Effect of Sublethal Concentrations of Pesticides on the Feeding Behavior of Daphnia magna

Daphnia magna was exposed to sublethal levels(image, image, and image LC50 and LC50) of endosulfan and diazinon to determine the effect of these pesticides on filtration and ingestion rates. The experiments were performed with the unicellular algae Nannochloris oculata in a density of 5 × 105 cells/ml. Prior to these experiments, the acute toxicy of both pesticides was evaluated to calculate the LC50s., The 24-hr LC50 values were 0.62 mg/liter and 0.9 μg/liter for endosulfan and diazinon, respectively. Rates of filtration and ingestion declined with increasing toxicant concentrations after a short exposure of 5 hr. The effective concentration at which feeding rates were reduced to 50% of those in controls (EC50) was calculated for both pesticides. These values were 0.44 and 0.61 mg/liter for filtration and ingestion rates, respectively, in the case of endosulfan and 0.47 and 0.60 μg/liter, respectively, in the case of diazinon.