Abstract

In Chile, there are currently eight authorized pharmaceutical chemical compounds for the control of sea lice (Caligus rogercresseyi), namely emamectin benzoate, diflubenzuron, lufenuron, hexaflumuron, hydrogen peroxide, deltamethrin, cypermethrin and azamethiphos; however, being this range of tools considered scarce, moreover, loss of sensitivity to some of these compounds have been described in previous studies. Imidacloprid is a neonicotinoid synthetic insecticide that was authorized in Norway in 2021 and has revealed good efficacy in controlling Lepeophtheirus salmonis on salmon farms; however, it has not been authorized for use in Chile. Therefore, in this study, we investigated the efficacy of imidacloprid on the copepodite and adult stages of C. rogercresseyi, which, to our knowledge, has not been investigated in previous studies. We observed that imidacloprid immobilized the parasite at both stages; however, adults were able to recover after the exposure, with 50 % of the adults exposed to concentrations <40 ppm for 24 h recovering, suggesting that a concentration > 20 ppm is required for 100 % mortality of this parasite. In contrast, the copepodite stage was immobilized at 20 ppm, suggesting that copepodites are more sensitive to imidacloprid than the adults. Further studies are required to understand the biological responses of the different stages of C. rogercresseyi to design effective control strategies, improve our understanding of the mechanisms of imidacloprid, and determine the optimal concentrations for control of the parasite.