thicker 

 than the others, which are long and cylindrical, the Inst 

 one grndunlly tapering to a slender point, its apical 

 portion being divided into small indistinct segments. 



This species is common upon wheat as early as the 

 first of June. When the grain ripens it probably for- 

 sakes it nnd becomes dispersed upon plants which flow- 



