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

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Recommended Citation DeWalt, R. Edward and Stewart, Kenneth W. (1995) "Life histories of stoneflies () 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

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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, , 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, bOOia (Hagen), and 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. 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 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). 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. A mixture of 70% setal margin of the eighth sternum of females ethanol and ethylene glycol (the latter to (Stewart and Stark 1988) and by developing retard evaporation) was used as a preservative. external genitalia of females. Sex-specific kite In 1988, 12 traps were installed 1 m from the diagrams were constructed by placing male stream at I-m intervals on an open beach with and female nymphs into 0.1- or 0.2-mm size nearby vegetation. This was expanded in 1989 classes. The frequency of these classes was to three transects, each consisting of 30 cans converted to a percentage of the total number set 1 m apart in transects 1 m, 5 m, and 8 m of nymphs (males + females + unsexed from the initial shoreline. These traps moni­ nymphs) collected for that month. Polygons tored not only adult presence of ground-tra­ were constructed for each month depicting versing, brachypterous stoneflies, but also the relative proportion of all nymphs at that their potential to move laterally from the size class. stream. Sweepnetting was conducted over a 15 X 2­ Adult Emergence m willow and cottonwood riparian zone. The Adults of winter- and early spring-emerg­ entire area was methodically swept, working ing stoneflies were collected from bridge abut­ from the base of each clump of vegetation up­ ments, from shoreline debris, and under the ward. Exuviae removal was the only method cobble at streamside to provide a general used to assess emergence of sabu­ emergence period for each species. Adults losa (Banks) and was used for no other species. were also reared from preemergent nymphs. In 1988 exuviae were removed daily from the A combination of sampling methods and same 15 X I-m area of cobble shoreline, and observational procedures was used during the the frequency of each sex was noted. In 1989 summers of 1988 and 1989 to evaluate emer­ the removal area was expanded to 30 X 1 m of gence, duration of adult presence, and behav­ shoreline area and up to 5 m into the water for ior of these species. Adult traps and methods collecting exuviae from emergent substrates. included a 2.25-m2 basal area BioQuip malaise Year and sex-specific kite diagrams of adult trap, two 0.25-m2 basal area floating emer­ presence were produced for all abundant sum­ gence traps, pitfall traps, sweepnetting of mer stoneflies by pooling all methods and streamside vegetation, exuviae collection, and expressing daily catches as a percentage ofthe day and night transect walks. Pitfall traps were total catch. Duration of emergence of Ptero­ emptied on alternate days, and the others narcys califomica Newport would be greatly were emptied daily between 0900 and 1100 h. overestimated by including pitfall trap collec­ All of these methods were used at site one; tions due to its synchronous emergence and sweepnetting was employed at site three on since pitfall traps were emptied on alternate several occasions. days. 4 GREAT BASIN NATURALIST [Volume 55

Dates of first capture, 50% cumulative mm plastic petri dishes in an environmental catch, and last collection, plus total duration of chamber. In both instances these were incu­ adult presence, were determined for the 11 bated at approximate stream temperature and most abundant species collected in the sum­ light regime. mers of 1988 and 1989. Emergence synchrony Fecundity was estimated from number of was estimated using linear regression of the egg batches deposited, number of eggs per cumulative percentage catch (all methods batch, and, for Skwala americana (Klapalek) pooled) versus days since first capture. Slopes only, total number of eggs remaining in the generated for each species were used as an ovarioles. Females were housed at streamside index of synchrony. Steeper slopes indicated a in screened, glass containers and provided more synchronous emergence. Slopes > 5%/d with moist cotton balls as a source of water. were chosen to be indicative of synchronous Alternatively, some species were reared in emergence since species with these slopes Denton and held under simulated streamside emerged their entire population within a few conditions in large cotton-stoppered shell days and had steep, j-shaped, cumulative emer­ vials. gence curves. Differences between slopes for RESULTS 1988 and 1989 were tested using a modified t test (Zar 1984). Common slopes were calculated Physical Conditions if no differences between years were noted. Mean daily stream temperatures in 1988 This was a purely descriptive approach de­ increased from near ID c e in early June to signed to detect and compare patterns; there­ 15°C in mid-July (Fig. 1). The stream cooled fore, it is not OUf aim to model emergence for dramatically between 8 and 12 July. This coin­ the purpose ofprediction, but only to describe cided with cool, damp weather conditions patterns ofemergence, (Fig. 2). Summer air temperature highs rarely Since most adult collection methods em­ exceeded 30°C in 1988, and rainfall occurred ployed in this study collected adults ofunknown at regular intervals throughout the summer age, results reflected adult presence rather (Fig. 2). However, 1989 was marked by many than, in the strictest sense, emergence. No days above 30°C with rainfall relegated to late attempt was made to discard old males and July and August (Fig. 2). The mean monthly dis­ females using any index of age. However, pat­ charge of the Rio Conejos during 1987-1989 terns of adult presence should follow that of a fluctuated predictably. Peak discharge true emergence pattern, and since longevity of occurred typically in June but occurred in May during the warm, windy spring of 1989 most adults approached only 1 wk in the labo­ (Fig. 3). ratory, we believe these results to be useful. Behavioral observations were made from Species Richness 0800 to 1300 h and from 2000 to 2300 h for sev­ More than 13,000 nymphs and adults were eral days during emergence of each species. studied over the 3-yr period. Among these Observations made during intervening hours produced little adult behavior. Timing of adult activities, their relative distance from the stream, and substrates on which activities took place were monitored by walking the stream margin, turning logs and rocks, and exposing leaf-entrained bases of marginal vegetation, !

~" Details of these observations have been narra­ ,". ,,,.).. ",( ,.,,,, ::',-\ ,~:" tively described for each species in this paper. _./\f ;'..j."/' \ ! t.,:: ~ ,:-\:". '., "":! f\ " \' ~ h 'I' ",: 'f \I'-~f"'" \: "::,''' Fecundity and Egg Incubation " ',' ~, , " .' """ ':',:, ",'" I , , ,...-, ,'"-, " Eggs of several species were incubated in • the laboratory to confirm proposed voltinism based on growth histograms. Eggs were 614 6114 7/4 7/14 7/24 613 B/13 placed into I-em-diameter dialysis tubing Dates bags and reared in a Frigid Units Living Fig. 1. Daily mean, high, and low stream temperatures in Streamn" or they were stored in 100 X 15- the Rio Conejos, summer 1988. 1995] STONEFLY LIFE HISTORIES 5

",------"., 1988 including an early waning and a more peaked T 30 distribution ofspecies richness in 1989. e , R mp " •i 1.5 n ·, " f Paraleuctra vershina Gaufin and Ricker. • ·t " i This was the only leuctrid found at OUf sites. u, '0 I No nymphs were recovered from the stream, e , Rain C 0.5 m indicating a probable hyporheic existence. c 0 '\ Adults were abundant in riparian vegetation ., 0 during June and Jnly (Fig. 5). No variation in 5/27 6/6 6/16 6/26 7/6 7/16 7/26 6/6 al16 8/25 adult presence parameters was noted for P. Dates vershina (Table 2). Emergence was classified .0,------" as extended in both years, although slopes of 1989 High T these cumulative emergence curves were sig­ e '0 R m l 1.6 a nifieantly different over the 2 yr (Table 3). p i '0 n •, f

•t V\rl' f u I TABLE 1. Stol1eflies collected from the Rio Conejos, , Colorado, March 1987 through March 1990. e o 0.6 C m Rain ...... Euholognatha om/h:m,,:J...\,l,::;i 0 Capnia coloradensis Claassenl 6/1 6/11 5/21 6/31 6/10 61208130 7/10 Tl20 7130 BI9 Dates Capnia confusa Claassen Capnia vernalis (Newport) Fig. 2. Daily high and low air temperatures and rainfall Isocapnia crinita (Needham & Claassen)l for summer 1988 and 1989, Utacapnia logana (Nebeker & Gaufio)l Utacapnia poda (Nebeker & Gaufin)l LEUCTRIDAE Paraleuctra vershina Gaufin & Rickerl '0,------·----, NEMOUIUDAE -8- MEAN -8- MAXIMUM -+ MINIMUM Amphinemura banksi Baumann & Gaufinl F '0 Prostoia hesemetsa (Ricker)l ,I Zllpadajrigida (Claassen)l w , '0 TAENIOPTERYGlDAE m Taenionema pallidurn (Banks)l p Taenionema pacijicurn (Banks)! '0 •, Doddsia occidentalis (Banks)l • Systellognatha • '0 , CHWROPERLIDAE , Paraperlafrontalis (Banks)l d 10 Plurniperla diversa (Frison)l Suwallia lineosa (Banks)l o ! I ! I'I Suwallia pallidula (Banks)l MONTH 10 12 2 4 8 8 10 12 2 4 8 8 10 12 2 4 8 8 Suwallia wardi Kondratieff & Kirchnerl VEAR 1907 '1188 19S9 Triznaka pintada (Ricker)l Fig. 3. Mean, minimum, and maximum monthly stream Triznaka signata (Banks)I discharge ofthe Rio Conejos during the study period. Claassenia sabuW,~a (Banks)l Hesperoperla pacifica (Banks)l were 31 species (Table 1) in eight families. The Isogenoides zionensis Hansoni Chloroperlidae, Perlodidae, and Capniidae Isogenoides prob. colubrinus (Hagen)l were the most speciose families with six, I.~operla fulva Claassen seven, and seven species, respectively. Seven Isoperla mormona Banks! Isoper/a phalerata (Smith)! genera were represented by more than one lsoperla quinqm'Punctata (Banks) species: Capnia, Utacapnw, Taenionema, Suwal­ Skwala americana (Klap:Hek) lia, Triznaka, [sogenoides, and [soperln (Table 1). PTER()NARCYIDAE Peak species richness occurred on or near (Hagen) l the summer solstice in both years (Fig. 4). Pteronarcys califarnica Nevvport Pattern differences existed between years, INew drainage and county rcwrds. 6 GREAT BASIN ATURALIST [Volume 55

12 -.1------, • I- 1989 l!!'l!! 1988 I S 10 p e c I 8 e s r 6 r c h 4 n e s s 2

o 5/19 5/29 6/8 6/18 6/28 7/8 7/18 7/28 8/7 8/17 Dates

Fig. 4. Temporal species richn~ss pattern ofadult sionellies collected daily from the Rio Conejos during the summers of 1988 and 1989.

Chloroperlidae data suggested a univohine-slow file cycle for this species. Representatives from two subfamilies in­ Suwallia pallidula (Banks) (Chloroper­ habited the stream. The early- and mid-instar linae). Only 59 nymphs of SuwaUia spp. were nymphs of the Chloroperlinae genera could collected from the Rio Conejos, even though not be reliably identified to genus. This neces­ adults were abundant. Nymphs were hyporhe­ sitated the illustration of a portion of the ic until immediately prior to emergence. This nymphal growth of Plumiperla diuffsa (Frison) habitat preference and our present inability to and Triznaka signata (Banks) as Chloroperlinae distinguish congeners of Suwallia nymphs spp. (Fig. 6). Crowth ofreliably identified mid­ precluded generation of meaningful his­ to late-instar nymphs was illustrated separately. tograms and designation ofvoltinism for either Paraperla frontalis (Banks) (Paraperlinae). species. Adults of Suwalli" wardi Kondratieff Nymphs were collected infrequently among & Kirchner were consistently larger than S. marginal substrates during the colder months paUidul«. This trend followed in nymphs, too, of the yea.r. All were pale, very thin, and had with proposed female nymphs of S. wardi in eyes set far forward as described for mature June (peak emergence) being 22.0% larger nymphs (Stewart and Stark 1988). These limit­ ed data are presented for the first year of the presumed semivoltine growth pattern of this M:F large chloroperlid (Fig. 6). Less than 10 adults 36:58 were collected in early June during the 3-yr Hlee study. Plutniperla diversa (Chloroperlinae). No adults were collected on which to base specif ic identity; huwever, nymphs of this genus are distinctive, and only P. diversa has been col­ lected in this region (Baumann et al. 1977). Nymphs were identifiable to genus by March. 20 30 • ,. 29 • ,. 29 Females were readily distinguished from MAY JUNE JULY males at this time. Crowth continued through Fig. 5. Emergence of Pum/euctra vershina from the Rio May when females attained a median HCW Conejos. 1988 and 1989. Polygons indicate daily relative 9.6% larger than males. The limited nymphal proportion oftotal catch. 1995] STONEFLY LIFE HISTORIES 7

TABLE 2. Range of dates for adult presence parameters for 11 summer-emerging staneOy species collected in 1988 (appears first) and 1989 from the Rio Conejos. Duration is mean ::t SO of the number ofdays. All parameters not avail· able for C. sabuloso' which emerged past OUf study period. Date 1st Date Last date Species n capture 50% catch capture Durntion (d)

P.~hina 94 2 June 12 June 5 july 35.0± 0.0 58 1 June 11 JUDe 7 july

S. tvardi 467 6 June 10 July 15 August 66.0 + 7.1 352 19 May 25 June 18 July

S. pallJdula 276 30 June 28 July 23 August 44.5 ± 4.8 162 I July 14]uly 4 August

T~ 662 9 June 28 June 23 August 59.0 ±24.0 2697 2June 19]une 12]u1y

C. sabuwsa 356 19]u1y 1195 16July

I·fulva 19 9 June 22 June 7 July 24.5±7.8 61 9 June 18 June 28 June

I. phalerata 12 20 June 28 June 24 July 22.5 ±3.5 20 18 June 25 June 8 July

I. quinquepunctata 9 24 June 14 July 27 July 30.0±4.2 12 19 June 5 July 15 July

1. zioMnsls 200 8 June 19 June 28 June 15.5 ± 4.9 75 10 June 17 june 24 June

P. badw 215 10 June 22 June 17 July 34.5 ±3.5 480 7 June 20 June 7 july

P. califo""",,, 55 6]une SJune 12 June 6.0 + 2.8 21 4 June 5 June 13 June than the July (peak emergence) females of S. Augusl (Table 2). It had the longest mean paRiJuUL. Only two proposed male nympbs of duration of presence (66 d) for any stonefly the latter were collected over the 3-yr peIiod. studied on the Rio Conejos (Table 2). Like its Adults ofS. pallidtlw were collected in July congener, S. wanli's 1989 date ofmedian catcb and August in both years (Fig. 7, Table 2). was advanced by 2 wk over that of 1988 (Table Slopes from regression models were different 2, Fig. 1). Emergence of S. wardi was extend­ between years (t = -64.7, p < .0001), but ed, and no significant slope differences were below the 5%/d cIiterion. We categoIized this noted between years (Table 3). No egg data species as an extended emerger (Table 3). The were collected for this species. median emergence date was advanced by 2 Riparian vegetation was used by this large, wk in 1989 over that of 1988 (Table 2). The yellow-green cbloroperlid as a staging ground adult sex ratio over the two seasons was 13 &: for adult bebaviors. Suwallia wardi was active 415 'I. Six field-collected and laboratory­ throughout tbe morning on sunny days and maintained females produced only one egg again for 2-3 h before sunset if conditions batch (Table 4). were warm and dry. During cool, rainy days StIWtJ1lia wardi (CWoroperlinae). Tbis was the low vegetation was devoid of S. wardi or tbe most abundant of tbe three Suwallia any other stonelly species. species collected from the Rio Conejos. Adults Trixnaka sigoota (Banks) (CWoroperlinae). were fIrst collected in late Mayor early Juoe, IdentifIable, late-instar nymphs were collect­ reacbed 50% cumulative catcb by mid-July, ed during a 5-mo period in the spring and and disappeared from streamside by early summer. Nympbs of this univoltine-slow 8 GREAT BASIN NATURALIST [Volume 55

TABLE 3. Synchrony and linear regression statistics for •- 2 individuals H .. 50 ~ of monthly catch the years 1988 (appears first) and 1989. Slopes between :~ years were tested: :t: ::: significance .05-.01, ** ::: <'.001 f ! +\ t - ""'''''";00 "•83 level or lower probability, and NT = not tested. ~ t II -0> 4:? t "",,,,,,,,, ~ PampfNfa frontalis R2 ---_ .._------_ .._------_ _---_ __ ._------.------Species Slope p Synchrony + t P. vet"shina 3.0 .85 .0001 extended 3.5** .90 .0001 extended . ~f~ ~ f ~"""_~~ -.--".------..------.. ".---.------.------.---.._------_. T. signata 1.5 .87 .0001 extended + t 3.0*'" .91 .0001 extended -~~, S.paUufula 2.5 .96 .0001 extended Trlznskaslgnata 3.5** .90 .0001 extended ~~~"r • S. wardi 2.2 .84 .0001 extended ~ Chloroperlinae spp. 2.2 .85 .0001 extended I II III IV V VI VII VIII IX X XI Months C. sabulosa 2.8 .94 .0001 extended 4.1 ** .99 .0001 extended Fig. 6. Growth of Chloroperlidae nymphs collected from the Rio Conejos, 1987-1990. I. ziornmsis 7.5 .92 .0001 synchronous 7.9 .95 .0001 synchronous they were collected in abundance during the Ebadw 3.6 .81 .0001 extended day. Adults inhabited marginal vegetation, 4.4* .92 .0001 extended where males were observed actively searching willow stems and leaves for females. No drum­ P. califomica 13.3 .84 .004 synchronous 18.9NT .97 .103 synchronous ming was observed during the two summers of intensive fieldwork. Large flights of adults of both sexes took place just before dark, at species were largely full grown by April (Fig. which time females were observed oviposit­ 6) with some degree of sexual dimorphism ing. Egg masses were dropped from up to 4-5 present at this time. m above the stream. Adults first appeared in early June, reached 50% cumulative catch 2 wk later, and could no Perlidae longer be collected by late August (Fig. 7, CUmssmia sabulosa. Although two perlids Table 2). Emergence was protandrous, but were present in the Rio Conejos (Table 1), slightly female-skewed sex ratios dominated in only C. sabulosa was sufficiently abundant for both 1988 and 1989 (Fig. 7). Triznaka signata growth and emergence interpretation. Nymphs displayed the greatest variation in last date of of this species were found among larger rub­ capture and duration of presence of all stone­ ble of midstream. The life cycle was semivol­ flies in the river (Table 2). It advanced its 1989 tine and appeared to require 3 yr of nymphal median emergence date by 9 d over that of growth (Fig. 8). Recruitment occurred 1988. Regression slopes indicated an extended throughout the fall with possibly some addi­ emergence in both years (Table 3). Differences tional recruitment in March from overwinter­ between slopes for 1988 and 1989 were signif­ ing eggs. Eggs containing eyespots were icant (t ~ -11.35, p < .0001). recovered from the stream in October and Attempts during the entire study to obtain November. Sexual dimorphism in botb size eggs from laboratory-reared and -mated and external genitalia occurred when nympbal females were unsuccessful. The mean number size reached 2.2 mm HCW The size disparity of eggs from six females caught during ovipo­ increased until the third year of growth when sition flights was lower than any first batches little overlap between the sexes remained. for other stoneflies studied (Table 4). Although A protandrous emergence began in mid~ these females were held for a prolonged peri­ July in both years (Fig. 9, Table 2). Exuviae of od of time, no additional egg batches were this species were abundant throughout August, laid. possibly into September. Emergence of C. Adults were never seen emerging in the sabulosa was extended and slopes were signif­ field, despite many hours of observation along icantly different between years (t ~ -10.7, p < the shoreline, day and night, in habitats where .0001, Table 3). 1995] STONEFLY LIFE HISTORIES 9

1=2ind. I = 5% of total catch Sell ratio Perlodidae -." _... IsogenoUks zionemis Hanson (: c:J ,,.. ---~ "la.~ ~ 1181;1515 ). The large range in size of nymphs . ... to " from July samples (Fig, 10) could not be "" SuwalllawanJi ,. ., ~ 19i18 accounted for by nymphs hatching from eggs lSC:ll1'1 laid hy June-mated females, June eggs reared _------

TABI.E 4. Mean eggs per batch, number of batches. and mean tolal egg complement for nine species of sloneflies occurring in the Rio Conejos. Colorado. Egg> lba.ch n

Species 1 2 3 4 ThlaL S. ""lIidula 54.7 + 26.6 54.7±26.6 6 6

I signaUl 42.2 ± 17.4 42.2± 17.4 6 6

C. sabulosa 2166.0 + 774.0 902.0 + 246.2 158.0 ± 91.0 40.0 3188.0 ± 613.0 7 5 5 1 7

I. zilmensis 588.0± 66.0 327.0 185.0 843.2 ± 141.4 4 I 1 4

I.jid"" 231.5±7.8 231.5± 7.8 2 2

I. plwlerata 703.0 703.0 1 1

S. americatW. 884.7± 267.3 884.7 ± 267.3- 6 6

P. badUI 339.0 + 86.0 58.4± 37.2 56.8 ± 39.7 351.0± 101.0 30 5 4 30

P. cal!forntca 393.0 ± 125.6 191.3 ± 130.2 94.3 ± 49.5 69.8 ± 24.7 4 4 4 4 5 6 7 51.3 ± 29.3 58.5 ± 23.3 57.0 845.3 ± 90.5 4 2 1 4

"1Otal /'e(:undity Incloo.e.. tkn.ce I.:((g:l reJlUlining in ovarioles. was observed at night. even when tempera­ Fecundity was difficult to assess since few tures approached 10·C. mature nymphs were available for rearing. lsoperla fi,lva Claassen (Isoperlinae). We One egg batch from each oftwo field-oviposit­ collected this species in benthic samples only ing females was coUected (Table 4). Longevity occa~ionally) but enough individuals were of three field-collected adult females was 5.7 obtained to allow a tentative interpretation of ± 0.58 d. voltinism. Recruitment of nymphs was first lsoperla pha/erata (Smith) (Isoperlinae). detected in August (Fig. 12). These measured Although the number ofnymphs coUected was 0.4-0.8 mm HCW and grew at a slow rate small, no month supported more than one size throughout the fall until a winter decrease in class (Fig. 12). Therefore, we have tentatively growth rate. 1beir size increased dramatically proposed a univoltine-slow growth pattern for after February, until emergence in June and this species. Adults were laken from mid-June July. This species conformed to a univoltine­ through mid-July (Table 2, Fig. ll). No assess­ slow growth pattern. ment of synchrony was made for l. phalerata Adults were collected for the first time on 9 due to low numbers of adulls captured. June in both years (Fig. 11, Table 2). Sex ratios Females did not produce eggs in captivity. A for the small number of 1988 adults were single egg batch from a field-collected individ­ approximately equal, hut heavily skewed ual contained 703 eggs. Four field-caught towards males in 1989. Numbers ofadults col­ females lived 11.3 ± 3.6 d past dale ofcapture. lected in both years were too small to warrant 18o],erla quinquepunctata (Banks) (Isoper­ an analysis ofsynchrony. linae). This species was more common at site 1995] STONEFLY LIFE HISTORIES 11

Claassen/a 8aOOlosa ~ Claassenia sabulosa H .. 20"" 01 mOOlhly calCh _ .. 2 indMdual M: F emerg9l1ce _I I I n_697 I = 4 % of total catch , d' 9 " oviposilioo 235:129 <;' 1988

803:401 L 1989 , I I ~~

III IV V VI VII VllI IX X x, 19 29 8 18 28 " Months 9 July August Fig. 8. Growth of Claasscnia sabulosa nymphs collected from the Rio Conejos, 1987-1990. Jolg. 9. Emergence of Claassenia sahulosa from the Rio Conejos, 1988 and 1989. Polygons indicate daily relative three. The data suggested that 1. quinquepunc­ proportion of total catch. tata had a univoltine-fast growth pattern. Recruitment occurred in January and February (Fig. 12), and growth was rapid from March through May. Sexual dimorphism in nymphal Pteronarcella badia (Hagen). This species size was not as evident in this species as in its was found to have a semivoltine growth pat­ congeners. Emergence began in mid-June and tern. Recruitment of nymphs began in March lasted through much of July (Table 2, Fig. 11). and April from eggs laid the previous June No eggs were collected. (Fig. 14). Many small nymphs were availahle Skwala americana (KlapaIek) (Perlodinae). iu benthic samples by mid-April when they This species displayed a univoltine-slow were at 0.2-0.4 mm HCvV This scenario was growth pattern and grew faster during sum­ corroborated by laboratory incubation ofseveral mer and fall months than all other perlodids in egg batches that hatched in March and April the Rio Conejos (Fig. 13). Nymphs were re­ after a 9-10-mo diapause. Growth of nymphs cruited in June and increased their median was rapid throughout their first spring. Size HCW from 0.4 mm to about 2.8 mm by differentiation among sexes was not apparent January. Growth was nearly completed by this until August, a full 14 mo after oviposition. time. Sexual dimorphism was apparent as early Median size of females just before emergence as August, and female nymphs reached a medi­ the following May was 21% greater than that an HCW before emergence that was 21.4% ofmales. greater than males. Female nymphs in April Emergence began by early June, with slight were found to contain fully sclerotized eggs in protandry and a preponderance ofmales being their oviducts; hence, this species is fully collected (Fig. 15). Median emergence occurred capable of mating and egg-laying immediately in the third week of June in both years (Table upon emergence. 2). Emergence was extended (Table 3) and Emergence was in April and early May when slopes were significantly different between our sampling was still on a monthly basis; years (t ~ -2.2, P < .05). therefore, no detailed analysis of emergence Females generally laid only single egg phenology and synchrony can be offered. batches, but a small number produced up to Adults were collected mainly from emergent three egg batches (Table 4). Most females laid logjam debris or under cobble at the stream their first egg batch within 24 h of mating and margin. often waited 2-d intenrals before laying others. Egg batches collected in mid-April from Longevity of seven females under simulated four laboratory-reared females hatched syn­ field conditions was 7.7 ± 4.2 d. chronously after a mean of 61.0 ± 7.3 d. This Pteronarcella badia emerged just after dusk corroborates field collections of early-instar and typically used willows, cottonwoods, and nYll1phs in June. Only a single egg batch was stream margin sedges as transformation sites. collected from each of six laboratory-reared Males were observed actively searching the females (Table 1). willows and drumming for females at night, 12 GREAT BASIN NATURALIST [Volume 55

6 Isogenoides zionensis • = 1 IND. Perlodidae

ema'IlllflCQ --- ...... oyipo!l~ion I = 20 % of lotal calch M: F 1--1 = 15% of monthly catch Isogenoides zionensls l' 9 1988 146:55 ~4 _ .. 4 individuals cf ..... 1989 53:18 ~ .~. ~3 1 lsoperla ftJlva 1988 11:9 a n w ~ II =i) .11" • 53:7 !2 ~ 1989 laboratory recn;~ment A .. /soperlaphalerata 1988 4:8 1 of previous year's eggs • '"Ql= • JO"w ~ I -- 1989 7:13 '------~. ~ ~ Isopeda quinquepunctata I II JJI IV V VI VII VIII IX X XI ~ 3:6 n 1988 ~ Months • A m ~1lI 1989 6:6 Fig. 10. Growth of lsogenoides zionensis nymphs col­ ii • .. • lected from the Rio Conejos, 1987-1990. ,. 29 ,. 2. • June • July even when air temperatures were near 100e. Fig. 11. Emergence of Perlodidae from the Rio Adults entered the leaf-choked bases of wil­ Conejos, 1988 and 1989. Polygons indicate daily relative lows as the night progressed and were often proportion oftotal catch. found the next morning in large mating aggre­ gations under these debris. These individuals Adults utilized marginal vegetation, much ~scended the willows as the sun warmed the as did P. badia, as a staging ground for mating air at streamside. Drumming, mate searching, and ovipositing. However, they tended to select mating, and egg batching took place in mid­ the taller cottonwoods and Engelmann spruce morning hours, while most activity ceased by rather than the shorter willows for their activi­ 1200 h when air temperatures reached ties. Salmonflies oviposited hy flying over the 22-25°C. Females oviposited by launching stream and dropping their salmon-colored or themselves from the tips of tall riparian shrubs bluish egg masses (dimorphism in egg color was toward the stream, where they would jettison observed) from as high as 10 m. Ovipositing their white egg mass a few meters above the adults were heavily fed upon by opportunistic surface offast-flowing water. Eastern Robins (Turdus migratorius) and Pteronarcys cali/arnica Newport. This Steller's Jays (Cyanocitta stelleri). species is commonly known as the salmonfly. Recruitment began in April (Fig. 16) after a DISCUSSION 9-1O-mo egg diapause. Nymphs grew to only about 1 mm HCW through their first year. Species Richness Sexual differences in size and morphology The Rio Conejos displayed a great diversity were apparent by June of their second year, of Plecoptera. Twenty of the 31 species were when they were nearly 1.5 mm HCW. evenly distributed among the Capniidae, the Nymphs grew for two more years, by the end Chloroperlidae, and the Perlodidae. The only of which lime preemergent females had North American family not represented was attained a 20% larger median HCW than the Peltoperlidae, which occurs transcontinen­ males. These data suggest a semivoltine life tally, but not in latitudes below the northern history of4-yr duration for this species. Rocky Mountains (Baumann et al. 1977). Nearly Adults were first found OIl 6 June during all species collected were adapted for a mon­ hoth years (Fig. 15, Table 2). Emergence was a tane existence and were characteristic of highly synchronous event (Table 3). Slopes streams with high biotic integrity. Twenty-five were not tested for significant differences due species were both new drainage and county to small sample size. records (Baumann et al. 1977, Szczytko and Most laboratory-reared females produced Stewart 1979, Nelson and Baumann 1989; Table five egg batches, but one individual produced 1), though all of them had been previously seven (Table 4). Egg production lasted reported from Colorado and neighboring New through 82% of the 15.0 ± 1.8 d (n = 4) aver­ Mexico. This demonstrates that we have yet to age adult female life span. adequately investigate the fine-scale diversity 1995] STONEFLY LIFE HISTORIES 13

Isoperlinae spp. 4 emergence - t I Skwala americana H _ 30 % of monthly catch • t__ . cJ 9 - oviposition

~ 3 11, "'" =F~ ... __ .D"' ~ ~ ~ 3\ i=: _. t Isopmfll phalemhl •&2 • !~ ~ "'b ..fj n '" 2S 8 • ~ l---' _ 30 'Ii of rnonthlv catch ~ • t Isoper/8 quinqueplUIOIafa 1 _ _ 3 indMduais ~ n_227 $. J:\ n '" 229 • ~I rI V VI VII V"I IX X II III IV VI VII Viii IX X XI Months " Months

Fig. 12. Growth of Isoperla spp. nymphs collected from Fig. 13. Growth of Skwala americana nymphs collected the Rio Conejos, 1987-1990. from the Rio Conejos, 1987-1990. and distribution ofthis order ofaquatic L. ferruginea (Walker). Snellen and Stewart in at least some portions of the southern (1979) record univoltine fast cycles for Rocky Mountains. Zeawuctra claasseni and Z. hitei in streams of Responses to Altered Thermal Regime north Texas. Additionally, Ernst and Stewart (1985a) report Leuctra tenuis as univoltine-fast We became aware of substantial climatic in an Ouachita Mountain stream. differences (Fig. 2) between the two summers when adults were intensively studied. Though CHLOROPERLIDAE no water temperatures were available for Most Chloroperlidae exhibit a univoltine­ 1989, air temperatures (Fig. 2) and hydrologic slow or -fast growth pattern. Haploperla brevis data (Fig. 3) suggested that the stream warmed (Banks) is widespread from Oklahoma to more quickly and attained peak summer highs Quebec and west to Alberta, Canada. Ontario much earlier than in 1988. Consequently, (Harper and Magnin 1969), Quebec (Harper development of several species was hurried, et al. 1994), and Oklahoma (Ernst and Stewart which narrowed the window of time adults 1985a) populations exhibited univoltine-fast were present streamside. At the assemblage growth with a 2--5-mo diapause, while Alberta level of organization, this trend is demonstrat­ populations were univoltine-slow (Barton ed by the species richness pattern of Figure 4. 1980). European populations of Chloroperla The 1989 pattern was more peaked and great­ tripunctata (Scopoli) (Elliott 1988), Siphono­ ly truncated over that of 1988. Species-level perla torrentium (Pictet) (Elliott 1967), and S. responses can be demonstrated by inspection hurmeisteri (Pictet) (Benedetto 1973) also ofthe flight diagrams for each species. Nine of exhibited univoltine-slow growth. Species the 11 species presented in Table 2 show in­ with semivoltine growth include Sweltsa creased median emergence dates. Additionally, onkos (Ricker) and possibly Utaperla gaspe­ slopes produced by linear regression that siana Harper and Roy (Harper 1973a, Harper were different between years (Table 3) were et al. 1994), S. 11l€diana (Banks) (Cushman et always higher in 1989. This result was consis­ al. 1977), and S. lateralis (Banks) (Huryn and tent with a hurried nymphal development and Wallace 1987). shorter emergence period for each species. Paraperla frontalis. Stanford and Gaufin (1974) presented some evidence for semivol­ Life History Parameters tine growth ofthis species. Emergence for this species and for P. wilsoni Ricker occurs from LEUCTRIDAE May through July (Stewart and Stark 1988). Paraleuctra versmna. Harper (1973b) reports Paraperlinae are rather robust chloroperlids that that most Leuctra ferruginea in an Ontario tend to be hyporheic for most oftheir nymphal stream are semivoltine, but that some univol­ development. Their larger size, the more sta­ tine individuals exist. Huryn and Wallace ble stream temperatures in the hyporheic (1987) propose a 2-yr life cycle for a composite environment (Hendricks 1993), and the possi­ of Leuctra spp., most of which were probably bly low availability of some nutrients in the 14 GREAT BASIN NATURALIST [Volume .5.5

• Pteronarcyidae emergence"t I Pteronarcella badia ... _ oviposition = % 3 I 20 of total catch M: F

9 Pteronarcys califomica 1988 23:32 cJ • 1989 11 :10 ~ - .. Pteronarce//a badia 1988 134:79 ,,1417 ~ 1 .. ~ • -* H - 40 % of monthly catch ~ f _ ~ 1989 308:172 <@> _unsexed • ~ . •• - II III IV V VI VII VIII IX X XI Moo'" 30 9 19 29 9 19 29 Fig. 14. Growth of Pteronarcella badia nymphs collect­ ed from the Rio Conejos, 1987-1990, June July

Fig. 15. Emergence of Pteronarcella badia and hyporheic hahitat (Stanford and Ward 1993) Pteronarcys califomica from the Rio Conejos, 1988 and may have contributed to a preponderance of 1989. Polygons indicate daily relative proportion of total semivoltinism in this subfamily. catch. Plumiperla diversa. Stewart et al. (1990) re­ ported a univoltine-slow cycle for this species fact that 0 0: 6.57 2 of the closely related S. on the North Slope of Alaska. Emergence lineosa were caught during concurrent sam­ occurred from May through Septemher, with pling on Massey Creek, a tributary of the Rio recruitment of nymphs from a direct hatch in Conejos. July. Growth occurred through the summer Triznaka signata. Hassage and Stewart months with most nymphs attaining maximum (1990) studied the widely distributed T signata size before a winter quiescence. This assess­ in the Rio Vallecitos of northern New Mexico. ment compared well with our limited data. They reported a univoltine-slow growth pat­ Failure to collect adults was probahly due to tern, with which we concur, No study of the our infrequent sampling during their pre­ emergence of this species has previously been sumed early May emergence. published. Suwallia paUidula and SuwaUia wardi. No aspects ofthe life histories ofeither S. pallidula PERLIDAE or S. wardi have heen reported. The latter was Claassenia sabulosa. Hassage and Stewart recently described from a Colorado Front (1990) and Barton (1980) report a merovoltine Range springbrook (Kondratieff and Kirchner (>2 yr) growth pattern for New Mexico and 1990). 11 was one of the most ahundant cbloro­ Alberta populations of this species. No egg perlids in the Rio Conejos. This suggests that batches from the Rio Conejos hatched in our its ecological tolerance is wide and that it may laboratory, hut this Colorado population showed soon he found in a variety of streams in the some evidence ofan extended hatch leading to southern Rocky Mountains, cohort splitting (Stewart and Stark 1988). Eggs Several explanations are possible for the may undergo a temperature-dependent quies­ heavily female-skewed sex ratio (13 0 :42.5 2) cence as occurs in Dinocras cephalotes (Curtis) of S. pallidula adults. The most probable is a when fall temperatures decline to 8°C (LilIe­ combination oflimited use ofemergence traps hammer et al. 1989). Presence of first-instar coupled with an inaccessible microhabitat of nymphs in the fall, eyed eggs in October and adult males, probably high in the vegetatiou. November, and more first-instal' nymphs in Parthenogenesis may also be possible, but it is March supported this contention. exceedingly rare in stoneflies. Harper (1973a) Life histories have been reported for at least reported that a few eggs of a perlid, Parag­ one species in every genus in the tribe Perlini, netina media (Walker), hatched without fertil­ to which C. sahulosa belongs. AlI growth pat­ ization. We did not attempt rearing of eggs terns involve 2-3 yr ofdevelopment. Agnetina from virgin females to check for parthenogen­ flavescens (Walsh), from an Ozark stream, esis in either Suwallia spp, These sex ratios exhibits a 2-yr life cycle, a short egg incuha­ are a perplexing problem, compounded hy the tion period, and an extended emergence period 1995] STONEFLY LIFE HISTORIES 15

occur in its congeners, but this will be con­ H - 20'4 of monthly calch 1> •_ 1 {ndividual firmed only when detailed studies using small n - 622 mesh nets, frequent sampling, and egg rearing have been conducted. !soperla spp. Of the three Isoperln whose partial growth patterns are presented here, only I. fulva has been previously reported. Hassage and Stewart (1990) reported a univol­ , tine-slow cycle, with a June emergence in the 1': Rio Vallecitos of New Mexico. We concur with l-unsexed the New Mexico study. Our results agree well ~ m rv V VI VIIVlI\ IX X Xl Months with reviews of Isoperln biology, summarized for 12 Nearctic species through 1987 (Stewart Fig. 16. Growth of Pteroruzrcys californica nymphs col­ and Stark 1988). Ten species were univoltine­ lected from the Rio Conejos, 1987-1990. slow, while only two were univoltine-fast. In more recent literature Stewart et al. (1990) (Ernst and Stewart 1985b). Agnetina capitata reported univoltine-slow growth for 1. petersoni (Pictet) was shown to bave a 3-yr cycle, ex­ Needham & Christenson ofAlaska. Additionally, tended emergence, and a 40-80-d egg incuba­ Harper et al. (1994) added as univoltine-slow tion period in Ontario (Harper 1973a). Tbis I. francesca Harper and 1. montana (Banks) range ofincubation coupled with a long emer­ from Quebec populations. These and our Rio gence promotes great differences in size of Conejos work bring to 17 the Nearctic Isoperln nymphs that ultimately prevents the separa­ species known to exhibit univoltine-slow tion of cohorts and determination ofvoltinism. cycles, while only three species appear to be This was also a problem for C. sabu1oso in the univoltine-fast. Isoperla grammatica (Poda) Rio Conejos. and I. difformis (Klapalek) (Malmqvist and Sjostrom 1989) and 1. obscura (Zetterstedt) PERLODIDAE studied by Ulfstrand (1968) are univoltine­ This family contains over 115 species (Stark slow in the Palearctic. et al. 1986, Stewart and Stark 1988) in the Up to seven species of Isoperla commonly Nearctic. Although life histories of only 26 occur in streams in North America (Stewart species are known, a clear trend toward uni­ and Stark 1988); conversely, in Scandinavia voltine-slow cycles occurs among the subfami­ rarely more than two species occur simultane­ lies Isoperlinae and Perlodinae (Stewart and ously (Malmqvist and Sjostrom 1989). Congen­ Stark 1988). Growth and emergence had not erics ofaquatic insects often partition resources previously been studied for three of the seven along one or more resource gradients (Grant perlodids in the Rio Conejos. These include 1. and Mackay 1969). Though only small numbers zionensis, 1. quinquepunctata, and I. phalerata. of adults were collected, a pattern of succes­ Isogenoides zianensis. Few detailed life his­ sive emergence of1. fulva, 1. quinquepunctata, tory studies of the genus have been reported and I. phalerata was clear in the Rio Conejos. (Stewart and Stark 1988). Barton (1980) supect­ Fifty percent cumulative catch dates for I. ed semivoltinism for an Alberta population of fulva, 1. phalerata, and 1. quinquepunctata were 1. coluhrinus, since two size classes ofnymphs 22 June, 28 June, and 14 July, respectively, for were collected in early May. Flannagan (1977) 1988. These dates for 1989 were 18 June, 25 reported great body length vanation in May for June, and 5 July. Temporal segregation this species in another Alberta watershed but brought about by a gradual change in domi­ concluded a univoltine-slow cycle. Hilsenhoff nance (Illies 1952) of these species may have and Billmeyer (1973) and Dosdall and Lehm­ accounted for the pres-ent coexistence of kuhl (1979) proposed univoltine growth pat­ these stoneflies. terns for the May-June-emerging 1. frontalis Skwala americana. Two other studies re­ in Wisconsin and Saskatchewan streams, ported univoltine-slow cycles with emergence respectively, based on samples taken a few from February through April for this species in months ofthe year. Semivoltinism, as reported northern New Mexico and central Colorado for 1. zionensis in the Rio Conejos, may also (Short and Ward 1980, Hassage and Stewart 16 GREAT BASIN NATURALIST [Volume 55

1990). Skwala curvata (Hauson) of California Pteronarcys californica. The egg diapause also exhibited a univoltine-slow cycle, with plus 38-mo nymphal life span places total life emergence in April and May (Sheldon 1972). span of this population at 4 yr. This is one of Otber Arcynopterygini with univoltine-slow the longest-lived aquatic insects known to growth include Frisonia picticeps (Hanson) in occur in the Nearctic. Additionally, this California (Sheldon 1972), signata species is perhaps our most synchronously (Hagen) in Utah (Cather and Gaufin 1975), emerging stonefly. and Perlinodes aurea (Smith) in California and Two- to 3-yr life cycles with a 9-1O-mo egg Alberta (Radford and Hartland-Rowe 1971, diapause occur in other Pteronarcys such as P. Sheldon 1972). dorsata (Barton 1980), P. proteus (Holdsworth Sbeldon (1972) estimated average total 1941a, 1941b, W. Perry et al. 1987), and P. fecundity of S. curvata to be near 1780 eggs scotti in the southern Appalachian Mountains for preemergent nymphs. This is much greater (Folsom and Manuel 1983). However, Lechleit­ than that proposed for S. americana from the ner and Kondratieff (1983) detailed a l-yr life Rio Conejos. He used interocular width as an history for P. dorsata in Virginia. index to predict fecundity. Conversion of inter­ Multiple-year life histories are common ocular width to HCW likely involves a factor among larger species of the Pteronarcyidae of 2X, which would make S. curvata the larger (Stewart and Stark 1988). Accompanying this of the two stoneflies. This largely accounts for long nymphal growth, and perhaps contribut­ differences in fecundity. Mutch and Pritchard ing to it, is another life history trait, long egg (1986) reported that S. ame1icana (as S. paralle­ diapause. Univoltine growth patterns and la) had a warm, stenothermal egg development. direct egg development are ancestral patterns, Most species in this family have conserved while the semivoltine growth and diapause of the life history traits that Lillehammer et aI. P. badia and P. califomica are derived traits (1989) proposed as ancestral. These traits (Lillehammer et al. 1989). Future studies of include univoltine-slow cycles, temperature­ egg incubation in lower latitudes of North dependent growth, and direct egg develop­ America will enable us to outline the range of ment. Isoperla quinquepunctata and 1. zionen­ responses of which Pteronarcys and Pteronar­ sis have likely abandoned all of these except cella are capable. temperature-dependent growth, Dnanswered Questions PTERONARCYIDAE Several largely unanswered questions per­ Pteronarcella badia. Gaufin et al. (1972) sist about the life histories of stonellies in and reported that a 2-yr life cycle was possible for along the Rio Conejos. We have found that this species in Utah; however, S. Perry et al. nymphs of many chloroperlids are not avail­ (1987) and Stanford (1975) reported a univol­ able in surface sediments until just prior to tine life history in Montana. No eggs were emergence. They must be hyporheic in their reared in either Montana study, and it is habitat choice. Second, chloroperlids of the apparent from their growth histograms that present study did not readily produce eggs in early instars were missed entirely. Therefore, captivity, and those incubated never hatched. semivoltiue life history is most probable We can still ask many questions about their tbroughout its range. life histories. The answers would require a Nymphs of this species are more likely to detailed study of the hyporheic habitat of an be found aggregated on filter paper leaf mod­ open-sediment stream like the Rio Conejos. els than alone (Hassage et aI. 1988). We have This study should concentrate only on the also observed nymphs aggregating under mar­ chloroperlids, since they are generally abun­ gin cobble immediately before emergence. dant and diverse. Such a study would still fit Adults aggregate in leaf debris at the base of within the comparative study approach of willow and cottonwood coppices at the Rio Sheldon (1972), but the guild would involve Conejos. This behavior may be attributable to hyporheic chloroperlids. the transformation and nighttime refuge sites To settle the dilemma of aberrant sex ratios being contagiously distributed. Hassage et aI. in this family, studies must concentrate on the (1988) also postulated that aggregation in P. presence of male nymphs in the stream. In badia lowers individual risk to predation. this way the search for adult males whose 1995] STONEFLY LIFE HISTORIES 17 whereabouts are unknown need not take Siplwlwperla torrentium and Chloroperla tripunctata place, since both sexes of nymphs presumably (Plecoptera: Chloroperlidae). Freshwater Biology 20: 11-18. enjoy a similar microhabitat. If no male ERNST, M. R, AND K. W. STEWART. 1985a. Growth and drift nymphs are located, then incubation of eggs of nine stonefly species (Plecoptera) in an Oklahoma from virgin females should be conducted to Ozark fOothills stream, and confonnation to regression confirm the possibility ofparthenogenesis. models. Annals of the Entomological Society of An exciting observation we made during America 78: 635-646. ___.. 1985b. Emergence patterns and an assessment of the study was that of basking in the sun of collecting methods for adult stoneflies (Plecoptera) nearly all adults of summer-emerging species. in an Ozark foothills stream. Canadian Journal of Most displayed a remarkably consistent pat­ Zoology 63: 2962-2968. tern of ascendence of riparian vegetation be­ FLANNAGAN, J. F. 1977. Life cycles of some common aqua­ ginning at about 0800 h. Activity usually ceased tic insects of the Athabasca River, Alberta. Alberta by 1300 h when air temperatures were hottest. Oil Sands Environmental Research Program, Report II. 20 pp. This ascendence culminated for females in FOLSOM, T. c., AND K. L. MANUEL. 1983. The life cycle of egg batching and oviposition flights, while PterotUlrcys scotti (Plecoptera: Pteronarcyidae) from males used these riparian staging grounds for the southern Appalachians, U.S.A. Aquatic Insects 5: mate searching, drumming, and mating. 227-232. Stoneflies should be investigated for potential GAUFIN, A. R., W E. RICKER, M. MINER, P. MILAM, AND R. A. HAYS. 1972. The stoneflies (Plecoptera) of to benefit from basking, an unreported phe­ Montana. Tmnsactions ofthe American Entomological nomenon for Plecoptera. Society 98: 1-161. GRANT, P. R, AND R. J. MACKAY. 1969. Ecological separa­ ACKNOWLEDGMENTS tion of systematically related stream insects. Cana­ dian Journal ofZoology 47: 691-694. We thank the Conejos Peak District of the HARPER, E E 1973a. Emergence, reproduction, and Forest Service for providing lodging and growth ofsetipalpian Plecoptera in southern Ontario. u.s. Oikos 24: 94-107. laboratory space during the study. Special _-"C.. 1973h. Life histories of Nemouridae and Leuctri­ thanks go to J. B. Moring for his help with dae in southern Ontario (Plecoptera). Hydrobiologia sample collection and D. Ziegler for providing 41, 309-356. some fecundity data for P. badia. This project HARPER, P. P., AND H. B. N. HYNES. 1972. Life histories of was partially funded by faculty research funds Capniidae and Taeniopterygidae in southern Ontario (Plecoptera). Archiv fur Hydrobiologie, Supplement of UNT and a National Science Foundation 40,274-314. grant, BSR 8308422, to KWS. HAUPER, P. P., AND E. MAGNIN. 1969. Cycles vitaux de quelques Plecopteres des Laurentides (Insecta). LITERATURE CITED Canadian Journal ofZoology 47: 483-494. HARPER, P. P, M. LAUZON, AND R HARPER. 1994. Life BARTON, D. R. 1980. Observations on the life histories and cycles of sundry stoneflies (Plecoptera) from biolo,!.,')' of Ephemeroptera and Plecoptera in north· Quebec. Review d'Entomologie Quebec 36: 28-41. eastern Alberta. Aquatic Insects 2: 97-11L HASSAGE, R L., AND K. W. STEWART. 1990. Growth and BAUMANN, R. W, A. R. GAUFIN, AND R. F. SURDICK. 1977. voltinism of £lve stonefly species in a New Mexico The stoneflies (Plecoptera) of the Rocky Mountains. mountain stream. Southwestern Naturalist 35: Memoirs ofthe American Entomological Society 31. 130-134. BENEDETI'O, L. A. 1973. Growth of stonefly nymphs in HASSAGE, R L., R. E. DEWALT, AND K. w: STEWART. 1988. 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