Rapid Communication / Communication RapideEmamectin benzoate induces molting in American lobster, Homarus americanus

Emamectin benzoate (nominal dose 1 μg·g body weight–1) caused female American lobster (Homarus americanus) to enter proecdysis and molt prematurely (44% vs. 0% of the control lobster, P < 0.001). Lobster bearing eggs when proecdysis was induced aborted their broods. This chemical is the active ingredient in a new feed additive being used to control sea lice (Lepeophtheirus salmonis and Caligus spp.) infestations on farmed salmon (predominantly Salmo salar). The response of the American lobster to emamectin benzoate was unexpected, as avermectins inhibit or delay ecdysis in insects. We hypothesize that emamectin benzoate is interfering with the neuropeptides that modulate the production of molting hormone in lobster and that the diametric response of insects and lobster to this chemical is due to the difference in the neuroendocrine control of the molting glands of these two groups of arthropods (inhibitory in crustaceans, but stimulatory in insects). This is the first report of a crustacean molting prematurely in response to chemical exposure and the first report that a GABAergic (γ-aminobutyric acid) pesticide can cause premature molting in an arthropod.