Response of Representative Aquatic Insects to Selected Chemical Vegetation Control Agents

Abstract

Static bioassays were used to determine the effect of selected herbicides and plant growth retardants on the nymphs of three mayfly species, Potamanthus neglectus, Ephemerella dorothea and Stenonema vicarium. Initial exposures were conducted over a 96-hour period at 12.8 + 0.5 C. Later experiments used an identical 96-hour exposure, followed by a (second phase) 7-day observation period. Response of the nymphs to DDT reference insecticide) was calculated in terms of a median lethal concentration (LC50). Following a 96-hour exposure to this insecticide, P. neglectus appeared to be the most sensitive, followed by S. vicarium and E. dorothea, respectively. Results of the two phase experiments indicated that the majority of the compounds tested in this investigation had little effect on P. ne,alectus. The survival of S. vicarium was significantly reduced at 3, 5, and 7 days following a 96-hour exposure at 1.0 and 10.0 ppm of paraquat, 2,4,5-T and CHE-8728. The mayfly species which may provide the greatest amount of significant data in future testing, and the use of ecdysis as a toxicological criterion are projected from laboratory results.