Growth Rates of Mayflies in a Subtropical River and Their Implications for Secondary Production

Mayflies were grown in artificial airlift streams on the bank of the Ogeechee River, Georgia, to estimate their productivity rates. Natural conditions were simulated in the streams by (1) providing flowing water pumped from the river as a natural food source, and (2) immersing the streams in large ambient temperature tanks to sustain diel temperature patterns. Early instars of Stenonema spp., Baetis spp., and Tricorythodes sp. were introduced into streams and their development was followed through late instars or to emergence. The daily instantaneous growth rate (g) was 0.265 mg mg⁻¹ d⁻¹ for Baetis, 0.123 for Stenonema, and 0.162 for Tricorythodes during summer months (mean daily temperature = 27.5°C). These rates allow Baetis to complete development in about 19 d in these warmwater rivers, Stenonema in about 41 d, and Tricorythodes in about 31 d. Each of these taxa is capable of completing several generations over a 6-mo period in which stream temperatures are >20°C. Calculation of instantaneous growth rates (or larval development times) of fast-growing insects in critical to estimation of their production. Approximations of 6-mo production/biomass (P/B) ratios range from 22 for Stenonema to 48 for Baetis. According to our analyses, mayflies in warmwater systems have considerably shorter development times and higher biomass turnover rates than most previous studies in streams have shown.