BACTERIVORY BY DEPOSIT-FEEDING MAYFLY LARVAE (STENONEMA SPP)

1. The importance of bacteria in the diet of deposit-feeding mayflies (Stenonema spp.) from the Ogeechee River, a sixth order lowgradient blackwater river in Georgia, U.S.A., was determined. Stenonema are abundant and productive on snags in blackwater rivers in the southeastern Coastal Plain of the U.S.A. Bacteria are abundant in the seston in this river, and are a potentially important food source. 2. Naturally occurring seston was fed to Stenonema larvae after bacterial DNA in the seston was labelled with methyl-[3H]thymidine. Larval respiration measurements and growth rate estimations were used to compare the amount of bacterial carbon assimilated and retained in larval tissue to the carbon requirements of the larvae. 3. Stenonema larvae incorporated 8.7 x 10(7) +/- 1.3 x 10(7) bacteria larva-1 h-1. This was equivalent to 93 +/- 6% of their daily growth, and 47 +/- 3% of their total daily carbon needs. Larger larvae incorporated more bacterial biomass, but mass specific incorporation was not related to size. Ingestion of bacteria while eating seston accumulated on snags appears to be an important component of the diet of Stenonema larvae in these rivers.