Effects of dimilin on the blue crab,Callinectes sapidus,in shallow-water habitats

Diffubenzuron (Dimilin) is used as an insecticide for control of the gypsy moth. Because it is a chitin synthetase inhibitor, it can be a potential threat to other arthropods, including crustaceans. We used a static renewal testing paradigm to determine the LC₅₀ of Dimilin WP-25 to juvenile blue crabs (carapace width: 25–60 mm). Both molt stage of dose frequency effect toxicity. When we exposed the crabs at random molt stages, LC₅₀=3.5 mg l^?1. When crabs were exposed on the day of molt, LC₅₀=300 μg l^?1. If initial exposure occurred on the day of molt and the crabs were subsequently exposed to repeated doses, LC₅₀=18.5 μg l^?1. Effects were age and molt-stage sensitive. We include a review of the data available on Dimilin effects in the marine and estuarine environments.