Mayfly Species Research Articles

Redundancy among three herbivorous insects across an experimental current velocity gradient.

We conducted streamside experiments to determine if the ability of herbivorous insects to remove algal periphyton varies with local current velocity. We used two mayfly species (Baetis bicaudatusand Drunella grandis) and one caddisfly species (Glossosoma verdona), which differ from one another in body morphology and mobility. Periphyton was grown for 30 days on ceramic tiles in constant velocity to create similar initial forage conditions for grazers. Tiles were transferred to three velocity regimes characteristic of the natural streambed: slow (3-5 cm s(-1)), medium (15-20 cm s(-1)) and fast (32-41 cm s(-1)). Four grazer treatments (Baetis, Drunella, and Glossosoma alone, and all species combined) were repeated for each velocity treatment to isolate the effect of local current on grazer ability to crop periphyton. Grazers differed in their abilities to remove periphyton across current treatments. Glossosoma removed significantly (P<0.05) more periphyton at fast versus either slow or medium velocities; Baetis showed a similar (but non-significant) trend; and, Drunella always removed about 75% of periphyton, irrespective of current. At fast current, periphyton removal was equivalent among the species. At medium current, Drunella removed significantly more than both Baetis and Glossosoma, whereas at slow current, Drunella removed more than Baetis, which removed more than Glossosoma. Periphyton removal under the combined three-grazer treatment was similar qualitatively to the combined effects of individual grazers. More periphyton tended to be removed as current increased, with the fast versus slow contrast showing marginal significance (P=0.10). Under all current regimes, the quantity of periphyton removed did not differ from the null model expectation of simple additive effects among individual grazers (i.e., no facilitation or inhibition). These experiments show that for some species, herbivory varies with current, which suggests that the herbivore "function" of cropping periphyton may vary with the environmental context of local current. Under some local velocities, however, different herbivore species "function" similarly and are potentially redundant with respect to periphytic removal. In naturally heterogeneous streams characterized by sharp gradients in local current velocity, we expect current-dependent species interactions to be common and at least partially contribute to intra-guild co-existence of species.

Response of macroinvertebrates to copper and zinc in a stream mesocosm

Metal pollution of streams and rivers is recognized as one of the major concerns for management of freshwaters. Macroinvertebrate communities were established within 12 artificial streams and exposed to three replicated concentrations of a metals mixture (copper and zinc) for 34 d. The cumulative criterion units (CCU = sigma[metals]/hardness-adjusted U.S. Environmental Protection Agency [U.S. EPA] 1996 chronic criterion value) of total metals in the low, medium, and high treatments were 2.4, 5.9, and 18 CCUs. Zinc comprised approximately 75% of the CCUs in each of the treatments. Effects on taxa richness and the number of taxa in the orders Ephemeroptera, Plecoptera, and Trichoptera (EPT) were moderate at the high exposure concentration (-23% and -26% respectively, p < 0.05). All of the five major mayfly species showed near extinction, whereas four of the seven caddisflies showed stimulation (up to +121%) and three were reduced (up to -76%). Redundancy analysis for this metal gradient indicated that 94% of the variance in community structure was explained by three quantitative variables: total mayfly abundance, a mollusk (Potamopyrgus antipodarum) abundance, and the number of EPT individuals, indicating that multiple indices do provide improved predictors of metal stress. Most species showed a threshold response relationship, whereas some community indicators showed apparent hormetic responses (e.g., number of mayfly taxa, total taxa, and number of EPT taxa). Model concentration-response relationships with generalized linear models were used to provide threshold of 20% effective concentration values for species and community metrics. Threshold effect values ranged upwards of 1.4 CCUs, indicating that U.S. EPA chronic criteria would be protective of species and community responses.

Observations on the occurrence and maturation of Spinitectus inermis (Nematoda: Cystidicolidae) in the Sousa River, Portugal.

Spinitectus inermis (Zeder, 1800) is a rare specific nematode of the European eel, Anguilla anguilla (L.), that ranges widely in Europe (North, Baltic and Mediterranean Seas basins) but occurs only locally, particularly in lakes, fishponds and in the lowland reaches of rivers (Moravec F. 1977: Folia Parasitol. 24: 85; Moravec F. 1979: Acta Soc. Zool. Bohemoslov. 43: 35-42; Moravec F. 1994: Parasitic Nematodes of Freshwater Fishes of Europe. Academia, Prague, 473 pp.). This nematode has been studied since the beginning of the 19 century but its morphology was little known until the redescription by Moravec (1979, op. cit.) plus additional data revealed by scanning electron microscopy (Moravec F. 1996: Parasite 3: 169-174). The knowledge of the biology of this nematode is also scarce. Recently, however, it was found that nymphs of several species of mayflies (Ephemeroptera) were suitable experimental intermediate hosts of this nematode (Saraiva A.M., Moravec F., Pereira A., Cruz C. 2002: Folia Parasitol. 49: 118-126). Since S. inermis is an abundant parasite of eels in the Sousa River, Portugal, its seasonal occurrence and maturation were followed and the results are presented herein. The population dynamics of S. inermis was followed in eels from the lowest reaches of the Sousa River, a tributary of the Douro River, from the locality of Senhora do Salto, situated about 20 km east of Porto, northern Portugal. Monthly samples were taken by electrofishing from November 1998 to October 1999 (total sample size 326; mean body length of fish 22.0 ± 4.42 cm). Fish were examined for parasites and the recovered nematodes were washed in physiological saline (0.9%), fixed in hot 70% ethanol, stored in 70% ethanol and cleared in glycerol for light microscopical examination for sex and maturity stage determination. The occurrence of nematodes, sex ratio and stages of development of females (gravid females with mature eggs / females in other developmental stages) throughout the year were compared by Chi-square test (Siegel S., Castellan N.J. Jr. 1989: Nonparametric Statistics for the Behavioral Sciences. McGraw-Hill Book Company, New York, 399 pp.). The prevalence and mean intensity of infection of S. inermis in eels during the studied period is shown in Fig. 1. S. inermis was present throughout the study period. Significant difference in the occurrence of this parasite (χ = 32.81, d.f. = 11, p < 0.05) was found during the year. Prevalence reached high values (30-57%) from November to February and low values (10% and 13%) in June and July. Intensity ranged from 1 to 26. The high values of mean intensity occurred in January (9) and June (14), with the minimum value (2) in December. Adults (males and females) of S. inermis occurred in eels Fig. 1. Monthly changes in the prevalence and intensity of Spinitectus inermis in eels from the Sousa River from November 1998 to October 1999. Fish sample size in parentheses.

River-floodplain linkage determines production dynamics of detritivorous and predacious mayflies (Ephemeroptera) in a sedge-meadow wetland

The macroinvertebrate communities of riparian sedge-meadows in Maine (U.S.A.) are unusual, compared to other types of freshwater wetlands, because they are dominated by mayflies during a 1-2 mo period of spring flooding, and because one mayfly species, Siphlonisca aerodromia, is a predator of the other mayflies. The objectives of this study were to determine temporal patterns of production for mayflies inhabiting a sedge meadow along Tomah Stream in sub-boreal Maine, and to identify key factors influencing their production in this wetland. During spring flooding, mayflies contributed 80-86 % of the total macroinvertebrate biomass. Leptophlebia cupida and L. johnsoni together contributed approximately 50 % of total biomass. Arthroplea bipunctata, Eurylophella cf. prudentalis, Siphlonurus mirus, S. rapidus and S. aerodromia were also important contributors. More than 80 % of the growth of Leptophlebia, S. aerodromia and Siphlonurus occurred on the floodplain. These taxa use the stream channel primarily as a nontrophic refuge for the remainder of the year. Depending upon the year, mayfly production ranges from 1.6 to 2.3 g ash-free dry mass (AFDM)/m 2 of mean inundated wetland area over a 44 to 53 d period. When weighted by the length of the boundary between the sedge meadow and stream, this is equivalent to 7.5-14.0 g AFDM/m 2 of stream channel. Estimates of production for similar streams indicate that this is within the range expected for total annual production by macroinvertebrates in the stream channel. Depending upon year, estimates of prey consumption by S. aerodromia ranged from 36 % to essentially all prey production. Water temperature and predation by S. aerodromia appeared to be key factors influencing the temporal patterns of mayfly production in the Tomah Stream wetland. The physical linkage of the stream and floodplain by the natural flow regime, however, is the fundamental factor determining the productivity of this unusual river-floodplain community.

The sizes, maturity stages and biomass of mayfly assemblages colonizing disturbed stream bed patches in central Kenya

AbstractThe sizes, maturity stages and biomass of mayfly species colonizing disturbed patches on the stream bed surface of the Naro Moru River, Kenya, were determined from June 1993 to January 1994. All maturity stages I–VI+ were present in the pre‐disturbance mayfly assemblages. Colonization of the disturbed patches by mayflies of different maturity stages was continuous, but slow or fast depending on the season and species. The overall post‐disturbance maturity structure of the mayflies colonizing the disturbed patches did not demonstrate any distinct pattern. The majority of Caenis nymphs colonizing the patches in wet season II (November–January) were in emerging maturity stage VI+, whilst the majority of the individuals of Afronurus and Choroterpes (Euthraulus) populations matured from stage I in the wet seasons to stage VI+ in the dry season. Furthermore, the majority of the individuals of Baetis (Nigrobaetis) sp.1 were maturing to stages IV–VI during the wet seasons. Small‐sized mayfly individuals (body length &lt;3.0 mm) of all mayflies colonized the disturbed patches in the majority of numbers. However, although having the highest densities, they contributed a very low biomass compared with the fewer large‐sized nymphs. There was no size gradation in the colonization of the disturbed patches, since all sizes were sampled at all times but in differing proportions. Colonization of the patches by mayflies was not size‐ or maturity stage‐specific. Size distribution patterns could be useful in assessing which mayfly size‐spectra are more or less susceptible to disturbance in streams.

Longevity minimalists: life table studies of two species of northern Michigan adult mayflies

Life table studies were conducted on both sexes of newly emerged subimagoes of the mayfly species, Hexagenia limbata (n=4472) and Ephemera simulans (n=1254), which have two- and one-year life cycles, respectively. The expectation of life at emergence for H. limbata was approximately 2.6 days for both sexes with the last individual (a female) dying on day 8. Expectation of life for E. simulans was 1.6 and 2.0 days for males and females, respectively, with the last individuals (both sexes) dying on day 3. The results reveal that mortality does not occur in one large step in this group of rapidly senescing organisms. Rather deaths are spread over several days when the adult mayflies are maintained under laboratory conditions.

Spatial and temporal niche overlap of two mayfly species (Ephemeroptera): the role of substratum roughness and body size

Intra- and interspecific niche overlap for two mayfly species with similar life cycle timing, Rhithrogena semicolorata and Ecdyonurus sp. gr. venosus, were investigated. The nymphs were classified into 5 classes according to size and spatial overlaps are measured along a substratum roughness gradient. Substratum roughness selection was investigated by defining utilisation curves, optimum and tolerance values of the nymphs in relation to larval growth. Differences between species and size classes within each species were observed. Ecdyonurus sp. gr. venosus dominated on rough substrates, whereas R. semicolorata was most abundant on smooth substrates. An intermediate value of total interspecific substratum roughness overlap (0.49) was found. Higher intraspecific than interspecific overlap values suggested a spatial niche segregation between the two species. The results suggested that the spatial niches measured, were closer to the `fundamental niches' than could be expected if competition was acting on the two studied populations.

Laboratory and field studies of mayfly growth in tropical Asia

Growth of seven species of mayflies in three families (Baetidae, Leptophlebiidae and Heptageniidae) was investigated in the laboratory (Procloeon sp. 2 and Chopralla sp.), in the field (Cinygmina sp. and Baetiella pseudofrequenta), or both (Afronurus sp., Procloeon sp. 1 and Choroterpes spp.). Animals were reared in laboratory tanks and or in field cages at three sites in two Hong Kong (lat. 22° 17'N) streams, Tai Po Kau Forest Stream (TPKFS) and an open and shaded section of the Lam Tsuen River (LTR: LTRO and LTRS, respectively). Growth rates (mg mg -1 d -1 ) in the laboratory ranged from 0.12 (Afronurus sp.) to 0.3 (Procloeon sp. 1), and from 0.059 (Cinygmina sp.) to 0.23 (B. pseudofrequenta) in the field. All species were multivoltine. Baetids could complete more than eight generations a year, heptageniids at least four, and Choroterpes (Leptophlebiidae) up to eight. The influence of food quantity on growth was measured under laboratory and field conditions, while the effect of temperature was studied by rearing mayflies in the field throughout the year. In the laboratory, some mayfly species grew faster when reared on food collected from LTRO than from LTRS but in situ growth rates of Afronurus sp., Cinygmina sp. and Choroterpes spp. were similar in both LTR sites. No significant differences in growth rates among any sites were found for B. pseudofrequenta and Procloeon sp. 1, but growth rates at TPKFS were generally lower than at LTR for most species. Mayfly growth increased linearly with temperature, explaining 23-77 % of the total variation in field growth rates throughout the year.

Longitudinal distribution of macroinvertebrates in two glacier‐fed New Zealand rivers

1. Environmental variables, benthic algal biomass and macroinvertebrate fauna were examined from September 1999 to January 2000 (austral summer) along two glacier‐fed rivers in South Island, New Zealand.2. The rivers were characterized by high flow variability, high turbidity and physically disturbed beds. Water temperature ranged from &lt;1 °C near the glacier margin to 10 °C further downstream.3. Epilithic algal biomass was very low (&lt;0.1 mg m–2) in months characterized by heavy rainfall, but ranged from 1.1 to 14.4 mg m–2 following an extended period with negligible precipitation.4. Abundance and diversity of invertebrates in both rivers was low. Dominant taxa were Chironomidae (Orthocladiinae, Podonominae, Diamesinae), although mayfly species (Deleatidium: Leptophlebiidae) also occurred at most sites. A species of Eukiefferiella (Orthocladiinae) was collected at all sites and was the most abundant invertebrate close to the glacier margins. No meiofauna were found in either river.5. Faunal diversity increased at the lowermost stations where species of Plecoptera, Trichoptera, Coleoptera and non‐chironomid Diptera also occurred.6. The faunas of the two New Zealand rivers conformed to the conceptual model of Milner &amp; Petts (1994) in that taxon richness increased downstream with water temperature. However, invertebrate abundance increased downstream in only one of the two rivers. Also in contrast to the model predictions, Leptophlebiidae and Orthocladiinae, rather than Diamesinae, dominated the fauna at the coldest sites.

THE MAYFLY FAUNA OF NEW YORK STATE (INSECTA: EPHEMEROPTERA)

Abstract A total of 173 species of mayflies, representing 15 families and 45 genera, are reported from the state of New York. First state records for 43 species and 891 new county reports for 129 species are included. Previously published reports are summarized, and pertinent remarks on species are annotated. The occurrence of Dannella provonshai, Heptagenia julia, and Plauditus gloveri in New York represent significant range extensions. The discovery of Epeorus frisoni in New York represents only the second report of the species. Species potentially of environmental concern are noted.

Observations on the biology of Rhabdochona kidderi texensis, a parasite of North American cichlids.

An examination of a sample of benthic invertebrates collected from the Upper San Marcos River in southwestern Texas, USA in September 1999 revealed that the nymph of the ephemeropteran Tricorythodes curvatus served as natural intermediate host of the nematode Rhabdochona kidderi texensis (Nematoda: Rhabdochonidae), an intestinal parasite mainly of the Rio Grande perch (Cichlasoma cyanoguttatum) in this locality; the prevalence of the parasite's third- and fourth-stage larvae in mayflies was 6.8% with the intensity of 1-2 larvae per nymph. Live R. kidderi texensis eggs collected from nematodes recovered from C. cyanoguttatum in Texas were transported to the Czech Republic, where they were used to experimentally infect nymphs of the palaearctic mayfly species Paraleptophlebia submarginata; the development of infective third- and fourth-stage larvae in this experimental intermediate host was completed after approximately 10 days at 19 degrees C. Infected nymphs were fed to aquarium-reared fishes, four Cichlasoma nigrofasciatum and one Oreochromis niloticus, of which only three of the former became infected. The last (fourth) moult of a male nematode was observed in C. nigrofasciatum 23 days p.i. and adult males and gravid females with not fully mature (non-embryonated) eggs in uteri on days 40 and 51 p.i. The prepatent period of R. kidderi texensis is approximately two months.

Stable-isotope determination of mayfly (Insecta: Ephemeroptera) food sources in three tropical Asian streams

Carbon and nitrogen stable isotopes were used to determine the foods assimilated by mayflies in three Hong Kong streams: Tai Po Kau Forest Stream (Forested 1), Shing Mun River (Forested 2), and an open (Open 1) and a shaded section (Shaded 1) of the Lam Tsuen River. Analyses were carried out during both wet and dry seasons. A total of seven mayfly species (Heptageniidae, Leptophlebiidae and Baetidae; four or five species per site) were included. During the dry season, mayflies in the two forest streams (I and 2) fed mainly on autochthonous foods (33-100 %) especially cyanobacteria and Cladophora spp. in Forested 1. During the wet season, the use of allochthonous food increased (13-100 %) in Forested 1 and 2, but the importance of autochthonous foods in shaded streams with ample stocks of detritus was nevertheless surprising. Mayflies in both Open 1 and Shaded 1 derived most of their biomass from a variety of autochthonous foods during both seasons, but epilithon was the dominant wet season food. Moreover, allochthonous foods did not appear to contribute significantly to the diet of mayflies during any season at Shaded 1. When compared with published literature, these results suggest that use of allochthonous foods in tropical streams may be greater than in temperate latitudes where allochthonous energy sources appear to dominate community energy flows in small streams.

New species of Baetidae (Ephemeroptera) from the Upper River Sigi, Usambara, Tanzania

Additional species of mayflies are described from the relatively well-studied fauna of the Upper River Sigi in the East Usambara Mountains of Tanzania. They comprise Cheleocloeon sigiense sp. n. and Centroptiloides ornatus sp. n. A species of Afroptiloides, of which only the adult is known, is figured but not named. The composition of the assemblage of genera known as the Bugilliesia complex is critically examined.

The duct connecting Malpighian tubules and gut: an ultrastructural and comparative analysis in various Ephemeroptera nymphs (Pterygota)

Malpighian tubules proper are connected to the gut by ducts called trunks, the organization of which is described at ultrastructural level in the nymphs of various mayfly species, namely Ecdyonurus venosus (Heptageniidae), Ephemerella ignita (Ephemerellidae), Choroterpes picteti (Leptophlebiidae), and Caenis luctuosa (Caenidae). Trunks are luminal tubes varying in arrangement, number, shape, and length. The main cell type of the trunk wall is represented by cells that are bordered by a thin cuticle along their luminal side (type-A cells). Whereas these cells are exclusive in the long trunks (such as those of C. picteti and C. luctuosa), in the shorter ones (such as those of E. venosus and Ephemerella ignita) cells with a microvillous luminal border (type-B cells) are also encountered. These cells are located close to the entrance of the collecting duct of the Malpighian tubules proper, and their long microvilli form a dense filamentous mesh filling up the lumen. Both cell types exhibit fine structural features that are characteristics of ion-transporting epithelia. Ultrastructural investigations show that trunks are not a simple conducting system but are involved in the regulation of the ionic composition of the primary urine for producing a fluid hypo-osmotic with respect to the hemolymph.

HEAVY METALS STRUCTURE BENTHIC COMMUNITIES IN COLORADO MOUNTAIN STREAMS

The development of field sampling designs that employ multiple reference and polluted sites has been proposed as an alternative to the traditional upstream vs. down- stream approach used in most biomonitoring studies. Spatially extensive monitoring pro- grams can characterize ecological conditions within an ecoregion and provide the necessary background information to evaluate future changes in water quality. We measured physi- cochemical characteristics, heavy-metal concentrations, and benthic macroinvertebrate com- munity structure at 95 sites in the Southern Rocky Mountain ecoregion in Colorado, USA. Most sites (82%) were selected using a systematic, randomized sampling design. Each site was placed into one of four metal categories (background, low, medium, and high metals), based on the cumulative criterion unit (CCU), which we defined as the ratio of the instream metal concentration to the U.S. Environmental Protection Agency criterion concentration, summed for all metals measured. A CCU of 1.0 represents a conservative estimate of the total metal concentration that, when exceeded, is likely to cause harm to aquatic organisms. Although the CCU was less than 2.0 at most (66.3%) of the sites, values exceeded 10.0 at 13 highly polluted stations. Differences among metal categories were highly significant for most measures of macroinvertebrate abundance and all measures of species richness. We observed the greatest effects on several species of heptageniid mayflies (Ephemeroptera: Heptageniidae), which were highly sensitive to heavy metals and were reduced by .75% at moderately polluted stations. The influence of taxonomic aggregation on responses to metals was also greatest for mayflies. In general, total abundance of mayflies and abundance of heptageniids were better indicators of metal pollution than abundance of dominant mayfly taxa. We used stepwise multiple-regression analyses to investigate the relationship between benthic community measures and physicochemical characteristics at the 78 randomly se- lected sites. Heavy-metal concentration was the most important predictor of benthic com- munity structure at these sites. Because of the ubiquitous distribution of heavy-metal pol- lution in the Southern Rocky Mountain ecoregion, we conclude that potential effects of

Heavy Metals Structure Benthic Communities in Colorado Mountain Streams

The development of field sampling designs that employ multiple reference and polluted sites has been proposed as an alternative to the traditional upstream vs. downstream approach used in most biomonitoring studies. Spatially extensive monitoring programs can characterize ecological conditions within an ecoregion and provide the necessary background information to evaluate future changes in water quality. We measured physicochemical characteristics, heavy-metal concentrations, and benthic macroinvertebrate community structure at 95 sites in the Southern Rocky Mountain ecoregion in Colorado, USA. Most sites (82%) were selected using a systematic, randomized sampling design. Each site was placed into one of four metal categories (background, low, medium, and high metals), based on the cumulative criterion unit (CCU), which we defined as the ratio of the instream metal concentration to the U.S. Environmental Protection Agency criterion concentration, summed for all metals measured. A CCU of 1.0 represents a conservative estimate of the total metal concentration that, when exceeded, is likely to cause harm to aquatic organisms. Although the CCU was less than 2.0 at most (66.3%) of the sites, values exceeded 10.0 at 13 highly polluted stations. Differences among metal categories were highly significant for most measures of macroinvertebrate abundance and all measures of species richness. We observed the greatest effects on several species of heptageniid mayflies (Ephemeroptera: Heptageniidae), which were highly sensitive to heavy metals and were reduced by >75% at moderately polluted stations. The influence of taxonomic aggregation on responses to metals was also greatest for mayflies. In general, total abundance of mayflies and abundance of heptageniids were better indicators of metal pollution than abundance of dominant mayfly taxa. We used stepwise multiple-regression analyses to investigate the relationship between benthic community measures and physicochemical characteristics at the 78 randomly selected sites. Heavy-metal concentration was the most important predictor of benthic community structure at these sites. Because of the ubiquitous distribution of heavy-metal pollution in the Southern Rocky Mountain ecoregion, we conclude that potential effects of heavy metals should be considered when investigating large-scale spatial patterns of benthic macroinvertebrate communities in Colorado's mountain streams.

Chronic Effects of an Insecticide, Fenobucarb, on the Larvae of Two Mayflies, Epeorus latifolium and Baetis thermicus, in Model Streams

Effects of the insecticide fenobucarb on 2 mayfly species, Epeorus latifolium and Baetis thermicus, were examined in indoor model streams. Aqueous concentrations of fenobucarb residues in the model streams were 69–71% of its nominal level until 24 h, except at low concentrations (less than 2 μg l−1 in the water) in the water. Chronic effects of fenobucarb on the growth and emergence of Ephemeropteran larvae were examined over 2 months. For concentrations of 1 and 2 μg l−1, the numbers of individuals of the third larval growth stage (average head width ≥3.0 mm) gradually decreased up to 20 days after the applications; the number of emergent individuals also remained 20 to 25 by the end of the experiment. The number of individuals to emerge at 1 to 2 μg l−1 fenobucarb was restricted in the long-term experiment. These results suggest that fenobucarb affects the emergence of this species through disruption of the endocrine system. On the other hand, the number of emergent individuals of B. thermicus at low concentrations of fenobucarb was not significantly less than that in the control.

Edmundsiops hickmani sp. nov., Ojfadens ftater (Tillyard) nov. comb. and description of the nymph of Cloeon tasmaniae Tillyard (Ephemeroptera: Baetidae) from Tasmania

This describes a new species (Edmundsiops hiclemani) of baetid mayfly (Ephemeroptera) from Tasmania, updates the earlier (1936) work by R.J. Tillyard with recognition of a new combination (Offadens frater) and provides the first description of the nymph of Cloeon tasmaniae Tillyard. E.hickmani and 0. frater are common throughout southeastern Australia, whereas C. tasmaniae has only been recorded from Tasmania.

Effects of differing inter-disturbance intervals on the diversity of mayflies recolonizing disturbed sites in a tropical stream

Field experiments to determine the effects of inter-disturbance intervals on the diversity of mayflies recolonizing disturbed subsites in the Naro Moru River, Kenya, were undertaken from June 1993 to January 1994. Stirring, shifting and relocation of streambed substrates by hand was used to delimit physical disturbance, which was also the act of sampling. Continuous disturbance had a distinct depressant effect on mayfly species diversity. No species diversity differences were observed between day and night (one-way ANOVA, p >0.05) at short inter-disturbance intervals of between 10 and 40 min. Medium/intermediate inter-disturbance intervals of between I and 10h had significant effect on species diversity (F (15, 132) = 5.25, p 0.05). The shorter the interval before the next disturbance, the greater was the species diversity decline. The short and long inter-disturbance intervals are important to stream ecosystems since they regulate species diversity in time and space. The increase and/or decrease in species diversity of the mayflies recolonizing the disturbed subsites, and the patterns thereof, may reflect mayfly mobility, especially in foraging for food and search for habitat and refuge.

Irpacaenis, a new genus of Caenidae (Ephemeroptera) from Australia

AbstractA new genus, Irpacaenis, is erected to include three new species of Australian caenid mayflies based on nymphal and subimago characteristics. The genus is diagnosed by weakly sclerotised straight forceps which are not grooved but are hooked apically; styliger plate and associated sclerites weakly sclerotised in the subimago; and, in the nymph, the absence of long setae over much of the body, rugose appearance caused by smooth tubercles which cover the body and legs, the presence of a medial projection on tergite 2 which is long and narrow with the length greater than the basal width, and the presence of a row of short sharp spines on the posterior margins of abdominal tergites 1, 2 and 7–10. The distribution of Irpacaenis extends from northern Queensland down the eastern coast of Australia to the Gippsland area of Victoria.