Quantitative studies on the eggs of Simulium (Simulium) ornatum Meigen and Simulium (Wilhelmia) equinum L. in a chalk stream in southern England

The egg masses of Simulium ornatum, S.equinum and S.vernum are described and information is given on numbers of eggs per egg mass and the size and number of batches laid by individual females. The oviposition sites were studied in relation to water velocity, wind speed and direction. The incubation periods at different river temperatures and the effects of desiccation on percentage hatch and incubation times were investigated. The numbers of eggs laid were assessed for the winter generations of S. ornatum and S.equinum. The relevance of these to the overall production estimates is discussed