A Review of the Genus Cricotopus in Ohio, with a Key to Adults of Species of the Northeastern United States (Diptera, Chironomidae)1
Total Page：16
File Type：pdf, Size：1020Kb
Copyright © 1983 Ohio Acad. Sci. OO3O-O95O/83/OOO3-OO74 $5.00/0 A REVIEW OF THE GENUS CRICOTOPUS IN OHIO, WITH A KEY TO ADULTS OF SPECIES OF THE NORTHEASTERN UNITED STATES (DIPTERA, CHIRONOMIDAE)1 M. W. BOESEL, Zoology Department, Miami University, Oxford, OH 45056 ABSTRACT. In the northeastern states, 21 species of Cricotopus are recognized: C. syl- vestris, uncommon in Ohio but abundant in California, the larvae feeding on rice plants, Spirogyra, Myrioph yllum and other vegetation; C. trifasciatus ( — remus), with larvae mining in and skeletonizing leaves of Potamogeton, Polygonum, Nuphar, Nymphaea and Nelumbo; C. bkinctus, living as larvae in masses of Spirogyra, capable of withstanding low oxygen levels and showing remarkable resistance to pollution by industrial wastes; C. tricinctus ( = lebetis), more or less questionably distinct from C. trifasciatus; C. triannulatus { — exilis), a northern Holarctic species associated with swift streams or shallow areas of lakes subject to wave action; C. politus, a clean-water species of lakes and streams; C. varipes and C. slos- sonae, closely related species showing a positive response to crude oil contamination; C. absurdus, with Neotropical affinities and apparently rare in the northern Nearctic; C. fugax, not recorded since it was described; C. flavibasis, closely related to C. sylvestris; C. infuscatus {=aratus, ceris), with larvae showing considerable resistance to heavy-metal pollution; C. vierriensis, easily confused with C. bicinctus, with larvae able to withstand high salt concentrations; C. trifascia ( = ithacanensis), having larvae present in small num- bers in streams; C. flavipes, relatively rare, the larvae making linear mines in submerged leaves of Potamogeton; C. elegans, rarely reported, with larvae riddling the floating leaves of Potamogeton; C. junus, with larvae inhabiting hard-bottom creeks; and C. nostocicola, with larvae feeding on Nostoc and attaching the algal colonies to rocks and other objects. New species are C. diversus, with similar to C. junus except for leg coloration and to the European C. festivellus except for details of abdominal coloration; C. baptistenis, known only from southern Canada but at the latitude of Michigan; and C. olivetus, probably most closely related to C. fugax and the European C. annulator. OHIO J. SCI. 83 (3): 74-90, 1983 INTRODUCTION present paper is an attempt to summarize The genus Crkotopus is of particular im- information available for species of north- portance in stream ecology. In a recent eastern United States and to provide a key study of a small limestone stream subjected facilitating determination of adults. So far to heavy-metal pollution, the relative as possible both dry and slide-mounted in- abundance of the genus proved to be dividuals have been studied. Dry speci- ecologically significant. In the area of mens reveal tralts such as wing reflections heaviest pollution, Cricotopus larvae made and surface texture but slide-mounted ma- up about 90% of the chironomid popula- tenal 1S hlBh[Y desirable for microscopic tion; at about 3.4 km downstream they details- Qmte certainly specimens will be constituted only about 20% of that popula- found which wl11 not flt mt0 any key, for tion (Winner et al 1980). Furthermore, aberrant individuals are not uncommon, species within the genus exhibit a wide No current study of Cr/r^^ can ignore range of environmental demands. The the monumental work of Hirvenoja (1973). He noted that color variation occurs widely 'Manuscript received 26 April 1982 and m re- m Crkotopus. In some species he recognized vised form 20 August 1982 (#82-10). and figured normal, dark and light forms 74 OhioJ. Sci. THE GENUS CRICOTOPUS IN OHIO 75 where in fact all gradations of color occur. ated with the genus. Species with strong, He also noted considerable variation in erect hairs with distinct bristle punctures size. Color in some chironomids is known were placed in Trichocladius, which was to vary with degree of maturity (Boesel commonly regarded as a subgenus of 1974). As indicated by Johannsen (1905), Orthocladius or Spaniotoma or given generic in making determinations in Cricotopus it is rank. The present paper adopts a broad extremely important to note that in mela- concept for Cricotopus but excludes the spe- nistic specimens areas of the abdomen that cies which have traditionally been assigned are normally yellow-white tend to be to Trichocladius and sometimes referred to black. However when such specimens are Rheocricotopus, Acricotopus or Paratricho- examined at an appropriate angle, surfaces cladius. Included, however, are species which are typically or commonly yellow- sometimes listed under Isocladius and white are shining whereas those that are Halocladius. Hirvenoja (1973) treated all of black are velvety or dull. Numerical char- these as relatives ("Verwandten") of acteristics must be viewed with caution. Cricotopus. To what extent some of these Figures cited in this paper were arrived at names should be retained as genera or even by constant revision as new specimens be- as subgenera is an open question. came available. Although a single most METHODS AND MATERIALS representative figure may be given, devi- Specimens used for the current study were col- ation from that figure is the rule. Com- lected principally in Ohio over a period of more than monly a deviation of 10 to 15% or even 50 years. Nearly all parts of the state are represented more may be expected in the case of leg ra- but particular attention has been accorded the island tio; antennal ratio varies even more. The area of western Lake Erie, which is particularly rich in midges. Naturally many specimens have been latter is probably best determined on slide- taken in the vicinity of Columbus and Oxford. For- mounted material that has never been al- tunately I have had the opportunity of collecting lowed to dry. Bristle counts on various rather extensively also in New York (Ithaca area) and parts of the body tend to be highly variable Michigan (Douglas Lake area). The majority of specimens, about 1350, are on points; about 500 are and are useful only where marked differ- in the form of permanent mounts in diaphane on ences occur. slides. Many of the latter have been reared so that lar- val and pupal exuviae are available, mounted on the Several species have been deliberately same slide with the adult. All specimens have been excluded from the discussion and keys. The examined critically. occurrence of C. tremulus in the Nearctic region is questionable. Early Nearctic KEYS TO ADULTS records should probably be referred to Systematists quite naturally have given C. slossonae. It is possible C. slossonae is a more attention to males than to females. In Nearctic form of C. tremulus. A second numerous instances the latter have been de- species, C. oceanicus, was inadequately de- scribed rather casually and briefly in terms scribed by Packard in 1869, probably from of the male. Evidence currently available teneral material, and has not been recog- suggests that it is hazardous to assume any nized since that time. A third species, particular degree of difference between the C. geminatus, described by Say in 1823, sexes. Unfortunately in a number of in- lacks the support of any solid records. stances only one sex is known. Males and Early workers limited the genus females are therefore keyed separately. If a Cricotopus to species with bicolored legs, sex is unknown it is omitted from the keys. hairy eyes and small or no pulvilli. Follow- In the couplets, characteristics enclosed in ing Edwards (1929), later workers placed brackets should be useful but are not neces- greater emphasis on the scutal hairs. Spe- sarily contrasting. The keys have been con- cies with minute, decumbent hairs were structed to accommodate both dry and included in Cricotopus even though they slide-mounted specimens by the use of lacked the whitish markings usually associ- multiple characteristics. For a variety of 76 M. W. BOESEL Vol. 83 reasons certain names are excluded from 4. Genitalia yellow-white; [abd 1 and part of abd the keys. Such exclusions have been dis- 2 greenish; rest of abd largely blackish, darker cussed in the introduction. posteriorly] C. fugax 4. Genitalia dark (5) Abbreviations adopted for use in the 5. Scutellar hairs sparse, largely confined to a keys and descriptions follow. All have ap- single transverse row; scutal ground color typi- peared previously in the literature. In cally pale (yellow, green, light brown); humeri Cricotopus, wing veins clearly expressed and pale; tarsal claws acute (fig. 1), not apically enlarged (6) reaching the wing margin are presumed to 5. Scutellar hairs numerous, scattered; scutal be Rl5 R2+3, R4+5, M, Cui and Cu2. ground color dark brown or black, including hu- Subcosta and the anal veins are relatively meri; tarsal claws, at least of mid legs, apically en- weak. Costa forms the anterior wing mar- larged, pectinate (fig. 2) (7) gin and may or may not extend beyond the 6. Scutum typically with dark greenish ground color and black vittae; LR 0.59; AR 1.3; abd tip of R4+5. blackish; scutellum usually blackish; C only L: total length, excluding antennae. slightly produced C. infuscatus WL: length of wing, from arculus to 6. Scutum typically with yellow ground color and tip. WW: maximum width of wing. AR: contrasting black vittae; LR 0.70; AR 1.7; abd yellowish or olive brown; scutellum usually more antennal ratio; terminal flagellomere/ or less yellowish; C distinctly produced C. polttus remaining flagellomeres. th: thorax, tho- 7'. Halteres blackish; scutum more or less pru- racic, abd: abdomen, abdominal, abdom- inose; basistyle with a single large basal lobe; inal segment, w, ww: wing, wings. fCu: scutellar bristles in a single transverse row; arculus cubital fork, f, ff; If, 2f, 3f: femur, femora; black C. nostocicola 7.