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.
