Becker, Wayne A.

Hamrum, Charles L.

English

University of Minnesota, Morris (UMM): Digital Well

Journal of the Minnesota Academy of Science Volume 30 Number 1 Article 8 1962 A Review of the Characters Used in Identification of Minnesota Eristalis, Latreille (Diptera, Syrphidae) Charles L. Hamrum Gustavus Adolphus College Wayne A. Becker Gustavus Adolphus College Follow this and additional works at: https://digitalcommons.morris.umn.edu/jmas  Part of the Zoology Commons Recommended Citation Hamrum, C. L., & Becker, W. A. (1962). A Review of the Characters Used in Identification of Minnesota Eristalis, Latreille (Diptera, Syrphidae). Journal of the Minnesota Academy of Science, Vol. 30 No.1, 27-30. Retrieved from https://digitalcommons.morris.umn.edu/jmas/vol30/iss1/8 This Article is brought to you for free and open access by the Journals at University of Minnesota Morris Digital Well. It has been accepted for inclusion in Journal of the Minnesota Academy of Science by an authorized editor of University of Minnesota Morris Digital Well. For more information, please contact skulann@morris.umn.edu. ZOOLOGY A Review of the Characters Used in Identification of Minnesota Eristalis, Latreille (Diptera, Syrphidae) 1 CHARLES L. HAMRUM and WAYNE A. BECKER GustavusAdolphus College, St. Peter The species of Eristalis comprise a conspicuous frac-tion of the insects commonly seen hovering about flowers or near the edges of lake.s and ponds. The superficial bee-like appearance of these flies has also served to dis-tinguish this group. Most zoologists even have some knowledge of the larval stage (rat-tailed maggot) as well as the adult, however, a specific identification problem remains in spite of the widespread general information concerning the group. Many of the characters used in species separation are variable or unreliable. A critical review of these characters and consideration of new char-acter combinations seems desirable. The family Syrphidae may readily be distinguished from other Diptera by the so-called false or spurious vein, which is a vein-like thickening of the wing mem-brane between the 3rd and 4th longitudinal veins (R4 + 5 and Ml + 2), and running through the anterior radio-medial cross vein. The present grouping of syrphid gen-era has been greatly influenced by Shannon (1921), how-ever, Malloch (1922) noted the presence of a patch of black spinules on the anterior surfaces of the bases of all femora only in Eristalinae. The spinule character in combination with the deep bending of vein R4 + 5 into cell RS serve to distinguish the Eristalinae. The genus Eristalis is characterized as follows: Face tuberculate, and a little produced downward. Antennae short; arista long and short, plumose basally, bare or microscopically pubescent. Eyes bare to pilose, unicolor-ous to dark vertical bands or numerous spots. Mesono-tum short; scutellum convex. Squamae large. Marginal cell of wing closed; loop of third vein deep; anterior cross-vein at or near middle of discal cell. Abdomen rather short and compact. Hind femora slender to mod-erately thickened without spines or processes; tibiae straight to moderately arcuate. Genotype: Musca arbus-torum Linne. Hull ( 1949) recognizes five subgenera based chiefly upon head characters. Characters Used In Eristalis Identification: Head Characters: The markings and pile of the eyes aid in the definition of two local Eristalis species. The facial profile and ground color of the face are helpful to a degree, however, the width of the facial stripe seems to have very limited significance. Antennal characters, i.e. length of segments and pilosity of arista, also have little influence in identification of Minnesota species. 1 This study was supported by a National Science Foundation undergraduate research participation grant. Proceedings, Volume Thirty, No. One, 1962 Thoracic Characters: The density and color of thoracic pile is a prominent and useful character in separation of species groups. In non-pilose species, the presence of dark or light bands on the mesonotum may be a signifi-cant character. The bright yellow scutellum readily iden-tifies E. transversus among our local species. Leg Characters: Abrupt color changes of tarsal seg-ments or portions of the tibiae have been used exten-sively. Bristles, spines, and other processes do not seem to be usable. Abdominal Characters: Considerable use has been made of color patterns and opaque markings of the two characters. The greater stability of the opaque markings provide a readily recognizable basis for identification of E. dimidiatus, however, these opaque markings are not an unmixed blessing. In some species, opaque markings occasionally appear on some specimens, but not on others. Wing Characters: Infuscated areas in the wing mem-brane are characteristic of most individuals of some Eris-talis species, however, the shape and extent of these pig-mented areas are too variable to be used as specific char-acters. Wing length may possibly be used as another sex differentiating character in several species. The wings of five Minnesota species were measured with the average length of the female wing at least a millimeter longer than that of the male. Genitalia Characters: It seems quite remarkable that the abundance of characters in the male genitalia have been used so little in separating Eristalis species. Illus-trations of Eristalis terminalia appear rarely in the liter-ature and no published dependence on these characters was found. Metcalf ( 1921) presented Syrphid fly work-ers with a useful description of male genitalia. Unfor-tunately, Metcalf all but ignored the Eristalinae termin-alia. The genital structures of Eristalis barda are shown in Fig. 1-3. The descriptive terminology is that used by Cole (1927). The styli are well developed and may vary significantly among species. The cerci are small and not particularly useful in separating species. The paraphalli are blade-like and seem to protect: the aedeagus. The interior for-ceps are articulated to the aedeagus and project upward between the blades of the paraphalli. In this study, con-siderable weight is given to variations in shape of the paraphalli and interior forceps. The male genitalia normally fit into a pouch and are 27 therefore concealed from view. The genitalia may be ex-tended in relaxed specimens and then snipped from the specimen for closer examination. In this study, the ab-domen was broken free from the specimen before treat-ment. All drawings of genitalia presented herein were prepared after boiling the abdomen in a 10 % solution of KOH for as long as necessary to soften and bleach the genitalia. The postabdomen was then dissected free from the abdomen and both parts neutralized in an acetic acid rinse. The postabdomen was then transferred to a drop of glycerine on a glass slide; the genitalia extended and examined with a compound microscope containing an ocular grid. All drawings were originally made on graph paper using the ocular grid as a scale basis. The abdomen and terminalia are kept with the specimen by storing them in small vials containing glycerine with the speci-men pin run through the cork. KEY TO MINNESOTA SPECIES I. Thorax and abdomen with dense long pile .............. 2 Thorax and abdomen bare or with short pile ............ 3 2. Legs black, except reddish hind tarsi; large hairy species .................................. barda (Say) Legs black, except reddish hind tarsi; smaller individuals with abundant reddish pile on third and fourth abdominal segments ...... barda var. rufipilis Hull (new combination) Legs black, hind tarsi dark brown or black, abdominal pile usually black although some yellow pile may be present ............................. bastardii Macq. 3. Eyes with small round black dots .......... aeneus Scopoli Eyes unicolorous or without such dots .................. 4 4. Third tergite of abdomen wholly able to reflect light. .... 8 Third tergite of abdomen with opaque markings unable to re-flect light ......................................... 5 5. Thorax with broad transverse stripe, scutellum bright yel-low ................................. transversus Wied. Thorax unicolorous or indistinctly vittate, scutellum glossy ............................................. 6 6. Posterior margin of third abdominal segment with a fringe of pale yellow pile; opaque markings limited to two widely separated oval spots on third segment. See fig. 6 ............................... latifrons Loew Fringe of pale yellow pile lacking on posterior margin of third abdominal segment ............................. 7 7. Third tergite of abdomen with three opaque spots. Fourth tergite with a rounded opaque spot near anterior edge. See fig. 5 ................................. dimidiatus Wied. Third tergite of abdomen with opaque posterior band or other opaque pattern ................................. 9 8. Basal portion of hind tibiae light yellow .... latifrons Loew Hind tibiae entirely dark brown or black; pile of eyes re-stricted to a broad vertical stripe ............ tenax Linne 9. Basal joints of hind tarsi pale in color; third antenna! joint red to dark reddish brown in female; infuscated spot on basal half of wing prominent in female .... ,:,rupium (Fab.) Basal joints of hind tarsi dark ....................... 10 10. Transverse band of opaque black on third abdominal tergite; face entirely pilose; basitarsi of middle leg. often yellow-ish ............................... arbustorum (Linne) Basal two joints of middle tarsi yellow; face with a shining black stripe ......................... *nemorum (Linne) * Were seen only in the University of Minnesota collection. This key separates only those species of which we have actual Minnesota collection records. Fluke (1922) lists E. saxort.1,m Wied., compactus Walk., and vinetorum Fab. 28 from Wisconsin. Eristalis hirtus Linne and obscurum Loew from South Dakota are listed in the South Dakota State College collection. Significance of Genitalia Characters: The foregoing key does not show the influence of the genitalia charac-ters which greatly influenced its construction. Genitalia examinations frequently reduced confusion resulting from varying specimens within an apparent series. Particularly the problem of color variation has plagued workers with-in this group. Hull (1925) divided the North American Eristalis species into a number of groups. He recognizes the scar-city of structural characters, but feels his grouping arrange-ment is strengthened when considered in the light of geo-graphic distribution. One of Hull's groups, the pilosus group, clearly shows how useful genitalia characters can be in separating species. Specimens resembling E. mon-tanus, anthophorinus, bastardii, and mellisoides may be found among pilose specimens taken in Minnesota. Hull ( 1925) states montanus Williston is the same as antho-phorinus Fallen, and that anthophorinus is a holartic species, which reduces the list by one. Hull differentiates bastardii and anthophorinus on the basis of the median black stripe on the abdominal segments and the color of the abdominal pile. Hull's species mellisoides is differen-tiated from bastardii by its larger size and more narrow opaque band on the posterior margin of the third ab-dominal tergite. There is little doubt that occidentalis Williston is also closely related to the other pilose species found in the Northern States. During the course of this study, the writers prepared a long series of pilose specimens starting with specimens with a narrow black median stripe on a predominantly yellow-orange abdomen, ranging through intergrades of black and yellow-orange to specimens with a predomi-nantly black abdomen. The specimens at either extreme of this color range could be readily assigned to antho-phorinus or bastardii. The intergrades could often be ten-tatively placed as mellisoides or bastardii. An examina-tion of male genitalia from all color variants showed the genitalia structures to be remarkably constant with one exception. The single variant (provided by Dr. Laffoon of Ames, Iowa) was collected at Grafenwohr, Germany, and neatly fits the description of anthophorinus (fig. 10). The constancy of male genitalia structure in this series certainly casts doubt regarding the reliability of color of pile and abdominal markings as specific characters in this group. This examination of male terminalia also cre-ates some doubt concerning the true range of anthophor-inus. In view of these findings, the writers feel that North-ern States specimens keying to montanus, anthophorinus, mellisoides, and probably occidentalis should be regarded as Eristalis bastardii Macquart. The paraphalli and interior forceps of the pilose spe-cies are shown in Figs. 3, 9-12. These terminalia por-tions of barda and barda var. rufipilis bear a close re-semblance to those of the other pilose species. In the absence of biological data, the similarity of genital struc-tures seem to provide additional evidence suggesting the close relationship of the pilose species. The Minnesota Academy of Science Another identification problem clarified by genitalia examination is the confusion between arbustorum Linne and brousii Williston. Hull (1925) regards brousii as a native species which has been seriously challenged by the imported arbustorum. Metcalf ( 1913) and others have considered meigenii Wiedemann conspecific with brousii. Curran ( 1926) maintained meigenii was dis-tinct from brousii on the basis of more extensive opaque abdominal markings and darker legs; and later (1930), upon examination of Wiedemann's type, declared mei-genii does not even exist in the neartic region. Another" frequently appearing synonym for brousii is androcles Osten Sacken, however, it appears that Osten Sacken did not publish a description for androcles. The usual distinction between brousii and arbustorum PLATE I LIIAROA AEDEAGUS 5.0IMD,UIJS 2.BARDA 6. LATlFRONS ? UJ1fR0NS 4 TRANSVERSUS 8 OIMJOIATUS FIGURE 1: Eristalis barda postabdomen, lateral view. FIGURE 2: Eristalis barda postabdomen, ventral view. FIGURE 3: Eristalis barda para phalli and aedeagus dissected free. FIGURE 4: Eristalis transversus paraphalli. FIGURE 5: Eristalis dimidiatus abdomen; white portion: yellow, solid black: opaque, stippled areas: shining black. FIGURE 6: Eristalis latifrons abdomen. FIGURE 7: Eristalis latifrons paraphalli. FIGURE 8: Eristalis dimidiatus paraphalli. Proceedings, Volume Thirty, No. One, 1962 has been the yellowish basal joint of the middle tarsi in arbustorum. This tarsal character agrees fairly well with an opaque band or spot on the third tergite. The writers have found specimens where these characters were re-versed. During the past summer five specimens of arbus-torum were reared from what was believed to be the same egg mass. Individuals among this short series could be placed in either arbustorum or brousii, however, one specimen showed the basitarsal markings of one species and tergite markings of the other. Subsequent efforts to rear arbustorum have thus far failed. An examination of the genitalia of arbustorum and brousii show them to be identical which further casts suspicion concerning the reliability of color patterns and abdominal markings. Pending accumulation of more biological data, the writ-ers consider brousii and arbustorum as conspecific and propose this population be considered as arbustorum. In all likelihood a genitalia study of the neartic Eris-talis species could ease many of the identification prob-PLATE II INTERIOR "13. BROUSIJ 10. ANTHPHORINUS 14. ARSUsTOl!UM ILMONTANUS 1:1. TENAX 11 IIARCA VAA f'UFIPII.IS FIGURE 9: Eristalis bastard ii para phalli. FIGURE 10: Eristalis anthophorinus paraphalli. FIGURE 11: Eristalis montanus paraphalli. FIGURE 12: Eristalis barda var. rufipi/is paraphalli. FIGURE 13: Eristalis brousii paraphalli. FIGURE 14: Eristalis arbustorum paraphalli. FIGURE 15: Eristalis tenax paraphalli. 29 lems within the species groups. The results of this frag-mentary study of the genus indicate the male terminalia may be valuable in designating closely related species. Wherever our local study touched Hull's species group-ings, the genitalia similarities within these groups tend to validate Hull's group separations. Damaged or discolored male specimens may still be usable through the examination of the genitalia charac-ters. The use of genitalia characters in combination with color, degree of pilosity, and opaque markings has sim-plified the identification of Minnesota Eristalis specimens. However, the variable nature of the abdominal markings is still a distraction to the writers. It is possible that color extension or restriction may represent an environmental influence. Perhaps the somewhat varied climate in the different regions of Minnesota may account for this vari-ation, although this was not obvious in our series. The most promising answer to this question seems to be the development of rearing techniques for Eristalis popula-tions. AcKNOWLEGDMENTS: The writers have met with a gen-erous response in respect to the loan of material. About a thousand specimens have been gathered in excess of the Gustavus Adolphus Eristalis Collection. We extend our gratitude to Dr. A. T. Ateyo, the University of Ne-braska, Dr. M. E. Smith, University of Massachusetts, Dr. J. L. Laffoon, Iowa State University, and Dr. How-ard Orr, St. Olaf College for specimen loans. We thank Dr. A. C. Hodson and Dr. E. F. Cook for the use of the University of Minnesota Collection. We also thank Dr. H. C. Severin of South Dakota State College for the list of Eristalis species in the South Dakota State Collection. LITERATURE CITED ALDRICH, J. M. 1905. A Catalogue of North American Diptera. Smithsonian Misc. Collections No. 1444, 680 pp. 30 CoLE, F. R. 1927. A Study of the Terminal Abdominal Structures of Male Diptera (Two-winged Flies). Proc. Calif. Acad. Sci. 16:397-499. CURRAN, C. H. 1925. Notes on Some Species of the Genus Eristalis ( Syrphidae, Diptera). Can. Ent. 5 7: 50. CURRAN, C. H. 1930. New Species of Eristalinae with Notes (Syrphidae, Diptera). Amer. Mus. Nov. No. 411, 27 pp. FLUKE, C. L., Jr. 1921. Syrphidae of Wisconsin. Trans. · Wisc. Acad. Sci. 20:215-253. HULL, F. M. 1925. A Review of the Genus Eristalis Latreille in North America. Ohio lour. Sci. 25:11-45; 285-312. HULL, F. M. 1949. Morphology and Inter-relationship of the Genera of Syrphid Flies, Recent and Fossil. Trans. Zoo!. Soc. London 24:251-408. HUNTER, W. D. 1896. A Contribution to the Knowledge of North American Syrphidae. Can. Ent. 28:87-101. MALLOCH, J. R. 1922. An Unused Taxonomic .Character in Syrphidae. Bull. Brooklyn Ent. Soc. 27:42. METCALF, C. L. 1913. Syrphidae of Ohio. Ohio State Univ.Bull.17:(31)1-123. METCALF, C. L. 1921. The Genitalia of Male Syrphidae: Their Morphology with Especial Reference to its Tax-onomic Significance. Ann. Ent. Soc. Amer. 14: 169-214. SHANNON, R. C. 1921. A Reclassification of the Subfam-ilies and Genera of the North American Syrphidae. Bull. Brooklyn Ent. Soc. 16:65-72; 120-128. TELFORD, H. S. 1939. The Syrphidae of Minnesota. Univ. of Minn. Agric. Exp. Sta. Tech. Bull. No. 140, 76 pp. WEHR, E. E. 1922. A Synopsis of the Syrphidae of Ne-braska with Descriptions of New Species from Ne-braska and Colorado. Univ. Studies, Lincoln, Nebraska, 22: 119-162. WILLISTON, S. W. 1886. Synopsis of North American Syrphidae. Bull. U.S. Natl. Mus. No. 31,335 pp. The Minnesota Academy of Science 

A Review of the Characters Used in Identification of Minnesota Eristalis, Latreille (Diptera, Syrphidae)

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A Review of the Characters Used in Identification of Minnesota Eristalis, Latreille (Diptera, Syrphidae)

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