Life History of Thalerosphyrus (Ephemeroptera: Heptageniidae) in Tropical Rivers with Reference to the Varying Altitude

The life history and the influence of environmental parameters on Thalerosphyrus were investigated in two first-order rivers-the Batu Hampar River and the Teroi River of Gunung Jerai, Kedah-in northern peninsular Malaysia. Based on nymphal body length, Thalerosphyrus was found to be trivoltine in both rivers, regardless of the altitudinal difference, but its population abundance was four times higher in the Teroi River, presumably related to its better survival in the lower water temperature. At least nine instars of Thalerosphyrus were detected in the field-collected nymphs. Its life cycle was completed within 2.5-3.0 months, with overlapping cohorts and continual emergence of up to 3 months. The main driving factors of the high abundance of Thalerosphyrus were the water temperature and habitat quality.