Survival and growth of early-instar nymphs of Ephemerella subvaria fed various diets

Abstract

In two laboratory tests at 15 °C early-instar nymphs of the mayfly, Ephemerella subvaria were kept on different diets and their survival and growth recorded. The diets were either conditioned maple leaf discs; maple leaf disc remnants + Gammarus faecal material; maple leaf disc remnants + Hesperophylax faecal material; a clump of Cladophora strands or periphytic growth on small stones. A control group received no food. In both the tests, nymphs kept on Cladophora showed significantly (P ⩽ 0.05 or P ⩽ 0.01) higher percentage survival than for those on any other diet and the growth of these nymphs was second only to nymphs given periphyton as a diet. Although the nymphs on a diet of periphyton showed significantly (P ⩽ 0.01) higher growth as compared to those on other food sources, the survival percentage of these nymphs was the poorest, presumably because of food limitation. As expected, a diet of maple leaf discs resulted in significantly higher survival and growth of nymphs as compared to the nymphs not given any food. The results clearly demonstrated that autochthonous sources of organic matter can serve as excellent food for stream invertebrates.