Life‐history and distribution of Simulium austeni (Diptera: Simuliidae) in relation to phytoplankton in some southern English rivers

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Abstract
SUMMARY. Regular sampling of larval and pupal simuliids in the River Stour (Dorset) showed that Simulium austeni produces a single generation of larvae per year, pupating in late April‐early May. The species is abundant in the middle and lower reaches of the Stour and its larger tributaries, but in nearby rivers of comparable size it is rare or absent, Unlike these other rivers, the Stour supports a true phytoplankton dominated by small centric diatoms (Stephanodiscus hantzschii). Peak concentrations of particulate chlorophyll‐α sometimes correspond with the growth period of S. austeni larvae. The distribution of S. austeni relative to that of phytoplankton is discussed and the importances of suspended bacteria and water chemistry are briefly considered.