Great Basin Naturalist Volume 35 | Number 1 Article 4 3-31-1975 Life history and ecology of Megarcys signata (Plecoptera: Perlodidae), Mill Creek, Wasatch Mountains, Utah Mary R. Cather University of Utah Arden R. Gaufin University of Utah Follow this and additional works at: https://scholarsarchive.byu.edu/gbn Recommended Citation Cather, Mary R. and Gaufin, Arden R. (1975) "Life history and ecology of Megarcys signata (Plecoptera: Perlodidae), Mill Creek, Wasatch Mountains, Utah," Great Basin Naturalist: Vol. 35 : No. 1 , Article 4. Available at: https://scholarsarchive.byu.edu/gbn/vol35/iss1/4 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]. LIFE HISTORY AND ECOLOGY OF MEGARCYS SIGNATA (PLECOPTERA: PERLODIDAE), MILL CREEK, WASATCH MOUNTAINS, UlAH^ Mary R. Gather- and Arden R. Gaufin- Abstract.— During an investigation of some of the stoneflies (Plecoptera) of Mill Creek, Wasatch Mountains, Utah, Megarcys signata, a large omnivorous stonefly, was found to have a univoltine life history and a slow seasonal life cycle. Temperature appears to affect the growth rate of Megarcys signata. Warmer stream temperatures accompany the acceleration of the growth rate, whereas cooler stream temperatures apparently retard the growth rate. Periods of maximum absolute growth rate con-espond with maximum carnivorous feeding from August to September and March to April. Ghironomidae, Ephemeroptera, and Plecoptera, in that order, were the most abundant prey in the foreguts. Young n^-mphs ingested considerable amounts of diatoms, filamentous algae, and detritus but not as much animal matter as did older nymphs. Megarcys signata was unifonnly distributed throughout Mill Creek, except at the lowest station, where few nymphs were found. Emergence occurred in May and June, the peak occurring in June. The mean size of females and males decreased as emergence progressed. This report is part of an eighteen-month calcium bicarbonate 109-189 mg/1, calci- study of some of the stoneflies of Mill vmi carbonate 0-2.4 mg/1, pH 7.5-8.3, Creek, Wasatch Mountains, Utah. Be- total hardness 100-340 mg/1, and conduc- cause a detailed description of the study tivity 312-859 mhos/cm. area and the methods and materials is given in another paper (Cather and Gau- Methods and Materials fin 1975, only a summary is included here. Nymphs of Megarcy signata were col- Mill Creek Canyon is located 11 km lected at least monthly from June 1971 to southeast of Salt Lake City, Utah, in the December 1972 at each of six stations. Wasatch Mountains of the Middle Rocky Additional nymphs were collected in Mountain Province. Six stations were se- spring 1973 for food habit studies. Hand- lected along a 12 km length of the stream screens of mesh sizes 7 and 9 sq/cm were in the Wasatch National Forest with ele- used, the smaller handscreen being used vations ranging from 1,605 to 2,280 m. during the majority of the study in an The sampling stations were nimibered attempt to collect the smaller instars. An consecutively. Station I denoting the high- area of about 80 cm- of the stream bottom est elevation. The three lower stations was disturbed in an attempt to collect at (1,605-1,785 m) are easily accessible all least 100 nymphs monthly. All nymphs year, but the three upper stations (1,995- were preserved in 80 percent ethanol. 2,280 m) are accessible only in the simi- Adults were collected weekly through- mer and fall. Average minimum and out the emergence period and biweekly maximum daily flows were 0.3 m^/sec during peak emergence using a sweep net and 1.2 mVsec, respectively, during the and handpicking from vegetation, rocks, study period. Depth averaged 11-45 cm, and bridges. All adults were preserved in and current averaged 0.2-0.7 m/sec during 80 percent ethanol. the fall when measurements were taken. The interocular distance of all nymphs The substrate of the sampling area at all and adults was measured to the nearest stations ranged from coarse sand to small 0.1 mm using an ocular micrometer in a cobbles. Minimum water and air tempera- dissecting microscope for determining tures recorded during adult emergence growth rates and to see if the mean size of were 3 C and 9 C, respectively. Maximum the adults decreased as emergence pro- water and air temperatures during this gressed. The nymphs were identified as period were 13 C and 26 C, respectively. males and females when possible. Water chemistry was similar at all sta- Foregut analyses were conducted on 200 tions. Dissolved oxygen ranged from 6.0 nymphs collected from the field. Nymphs to 8.5 mg/1 (70-120 percent saturation). were selected from an upper (I) and a ^Study supported by Environmental Protection Agency Traineesliip Grant No. 5T2-WP-542-03. ^Department of Biology, University of Utah, Salt Lake City. 39 40 GREAT BASIN NATURALIST Vol. 35, No. 1 lower (IV) station during each season lowed Gaufin et al. (1966), and nomen- (Station V had to be substituted for Sta- clature followed lilies (1966) and Zwick tion I during winter and spring). The (1973). method used followed Swapp (1972). All prey animals were enumerated and identi- Results and Discussion fied to order except where family or generic determination was possible. Three The only systellognathan stonefly pres- types of the family Chironomidae were ent in Mill Creek in numbers large enough recognized and designated as species a, b, for analysis is Megarcys signata. This and c (based on morphology of head species exhibits a slow seasonal type of capsule). These are discussed under re- life cycle. Emergence and oviposition oc- sults and discussion but are not separated cur in May and June with hatching soon in Table 1. All algae were determined to after. Small nymphs (0.5 mm interocular genus where possible. Percentage compo- distance) appear in July at the lower sta- sitions of algae and detritus were esti- tions. Nymphs of comparable size gen- mated when present, and dominant items erally appear for the first time in August, were recorded. A volume analysis was September, and October at the upstream not conducted. stations. Rapid growth occurs from Aug- Identification of nymphs and adults fol- ust to emergence (Figs, la, b, c). The size lOOn 75 50- 25 2.5- -. 2.0- E o ].o^ 0.5 Month Fig. 1. Growth of Megarcys signata. Arrows indicate emergence. I. O. indicates interocular dis- tance: (a) Monthly mean size as a percentage of total mean size at Station IV; (b) Monthly mean cumulative growth at Station IV; (c) Monthly mean absolute growth rate (data pooled from all sta- tions). A indicates change in I. O. distance. March 1975 GATHER, GAUFIN: UTAH PLECOPTERA 41 frequencies of nymphs and the mean (September-January). Growth apparently cumulative growth at each station are slows, but does not stop, during the winter shown in Figs. 2 and 3, respectively. (January-March), increases from March A comparison of the cumulative growth to April, and then decreases from April to at all stations reveals that the most rapid May, prior to emergence. Sheldon (1972) growth occurs at the lowest (warmest) reported similar results in his study on the stations (Fig. 4). Thus, there seems to be Arcynopteryx species complex he studied a direct correlation between growth and in California. However, Schwarz (1970) temperature. Baumann (1967) found no reported no growth at times during the direct correlation in this species in Mill winter in other Systellognatha. The corre- Creek. Seasonally the most rapid growth lation between growth and food habits will occurs during the fall and early winter be discussed later. 2.0' 34 103 2 A 27 101 II J 4 3 O 1,0 2.0- •l 'h 33 1.0- 50 F J J "n ^ J A 30 ND J MAM ASO Month AC 15 9 1 ^^ 38 33 <^h°^n r Sfa 2.0-| b 10 5 'l'^ IV 1.0-1 ly ,3 1/ 1 2.0- O 1.0- 9 6 ? cf: 2 3 10' ' I 50 J A S 5 S 5 ] F M A ?ir 5 6 N F Month Fig. 2. [Frequency distribution of nymphal size classes of M. signata. Number of individuals shown above each polygon; males and females as indicated: (a) Stations I, II, and III; (b) Stations IV, V, and VI. r 42 GREAT BASIN NATURALIST Vol. 35, No. 1 Megarcys signata seems to show no The emergence of M. signata began in preference for either the upstream or early May at the lower stations and lasted downstream stations. This species is even- until late June at the higher stations (Fig. ly distributed throughout the stream ex- 5). Peak emergence was in June. Bau- cept at Station VI. Here the substrate is mann (1967) found this species emerg- almost entirely cemented. Where the ing from late April to mid-July in Mill water is deep enough for this large insect, Creek. Emergence is progressively later the current is too slow; where the current as the elevation increases. Baumann is fast enough, the water is too shallow (1967), Hynes (1970), and Nebeker and the substrate too homogeneous. More (1971) reported similar results. They individuals were collected at Station IV were first collected at Stations III and V than at any other station. in early May, when the water tempera- Sta 2.0- --HH O ).0- 2.0- J ASONDJ FMAMJ JASOND Month Sta 2.0- 1.0- o - la T~y ~r~T T— Fig.