Semivoltine Life Cycle Research Articles

Ecology ofPeltoperla arcuataandTallaperla maria(Plecoptera: Peltoperlidae) at the Fernow Experimental Forest, Tucker County, West Virginia

We examined the abundance, life history, and production of the stonefliesPeltoperla arcuataandTallaperla maria(Plecoptera: Peltoperlidae) in four forested headwater streams at the Fernow Experimental Forest, Tucker County, West Virginia.Peltoperla arcuatawas most abundant in the smallest watersheds (<100 ha), and was present at all sites.Tallaperla mariawas most abundant in watersheds >200 hectares (ha), was restricted to sites with a base-flow alkalinity of >2 mg L-1CaCO3, and was the dominant peltoperlid only at sites with an alkalinity >15 mg L-1. We conclude that water chemistry overrides stream size as a determinant of species-specific distribution of Fernow peltoperlids. Both taxa had semi-voltine life cycles with an 18-month naiadal period following a 6-month egg diapause. Emergence was during May-July for both species.Peltoperla arcuatahad about 15 instars;T. mariahad about 14 instars. Peltoperlid production was highest (509 mg m-2y-1) in a 128 ha watershed where onlyP. arcuatawas collected;P. arcuataproduction was lowest (17 mg m-2y-1) in a 4th order stream (1536 ha).Taltaperla mariaproduction was highest (271 m-2y-1) in a 257 ha watershed partially underlain by limestone. Production across streams was higher forP. arcuata(205 mg m-2y-1) than forT. maria(91 mg m-2y-1).

Long‐term dynamics of leaf miners,Eriocraniaspp., on mountain birch: alternate year fluctuations and interaction withEpirrita autumnata

Abstract.Abundance of leaf‐mining larvae of the outbreak speciesEriocraniaspp. was monitored in northern Sweden in 1955–67 and 1984–92 in a mountain birch forest rejuvenated by anEpirrita autumnataoutbreak in 1954–55.Eriocraniamine density fluctuated in a regular biennial pattern, probably due to a semivoltine life cycle. The alternate year fluctuations had shifted phase between the two study periods.The density fluctuated at a significantly higher mean level and with a lower amplitude in thec.10‐year‐old forest in the 1960s than in the 30‐year‐old forest in the 1980s. However, no difference was found in mine density betweenc.30‐ and >60‐year‐old stands in the 1980s.Significant correlations between the density of mines in high‐density years and date of budburst, and between rate of change between high‐density years and the time between snow‐melt and budburst indicate effects of weather. No correlation was found between yearly average mine density and date of budburst, precipitation or temperatures in May or June.No correlation was found between the mean densities ofEriocraniamines andE.autumnatacaterpillars in the same and the two preceding years. However, in the first (1955) and highest of three studiedE.autumnatapeaks a negative effect on population density ofEriocraniawas indicated.A significant, negative correlation between the number ofEriocraniamines andE.autumnatacaterpillars on single branches was found in three out of eighteen years. The separation of caterpillars and mines at branch level indicates an effect of avoidance at intermediate population densities.

Life History Characteristics and Prey Selection of LarvalBoyeria vinosa(Odonata: Aeshnidae)

ABSTRACT Life cycle and feeding habits of Boyeria vinosa nymphs (Odonata: Aeshnidae) were examined over a three year period in Chestnut Creek, Virginia. Boyeria vinosa was univoltine with a synchronous emergence in late May to early June. These results differ from previous studies which report a semivoltine life cycle. Chironomids, hydropsychids and baetids comprised the majority of prey consumed. Seasonal variation in available prey and prey selection occurred, however proportions of prey consumed did not always correlate with prey availability. Chironomids were consumed throughout the year in roughly the same proportions as they occurred in the environment. Baetids served as the major food source in summer and autumn during which time hydropsychids were under-utilized as prey. We speculate that the conspicuous swimming behavior of baetids drew the attention of B. vinosa nymphs and caused them to be preferentially selected.

Life history and production of the predatory caddisfly Rhyacophila vao Milne in a spring‐fed stream

SUMMARY1. The predatory caddisfly Rhyacophila vao Milne (Rhyacophilidae) displayed a 2‐year, semivoltine life cycle in a small, spring‐fed stream in southern Alberta, Canada. Three overlapping cohorts were identified throughout the 2‐year sampling program, with five larval instars recognized. Larvae overwintered in instars I —ELI, developed to instar IV by summer and instar V by autumn. The second winter was spent in instar V, Pupation occurred from late May to August and did not commence until stream temperature exceeded 3°C. Adults were collected from mid‐June to early September.2. Larvae displayed a diphasic growth pattern: Phase I, a positive, non‐linear growth rate for instars I‐IV; Phase II, a constant growth rate during instar V. Phase I coincided with increasing stream temperatures in late winter and spring, where mean instantaneous growth rates (maximum of 2.78% dry wt day−1) were significantly correlated with stream temperatures. Although the duration of Phase II spanned a temperature range similar to that in Phase I, the instantaneous growth rate remained temperature‐independent at 0.87% dry wt day−1.3. Larvae exhibited a type III survivorship curve (i.e. an exponential decrease on an arithmetic scale), with the finite rate of mortality averaging 0.80% larvae day−1.4. Cohort 1 (later part of 1983 year class) displayed lower total production compared with the equivalent growth phase in the 1984 year class (Cohort 2). In contrast, production of the non‐linear and linear growth phases of Cohort 2 was similar. Periods of similar growth characteristics for Cohorts 1 and 2 had comparable P/B ratios for both the unadjusted and time‐adjusted annual estimates, although higher ratios were observed for the non‐linear growth phase of Cohort 2. Total cohort production (linear + non‐linear growth phases) could only be calculated for Cohort 2, and was 870.2 ± 1011.4 mg dry wt m−2. The corresponding cohort P/B ratio was 5.01 and the adjusted annual P/B, 3.01.5. Annual larval production (±SE) for the first and second years of the study was similar (Year 1, 480.0 ± 387.5mg dry wt m−2; Year 2, 526.9 ± 967.5mg dry wt m−2) as were unadjusted and annual P/B ratios.

Larval morphology, biology and distribution of Agabus setulosus (Coleoptera: Dytiscidae)

AbstractA lectotype is designated for Agabus setulosus (J. Sahlberg, 1895), a rare rheophilous dytiscid known mainly from northern Fennoscandia. The larval instars are described for the first time, based on material from northern Sweden. The first-instar larva is characterized by the presence of two dorsal spines on each femur and a pair of mediodorsal setae on last abdominal segment; both characters are seemingly unique among Agabus. The third instar differs from all other Palaearctic Agabus species in the complete sclerotization of the ring-like abdominal segment 6. The biology of A. setulosus is described from a Swedish population; semivoltine life cycle with overwintering eggs laid in summer followed by adult overwintering prior to breeding is suggested.

Growth and Drift of Nine Stonefly Species (Plecoptera) in an Oklahoma Ozark Foothills Stream, and Conformation to Regression Models

Growth and drift of nine stonefly species, in a second-order, northeastern Oklahoma stream were elucidated from 19 and 13 months of sampling, respectively. Observed growth of each species (head-capsule width versus days) was analyzed with five different regression models. Growth patterns generally conformed to either a power curve (double log) or semilog regression. Coefficients of determination for best fit models ranged from 0.41 to 0.79 and were all highly significant. Haploperla brevis (Banks), Leuctra tenuis (Walker), and Amphinemura delosa (Ricker) exhibited univoltine, fast life cycles that were best modeled by semilog regressions. The univoltine, slow cycle of Acroneuria evoluta Klapalek showed good fit with a power curve. The univoltine, fast life cycles of Isoperla namata Frison, I. signata (Banks), Prostoia completa (Walker), and Allocapnia rickeri Ricker fit different types of regressions. Intraspecific differences in their growth curve shapes and rates were primarily attributed to temperature. Instars of Agnetina capitata (Pictet) nymphs were greatly spread over time and overlapped, making discretion of cohorts difficult. However, a semivoltine life cycle was suggested. This study suggests that growth characteristics of some stonefly species can be determined from lower sampling frequency, adequate to establish growth curve shape rather than the typical monthly increments. Comparison of significant semilog growth rates for each species corroborates the descriptive fast and slow classification. Stonefly drift density (0.1–7.5 nymphs per m3) was significantly lower than that of mayflies and Diptera and demonstrated a postsunset pulse. Multivariate regression of stonefly numbers in drift on current velocity and specific benthic densities accounted for a significant 25% of the variation in numbers drifting. Additional variation appears to be attributable to a greater degree of nymphal maturity as suggested by drift of predominantly pre-emergent nymphs.

The life cycle ofPteronarcys scotti(Plecoptera: Pteronarcyidae) from the Southern appalachians, U.S.A.

Abstract Larval and adult Pteronarcys scotti Ricker were collected from a mountain stream in northwestern South Carolina, USA. The pattern of larval growth indicated a semivoltine life cycle. Emergence occurred in April and early May, and small larvae first appeared in May. Sexual dimorphism in adult size was apparent; males were 0.8 as large as females in head capsule width. Female larvae possess a midventral notch on the eighth abdominal segment that can be used to sex larvae as small as 2.5 mm in head width. Female larvae as small as 1 mm in head width have a midventral break in the posterior setal row of segment 8. These characters are illustrated.

Developmental strategies inEctobius pallidus(Dictyoptera: Blattidae)

Ectobius pallidus has a semivoltine life cycle, overwintering as an egg and intermediate nymphal instar. A range of instars may overwinter, although the exact composition of an overwintering population varies annually. A number of developmental pathways are defined, involving both quiescence and diapause. The proportion of an instar following each pathway also varies annually. In ‘advanced’ years more 3rd and 4th instars enter diapause. The ecological significance of the different developmental strategies is discussed.