The diet of Cercobrachys winnebago (Ephemeroptera: Caenidae) in two western Oklahoma sandy bottom streams

Cercobrachys winnebago nymphs inhabit the fine, sandy sediments of streams in western Oklahoma.  Sand is an unusual habitat for mayfly nymphs, and so our goal was to determine the diet of C. winnebago in this substrate.  A total of four collections in two streams were made in July and August 2012. The gut contents of individual nymphs were removed, placed on a slide, and covered with a gridded cover slip. The contents of 26 randomly chosen grids were counted on each slide and the results expressed as percent occurrence. The three most common items in the gut were UFPOM (82.9%), sand (12.3%), and VFPOM (2.4%). All other categories (FPOM, diatoms, unicellular algae, filamentous algae, and animal fragments) occurred less than 1%. These results were consistent among nymphs from both streams and all four sampling dates.  In comparing the composition of the gut contents to that of the substrate, nymphs in both streams had a higher percentage of UFPOM and a lower percentage of sand.