Historic, archived document Do not assume content reflects current scientific knowledge, policies, or practices. at ASE, Contribution from the Bureau of Entomology L. O. HOWARD, Chief , Washington, D. C. PROFESSIONAL PAPER March 6, 1916 NOTES ON FIVE NORTH AMERICAN BUFFALO GNATS OF THE GENUS SIMULIUM. By AgtHur W. Joppins-PomERoy, Entomological Assistant. CONTENTS. Page. Page. Introduction] 22 eo ee ee. 1 | Life cycle and number of generations_ 26 Where dultistase: 2) oy Berea Sa 2 | Insect enemies and parasites________ 27 helesoistagew he we ee ee 11 | Simulium as a possible carrier of dis- Mune darvalsstage2 sie. eel a 12 AIS Cree er ED bOI Se 2. I Sines 28 Pihespupal Sta gew os Sale. awe Py | Bil oboe oy ae ee Te ee 30 INTRODUCTION. Certain species of the insects known as “buffalo gnats” are im- portant enemies of man and domestic animals in the United States as well as in other countries. Although the principal area of abund- ance in North America is in Canada and the Northern States, out- breaks of pests of this group occur as far south as Louisiana and Florida. While they are dependent upon running water for develop- ment, they make use of very small streams and, to some extent, of irrigation ditches, and are consequently found occasionally in con- siderable numbers in the drier parts of the country. About 20 years ago buffalo gnats attracted great attention along the lower Mississippi River. They frequently became so abundant that plantation operations were stopped~on account of very painful attacks against live stock as well as human beings. These great outbreaks were due to conditions established by the overflow of the Mississippi River. The perfection of the levee system has changed these conditions so that the outbreaks are less frequent and of greatly reduced severity. Nevertheless, these insects are still abundant enough to be considered a pest in the Mississippi Valley as well as in many other portions of the South. The damage done by buffalo gnats results from their painful bites and the loss of blood which ensues. When they are abundant they 1 Resigned Nov. 20, 1914. Noty.—This paper is of interest to persons living east of the Mississippi River. 10981°—Bull. 329—_16——1 9 BULLETIN 329, U. S. DEPARTMENT OF AGRICULTURE. sometimes cause the death of live stock. At the present time no cases of disease transmission can be attributed definitely to buffalo gnats, but there is a possibility that future investigations will show some important connection with the transmission of diseases. All of these considerations make it advisable to place on record a considerable number of observations which will serve as a basis for the control of these insects wherever they occur. The major part of the biological experiments outlined in this paper were carried on at Spartanburg, S. C. The author wishes to ex- press his thanks to Mr. A. H. Jennings, under whose direction the work was done, to the Thompson-McFadden Pellagra Commission for many courtesies received, and to the directors of the Spartan- burg Hospital for the generous way in which they afforded labora- tory accommodations and facilities. THE ADULT STAGE. DESCRIPTION OF EXTERNAL ANATOMY. The adults of the genus Simulium are usually very small, the largest Inown North American species (S. pictipes) not measuring more than 4 mm. in length. They are compact in shape, the head being decidedly small in proporticn to the rest of the body, and the thorax greatly developed and curiously humped. In some species | the thorax and abdomen are very pubescent, in others almost naked. In color the different species vary greatly, ranging from brilliant iridescent yellow and various shades of gray to almost black. The species of Simulium are holoptic in the male and dichoptic in the female. In the female the facets of the eyes have an equal grada- tion in size, diminishing somewhat toward the margin. In the male the facets suddenly decrease in size along a line extending on each side from the antennal socket around to the post-gene, giving the lower portion of the eye the appearance of being divided off by a suture. In color the eyes are usually iridescent bronze in the female and deep iridescent red in the male. Ocelli are wanting in both sexes. The antenne are short, moniliform, and 11-segmented. In the species here dealt with the antenne of the female have the first seg- ment short and cup-shaped. The second is longer, the apical end bearing a chitinous ring which serves as the point of attachment for the third segment, which is nearly the same in length as the second, but pedicellate. The remaining segments are nonpedicellate, broadly joined. Segments 4, 5, 6, 7, 8, and 9 are subequal. The tenth seg- ment is slightly longer. The eleventh is the longest of the entire antenna, narrows to a point at the apical end, and bears from two to three short, strong bristles. The first two segments are minutely pubescent, with a few strong bristles on the apical portion; the re- TRANSFORMATIONS OF BUFFALO GNATS. 3 maining segments are densely covered with minute pubescence inter- spersed thickly with stronger hairs. The antennz of the male are similar in structure to those of the female, except that they are more slender and have the third segment much longer, twice the length of any of the succeeding segments, and the tenth segment usually the same length as the one immediately preceding it. (Figs. 1 and 2.) The mouth parts are modified in both sexes into a piercing beak, somewhat similar to that of the Tabanide. In the male the organs have become greatly reduced both in strength and armature, so that they are apparently unable to pierce the skin of vertebrates. DESCRIPTIONS OF INTERNAL ANATOMY. Fig. 1.—Stmulium venustum. y 2 % ¥ 1 a Z TRANSFORMATIONS OF BUFFALO GNATS. 25 DESCRIPTION OF PUPA OF SIMULIUM BRACTEATUM. The pupa of S. bracteatum (P1. IV, fig. 3) measures about 4 mm. in length and is of a golden yellow color when first formed. The respiratory filaments are composed of a single main trunk on either side of the thorax, each of which divides in the following manner: Two long branches arise from the base of the main trunk, which again divides a short dis- tance farther up, making four long branches on each Side, counting the branches at the distal ends. The hooks on the abdomen are arranged as usual. The pups were reared from larve and determined from adults reared from them and compared with the type. DURATION OF PUPAL STAGE. The duration of the pupal stage of S. venustwm, according to Mrs. Sarah J. McBride, at Mumford, N. Y., is three weeks. The maximum period in the pupal stage of the same species observed by the writer was nine days at Havana, IIL., late in the fall, the average temperature during that period being 36° F. The minimum period in the pupal stage of S. venustum was a little over 84 hours at Spartanburg, S. C., during the month of June, with a temperature from 70° to 90° F. The average length of the pupal period for the five species under consideration, during the summer, is from five to seven days. The general effect of low temperature seems to be to retard, and of rising temperature up to 90° F. to hasten the emergence of the adult from the pupa. The effect that low air temperature has on the pupa in retarding development is much less in proportion than the effect that a rising temperature between 60° and 80° F. has in hastening emergence. Though their structure is normally adapted for aquatic life, yet when they are exposed to the air, as sometimes happens when the water falls, they will often emerge even after 24 hours spent out of water if the adult is sufficiently developed within the pupal skin. This was especially noticeable at Havana, IIl., in 1912, when the river began to fall. The respiratory system of the pupa is a modification of the general tracheal system of the larva. The rectal gills having been cast off, their function appears to be assumed by the tubelike filaments arising on each side of the thorax. There are two long main trunks extending down each side of the abdomen. These give off branch trachez, connected by commissures, which lead to the abdominal spiracular chambers, from which arise the initial threads leading to the spiracles. The spiracles are cuticular invaginations and become closed, according to Taylor, on the withdrawal of the old trachee at the time of the 1Taylor, T. H. On the tracheal system of Simulium. Jn Trans. Ent. Soc. London, f. 1902, p. 701-716 (p. 703), 8 fig., 1902. 26 BULLETIN 329, U. S. DEPARTMENT OF AGRICULTURE. shedding of the larval skin. From the mesothoracic spiracular cham- ber extends a broad tracheal trunk leading to the base of the main trunk of the respiratory filaments, which do not contain trachee, but are hollow. According to Taylor,! the air is not taken directly into the gill base from this hollow space, but is absorbed through the external chitinous fibrille and thence into the tracheal extension through a membrane. EMERGENCE FROM THE PUPAL STAGE. Four or five hours before emergence there is a very noticeable in- termittent movement of the adult within the pupal skin, which is gradually distended with air toward the anal extremity, the abdomi- nal trachez being probably withdrawn through the spiracular open- ings. Coincident with this the anal portion of the adult is with- drawn from the pupal skin and a threadlike membrane, seemingly the lining of the hind intestine, may often be seen extending from the anus of the adult to the pupal skin, to which it remains attached after emergence. As the pupal skin is locked by the strong chitinous hooks to the pupal case, the adult exerts a strong pressure toward the cephalic end and the pupal skin splits along the dorsal portion of the thorax and head, forming a T-shaped aperture. The adult at once rises to the surface of the water surrounded by a bubble of air which has been collected in the distended pupal skin, and running along the surface of the water at once takes flight. The curious way in which the adult rises to the surface surrounded by a bubble was commented on by the earliest writers on the group, and in situations where the pupe are found in thousands, as in parts of Hungary, and along the Illinois and Mississippi Rivers in America, the water seems almost to boil as they emerge. LIFE CYCLE AND NUMBER OF GENERATIONS. The number of generations varies according to the species and the latitude. In the Southern States the species seem to breed con- tinuously from about the middle of March until the approach of severe cold weather, generally about the end of November. The life cycle of one generation during the summer takes approximately four weeks; 7 days in the egg stage, 17 days as larve, and 4 days as pupe. The time from the egg to the adult stage varies according to the rise and fall of the temperature. There are probably from five to six generations annually in South Carolina of the species here dealt with, except S. pictipes, which normally has three generations. In Illinois there are only three or four generations of S. venustwm annually. 1 Loe. cit. TRANSFORMATIONS OF BUFFALO GNATS. at INSECT ENEMIES AND PARASITES. The larvee of Simulium are often parasitized by nematode worms of the genus Mermis, specimens of which have been found by the writer measuring 12 mm. in length. These were found in larve of S. venustum, coiled around the intestines, and extended from near the _ caudal end to the thorax. The specimens that attained the greatest length were found singly, but as many as four have been found in individual larve. According to Strickland (1911), the Mermis retard the development of the pupal and adult histoblasts, cause the death of the larvee, and escape through punctures made in the epidermis. He also states that in the vicinity of Boston, Mass., Mermis was found parasitizing larve only during the spring, and that there is a seasonal variation of parasitism. The writer, while in South Carolina, found species of Mermis parasitizing larve from May until late in October, and these larve seemed to have developed the pupal histoblasts to a much greater extent than is estimated by Strickland. The larve are also heavily attacked by glugeid and gregarine species of Myxosporidia. The writer has found the larve being attacked by species of Hydropsyche in Illinois and South Carolina. Dr. Howard (1888)? also mentions this fact in his article on a species of Simulium at Ithaca, N. Y., and gives a fuller account in the Annual Report of the U. S. Commissioner of Agriculture for 1886, page 510. Species of minnows attack the larvee frequently, and Riley? mentions that the small fishes of the family Cyprinide also feed on them. The pups, so far as is known, are not parasitized by Mermis or Myxosporidia. The udults have been found by the writer at Spar- tanburg, S. C., to be frequently parasitized by nematode worms of the genus Mermis, which were usually found singly. In one in- stance three of the worms were found in a female S. venustum. The same number were found in a female of S. bracteatum. They were situated in the abdomen, coiled around the Malpighian tubes and intestines, and in some cases extended into the thoracic region. The vitality of these specimens infested by the Mermis seemed to be seriously affected, though they lived for some time, 31 hours being the minimum and 72 the maximum period. All of these specimens thus parasitized were reared from pupz, with the exception of one adult female of S. bracteatum, which was taken flying around a lamp at night. No adults taken biting on animals were ever found to contain Mermis. 1See Bibliography, p. 35. 2 Riley, C. V. Report of the Entomologist. Jn Rept. U. S. Comr. Agr. f. 1886, p. 459- 592 (p. 510), 11 pl., 1886. 28 BULLETIN 329, U. S. DEPARTMENT OF AGRICULTURE. Georgewitch? describes a trypanosome, Crithidia simuliae, which he found in the stomachs of adult females taken biting cattle, ete. The locality in which the animals were attacked was a district in Servia, and the species S. reptans (=S. columbaschense). He did not, however, find any similar organism in the blood of the animals attacked. Riley? states that Lugger observed them being attacked by Asi- lide and Odonata. Wise (1911) reports that in British Guiana the adult females of Simulium are attacked by a voracious enemy in the nature of a black and white wasp (probably Monedula signata), which follows the aboriginal Indian to obtain the “ Pium” (Simulium). This wasp reduces the “ Pium” to unconsciousness, deposits eggs, and leaves the body to be fed upon by the resulting larve. SIMULIUM AS A POSSIBLE CARRIER OF DISEASE. In 1874 J. P. Megnin* strongly advanced a theory that two species of Simulium in the Department of the Rhone, France, are the trans- mitting agents of virulent charbon. He also mentions Stomoxys and Haematobia in this connection, but places most emphasis on Simulium, whose habits more closely conform to the outbreaks and distribution of the disease in that locality. He also states that, in his opinion, M. Tisserant, sent by the French Government to investigate the subject, proved that Simulium was the cause or the transmitting agent of the disease. In a later paper he reaffirms his statements and mentions that he has found a “ Psoriasis guttata”’ prevalent in the ears of horses, and believes it is due to the bites of Simulium. The writer has found a similar condition to be very common in the ears of horses, undoubtedly due to the bites of Simulium, in Illinois, South Carolina, and the vicinity of Wash- ington, D. C. As this condition may be of a purely secondary nature, and as apparently no experimental or careful analytical work has been done on the subject, all statements regarding the transmission of a disease of cattle by Simulium must be regarded as purely theo- retical. According to Riley and other authors, S. pecuarum Riley and S. meridionale Riley were supposed to carry cholera among chickens and hogs, but nothing definite was ascertained on this point. 1 Georgewitch, Jivoin. Sur un Trypanosomide nouveau, Crithidia simuliae, n. sp. d’une Simulie (Simulium columbacensis) de la Serbie septentrionale. In Compt. Rend. Soc. Biol., t. 67, no. 31, p. 480—482, 1 fig., Nov. 12, 1909. 2 Op. cit., p. 510. 3 See Bibliography, p. 35. 4Du role des mouches dans la propagation du charbon et autres affections virulentes. In Jour. Med. Veter. Mil., t. 12, no. 8, p. 461-475, Paris, Jan., 1875. TRANSFORMATIONS OF BUFFALO GNATS. 29 In 1905 Dr. Louis Sambon advanced the theory that pellagra might be transmitted by a blood-sucking fly of the genus Simulium. An accurate knowledge of the biology of the genus 1s very necessary in order to prove or disprove such a theory. It must be proved that Simulium not only bites in very large numbers, in order that a sufli- cient percentage of specimens will become infected which will live and become capable of transmitting pellagra, but it must also be proved that they will bite man after they have become infected, since hereditary transmission is probably entirely out of the question. Simulium exists in many places in large numbers, and if it should be proved that it normally requires a meal of the blood of vertebrates before it can fully develop the ovaries, then the chances that it may become infective are greatly increased. Evidence on these points may be obtained in the following three ways: (1) By rearing adult females from the immature stages, and then allowing them to engorge, oviposit, and reengorge. This method was tried a number of times, but with no success, for the fly will not readily engorge while in captivity, as was noted in the discussion of the feeding habits of the adult. (2) By the capture of adults actually feeding on mammals, and by inducing them to oviposit and then to reengorge. This method also was unsuccessful for the same reasons. (3) By dissections. If it could be proved that when a Simulium, which has once engorged on blood and oviposited, is still in a condi- tion favorable to a second oviposition—that is, if rudimentary eggs are present in the ovaries awaiting only a second blood meal for their successful development—then there would be a more definite basis for a theory of disease transmission as opposed to the theory of merely a close coincidence in the distribution of pellagra and Simulium. This is the method adopted by the writer and is the one discussed in the following pages. The experiments were concluded in Spartan- burg County, S. C., a country very favorable for the production of Simulium, being hilly and with a network of small streams, rapid and especially suitable for the development of the immature stages. The experiments on the actual biting and feeding habits were carried on more or less continuously from June 13 to September 16. The ma- terial for these experiments consisted of specimens of S. venustum,; a good series of reared specimens (about 30); a number of females found engaged in oviposition; about 300 females all of which were taken in the act of engorging on mammals. Of the last named only about 90 were successfully dissected, as the engorged adults after death became internally disintegrated and hardened after an hour or so, despite every precaution. Many also died between midnight and 7 a. m., or while they were being transported from the place of 30 BULLETIN 329, U. S. DEPARTMENT OF AGRICULTUZE. capture to the laboratory. The adults, with the exception of 10 speci- mens killed at the time of capture, were kept alive as long as possible and dissected as soon as death was imminent. Some, in order that data might be obtained on their condition at the time of engorge- ment, were killed when captured and dissected within an hour. RECORDS OF DISSECTIONS. DEVELOPMENT OF THE OVARIES OF REARED NONFED ADULTS. In order to have a check on the experiments with engorged adults, 32 females reared from isolated pup were kept alive as long as possi- ble, without food, in bottles containing damp cloths. ‘There were a number of males, reared from this same lot of pups, at liberty within the breeding cage together with these females, and copulation prob- ably took place, but no definite statement can be made with regard to this point. Four females were killed and dissected within 6 hours after emergence. The remainder lived from a minimum period of 144 hours to a maximum of 119 hours. All these specimens on dissec- tion contained rather transparent ovaries of great potential develop- ment and full of round eggs (stage 1) (PI. I, fig. 1, p. 4). In no instance did any one of these specimens develop the eggs within the ovaries as far as even the second stage. The maximum longevity of any nonfed reared specimen exceeded the maximum longevity of any specimen taken after engorgement by 52 hours. It would seem, therefore, that of these 32 reared specimens, there would have been 1 or 2 which would have developed the eggs within the ovaries, if it had been in the natural course of events for them to do so. CONDITION OF THE OVARIES OF FEMALES FOUND OVIPOSITING. Eleven females were taken actually engaged in oviposition on grass blades in streams. When these specimens were dissected, there was found in each stomach a certain amount of substance closely resem- bling the digested blood found in engorged specimens which had lived after engorgement for 40 hours or more previous to their dis- section. A chemical test for hematin was applied to the substance found in the stomachs of the females found ovipositing, in order to prove beyond doubt whether it contained animal blood or not, but, owing to the small quantity and the changes consequent to the process of digestion, it was impossible definitely to determine its character. Three specimens were taken from grass blades in a stream on which they had just alighted and had not begun to oviposit. These speci- mens were at once dissected, and their ovaries were found to contain — from 250 to 300 fully developed eggs. Four specimens were taken from egg masses deposited in the same situation, which had evidently TRANSFORMATIONS OF BUFFALO GNATS. 31 just finished ovipositing. Four others which subsequently laid from 89 to 349 eggs while in captivity were also captured. The adults lived after oviposition from 15 minutes to 674 hours, and were dis- sected immediately after death. Their ovaries were found to contain in each case a large quantity of eggs of the round type corresponding to stage 1 (PI. I, fig. 1) with the exception of the specimen which lived only 15 minutes after oviposition and in which the eggs within the ovaries were only visible under a high magnification. The ovary of one specimen contained in addition, near the oviduct, a large fully developed egg which had not been deposited. This last-mentioned condition (stage 5, Pl. 1, fig. 5) was also found in adults taken engorging upon mammals and killed at the time of capture. CONDITION OF THE OVARIES OF ADULTS TAKEN FEEDING ON MAMMATS. In order to demonstrate the relation between the amount of en- gorgement and its apparent effect upon the development of the eggs within the ovaries, the condition of the ovaries is discussed collect- ively with regard to the previous amount of engorgement by adults, irrespective of the dates on which the adults were captured. The following symbols are used in description to separate the varying degree: (+) Slight and partial engorgement, or about one- fourth the utmost capacity; (++) fair engorgement, or one-half the utmost capacity; (+-+-++) well engorged, or three-fourths the utmost capacity; (++-+-++) complete engorgement, or distension of the ab- domen to its utmost capacity. CONDITION OF THE OVARIES OF ADULTS KILLED AT TIME OF CAPTURE. Ten adults were taken from time to time engorging on the blood of mules. They were killed at once to obtain data on the condition of the ovaries at the time of engorgement. Two specimens were slightly engorged (-++); in one the ovaries showed a condition corre- sponding to stage 5, each ovary containing about 12 fully developed eggs, the remainder of the ovary being filled with eggs of the round type; in the other the ovaries contained only eggs of the round type in large quantity (stage 1). One specimen was half engorged (+-++) ; its ovaries were in a condition typical of stage 5, being filled with small round eggs and containing in addition 8 large fully de- veloped eggs in a free condition, which seem positively to have been developed at a different period from the rest of the ovaries. One specimen was fairly engorged (+-+-+); the ovaries contained only eggs of the first stage in large numbers (stage 1). Six specimens were taken fully engorged (+-+-+-++); all of the ovaries were in a condition typical of stage 1, the eggs being of the small round type, translucent, and in large numbers. 32 BULLETIN 329, U. S. DEPARTMENT OF AGRICULTURE. In conclusion, there were only two stages found in the ovaries of adults killed at the time of capture, either small, round, undeveloped eggs in large quantity (stage 1), or round undeveloped eggs with the addition of a very few large, fully developed eggs (stage 5). This latter stage is presumably the result of a previous engorgement and oviposition. CONDITION OF THE OVARIES OF NONENGORGED ADULTS TAKEN ON ANIMALS. Six specimens, which had evidently just alighted and had not fed on that particular animal, were taken at various times from mules’ ears. They lived from 2 to 47 hours after capture, and the condition of the ovaries in all these specimens was typical of stage 1. There was no development of the eggs within the ovaries, and the condition seemed to be the same as in adults reared from pup and dissected shortly after emergence. CONDITION OF THE OVARIES OF PARTLY ENGORGED ADULTS. Twelve specimens were taken which had partly engorged (+). The eggs within the ovaries of five of these specimens were not de- veloped at all, and showed a condition corresponding to stage 1. These lived from 16 to 30 hours after capture. Three specimens showed the ovaries in a condition typical of stage 5, with from 1 to 4 fully developed eggs near the oviduct, and with the remainder of the ovaries filled with the small round type. These individuals lived from 12 to 21 hours after capture. The ovaries of two speci- mens which lived for 52 and 53 hours, respectively, contained a large number of eggs between stages 2 (Pl. I, fig. 2) and 3 (PI. I, fig. 3), almost oval in shape, about 200 in all. Two adults were slightly more engorged than the rest, though not quite half engorged. They contained ovaries with eggs fully developed, of the same size and shape as eggs freshly deposited, but in very small numbers as com- pared with those found in adults dissected before oviposition. There were about 30 eggs in the ovaries of one and 50 in the other, which lived 45 and 47 hours, respectively. These adults had possibly en- gorged once, oviposited, and then developed the remaining eggs in the ovaries. In the condition of the ovaries of partly engorged adults these two points are worthy of notice: (1) No development of the ovaries took place unless the longevity of a specimen exceeded 40 hours; (2) stage 5 recurred in three cases. CONDITION OF THE OVARIES OF HALF-ENGORGED ADULTS. Five half-engorged (+--+) adults were taken. The ovaries of two specimens contained eggs of the round type typical of stage 1. They lived for 7 and 21 hours, respectively. One adult contained ovaries filled with eggs of the typical oval shape (stage 3) in large TRANSFORMATIONS OF BUFFALO GNATS. 33 numbers and dense white in color. This adult lived for 53 hours after engorgement. Two adults contained ovaries with fully de- veloped eggs in small numbers. In one adult there were 25 eggs in each ovary and in the other 18. Both these adults hved for only 4 hours and 35 minutes after capture. This is probably a case of second feeding, because adults which lived for so short a period after engorgement could not have developed fully formed eggs in that time. The explanation of this condition is that they had prob- ably deposited only part of the full number of eggs at a previous oviposition. CONDITION OF THE OVARIES OF WELL-ENGORGED ADULTS. Twelve well-engorged (+-+-++) adults were taken on various dates, these specimens lived after capture from 7 to 47 hours. Only one specimen contained ovaries corresponding to stage 1. This specimen lived only seven hours and evidently had not had sufficient time in which to develop the ovaries. One specimen, which lived 17 hours, contained ovaries filled with eggs of stage 2, thus showing that the amount of development corresponds to the amount of engorgement and the requisite length of time after feeding. Six specimens, which lived from 174 hours to 24 hours 45 minutes, contained ovaries filled with eggs of the oval type typical of stage 3, again showing a. con- stant amount of development in proportion to the previous engorge- ment and subsequent longevity. One specimen, which lived for 43 hours, contained eggs of the oval type in a very small number, about 20 in each ovary, with the remainder of the ovary apparently filled with the eggs of the round type (stage 1). One adult contained ovaries with fully developed eggs, but only 27 in each ovary. This specimen lived for 80 hours. Two adults contained ovaries filled with fully developed eggs, over 100 in each ovary. These lived for 47 hours and evidently had the required factors, presumably a suffi- cient blood meal and sufficient time in which to digest, in order to develop the eggs within the ovaries. The foregoing data seem to show again that the development of the eggs within the ovaries is increased by the amount of food plus the length of the period of digestion. CONDITION OF THE OVARIES OF FULLY ENGORGED ADULTS. Thirty-one fully engorged (+-++-+) adults were taken from time to time and successfully dissected. They lived from 30 minutes to 673 hours. Six specimens contained ovaries corresponding to stage 1. These lived from 30 minutes to 4 hours 35 minutes. Two adults, which lived 17 and 24 hours, respectively, contained ovaries with the eggs between stages 2 and 3. Six specimens contained ovaries with eggs typical of stage 3 in large numbers. These lived from 18 to 34 BULLETIN 329, U. S. DEPARTMENT OF AGRICULTURE. 284 hours. One specimen which lived 234 hours contained ovaries with only a small number of eggs, about 25 in each ovary. One adult which lived for 44 hours contained ovaries between the third and fourth stages, and showed the transition from stage 3 to stage 4 very clearly. Twelve adults contained ovaries filled with fully developed eggs (stage 4, Pl. I, fig. 4), ranging in num- ber from 200 to 300. These adults lived from 30 to 674 hours. Two adults contained ovaries with eggs of stage 4, but in small numbers, about 50 in each ovary. They lived 48 and 56 hours, respectively, and possibly had developed the remainder of the eggs left within the ovary after a previous oviposition. One adult con- tained ovaries with eight fully developed eggs, and the remainder of the ovary filled with eggs corresponding to stage 3. This adult lived 34 hours and had presumably oviposited once, as is indicated by the presence of the eight fully developed eggs, and then devel- oped the remainder of the ovaries to stage 3. A comparative study of the ovaries of well-engorged (+++) specimens shows that no adult which died before reaching a period of longevity of 30 hours after engorgement developed the eggs within the ovaries to full degree. On the other hand, with one exception, all adults which lived for 30 hours after engorgement developed the eggs within the ovaries to the fullest extent. The fully developed eggs within the ovaries were of the same shape as eggs freshly laid, and only a fraction smaller. THE APPARENT EFFECT OF A BLOOD MEAL UPON THE DEVELOPMENT OF THE OVARIES. In the studies which have been made of the ovaries of females of Simulium venustum under various conditions the following points are worthy of emphasis: (a) In all adults taken while oviposit- ing, apparently digested blood was found in the stomach. (6) No eggs within the ovaries developed to the fullest degree without en- gorgement and the requisite time in which to digest the blood meal. | (c) The condition designated as stage 5 occurred both in adults which had just oviposited and also in adults which were taken on animals and killed at the time of capture. This condition (stage 5) seems to furnish strong evidence that adults feed again after oviposit- ing, as the majority of engorged adults showed the entire contents of the ovaries developed. In addition the exact cause of the similar condition found in adults which had just oviposited is known; namely, that a few fully developed eggs were left in the ovaries after oviposition and the remainder of the eggs were in a rudimentary condition apparently awaiting the necessary factors for development. (d) The males have reduced mouth parts and are not found engorg- ing on blood, indicating the acquisition of this habit by the females for a special purpose, as is the case with other blood-sucking Diptera. TRANSFORMATIONS OF BUFFALO GNATS. 35 BIBLIOGRAPHY.’ *ADAMS, C. F. Notes on and description of North American Diptera. Kan. Univ. Sci. Bul., v. 2, no. 14 (whole ser. v. 12, no. 14), p. 484, June, 1904. Description of new species, Simulium notatum. Arizona. *Agassiz, Louis. Lake Superior: Its Physical Character, Vegetation, and Animals, p. 84-35, 55, 61, 79, 115. Boston, 1850. On species of Simulium, probably 8. venustum, biting travellers in the North Woods. * AIGNER-ABAFI, VON L. Die Kolumbacser Fliege. Jn Allg. Ztschr., Ent., Bd. 8, no. 5, p. 93-96, 124-127, March, 1903. Simulium in Austria. *AtpDRICH, J. M. A catalogue of North American Diptera. Jn Smithsn. Mise. Collect., v. 46, no. 1444, 680 p., 1905. Pages 169-171. Simulium. *AUSTEN, ERNEST EDWARD. 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In 27th Rpt. State Ent. Ill. f. 1912, p. 21-55, fig. 1-25. Descriptions of S. johannseni Hart. and S. venustoides Hart n. sp. *WRIES, B. F. Observationes entomologice, Pt. I. Monographia Simuliarum sveciz, Lunde, 1824. *GARMAN, H. Silk spinning fly larve. In Science, v. 22, no. 559, p. 215-217, 4 fig., Dece., 1898. *GARMAN, H. A preliminary study of Kentucky localities in which pellagra is prevalent. Kentucky Agr. Expt. Sta. Bul. 159, 79 p., 65 fig., Jan., 1912. On the life history and early stages of Simulium venustum with several very good figures of structural characters, 38 BULLETIN 329, U. S. DEPARTMENT OF AGRICULTURE. *GEORGEVITCH, JIVOIN. Sur un Trypanosomide nouveau, Crithidea simulie, n. sp. d’une Simulie (Simuliuwm columbacensis) de la Serbie septentrio- nale. Jn Compt. Rend. Soc. Biol., t. 67, no. 31, p. 480-482, Paris, 1909. An organism found in the digestive tract of blood-sucking female Simulium. *QGEORGEVITCH, JIvoin. Note relative a la Biologie et au systéme digestif de Simulium columbacensis. In Compt. Rend. Soe. Biol., t. 67, no. 33, p. 540- 542, Paris, 1909. *GOELDI, Emitio Auceusto. Os Mosquitos no Para. In Memorias do Museu Geeldi, v. 4, p. 188-139, Para (Brazil), 1905. On the “ pium ”’; original description of Simulium amazonicum. *GORDON-HEWITT, C. Simulium flies and pellagra. In Nature, v. 85, p. 169-170, 1910. Short note. *GRABER, V. Simulia, Chironomus. Jn Denkschriften der kaiserlichen Akademie der Wissenschaften, Bd. 55, p. 142-144, pl. 8, fig. 48-54, Wien, 1889. *GRUNBERG, K. Diptera, Zweifltigler. In Die Sitisswasserfauna Deutschlands, - Heft 2A, 312 p., 348 fig. Jena, 1910. Pages 106-112, figures 126-130. List of most of the European species of Simu- lium to date, with descriptions of the adults, larve, and pup. *HAGEN,.H. A. A new species of Simulium with a remarkable nympha case. In Proc. Boston Soe. Nat. Hist., v. 20, p. 305-307, Oct., 1879. *HacreN, H. A. On Simulium. Jn Canad. 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Jn Insect Life, v. 1, no. 4, p. 99-101, Oct., 1888. *Howarp, L. O. Death web of young trout. Jn Insect Life, v. 7, no. 1, p. 50, Sept., 1894. . Note on a Simulium in relation to fish. *Howarp, L. O. The buffalo gnat. In Insect Life, v. 7, no. 5, p. 426, July, 1895. Note on occurrence in Louisiana. *Howarp, L. O. Simulium and pellagra. In U. S. Dept. Agr. Ann. Rpt. Ent. f. 1911, p. 34. *HUNGERFORD, H. B. Anatomy of Simuliwm vittatum. In Kansas Univ. Sci. Bul., v. S, no. 10 (whole ser., v. 18, no. 10), p. 865-882, pl. 48-45, 1914. *HUNTER, S. J. The sand-fly and pellagra. Jn Jour. Econ. Ent., v. 5, p. 61-64, 1912. - *HuNTER, S. J. University experiments with sand fly and pellagra. Kansas Univ. Sci. Bul., v. 8, no. S (whole ser., v. 18, no. 8), p. 818-820, 1914. * JENNINGS, ALLAN H., and Kine, W. V. One of the possible factors in the causa- tion of pellagra. Jn Jour. Amer. Med. Assoc., v. 60, p. 271-274, Jan., 1913. 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Beurtheilung des von Dr. Medovics an die serbische Regierung erstatteten Berichtes tiber Enstehung und Vertilgung der Gollubatzer Mucken. Jn Sitzber. K. Akad. Wiss. [Vienna], Math. Naturw. K1., Bd. 1, p. 92-107, pl. 1-3, 1848. On Simulium sericeum Meig. *KOLLIKER, ALBERTO. Observationes de prima insectorum genesi. Jn Ann. Sci. Nat. Zool., ser. 2, t. 20, p. 253-283, pl. 11. Paris, 1843. Pages 265-266. Simulia canescens, embryology. *LATREILLE, P. A. Histoire Naturelle, v. 14, 432 p. Paris, 1805. Page 294. The 477th Genre Simulie: Simulium. Original description of the genus. *LAVINDER, C. H. The theory of the parasitic origin of pellagra. In Public Health Reports, v. 25, no. 21, p. 285-237. Washington, June, 1910. Summary of the ‘‘ Simulium theory.” (Simulium reptans.) *LAVINDER, C. H. A report of the second triennial meeting held at Columbia, S. C., Oct. 8-4, 1912. In Public Health Reports, v. 27, no. 44, p. 1776-1778, Nov., 1912. *Lerroy, H. MAXWELL. Indian Insect Life, 786 p., 83 pl., 5386 fig. Calcutta and Simla, 1909. Pages 587-588, pl. 61. Simulium in India. Observations on Simulium indicum Becher and S. indianum Big. *Lron, N. Le Simulium columbaczense de Roumanie. Jn Centbl. Bakt., Abt. 1, v. 51, p. 659-668, 11 fig. Jena, 1909. A careful study of the structure of the mouth parts of Simulium. *LETHO, JULIUS. Hungarian Earthquakes and the Kolumbacs flies. In Nature, Ve2i wp: 202 san. Sse: *LIEBE, JOHANNES. Die larva von Simulia ornata Mg. (with 16 figs. in the text). In Zeitschrift fur Naturwissenschaften, Bd. 82, Heft 3-5, p. 345-372. Leipzig, 1910. *LINNZUsS, Carotus. Lachesis Lapponica. Translated by J. E. Smith, v. 1, 366 p. London, 1811. Pages 208-209. On attacks of Culex reptans in Pithoea. TRANSFORMATIONS OF BUFFALO GNATS. 41 *LINNZUS, CaRoLus. Flora Lapponica, 390 p., 12 pl. London, 1792. Pages 382-383. Description of Culex pulicaris=C. reptans=Simulium reptans. Known locally as ‘ knort.”’ *Lorew, H. Diptera Americe septentrionalis indigena. Centuria secunda. In Berlin. Ent. Ztschr., v. 6, p. 185-232. Berlin, 1862. Page 186. Simulium quadrivittatum, description of new species. *LOUNSBURY, CHARLES P. Insect pests in South Africa. In Science in South Africa, p. 862-374, 1905. Simulium attacking poultry (brief mention), South Africa. *LuGcEeR, OTTo. Insects injurious in 1896. Univ. Minn. Agr. Expt. Sta. Ent. Div. Bul. 48, 270 p., 16 pl., 187 fig., 1896. Pages 198-208. Description of new species: Simulium minutum; S. irritatum ; S. tribulatum=S, vittatum. *LUNDBECK, WILL. Diptera Groenlandica. In Videnskabelige Meddelelser fra den naturhistoriske Forening i Kjobenhavn, p. 281-816, 5 fig., 1900. *LUNDSTROM, CARL. Sliktet Simulium Latr. In Meddelanden af Societas pro Fauna et Flora Fennica, Heft 36, p. 103-104, 1910. *LUNDSTROM, CARL. Beitrige zur Kenntnis der Dipteren Finlands, VII. Mo- lusinids (Simuliide). Jn Acta Soc. pro Fauna et Flora Fennica, v. 34, no. 12, 24 p., 26 fig., Dec., 1911. A study of the male genitalia, showing the systematic value of the structures. *LutTz, A. Memorias do Instituto Oswaldo Cruz, t. 1, p. 124-146. Rio de Janeiro, 1909. Page 132, description of Simulium rubrithorar; p. 1338, S. scutistriatum ; p. 135, 8. hirticosta; p. 141, S. exiguum and 8S. varians; p. 187, spp. nu. Brazil. S. venustum var. infuscata. ° *Lutz, A. Memorias do Instituto Oswaldo Cruz, t. 2, p. 213-267, 1910. Descriptions: S. infuscatum, p. 236; S. orbitale=nigrimanum Macq., p. 231; S. auristriatum, p. 245; S. incrustatum, p. 243; S. distinctum, p. 241; S. sub- nigrum, p. 239; 8. subpallidum, p. 247; S. flavopubescens, p. 248; 8. pruinosum, p. 290; 8S. simplicicolor, p. 251; S. minusculum, p. 253; S. rotulibranchiuwm, p. 256; S. clavibranchium, p. 257; S. diversifurcatum, p. 258; S. arquifurcatum, S. bre- vibranchium, p. 260, spp. n. Brazil. _*McBripe, Sara J. The so-called web-worm of young trout. In Amer. Ent. and Bot., v. 2, no. 12, p. 865-866, Dec., 1870. *Macquart, M. Histoire Naturelle des Insectes, Diptéres. v. 1, p. 173-175, pl. 4, fig. 15. Paris, 1834. Simulie. Simulium Latr. Description of genus and list of species. One colored figure of S. ornatum. *MALLOCH, J. R. One new genus of dipterous insects in the U. S. National Museum collection. Jn Proc. U. 8S. Nat Mus., v. 48, no. 1945, p. 649-658, pl. 46, 1913. Page 649, pl. 46, fig. 67, Simulium bicoloratum ; p. 650, fig. 8, S. bipunctatum ; p. 650, fig. 9, S. townsendi; p. 652, S. nitidum. Locality, Peru. *MatitocH, J. R. American black flies or buffalo gnats. U. S. Dept. Agr. Bur. Ent. Tech. Ser. no. 26, 71 p., 6 pl., 1914. Descriptions of new species: Prosimulium pleurale; Prosimulium mutatum ; Parasimulium new genus; Parasimulium furcatum; Simulium aureopunctatum ; S. hippovorum,; 8. trivittatum; S. bivittatum; 8. parnassum; 8S. arcticum; 8. jen- ningsi; S. clavipes; S. hunteri; S. hematepotum; 8. forbesi. *MarRLaTT, C. L. Report of a trip to investigate buffalo gnats. Jn Insect Life, v. 2, no. 1, p. 7-11, July, 1889. 49 BULLETIN 3829, U. S. DEPARTMENT OF AGRICULTURE. *MARSHALL, P. New Zealand Diptera. In Trans. and Proc. N. Zeal. Inst., v. 28, art. 26, no. 3 (Simulidee), p. 310-311, pl. 14, June, 1896. Simulium australiense in New Zealand. *MECZNIKOW, ELIAS. Embryologische Studien an Insecten. Jn Ztschr. Wiss. Zool., Bd. 16, Heft 4, p. 8389-500, pl. 23, fig. 1-24. Leipzig, Dec. 6, 1866. A detailed study of the embryology of several insects. Aphis rose, Chironomus etc., including detailed account of the embryology of Simulium with excellent illustrations. *MEGNIN, J. P. Du rdle des mouches dans la propagation du charbon et autres affections virulentes. Jn Jour. Med. Veter. Mil., t. 12, no. 8, p. 461-475. Paris, Jan..1875: Simulium maculatum and S. cinerewm transmitting diseases of cattle. *MEGNIN, J. P. Les Parasites et Les Maladies Parasitaires chez l’7Homme, les Animaux Domestiques et les Animaux Sauvages avec Lesquels ils Peuvent etre en Contact; Insectes, Arachnides, Crustacés. 478 p., 26 pl., 63 fig. Paris, 1880. Pages 47-51. Mouches piquantes, Simulium, causing a psoriasis in the ears of horses, and also transmitting charbon. *MEIGEN, J. W. Versuch einer neuen Gattungs-Hintheilung der europiischen zweifltigligen Insekten. Jn Magazin fiir Insektenkunde herausgegeben von Karl Tiliger, v. 2, p. 259-281. Braunschweig, 1803. *MnIGEN, J. W. Klassification und Beschreibung der europiischen zweiflii- glichen Insecten, t. 1. Braunschweig, 1804. *MEIJERE, J. C. H. pe. Studien tiber Siidostasiatische Dipteren. In Tijdschr. 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Formula for a buffalo gnat application. Let- ter by Miss P. H. Skipwith. Jn Insect Life, v. 1, no. 5, p. 148, Nov., 1888. *RitEy, C. V. Buffalo gnats on the Red River. (Letter by G. A. Frierson and reply.) Jn Insect Life, v. 1, no. 10, p. 318-814, April, 1889. *RILEY, C. V., and Howard, L. 0.