Life cycle and secondary production of two mayflies Leptophlebia sp and Ephemera sp in Heizhuchong stream, Hubei, China

From June 2003 to June 2004, an investigation on the life cycle, production and trophic basis of dominant species of macrozoobenthos community in a second-order river of the Hanjiang River basin, Hubei, China was carried out. The results showed that the dominant species Leptophlebia sp. and Ephemera sp. appeared to develop two generations per year, and there was a small overlap in the two generations of both species. The pupation of Leptophlebia sp. mainly occurred in autumn and winter, while pupation of Ephemera sp. mainly took place in summer and winter. The standing stocks of the Leptophlebia sp. population and Ephemera sp. population had two peaks in a year. The cohort production and cohort P/B ratio of the Leptophlebia sp. population estimated by size frequency method were 19.018 1 g/m(2).a and 5.7 respectively, while its annual production and P/B ratio were 38.036 2 g/m(2).a and 11.4. The cohort production and cohort P/B ratio of the Ephemera sp. population were 38.015 9 g/m(2).a and 5.9, while its annual production and P/B ratio were 76.031 8 g/m(2).a and 11.8.