Ovipositional behaviour of Simulium argyreatum and S. variegatum and its relationship to infection by the fungus Erynia conica (Entomophthoraceae)

1. At two sites in Devon S. argyreatum and S. variegatum only oviposited on water‐splashed boulders. The oviposition season was from 15 March to 9 November at Steps Bridge and from 28 March to 7 December at Fingle Bridge. Flies laid eggs only during a brief period after sunset. 2. Flies infected with the fungus E. conica returned to the oviposition sites at the same times as healthy flies, but infected flies appeared to be unable to lay eggs. 3. At least 10.9% of healthy flies were found to have infective conidia of E. conica on their wings after laying eggs.