Responses of sea lice to novel parasiticides and their differing modes of action

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Salmon lice, Lepeophtheirus salmonis (Copepoda: Caligidae), are important ectoparasites both ecologically and economically. Sea lice cause multi-million dollar losses to the marine salmon aquaculture industry each year, and can negatively impact wild stocks of salmonids as well. Over the past two decades perhaps the greatest emerging issue with respect to sea lice has been the development of resistance to chemical treatment. All of the major salmon producing countries (i.e. Norway, Scotland, Chile, Canada, etc.) have observed declines in efficacy of anti-parasitic treatments, and development of resistant strains of lice. Within Eastern Canada, the major impact has been observed in reduced efficacy of emamectin benzoate (Jones et al, 2012), and recently our research group has identified louse gene clusters associated with reduced efficacy of this drug in Pacific Canada (British Columbia). Currently there is a lack of compounds of different classes and different modes of action for treatment of sea lice in Canada, however, use of organophosphates and pyrethroids occurs in other countries, and have also exhibited issues with resistance development. In order to target this gap in effective management tools for sea lice globally, Elanco Animal Health has developed an in-feed treatment (lufenuron) against sea lice to be administered at the hatchery and provide long-term protection of salmon against infection at sea. Lufenuron is currently undergoing clinical trials in Canada, Chile and Norway, to determine the protection period conferred by the developmental product. It is the goal of the current work to identify the mode of action (MoA) of lufenuron in sea lice and potential future mechanisms of drug resistance. This will be achieved through (1) Determining physiological impacts of lufenuron on the life cycle of L. salmonis, (2) Identifying genes/genotypes associated with resistance to lufenuron in L. salmonis populations, and (3) Developing a lufenuron-specific modelling framework to identify genetic interactions in different farming regions.