Sensitivity of Daphnia pulex of Different Ages to the Insecticide Carbaryl

Abstract

We evaluated differences in the sensitivity of Daphnia of different ages to an insecticide in acute toxicity tests. The sensitivity was higher in younger individuals and lower in older ones, and was correlated with body length. However, first- instar individuals < 12 h old were less sensitive than those 12 to 24 h old. This phenomenon seems to be related to the timing of molting. Our results suggest that the sensitivity of a Daphnia population to toxic chemicals depends on its life stage composition, which should be considered in evaluating the effects of chemicals on populations in the natural environment.