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Representative samples of biota collected relative to environmental gradients are important for measuring present distributions and predicting shifts in distribution of taxa in response to climate change or reduced river connectivity. Based on river ecology theory and established measures of species diversity, we present a method to identify suitable river segments for sampling and monitoring changes in taxon diversity. Alpha and beta diversities of selected aquatic macroinvertebrates were assessed in seven South African rivers. Data were drawn from historical and field samples and represented longitudinal species patterns down longitudinal river axes. Representative sampling sites were identified using a logistic regression model to predict the probability of site pairs that were more than 50% similar as a function of up-/downstream distance. Alpha diversities peaked in the upper third of river lengths; beta diversities showed predictable exponential decay rates down river axes up to and excluding the start of estuarine conditions. Application of the model to a 370-km long river indicated that 14 sites should be selected for sampling to capture overall biodiversity patterns. Additional factors, such as confluences tributaries, which influence alpha diversity at sites, are identified and incorporated into site selection. [ABSTRACT FROM AUTHOR]

A collection of microcaddisflies from sites on the Cuito, Cuanavale, Cuembo, Cuando, Cubango, and Lungue Bungo Rivers in Angola has yielded seven new species and led to new records for a further five species. The new species include Hydroptila cuembica sp. nov., Hydroptila moxica sp. nov., Oxyethira palisada sp. nov., Orthotrichia ferreirae sp. nov., Or. meyi sp. nov., and Or. mlamboi sp. nov., and another species for which we erect a new genus, Aenigmatrichia asymmetrica gen. et sp. nov. The new records are for Catoxyethira kunenica Mey de Moor 2019, Hydroptila brigittae Gibon 1987b, Hydroptila cruciata Ulmer 1912, Hydroptila maoae Gibon, Guenda, Coulibaly 1994, Oxyethira sechellensis Malicky 1993, and a larva identified as that of a species of Tricholeiochiton. Beyond the known Angolan microcaddisfly fauna we resolve several taxonomic problems: We refer to Orthotrichia a species described by Jacquemart in Hydroptila, to become Orthotrichia trifurcata (Jacquemart 1962), comb. nov., with Orthotrichia hydroptiloides Wells Andersen 1995 (from Tanzania) as a junior synonym; and we recognise Orthotrichia kivuensis Jacquemart 1956 (from Bukana, on Lake Kivu) as a junior synonym of Or. sanya Mosely 1948a from the Orange and Fish rivers. A list is given of the 16 microcaddisfly species now known from Angola: Representation is probably typical of sand and silt-based streams and pools, with the exception of Catoxyethira and Orthotrichia.

Background: Baetis harrisoni Barnard is a mayfly frequently encountered in river studies across Africa, but the external morphological features used for identifying nymphs have been observed to vary subtly between different geographic locations. It has been associated with a wide range of ecological conditions, including pH extremes of pH 2.9-10.0 in polluted waters. We present a molecular study of the genetic variation within B. harrisoni across 21 rivers in its distribution range in southern Africa., Results: Four gene regions were examined, two mitochondrial (cytochrome c oxidase subunit I [COI] and small subunit ribosomal 16S rDNA [16S]) and two nuclear (elongation factor 1 alpha [EF1α] and phosphoenolpyruvate carboxykinase [PEPCK]). Bayesian and parsimony approaches to phylogeny reconstruction resulted in five well-supported major lineages, which were confirmed using a general mixed Yule-coalescent (GMYC) model. Results from the EF1α gene were significantly incongruent with both mitochondrial and nuclear (PEPCK) results, possibly due to incomplete lineage sorting of the EF1α gene. Mean between-clade distance estimated using the COI and PEPCK data was found to be an order of magnitude greater than the within-clade distance and comparable to that previously reported for other recognised Baetis species. Analysis of the Isolation by Distance (IBD) between all samples showed a small but significant effect of IBD. Within each lineage the contribution of IBD was minimal. Tentative dating analyses using an uncorrelated log-normal relaxed clock and two published estimates of COI mutation rates suggest that diversification within the group occurred throughout the Pliocene and mid-Miocene (~2.4-11.5 mya)., Conclusions: The distinct lineages of B. harrisoni correspond to categorical environmental variation, with two lineages comprising samples from streams that flow through acidic Table Mountain Sandstone and three lineages with samples from neutral-to-alkaline streams found within eastern South Africa, Malawi and Zambia. The results of this study suggest that B. harrisoni as it is currently recognised is not a single species with a wide geographic range and pH-tolerance, but may comprise up to five species under the phylogenetic species concept, each with limited pH-tolerances, and that the B. harrisoni species group is thus in need of taxonomic review.

The monotypic South African alderfly genus Leptosialis Esben-Petersen, 1920 is reviewed and Leptosialis africana Esben-Petersen, 1920 is redescribed. In the process a new species of alderfly Leptosialis necopinatasp. n. from the Eastern Cape and KwaZulu-Natal provinces of South Africa is recognised and described. Within Sialidae the new species most closely resembles Leptosialis africana. A key to the two species of Leptosialis using both adult and larval characters is provided.

Two trials to test the efficacy of Bacillus thuringiensis Berliner var. israelensis de Barjac (serotype H-14) against target simuliid and non-target aquatic invertebrates were undertaken in the Vaal River near Warrenton in South Africa. In the 1st trail an application of 1,6 ppm/10 min of B. thuringiensis resulted in a significant (P less than 0,05) reduction of simuliid larvae in rapids 70 m below the treatment point 40 hours after its application. Further downstream the larvicide was ineffectual because the low flow of the river (6 m3/s) allowed the Bacillus pores to settle out in calmer stretches. The 2nd trial was carried out upstream of small rapids with a calculated flow of 0,5 m3/s at a spore concentration of 2,3 ppm/7 min. The effect of B. thuringiensis on the benthic population density and drift activity of the benthos was recorded. A high mortality of simuliid larvae and Ephemeroptera was observed 35 m below the application point 9 hours after the application of the larvicide. The mortality in Ephemeroptera was partially due to the handling of these animals. Population densities of simuliid larvae in the treated rapids decreased 18 hours after application of the larvicide, but small simuliid larvae showed a numerical increase again after 72 hours, indicating rapid recolonization from drifting larvae. Tanytarsine Chironomidae decreased after the application of B. thuringiensis, but most other fauna either increased or did not decrease significantly (P greater than 0,05). Within 43 minutes after treatment of the rapids with the larvicide, simuliid drift increased more than sixtyfold, revealing the immediate irritating effect of the product on the target organisms.(ABSTRACT TRUNCATED AT 250 WORDS)

Bacillus thuringiensis Berliner var. israelensis de Barjac (Serotype H-14) (B.t.i.) at a concentration of 1.6 ppm/10 min and a toxicity of 1500 AAU/mg was tested against Simulium chutteri Lewis larvae in the Orange River near Prieska, South Africa. Samples of benthic fauna from the stones-in-current biotope were collected before application of the product and at various intervals up to 80 h afterwards at 4 stations from 200 m to 11 km downstream of the application site. Fauna drift increased slightly after the arrival of the Bacillus at 2 stations 1.4 and 6 km respectively downstream of the application site. Large numerical decreases in benthic simuliid larval numbers after the application of B.t.i. in the Orange River were not statistically different (P greater than 0.05). This indicated that the size of replicated samples that showed significant decreases (P less than 0.05) of simuliid numbers in the Vaal River was not adequate to show statistical differences in the Orange River. The quantity of dead larvae on stones collected from rapids after application of the B.t.i., and the numerical decreases found by comparing median values of larval counts on stones indicated that B.t.i. effectively killed simuliid larvae. Three days after application of the Bacillus, recruitment of small simuliid larvae on stones 1.4 km downstream of the application site was discernible again. Tanytarsini were also numerically reduced after B.t.i. application. At a flow rate of 38 m3/s B.t.i. was visibly effective in killing S. chutteri up to 6 km downstream of the application site and statistically significant decreases (P less than 0.05) in numbers of larvae were seen at a site 11 km downstream of the application site.(ABSTRACT TRUNCATED AT 250 WORDS)