Influence of food type on the growth of early and late instars of three mayfly (Ephemeroptera) species

Abstract

Growth of Ephemerella subvaria, Epeorus sp. and Paraleptophlebia sp. were determined while on diets restricted to diatoms, microbially colonized leaves, uncolonized leaves, or cultured bacteria. Early-instar E. subvaria showed significantly higher percent weight increases (>1011 %) on diatom and colonized leaf diets than uncolonized leaves and bacteria, whereas late instars showed significant weight increases only on diatoms: both leaf diets and cultured bacteria produced little growth (<30%) in late instars. Early instar Epeorus larvae showed similar growth responses (20-60% increase) for all four diets in early instars. However. late instars of Epeorus showed significant growth (60% only on diatoms; little or no growth was shown for leaf diets and bacteria. In contrast, early-instar Paraleptophlebia lost weight on diatoms and showed significant growth (ca. 30%) for both leaf diets and bacteria. Late-instar Paraleptophlebia showed a 25 % weight increase for all four diets. Our data suggest that early instars of all three species may rely heavily on detrital food resources, whereas late instars of E. subvaria and Epeorus appear to shift to algal resources; these two species also may occupy different functional-feeding groups at different developmental stages since E. subvaria and Epeorus larvae did shred leaves in their early instars. Paraleptophlebia larvae showed little evidence of leaf-shredding activity but instead appeared to act as detritivores (feeding on fine particulates even from leaf surfaces) throughout their life cycle.