Life history and ecology ofStenonema modestum(Banks) (Ephemeroptera: Heptageniidae) in Virginia, USA

Abstract

Abstract The life history and ecology of Stenonema modestum was investigated in the North Anna River, a 5th order stream in the Piedmont Physiographic Province of Virginia. S. modestum subimagines emerged in late‐afternoon to early‐evening from April to October. The duration of the subimago stage was ca. 24 hrs. There was seasonal size variation among adults with larger individuals emerging in the spring. There was also seasonal fluctuation in fecundity positively correlated with the seasonal variation in adult size. Nuptial flights occurred just before dusk with males forming swarms of 30–50 individuals above large riffles. Copulation occurred in the air. 5. modestum exhibited a multivoltine life cycle. Most of the overwintering brood emerged in April and deposited eggs; larvae from these eggs grew through the summer and emerged in mid‐August. Sporadic emergence of stragglers from the overwintering brood occurred throughout June and July; larvae from these eggs emerged in September and October. It appears that differential egg hatching was responsible for the continuous emergence pattern. There were at least 14 to 15 instars for the overwintering brood. Larvae were found most frequently under loose cobble and boulders. Larvae of S. modestum were opportunistic generalists in their feeding habits, primarily ingesting detritus and diatoms and occasionally early instars of Chironomidae.