Summary
1. Dispersal of adult stream insects may be of considerable importance in regional population dynamics and colonisation of new sites, but quantifying the rate and extent of dispersal is ...difficult.
2. We used stable isotope (15N) enrichment to mark more than 1.5 million larval stoneflies (Leuctra inermis) before they emerged from an upland stream in the Plynlimon area of mid‐Wales, in order to determine directly the rate and pattern of inter‐site dispersal.
3. A small number of isotopically enriched adult stoneflies were captured in samples taken at adjacent streams between 800 m and 1.1 km away from the source population, including a headwater of a different river system.
4. The distribution of marked individuals suggested that wind influences dispersal direction in the uplands, but the low number of captures limits our ability to draw firm conclusions.
5. This is the first direct demonstration of dispersal of insects between streams. The dispersal distances recorded were significantly greater than those suggested by previous direct studies, but much more consistent with indirect studies based on genetic differentiation of populations.
Two new species of Rhopalopsole Klapálek from China are described: Rhopalopsole exiguspina Du & Qian, sp. n. and Rhopalopsole ampulla Du & Qian, sp. n., which were collected in Guizhou province, ...China.
1. Emergence and inland dispersal of adult stoneflies (Plecoptera) and caddisflies (Trichoptera) from Broadstone Stream, an acidic and iron‐rich stream in southern England, were studied over 10 ...months in 1996–1997. Fifteen pyramidal emergence traps were placed randomly in a 200‐m stretch. Three Malaise traps were placed above the stream and six more on each side (one wooded, one open) along a transect at distances of 1, 15, 30, 45, 60 and 75 m from the channel.
2. More than 16 000 stoneflies, belonging to 11 species, and just under 400 caddisflies (22 species) were caught. Four dominant stoneflies (Leuctra fusca, Leuctra nigra, Leuctra hippopus and Nemurella pictetii) accounted for 96% and 95% of the catches in the emergence and Malaise traps, respectively. Two caddisflies (Plectrocnemia conspersa and Potamophylax cingulatus) accounted for 63% of the catch in the Malaise traps. Few caddisflies were taken in emergence traps.
3. The emergence periods of L. fusca, L. nigra and L. hippopus were well‐defined and unimodal, whereas that of N. pictetii was prolonged and erratic. Overall, more females (1285) emerged than males (740).
4. Female stoneflies and caddisflies were in the majority in the Malaise traps above the stream. On land, significantly more females than males of L. fusca, L. nigra and P. cingulatus were caught. The sex ratio of the remaining species did not deviate significantly from 1:1.
5. The three Malaise traps placed above the stream caught most of the stoneflies though there was also dispersal away from the channel, the numbers caught declining with distance. Exponential models explained between 67% and 99% of the variation in numbers of individuals with distance from the channel in the four common stoneflies. Half the individuals went less than 11–16 m from the stream, while 90% travelled less than 51 m. Significantly more L. nigra and N. pictetii were caught in the woodland than on the open side, whereas L. hippopus showed no overall preference for either side.
Adult males and females of Leuctra duplicata Claassen, 1923 and L. maria Hanson, 1941, the two proposed members of the L. duplicata group, were compared using standard light microscopy and scanning ...electron microscopy. Characteristics of the male paraprocts and female subgenital plate of L. duplicata are consistent across the broad range of this common species and allow for easy differentiation from L. maria. Distribution maps based on material examined are provided for both species.
1. Physico‐chemical conditions and benthic macroinvertebrates were studied in two adjacent alpine streams in the Tyrolean Alps, Austria, for 2 years, and aquatic insect emergence was recorded for 1 ...year.
2. In the spring‐fed system, maximum discharge and increased concentrations of suspended solids, nitrate and particulate phosphorus occurred during snowmelt in June. In the glacier‐fed stream, high discharge and strong diel fluctuations in flow and concentrations of suspended solids created a harsh and unstable environment during summer. Glacial ablation, variation in groundwater inflow, and water inputs from tributaries draining calcareous rocks caused water chemistry to vary both seasonally and longitudinally in glacier‐fed Rotmoosache.
3. A total of 126 aquatic or semi‐aquatic invertebrate taxa were collected, 94 of which were found in the glacier‐fed stream and 120 in the spring‐fed stream. Chironomid abundance was 2–8 times and taxa richness 2–3 times lower in the glacier‐fed stream than in the spring‐fed stream, as was the number of chironomid taxa (72 versus 93 total).
4. These results broadly support the conceptual model by Milner & Petts (1994) concerning glacier‐fed stream systems. However, single samples and seasonal means showed relatively high invertebrate abundance and richness, especially during winter, indicating a considerable degree of spatial and temporal variability.
5. We suggest that the seasonal shifts from harsh environmental conditions in summer to less severe conditions in autumn and a rather constant environment in winter are an important factor affecting larval development, life‐history patterns and the maintenance of relatively high levels of diversity and productivity in glacier‐fed streams.
Within the investigated river basins the deforestation ranged from 0-45.5%, dependent on the amount of windstorm damage. Our water temperature readings revealed that the canopy elimination above the ...streams in the areas damaged by the windstorm caused increase in daily and annual water temperature and also wider daily water temperature range, than those in the undisturbed reference stream, which caused the decline of cold stenotherm species abundance. The stream basins deforestation was collinear with FPOM and UFPOM concentrations, water temperature gradient and nitrate concentrations. Statistical analysis showed that size of stream, conductivity, catchment area and discharge were negatively correlated with the stonefly mesotherm ratio and nitrate contents. Higher average concentrations of nutrients (like NOâ»â) in samples from some streams are a consequence of their mobilization from disturbed forest soils due to the windstorm. Most streams located in the deforested area were found by us in a higher trophic status, especially due the particulate organic matter (POM) content and biofilms amount, what caused increase in some functional feeding groups occurrence (collectorgatherers, scrapers and mainly predators). Stream degradation positively correlated with the percentage of deforested area, ratio of eurytherm taxa, transported organic matter, dissolved organic matter, and biofilms occurrence. The conductivity values measured in water samples were collinear with alkalinity and pH values and increased with watersheds areal extent. We established environmental variables influenced by the windstorm event along the catchment degradation gradient using measurable characteristics of stonefly assemblages and metrics. The proportion of the Leuctridae family and the Nemoura genus expressed as the LN áµ¢âdââ (1) shows a negative correlation with part undisturbed forested areas and channel stability, and positive correlation with stream erosion (expressed as the TAM quantity) in river basins. Proportion of shredders among the investigated streams was significantly higher in deforested streams, and shows lower stability of stonefly community in these habitats, where significantly fluctuate channel stability, water temperature and discharge of these streams.
A distinct new species of Rhopalopsole, R. fengyangshanensis, in the family Leuctridae is described. Its diagnostic characteristics are discussed with the closely related congener R. sinensis.
The stonefly genus Zealeuctra (Plecoptera: Leuctridae) is endemic to the central and eastern Nearctic regions and is presently comprised of 10 species. Scanning electron microscopy (SEM) was used to ...examine and redescribe two important diagnostic features typically used to identify and define the adult male stage: the large, anteriorly-recurved epiproct and the medial cleft of the ninth abdominal tergite. SEM was also employed to depict the posteromedial portion of female 7(th) sternum. A new species, Z. ukayodi sp. n., is described from the Cumberland Plateau region of northeastern Alabama and Tennessee. The new species appears superficially similar to Z. talladega Grubbs, but is easily differentiated by characteristics of the male medial cleft. An updated taxonomic key to the males of Zealeuctra is provided.
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