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

The pesticide formulation Excis(R) (1% w/v cypermethrin) is currently regis tered for use in the State of Maine, USA to treat farmed salmon for infesta tions of the copepod parasites, Lepeophtheirus salmonis and Caligus elongat us (sea lice). In Canada, the product has yet to receive regulatory approva l. We have determined the acute lethality of this product to the three larv al stages and the first post-larval stage of American lobster (Homarus amer icanus), a species of significant economic importance in eastern Canada and the northeast United States. The 48-h LC50 (as cypermethrin) is: 0.18 mu g /l for stage I, 0.12 mu g/l for stage II, 0.05 mu g/l for stage III, and 0. 12 mu g/l for stage IV (the first post-larval stage). The differences in se nsitivity among the larval stages are not statistically significant. These data, when interpreted in conjunction with known physical oceanographic dat a and results of chemical dispersion studies, indicate that single anti-lou se treatments are unlikely to result in lobster mortality. However, the sub lethal effects of this product on lobsters and the consequences of repeated exposures have yet to be determined. (C) 2000 Elsevier Science B.V. All ri ghts reserved.