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We investigated the relative importance of dispersal and vicariance in forming the Madagascar insect fauna, sequencing approximately 2300bp from three rRNA gene regions to investigate the phylogeny of Afrotropical small minnow mayflies (Ephemeroptera: Baetidae). Six lineages contained trans-oceanic sister taxa, and variation in genetic divergence between sister taxa revealed relationships that range from very recent dispersal to ancient vicariance. Dispersal was most recent and frequent in species that spend the larval stage in standing water, adding to evidence that these evolutionarily unstable habitats may select for ecological traits that increase dispersal in insects. Ancestral state likelihood analysis suggested at least one Afrotropical lineage had its origin in Madagascar, demonstrating that unidirectional dispersal from a continental source may be too simplistic. We conclude that the Malagasy mayfly fauna should be considered in a biogeographical context that extends beyond Madagascar itself, encompassing trans-oceanic dispersal within multiple lineages.

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Data on the hydrology, chemistry, and benthic invertebrates of the Great Fish River prior to the opening of the Orange River/Fish River interbasin.water transfer scheme in 1977, are compared with similar data for post transfer conditions. As a result of the transfer of water the once irregular seasonal flow of the Fish River has now become perennial. The mean annual runoff of the upper river has increased by between 500 and 800 per cent. Mainly because of abstractions for irrigation, the mean annual discharge of the lower river has changed little, but seasonal flow variation in the lower river has been considerably reduced. The inflow of low salinity water from the Orange River has diluted the highly mineralized Fish River water, reducing concentrations of sodium, magnesium, chloride, and sulphate, but not of calcium or total alkalinity. The invertebrate communities of riffles have changed substantially as a result of the water transfer, and only 33 per cent of taxa identified were common to both pre-and post-transfer surveys. In particular, the dominant chironomid, hydropsychid, and simuliid species have changed, although there is no evidence that overall invertebrate densities have been altered. The most striking change in the fauna has been the replacement of the pre-transfer dominant simuliids (Simulium adersi and S. nigritarse) by S. chutteri, a blood-feeding pest of livestock, which now causes considerable problems to farmers. The major changes in invertebrate species can be attributed to the more permanent flow and increased area of erosionaI habitats.

Morphometric studies show that there are seven larval instars in Simulium chutteri. A guide for separating instars of S. chutteri is included. Seasonal and sexual size variation and seasonal variation in biomass in larvae and pupae of S. chutteri are statistically analysed and discussed. Water temperature is a major factor in determining larval and pupal size variation and duration of the pupal stage. Growth in S. chutteri follows a geometric pattern and is in agreement with previous works on other species. An overlap of larger and smaller larvae at the same developmental stage resulted from the coexistence of early winter and late summer generations, respectively. Larger larvae and pupae can result in autogenous and more fecund adult females. This is important in the population dynamics of this pest species and can lead to sudden unexpected population explosions. It is suggested that population explosions could be controlled by sharply reducing the population of large individuals of S. chutteri in the spring.

Fish predation is one of the driving forces of freshwater invertebrate community structures, with alien predators having a pronounced effect. A quantitative assessment of aquatic invertebrates in the Wit River, Sundays River catchment, Eastern Cape, South Africa, was undertaken to assess the impact of the alien fish Micropterus salmoides on their relative abundance and community structure. Communities in the stones-in-current and marginal vegetation biotopes were sampled in the presence and absence of M. salmoides in late summer (February-April) 2008. Results suggest that the presence of M. salmoides does have an impact on indigenous macroinvertebrate fauna and communities. Community structure in the stones-in-current biotopes did not differ significantly between sections of the river with or without fish. However, there was a significant difference in community structure in marginal vegetation between sections of river. In sections with M. salmoides several large or conspicuous taxa (Odonata, Hemiptera and Coleoptera) were significantly reduced (p < 0.05) or even absent, while cryptic/inconspicuous taxa (Trichoptera, Leptoceridae and Mollusca, Physidae) were significantly more abundant (p < 0.05).

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