The loss of sensitivity to emamectin benzoate recorded in Caligus rogercresseyi in the Region X in Chile (41(sic)46'S72(sic)56'W; 43(sic)07'S73(sic)38'W) has been attributed to the exclusive use of this product to control sea lice for more than seven years. In order to evaluate the sensitivity through successive generations of lice, a study was carried out between August 2006 and April 2007. Seven successive generations from a presumably resistant population of C. rogercresseyi were cultivated in the laboratory without the selection pressure of the antiparasitic drug. Results of the bioassay applied to the progenies showed that there was no recovery of sensitivity over the seven inbred generations studied. This may point to a long-standing resistance problem against emamectin benzoate.

This study was carried out as a part of the Project Fondef DOI1255, with financial support by Conicyt. The authors thank to Francisca Erranz for her assistance and help with the Caligus cultivation.

Fondef [DOI1255]; Conicyt

sbravo@uach.cl

FONDEF

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