The lethality of the cypermethrin formulation Excis® to larval and post-larval stages of the American lobster ( Homarus americanus)

Abstract

The pesticide formulation Excis® (1% w/v cypermethrin) is currently registered for use in the State of Maine, USA to treat farmed salmon for infestations of the copepod parasites, Lepeophtheirus salmonis and Caligus elongatus (sea lice). In Canada, the product has yet to receive regulatory approval. We have determined the acute lethality of this product to the three larval stages and the first post-larval stage of American lobster ( Homarus americanus), a species of significant economic importance in eastern Canada and the northeast United States. The 48-h LC50 (as cypermethrin) is: 0.18 μg/l for stage I, 0.12 μg/l for stage II, 0.06 μg/l for stage III, and 0.12 μg/l for stage IV (the first post-larval stage). The differences in sensitivity among the larval stages are not statistically significant. These data, when interpreted in conjunction with known physical oceanographic data and results of chemical dispersion studies, indicate that single anti-louse treatments are unlikely to result in lobster mortality. However, the sublethal effects of this product on lobsters and the consequences of repeated exposures have yet to be determined.