Life-cycle and production of the burrowing mayfly, Ephemera danica: a new method for estimating degree-days required for growth.

A maximum likelihood method was used to estimate the number of degree-days required to complete E. danica nymphal growth in the River Tud, Norfolk. Minimum threshold temperatures for growth were 2.6oC for males and 3.1oC for remales. From the estimates of degree-days required to reach maturity and the temperature regime of the study site, it was concluded that some larger males should emerge as adults in 1yr, whereas the rest, and all females, should take 2yr to mature. This agrees with the pattern observed in size-frequency distribution of E. danica nymphs throughout the year. Annual population production of the 2yr classes combined was 5.58g dry weight m^-2yr^-1, with the older year-class contributing approx 85% of the total. Females accounted for 60-70% of production. Monthly production in summer was as much as 10- times that in winter. Production biomass ratios showed relatively low values (<2.1), a pattern that may be general in semi-voltine species.-from Author