Combined effects of the pesticide spinetoram and the cyanobacterium Microcystis on the water flea Daphnia pulex

Spinetoram is one of the most worldwidely used pesticides for its high insecticidal efficacy and low human toxicity. Following the large usage of spinetoram, the ecotoxicity and environmental risks to aquatic ecosystems have call for urgent study. In the present study, we investigated the combined effects of spinetoram and the harmful alga Microcystis aeruginosa in freshwater, on survival and reproduction of Daphnia pulex. Acute toxicity test of spinetoram resulted in negative effects on survival, with a 48-h LC50 value of 37.71 μg L-1. Under the long-time exposure to environmentally relevant concentrations (0.18 and 0.35 μg L-1) of spinetoram and a low composition of Microcystis (30%) in the diet, D. pulex showed both shorter longevity and lower fecundity; the time to first brood also increased. At population level, carrying capacity was highly decreased by spinetoram and Microcystis, whereas a significant decrease of intrinsic growth rate was observed at 0.35 μg L-1 spinetoram with 30% Microcystis as food. The present study highlighted that pesticide spinetoram had highly toxic effects on D. pulex and could reduce the tolerance of D. pulex to M. aeruginosa, causing great effects on D. pulex population in natural waterbodies.