Beyond insects: High sensitivity of the water fleas to insecticides and implications for ecotoxicological assessment.

Although many model species are widely used in toxicity testing, the sensitivity and ecological relevance of water fleas in the genus Simocephalus remain underexplored. We compiled acute toxicity data for Simocephalus, 73.1% involving insecticides, and compared their responses with those of other aquatic taxa. Simocephalus were generally more sensitive to insecticides than several major groups, including insects, their intended targets. Although they showed higher sensitivity than Daphnia magna, the differences from crustaceans overall were modest. Species sensitivity distributions for chlorpyrifos indicated that hazardous concentrations for 5% of water fleas and crustaceans were lower than values derived from other taxa or pooled datasets, suggesting limited insecticide selectivity toward these groups. Beyond their high sensitivity, Simocephalus offer practical advantages, including broad distribution, compatibility with standard test conditions, suitability for physiological assays, and strong cross‑taxa sensitivity correlations. These attributes position Simocephalus as a valuable complement to standard water-flea models in targeted ecotoxicological applications.