Mayfly Species Research Articles

Growth and voltinism in the aquatic insects of a regulated river subject to groundwater inflows

AbstractThe water temperature and discharge of the Vassbygdelvi River, Aurland watershed, was altered after regulation due to transfer of cold water from the higher parts of the catchment. The lower part of the river receives a considerable amount of groundwater, which affected the water temperature due to reduced discharge. Compared to a closely situated reference station, the temperature increased by 9% on a yearly basis. The temperature differences were most pronounced during the winter when average January water temperature at the reference and the stretch influenced by groundwater was 0.8 and 3.3°C, respectively. Studies of benthic insects in the two habitats showed that the temperature differences had little effect on the length of the life cycle. Although some species show significant differences in growth pattern during parts of the year, with more rapid development in the winter‐warm locality, there was a trend for synchronous growth at both localities. Compared to the situation before regulation, two species of stoneflies became extinct and one mayfly species colonized the area, probably as a result of the increased number of annual degree‐days. Copyright © 2008 John Wiley & Sons, Ltd.

Predator effects on prey population dynamics in open systems

Animal population dynamics in open systems are affected not only by agents of mortality and the influence of species interactions on behavior and life histories, but also by dispersal and recruitment. We used an extensive data set to compare natural loss rates of two mayfly species that co-occur in high-elevation streams varying in predation risk, and experience different abiotic conditions during larval development. Our goals were to generate hypotheses relating predation to variation in prey population dynamics and to evaluate alternative mechanisms to explain such variation. While neither loss rates nor abundance of the species that develops during snowmelt (Baetis bicaudatus) varied systematically with fish, loss rates of the species that develops during baseflow (Baetis B) were higher in streams containing brook trout than streams without fish; and surprisingly, larvae of this species were most abundant in trout streams. This counter-intuitive pattern could not be explained by a trophic cascade, because densities of intermediate predators (stoneflies) did not differ between fish and fishless streams and predation by trout on stoneflies was negligible. A statistical model estimated that higher recruitment and accelerated development enables Baetis B to maintain larger populations in trout streams despite higher mortality from predation. Experimental estimates suggested that predation by trout potentially accounts for natural losses of Baetis B, but not Baetis bicaudatus. Predation by stoneflies on Baetis is negligible in fish streams, but could make an important contribution to observed losses of both species in fishless streams. Non-predatory sources of loss were higher for B. bicaudatus in trout streams, and for Baetis B in fishless streams. We conclude that predation alone cannot explain variation in population dynamics of either species; and the relative importance of predation is species- and environment-specific compared to non-predatory losses, such as other agents of mortality and non-consumptive effects of predators.

Effects of arsenic speciation and low dissolved oxygen condition on the toxicity of arsenic to a lotic mayfly

The influence of site-specific conditions on contaminant bioavailability and toxicity to benthic invertebrates is a key consideration in the environmental risk assessment process. This is particularly relevant for contaminants with complex speciation chemistries, such as arsenic. The present study addressed uncertainties regarding arsenic toxicity to a mayfly (Baetis tricaudatus) under low dissolved oxygen (DO) conditions characteristic of many contaminated sites. Arsenic toxicity (arsenite, As(III); arsenate, As(V)) to mayfly nymphs was assessed under two DO scenarios (68 and 84% saturation). Arsenic speciation ratios were determined during testing to confirm the nature of arsenic exposure. The present study found that As(III) was more lethal and bioaccumulated to a greater degree in B. tricaudatus compared to As(V), but the sublethal toxicities of the two arsenic species were similar. Nymph growth and development were significantly inhibited after 12 d of exposure to both 1 mg/L of As(III) and As(V). Exposure to arsenic under low DO conditions (6.5 mg/L, 68% saturation) did not significantly affect As(III) or As(V) toxicity and bioaccumulation over 12 d. The DO level of 6.5 mg/L, however, appeared to be marginally lethal to B. tricaudatus. Results indicate that the Canadian arsenic criterion for the protection of aquatic life (5 microg/L) is protective of B. tricaudatus and is low enough to accommodate differences in arsenic toxicity because of the interconversions between As(III) and As(V). These findings provide insight regarding the toxicity and speciation of arsenic under DO conditions considered to be low for this lotic mayfly species and representative of existing conditions at mine sites in northern Canada.

Mayfly production in a New Zealand glacial stream and the potential effect of climate change

In contrast to the northern hemisphere where species of Chironomidae are usually the dominant benthic invertebrates in the coldest upper reaches of glacial streams, mayflies (Deleatidium spp.: Leptophlebiidae) predominate in equivalent conditions in New Zealand. We examined the life histories and annual production of Deleatidium spp. at two sites on the Matukituki River (South Island, New Zealand) and at three sites in its glacier-fed tributary, Rob Roy Stream. Mean annual water temperature at the five sites ranged from 2.1 to 7.0°C. Monthly sampling showed that mayfly populations were poorly synchronised at all sites but were probably univoltine. The large Deleatidium cornutum was the dominant mayfly species found at the upper sites (Sites 1 and 2) on Rob Roy Stream, whereas above the confluence with Matukituki River (Site 3) it co-existed with a complex of smaller species we refer to as D. “angustum”. Deleatidium “angustum” also dominated at the Matukituki sites. Deleatidium production calculated for the five sites, assuming an 11-month nymphal life, ranged from 0.48 g dry weight/m2/year (Site 1) to 3.07 g dry weight/m2/year (Site 3). The values for D. cornutum at Sites 2 and 3 are high for a species of Deleatidium and reflect its large size. This species appears to be strongly adapted for growth at low temperatures. Climate change scenarios for New Zealand predict the gradual and ultimate loss of small South Island glaciers and a consequent warming of streams as runoff from rainfall and snow melt becomes more dominant in spring. As a result, suitable habitats will be lost for cold-water specialists such as D. cornutum, and they are likely to suffer reductions in their distributional range and local extinction. In contrast, species such as those in the D. “angustum” complex may extend their ranges into streams formerly dominated by glacial meltwater.

Do lowland habitats represent barriers to dispersal for a rainforest mayfly, Bungona narilla, in south-east Queensland?

Long-distance dispersal might be an important mechanism for the maintenance of aquatic insect populations in heterogeneous landscapes. However, these events can be difficult to measure by direct observation because the techniques can be time-consuming, expensive and technically difficult. When dispersal results in gene flow within and between populations, patterns of variation can be detected by genetic methods. The levels of population genetic structuring and the relationship between gene flow and geographical distance were assessed in the mayfly species Bungona narilla (Harker, 1957) in rainforest streams in south-east Queensland that are separated by lowland habitats. An analysis of molecular variance based on mitochondrial DNA data, using a fragment of the cytochrome oxidase I gene, revealed significant differentiation between regions, suggesting that maternal gene flow was restricted. A nested clade analysis revealed patterns of historical (contiguous) range expansions and recent restricted gene flow along with some long-distance dispersal events. Our analyses have shown that populations of B. narilla are significantly structured throughout the species range in south-east Queensland and that the low elevation habitats separating the northern and southern populations are restricting gene flow to some extent.

A new species and new synonym in Heptagenia walsh (Ephemeroptera: Heptageniidae: Heptageniinae) based on molecular and morphological evidence.

A new mayfly species, Heptagenia whitingi Webb & McCafferty n.sp. is described from larvae, a male subimago, a female adult, and eggs collected from large rivers in the west-central portion of North America. Larvae are differentiated from other North American Heptagenia Walsh by a pair of large, rectangular pale markings on abdominal tergum 4, and the combination of having the posterior margin of the abdominal terga with bluntly pointed spines less than half the length of the fine setae, small blunt spines on the posterior margin of the caudal filaments, and numerous rows of setae laterally on the ventral surface of the labrum. A 630 bp partial sequence of the mitochondrial gene cytochrome oxidase 1 (COI) from three specimens of H. whitingi n.sp. was compared with those of 12 specimens representing eight other North American species of Heptagenia. Intraspecific sequence divergences based on Kimura-2-parameter (K2P) distance ranged from 0–1.1%. Interspecific sequence divergence based on K2P distance ranged from 8.9–20.0%. Heptagenia whitingi n.sp. differed from its sister taxon H. flavescens (Walsh) by 11.7%. Heptagenia diabasia Burks and H. elegantula (Eaton) differed from each other by only 1.1%; these two alleged species show a clinal pattern in larval abdominal coloration and there are no structural differences between the semaphorants. On this basis, H. diabasia is placed as a junior subjective synonym of H. elegantula, n.syn.

Life history of the northern mayfly Baetis bundyae in Rankin Inlet, Nunavut, Canada, with updates to the list of mayflies of Nunavut

AbstractMayflies (Ephemeroptera) were collected from 35 sites (streams and tundra ponds) across southern Nunavut in 2002–2005. Nine mayfly species were previously reported for Nunavut: Acentrella feropagus Alba-Tercedor and McCafferty, Acerpenna pygmaea (Hagen), Baetis bundyae Lehmkuhl, B. flavistriga McDunnough, B. foemina McDunnough, Diphetor hageni (Eaton) (Baetidae), Ephemerella aurivillii (Bengtsson) (Ephemerellidae), Leptophlebia nebulosa (Walker) (Leptophlebiidae), and Metretopus borealis (Eaton) (Metrotopidae). We add 7 species to this list, bringing the total to 16: Ameletus inopinatus Eaton (Ameletidae), Acentrella lapponica Bengtsson, Baetis hudsonicus Ide, B. tricaudatus Dodds, Heptagenia solitaria McDunnough (Heptageniidae), Rhithrogena jejuna Eaton (Heptageniidae), and Parameletus chelifer Bengtsson (Siphlonuridae). Based on numbers collected, the dominant mayfly family was Baetidae. Baetis bundyae was the most common mayfly collected, particularly in coastal areas, where larvae were found in permanent and temporary streams and in small or shallow tundra ponds. Larvae hatched 2–3 weeks after ice-out and developed rapidly in 2.5–4 weeks, emerging as adults by early August. All populations containing larvae that were large enough to sex showed female-biased sex ratios, suggesting parthenogenesis. A combination of freeze-tolerant eggs, good dispersal ability, and probable parthenogenesis is probably responsible for the success of Baetidae across the Arctic.

Temporal dynamics of production and ingestion of the dominant mayflies in a subtropical stream in China

We investigated temporal dynamics of secondary production and trophic basis for four dominant mayfly species in a second-order river of the Hanjiang River basin in Middle China from June 2003 to June 2004. The secondary production of the dominant four mayfly species, comprising nearly 90% of the total density of mayflies, was 14.45 g m−2 per year for Ephemera sp., 9.15 g m−2 per year for E. sinensis, 7.23 g m−2 per year for Leptophlebia sp. and 1.55 g m−2 per year for C. nigropunctata. C. nigropunctata and Ephemera sp. had most of their production in winter (from January to March), while E. sinensis and Leptophlebia sp. produced in two intervals, from June to September (summer) and from December of the first year to March of the next year (winter). Overlap in temporal distribution of production among the four mayflies was generally high (>0.60), especially those of C. nigropunctata, Ephemera sp. and Leptophlebia sp. Overlap of Leptophlebia sp. and Ephemera sp. was >0.85. Patterns of the four food types (amorphous detritus, vascular plant detritus, fungi, and diatoms) for each mayfly varied significantly (P < 0.01) over time, and patterns of food ingestion between the four mayflies were also significantly different (P < 0.05–0.01). Among the four main food types, all mayflies used amorphous detritus the most, which constituted 53–96% of their diets and contributed 54–97% to their production. Thus, temporal changes in the food web for mayflies in Heizhuchong stream are quantitative rather than qualitative.

A comparative study of the costs of alternative mayfly oviposition behaviors

Oviposition behavior of insects has associated fitness costs related to the probability that females survive to oviposit. During summer 2003, we observed the oviposition behavior and compared the mortality rates of females of 17 mayfly species in one western Colorado watershed. We dissected adult females collected on terrestrial sticky traps, in drift nets submerged in streams, and in stomachs of brook trout to determine whether the mayflies had oviposited before capture, drowning, or consumption. Females oviposited by either splashing on the water surface releasing all their eggs (splashers), dropping their eggs from the air (bombers), dipping their abdomens multiple times releasing a few eggs at a time (dippers), landing on rocks and ovipositing on the undersides (landers), or floating downstream while releasing their eggs (floaters). Almost 100% of lander and 50% of dipper females had not oviposited when captured on sticky traps, increasing their vulnerability to preoviposition mortality by aerial predators compared to mayflies with other behaviors. In contrast, most females had laid their eggs before drowning or being eaten by a fish (50–90%). However, groups with oviposition behaviors most exposed to the water surface (floaters, then splashers, dippers, and landers) were more vulnerable to drowning before completing oviposition. In addition, splashers and floaters were most vulnerable to predation by brook trout before ovipositing. These data suggest that fitness costs associated with preoviposition mortality may be considerable depending on mayfly oviposition behavior. Furthermore, previously demonstrated benefits of low predation rates on eggs of lander species may be offset in part by costs to female survival.

Life history, secondary production and trophic basis of two dominant mayflies in a subtropical stream of China

Mayflies constitute a major part of macroinvertebrate biomass and production in lotic ecosystems, and play an important role in material cycle and energy flow. There are more than 250 species of mayflies in rivers and streams of China. In order to learn their ecological functions, an investigation on life cycle, production and trophic basis of dominant species of mayflies in a second-order branch of Hanjiang River basin, Hubei, China was carried out during June 2003 to June 2004. The results showed that the dominant mayfly species Epeorus sp. and Caenis sp. developed two generations per year; in term of Epeorus sp., putation mainly occurred in spring and then from late summer to early autumn, while Caenis sp. pupated in spring and autumn. The abundance and biomass of the Epeorus sp. population peaked twice (1 226 ind/m2, 3.142 5g/m2) in April and June. Caenis sp. also had two peaks (307ind/m2, 1.590 g/m2), but in February and June. Cohort production and cohort P/B ratio of Epeorus sp. were 161.009 g/m2 wet weight and 7.7, respectively, and annual production and P/B ratio were 267.46g/m2.a wet weight and 15.4, respectively; cohort production and P/B ratio of Caenis sp. were 26.7995g/m2 wet weight and 4.7, its annual production and P/B ratio were 53.60 g/m2.a wet weight and 9.4, respectively. For Epeorus sp., the proportions contributing to secondary production of the main food types were: amorphous detritus, 33.46%; fungi, 10.83%; vascular plant detritus, 1.80%; diatoms, 53.90%; for Caenis sp., the proportions were 70.79%, 6.90%, 3.52% and 18.77%, respectively.

Habitat preference and life history of the mayflies Metamonius anceps Eaton (Nesameletidae) and Meridialaris chiloeensis Demoulin (Leptophlebiidae) in a Patagonian mountain stream

The habitat preferences, temporal dynamics in density and the life history of two species of mayflies, Metamonius anceps and Meridialaris chiloeensis, were investigated in a Patagonian mountain stream over a period of one year. Benthic samples were taken in a low order Nothofagus forested stream. M. anceps was univoltine with small nymphs predominating in winter and emergence occurring in summer. M. chiloeensis showed a bivoltine life cycle with a winter and summer generation, and emergence period in spring and summer. Both species were significantly more abundant in the low water period than in the high discharge season. Gravels supported significantly more individuals of M. chiloeensis than sand in pools and leaf packs. Temporal overlap of abundance between species was low. The existence of different life history strategies and the temporal shift of main generations and density peaks were critical to allow species coexistence.

Sub-lethal and chronic salinity tolerances of three freshwater insects: Cloeon sp. and Centroptilum sp. (Ephemeroptera: Baetidae)and Chironomus sp. (Diptera: Chironomidae)

Increased salinity in rivers and streams is a serious environmental concern, and in Australia there is growing information about the acute tolerances to salinity for freshwater macroinvertebrates, but much less information about chronic and sub-lethal tolerances. The effects of increased salinity on the growth and survival of two mayflies, Cloeon sp. and Centroptilum sp. and one midge Chironomus sp. are reported. In both mayfly species survival was variable. Complete mortality was observed in salinities with electrical conductivity of 10 mS cm(-1) and higher. Salinities causing chronic mortality in mayflies were measured as 21-day LC50, and ranged from 0.90 to 2.7 mS cm(-1). Growth rates were not significantly different between treatments. In Chironomus, salinity affected the mean number emerging as flying adults as well as the time to emergence. An inverted 'U' shape response was observed for percentage emergence, with the greatest numbers emerging at intermediate salinities (0.65-5.0 mS cm(-1)). No emergence occurred at salinities of 20 mS cm(-1) and higher. Time to emergence was delayed by 15-88% with increased salinity, however the size of emerged adults was the same for all treatments. Growth rates were reduced with increased salinity, showing a slow, steady reduction up to 10 mS cm(-1) then a steep decline between 10 and 15 mS cm(-1). The implications of altered growth rates and changes in developmental times are discussed. This study illustrates the variability in responses to increased salinity, and highlights the need to continue studying sub-lethal and chronic exposures in a range of freshwater invertebrates, in order to predict impacts of salinisation on freshwater biodiversity.

Structure and spatial variability of mayfly (Ephemeroptera) communities in the upper Hron River basin

Mayflies were sampled from eleven sites in six tributaries of the upper Hron River. Mayfly communities were ordinated and related to environmental factors using multiple regression and principal component analysis. Communities of headwater sites were dominated by Rhithrogena iridina which was gradually replaced by Baetis alpinus, at the lower reaches. Total mayfly species richness was inversely related to stream slope and overall abundance was inversely related to altitude. The prominent factor influencing mayfly communities was a complex longitudinal gradient as proposed by the river continuum concept. There were no significant differences in community composition and structure between the left-and right-hand tributaries of the Hron River.

The management of metabolic energy storage during the life cycle of mayflies: a comparative field investigation of the collector-gatherer Ephemera danica and the scraper Rhithrogena semicolorata

The concentration and seasonal dynamics of the major energy storage components, triglycerides and glycogen, were measured in two species of mayfly (Rhithrogena semicolorata and Ephemera danica) with contrasting life cycle strategies living in a small mountain stream. E. danica is a burrowing, semivoltine collector-gatherer; R. semicolorata is univoltine and scrapes periphyton from stones. This is the first publication which focuses on the role of metabolic energy sources during the larval life span of two mayfly species until the larvae emerge. Although triglycerides are the major energy reserve in both species (>84% of total energy storage) throughout the whole larval development their seasonal dynamic differed considerably. In R. semicolorata the triglyceride concentration declined during the last weeks prior to emergence in both sexes. The same pattern was found in female larvae of E. danica, but not in male E. danica. It is suggested that females use triglycerides in the last larval stages for egg maturation, which is completed in the last larval instar. In male E. danica the triglyceride concentrations remained high until emergence, presumably due to their high energy demands as adults for their swarming flights. Glycogen concentrations did not show such a difference between species and sexes. Its significance as a storage substrate for energy is rather low; however, concentrations decreased in both species and sexes prior to emergence.

Macrozoobenthos of two different catchment areas of the tatra mountain lakes with a special reference on the effects of acidification

The structure of macrozoobenthos of two different high-mountain Tatra lakes, namely Starolesnianske pleso (strongly acidified) and Nižne Terianske pleso (reference site) is described. The latter is characterised by a large catchment and total area, and is relatively deep with strong inlet and outlet. It is not affected by acidification. Univoltine species of mayflies, stoneflies and caddisflies dominate in the littoral, mainly scrapers. Predators are represented by stoneflies. Shredders dominate in the lake outlet. From the zoogeographic point of view, Carpathian endemites and Central European species prevail. Forty percent of species are sensitive to acidification. The former has a smaller catchment and total area, and is relatively shallow, without inlet. It is strongly affected by acidification. Semivoltine species, mainly predators (beetles) and shredders prevail. From the zoogeographic point of view Palaearctic species dominate. Species sensitive to acidification are missing. Emergence of water insects has two peaks during spring and fall circulation.

The use of in situ and stream microcosm experiments to assess population‐ and community‐level responses to metals

We conducted field and stream microcosm experiments to assess population-level (density, size distribution) and community-level (species richness metrics, multivariate analysis of community composition) responses of macroinvertebrates to heavy metals in the Arkansas River, a mining-polluted stream in Colorado, USA. Experiments were conducted in spring and summer to coincide with early and late developmental stages (i.e., instars) of the mayfly Rhithrogena hageni. Results of field experiments showed significant mortality at metal-contaminated sites during summer when mayfly populations were dominated by small, early instars (mean dry wt = 0.13 mg). In contrast, no significant mortality was observed in spring when organisms were larger (mean dry wt = 1.78 mg). Multivariate analyses based on abundance of dominant taxa clearly separated reference and metal-impacted stations in summer experiments but showed little separation in spring. We observed no significant effects of metals on species richness, number of mayfly species, or EPT (species richness of Ephemeroptera, Plecoptera, and Trichoptera) in.either field experiment. Using stream microcosms, we established concentration-response relationships between heavy metals and R. hageni density, species richness, mayfly richness, and EPT. Density of R. hageni was generally more sensitive to metals than measures of species richness, and summer populations of R. hageni were more sensitive to metals than spring populations. Because the presence of large, relatively tolerant individuals in spring coincided with periods of higher metal concentrations, R. hageni was protected from toxic effects in this system. We conclude that phenology and developmental stage are important factors influencing responses of some aquatic macroinvertebrates to metals. Thus, timing bioassessments to coincide with the presence of these sensitive life stages can improve our ability to detect subtle contaminant effects.

Egg development in the mayflies of a Swiss glacial floodplain

The duration and timing of egg development is crucial to the survival of invertebrates in glacier-fed rivers. The relationship between egg development and environmental conditions was investigated in 3 mayfly species, Baetis alpinus, Rhithrogena nivata, and Ecdyonurus picteti, in an alpine glacier-fed alluvial system. Field-collected eggs were reared in the laboratory at temperatures representing field conditions (1.5, 3, 5, and 7°C). Egg-incubation period and degree-days demand (DD) were determined, and hatching in the field was predicted from field temperature records. Egg development and temperature relationships for B. alpinus and R. nivata were documented for the first time. Baetis alpinus had synchronous egg development and high hatching success. Faster development in warmer habitats enabled it to hatch during favorable autumnal conditions. Ecdyonurus picteti had a very long development time that decreased slightly at higher temperatures. However, the variation in DD was considerable. The observed long and delayed hatching would favor successful development in unpredictable habitats at the low temperatures experienced in these glacial conditions. Rhithrogena nivata, one of the most extreme cold-adapted mayfly species, had a long egg incubation period, and success in development largely depended on the timing of hatching and discharge conditions. This species could exploit extremely unstable and cold habitats where other species are limited by low water temperatures.

Taxonomy and genetics of the parthenogenetic mayfly Centroptilum triangulifer and its sexual sister Centroptilum alamance (Ephemeroptera:Baetidae)

Allozymes were used to examine population genetic structure and species boundaries in the clonal, obligately parthenogenetic Centroptilum triangulifer and its sexual sister species Centroptilum alamance from 3 sites in Pennsylvania and 1 site in North Carolina, USA. Genotype frequencies in field populations of C. triangulifer showed numerous departures from Hardy-Weinberg expectations (mostly heterozygote excesses) and significant linkage disequilibrium at most testable locus combinations, as expected for a clonal parthenogen. A total of 51 distinct clones of C. triangulifer was identified, some of which were found at multiple sites (separated by .700 km in one case). Each stream contained from 7 to 25 clones and clonal frequencies at a given site varied greatly over time. Allelic patterns in laboratory hybrids suggest that parthenogenesis in C. triangulifer is diploid and automictic, and that crossing over is suppressed. In contrast, C. alamance populations had only a few Hardy-Weinberg departures (all heterzygote deficiences) and little or no linkage disequilibrium. No published work provides characters to distinguish the 2 species, but our data support retention of specific status for C. triangulifer and C. alamance because: 1) consistent, fixed allelic differences were found over a broad geographic area (.700 km) with no evidence of introgression despite co-occurrence (sympatry) in the same stream, 2) laboratory hybridization experiments demonstrated the existence of postzygotic barriers to gene flow between the species, and 3) measures of both interspecific and intraspecific genetic similarity were comparable to those found between other mayfly species. Phylogenetic analysis of the genetic data suggests speciation preceded the transition to obligate parthenogenetic reproduction in C. triangulifer. Morphological examination of genetically identified specimens enabled us to describe subtle but consistent differences that can be used to distinguish the species. Thus, what initially appeared to be single populations with skewed sex ratios (7, 11, and 24% male) at 3 of our study sites was, in fact, 2 populations at each site—1 exclusively female (C. triangulifer) and the other a normal, sexual (1:1 sex ratio) population (C. alamance). A similar approach, combining detailed genetic and breeding experiments with close morphological study, could help resolve taxonomic problems in some of the numerous other bisexual/parthenogenetic mayfly taxa.

Secondary Production and Its Trophic Basis of Two Mayfly Species in a Subtropical Stream of China

During June 2003 to June 2004, an investigation on life cycle, production and trophic basis of two species of mayfly in a second-order river of Hanjiang River Basin, Hubei, China was conducted. The results showed Epeorus sinensis UMLER and Caenis nigropunctata WU both developed two generations a year. The mean annual production and P/B ratio of E. sinensis were 9.154 g m ‐2 a ‐1 dry weight and 16.0, and those of C. nigropunctata were 1.554 g m ‐2 a ‐1 and 9.6, respectively. For E. sinensis, the proportions contributing to secondary production of the main food types were: amorphous detritus 33.46%, fungi 10.8%, vascular plant detritus 1.8%, diatoms 53.9%; for C. nigropunctata, the proportions were 70.8%, 6.90%, 3.5% and 18.8%, respectively. Compared with those species reported in North America and Europe, although land use mode and local climate were greatly different in China, life history and trophic basis of the mayflies seemed roughly similar, yet secondary production appeared to be much higher.

The mayflies (Ephemeroptera) of New Hampshire: Seasonality and Diversity of the Stream Fauna(1)

Season-long sampling in streams and rivers produced 112 species of mayflies, which with other records totals 121 species for New Hampshire; 88 of these are new state records. Appearance of blackwing/mature larvae were used to develop statements on seasonality of species. Distinct differences were found between the faunas of southern and north-central New Hampshire, with an important factor being water temperatures through the season. A biogeographic analysis coupled with known habitat preferences reinforced the hypothesis that water temperature was a critical factor in determining species distributions in the state.