Great Basin Naturalist Volume 55 | Number 1 Article 1 1-16-1995 Life histories of stoneflies P( lecoptera) in the Rio Conejos of southern Colorado R. Edward DeWalt University of North Texas, Denton Kenneth W. Stewart University of North Texas, Denton Follow this and additional works at: https://scholarsarchive.byu.edu/gbn Recommended Citation DeWalt, R. Edward and Stewart, Kenneth W. (1995) "Life histories of stoneflies (Plecoptera) in the Rio Conejos of southern Colorado," Great Basin Naturalist: Vol. 55 : No. 1 , Article 1. Available at: https://scholarsarchive.byu.edu/gbn/vol55/iss1/1 This Article is brought to you for free and open access by the Western North American Naturalist Publications at BYU ScholarsArchive. It has been accepted for inclusion in Great Basin Naturalist by an authorized editor of BYU ScholarsArchive. For more information, please contact [email protected], [email protected]. The Great Basin Naturalist PUBLISHED AT PROVO, UTAH, BY BRIGHAM YOUNG UNIVERSITY ISSN 0017-3614 VOLUME 55 31 JANUARY 1995 No.1 Great Basin Naturalist 55(1), © 1995, pp. 1-18 LIFE HISTORIES OF STONEFLIES (PLECOPTERA) IN THE RIO CONEJOS OF SOUTHERN COLORADO R. Edward DeWalt1,2 and Kenneth W Stewart1 ABSTRACT,-Thirty-one stonefly species representing eight families were collected during the March 1987 to May 1990 study period. Genera represented by more than one species included Capnia, Utacapnia, Taenionema, Suwallia, Triznaka, Isogenoides, and [soperla. Peak species richness was recorded on or near the summer solstice in 1988 and 1989. Climatic differences between years were reflected in nymphal development and emergence phenology of most species. New or important corroborative life history data are presented for 11 stonefly species of this assemblage. The hyporheic nymphal development of most chloroperlid species limited the number of early instars sampled and our capacity to interpret voltinism. Limited nymphal data suggested a univoltine-slow cycle for Plumiperla diversa (Frison). Adults of Suwallia pallidula (Banks) and S. wardi (Banks) were present for an extended summer period, but the bulk of their respective emergence times was temporally separated. Isogenoides zionensis Hanson, Pteronarcella bOOia (Hagen), and Pteronarcys californica Newport were all shown for the first time to have a 9-10-mo egg diapause, and all three species have a semivoltine life cycle. Skwala americana (KlapaIek) and Isoperla fulva Claassen were further confirmed to have univoltine-slow cycles. Univoltine-fast and univoltine-slow life cycles are reported for the first time in 1. phalerata and 1. quinquepunctata, respectively. Regression analysis revealed that six of the eight abundant species had extended emergence patterns (slopes of <5%/d), while only two had synchronous patterns. Warmer spring and summer tempera­ tures in 1989 increased the slopes for five of the eight species studied, but did not change their synchrony designation. Nine of 11 abundant species advanced their median emergence date in 1989 over 1988. This and the higher slope values are consistent with a hurried nymphal development and narrower emergence period due to the warmer thermal regime ofI989. Key words: Plecoptera, life history, biodiversity, life cycle, Rocky Mountains. Stoneflies (Plecoptera) are one ofthe integral understood (Sheldon and Jewett 1967, Stewart and often dominant insect orders in stream and Stark 1988). Precise life bistories are ecosystems; therefore, they are important as known for <5% of the more than 575 Nortb biological indicators, as fish food, and as part American species, and knowledge of stonefly ofthe energy and nutrient economy ofstreams life histories and ecology in southern Rocky (Stewart and Stark 1988). Taxonomy of the Mountain streams is sparse. This has limited North American fauna is now well known; our ability to increase understanding of eco­ however, information on their life histories, logical relationships between cohabiting stone­ local species richness, and ecology is still poorly fly species in this region. lDepartmeot ofBiological Sciences, University of North Texas, Denton, TX 76203, 2Present ~dress, D~rtment ofZoology and Physiology. Louisiana State University, Baton Rouge, LA 70803, 1 2 GREAT BASIN NATURALIST [Volume 55 One objective of tbis study was to deter­ highway 17, and 4 km north of Antonito at the mine richness of the stonefly assemblage of Colorado highway 285 bridge, respectively. the Rio Conejos of southern Colorado, a large Stream temperatures varied from below drainage that has not been previously studied. freezing during the winter months to near Second, we documented the important life 20°C in August. Ice cover was common from history events of its dominant species for December through March. Snowmelt began which sufficient individuals and observations in April, usually leading to peak flows in June. could be gathered by intensive monthly sam­ Base flows were attained by late August and pling and by living streamside during spring continued through the winter. Water released and summer. from Platoro Reservoir, 48 km upstream, aug­ Research was patterned after tbe classic mented river flow during summer low-flow studies of Harper (1973a, 1973b) and Harper periods. Bottom substrates were characterized and Hynes (1972), who studied a substantial by large boulders, cobble, gravel, and sand. portion of the eastern Canadian fauna and These were covered by a thin layer of silt in addressed critical aspects of life histories such quiet water. Important organic substrates as egg development, diapause, and adult included the flooded coppices of willows and behaviors that are often overlooked. H. B. N. cottonwoods and their entrained leaf packs. Hynes, in an address to the International Ple­ Willow (Salix spp.), cottonwoods and aspens coptera Symposium (1992), emphasized the (Populus spp.), and alder (Alnus sp.) con­ need for more attention to these aspects to tributed to the riparian corridor. support the eventual development of a para­ Physical Conditions digm of life history evolution within the Ple­ coptera. We have also adopted the approaches Stream temperature was monitored at site of Knight and Gaufin (1966), Harper and one from June through August 1988 using a Magnin (1969), Sheldon (1972), Barton (1980), Ryan ™ continuous recording thermograph. Ernst and Stewart (1985a, 1985b), and High, low, and mean daily stream tempera­ tures were calculated from temperatures Hassage and Stewart (1990) in comparatively recorded at 0400, 0800,1200,1600,2000, and studying an assemblage of species. This report 2400 h. Water temperatures were uot record­ is the first to address, on a large scale, such an ed during 1989 due to equipment failure. assemblage in a western North American However, summer air temperature highs and stream since the works of Knight and Gaufin lows and rainfall were recorded (1300 h daily, (1966), Sheldon (1972), and Stanford (1975). mountain time) for both 1988 and 1989 at the Conejos Peak U.S. Weather Service reporting METHODS station at site one. Flow data for site two were gathered from Petsch (1987-90). Study Stream The Rio Conejos is located in the southern Nymphal Growth Rocky Mountains of south central Colorado. Nymphs were collected monthly (except The river flows east to west for 145 km from December due to poor weather conditions) at its headwaters in the Rio Grande National all sites from March 1987 to May 1988. Forest ofthe San Juan range to the Rio Grande Additional collections were made at irregular 32 km northeast of Antonito, CO. Three sam­ intervals until March 1990. Samples were col­ pling sites were established along the Rio lected by disturbing the substrate (mineral Conejos to ensure access to at least one of and organic) upstream of a BioQuip rectangu­ them during the winter and to enhance collec­ lar dipnet until debris clogged the net. The tion ofstonefly species that were not abundant net was composed of a coarse, I-mm mesh at all sites. These were located at elevations be­ first stage, modified by the addition of a coni­ tween 2400 and 2600 m above sea level. The cal second stage of 153-/Lm mesh size. The lat­ primary site (106 °15'W longitude, 37°03'N ter collected even the smallest instars. A latitude) consisted ofa l-km stretch located 24 plankton bucket was attached to the second km west of Antonito, Conejos County, CO, off stage to facilitate sample removal. Contents of Colorado highway 17. Sites two and three the plankton bucket and the coarse stage con­ were located 22.5 km west ofAntonito, also on stituted a sampling unit and were stored in 1995] STONEFLY LIFE HISTORIES 3 70% isopropyl alcohoL The number of sam­ The malaise trap was deployed among wil­ pling units per month varied with the effort low and cottonwood coppices, where its olive­ necessary to secure approximately 50 nymphs drab coloration mimicked the surrounding of all abundant species. vegetation. Flying, or crawling, adults inter­ Nymphs were separated from sample cepted by the trap ascended the screening debris with the aid of 4-lOX magnification on into a dry apical collection chamber. Addition­ a stereo-dissecting microscope, sorted to ally, all adults on the trap mesh were collected species when possible, and stored in 80% using an aspirator. ethanol until measurement. Head capsule Emergence traps were anchored over shal­ width (HeW, greatest distance across the low riffles during the 1988 field season. eyes) was measured with a calibrated ocular Natural diurnal changes in water level and micrometer fitted to a stereo-dissection micro­ erratic discharges due to water release from scope. Nymphs from all sites for the 3-yr sam­ Platoro Reservoir rendered these ineffective pling period were pooled by species and at times; therefore, their use was discontinued month of collection to increase the number of in 1989. nymphs per month and to allow construction Pitfall traps consisted of 28.3-cm2 modified of more robust growth histograms. Gender of aluminum soda cans that were buried flush in nymphs was assessed by a gap in the posterior streamside substrates.