Toxicities of Aldrin and Dieldrin to the Freshwater Ostracod Chlamydotheca arcuata12

Acute toxicities of various mixtures of aldrin and dieldrin against laboratory-reared, insecticide-free ostracods, Chlamydotheca arcuata (Sars), were determined. The 24-hr immobility EC50 values were 1.15 and 2.45 parts per billion for aldrin and dieldrin, respectively. Bioassay results from using combinations of aldrin and dieldrin demonstrated no synergism or potentiation with respect to the 2 insecticides. Ostracods which were laboratory-reared in the presence of insecticide were also tested to determine if increased resistance or sensitivity to the chemicals had occurred by virtue of chronic exposure. Sublethal exposure to either insecticide through several generations produced populations which were more susceptible to both insecticides. In all instances, aldrin was about twice as toxic as dieldrin.