Toxicity of the lampricides 3-trifluoromethyl-4-nitrophenol (TFM) and 2',5-dichloro-4'-nitrosalicylanilide (Bayer 73) to eggs and nymphs of the mayfly (Hexagenia sp.)

Eggs and nymphs of mayflies (Hexagenia sp.) were exposed to the lampricides 3-trifluoromethyl-4- nitrophenol (TFM) and 2',5-dichloro-4'-nitrosalcylanilide (Bayer 73) and to a mixture of 98% TFM and 2% Bayer 73 (TFM-2B) to determine the sensitivity of various life stages to these compounds. Some eggs and newly hatched nymphs survived concentrations of TFM up to 10 mg/L; and nymphs of the other groups tested (7, 16, 23, and 27 mm long) died at concentrations of 5 mg/L or more. Eggs and nymphs were unaffected by Bayer 73 concentrations up to 0.4 mg/L, the highest concentrations tested.