Maternal inheritance of deltamethrin resistance in the salmon louse Lepeophtheirus salmonis (Krøyer) is associated with unique mtDNA haplotypes

Abstract

Parasitic infections by the salmon louse, Lepeophtheirus salmonis (Krøyer), cause huge economic damage in salmon farming in the northern hemisphere, with combined treatment costs and production losses in 2014 having been estimated at US$ 350 million for Norway (annual production 1.25 million tonnes). The control of L. salmonis relies significantly on medicinal treatments, supplemented by non-pharmacological approaches. However, efficacy losses have been reported for several delousing agents, including the pyrethroid deltamethrin. The aim of the present study was to analyse the genetic basis of deltamethrin resistance in L. salmonis. Deltamethrin median effective concentrations (EC50) were 0.28 μg L-1 in the drug susceptible L. salmonis strain IoA-00 and 40.1 μg L-1 in the pyrethroid resistant strain IoA-02. IoA-00 and IoA-02 were crossed to produce families spanning one parental and three filial generations (P0, F1-F3). In three families derived from P0 crosses between an IoA-00 sire and an IoA-02 dam, 98.8% of F2 parasites (n = 173) were resistant, i.e. remained unaffected after exposure to 2.0 μg L-1 deltamethrin. F3 parasites from these crosses showed a deltamethrin EC50 of 9.66 μg L-1. In two families of the inverse orientation at P0 (IoA-02 sire x IoA-00 dam), 16.7% of F2 parasites were resistant (n = 84), while the deltamethrin EC50 in F3 animals was 0.26 μg L-1. The results revealed a predominantly maternal inheritance of deltamethrin resistance. The 15,947-nt mitochondrial genome was sequenced and compared among six unrelated L. salmonis strains and parasites sampled from wild salmon in 2010. IoA-02 and three further deltamethrin resistant strains, established from isolates originating from different regions of Scotland, showed almost identical mitochondrial haplotypes. In contrast, the mitochondrial genome was variable among susceptible strains and L. salmonis from wild hosts. Deltamethrin caused toxicity and depletion of whole body ATP levels in IoA-00 but not IoA-02 parasites. The maternal inheritance of deltamethrin resistance and its association with mitochondrial haplotypes suggests that pyrethroid toxicity in L. salmonis may involve molecular targets encoded by mitochondrial genes.

Phylogeography of Diaphorina citri (Hemiptera: Liviidae) and its primary endosymbiont, ‘Candidatus Carsonella ruddii’: an evolutionary approach to host–endosymbiont interaction

“…Varying levels of susceptibility to different pesticides exist in D. citri populations across citrus‐growing areas worldwide . Some pesticide resistance can be inherited and is associated with the genotype . Thus, understanding the population genetics and migration of the pest can be essential to developing sustainable integrated pest management program.…”

Mutations in voltage‐gated sodium channels from pyrethroid resistant salmon lice (Lepeophtheirus salmonis)

“…The laboratory‐maintained strains of L. salmonis used in this study were established from egg strings collected from Scottish salmon production sites . No drug selection has been applied during the isolation or maintenance of the strains.…”

“…Strain IoA‐00 was established in 2003 from an isolate originating in the Firth of Clyde and is susceptible to all current delousing agents including deltamethrin. Strain IoA‐01, derived in 2008 from material collected in Sutherland, is susceptible to deltamethrin but resistant to emamectin benzoate . Strains IoA‐02 and IoA‐03, which were established in 2011 and 2014, respectively, from the Shetland Islands and Sutherland, are resistant to emamectin benzoate and deltamethrin .…”

“…Similarly, the involvement of cytochrome P450 monooxygenases in the detoxification of pyrethroids in L. salmonis has been demonstrated, but its relation to resistance is unknown. Recently, it has been demonstrated that pyrethroid resistance is inherited maternally in L. salmonis . While the results suggested that both mitochondrial and nuclear genetic determinants contributed to the resistance, the molecular mechanism causing resistance remains to be identified.…”

Genetic fingerprinting of salmon louse (Lepeophtheirus salmonis) populations in the North-East Atlantic using a random forest classification approach

“…In the northern hemisphere, the salmon louse (Lepeophtheirus salmonis) is the species most commonly infecting farmed and wild salmonids (Boxaspen 2006), at considerable cost to animal health, biodiversity security, and economic growth. Conservative estimates of costs and losses attributed to sea louse infections, (estimated at €350M million in 2014 in Norway alone (Carmona-Antoñanzas et al 2017) suggest these are the single greatest pathogen burden on the global salmonid aquaculture industry. The life cycle of the sea louse involves high levels of replication, dispersal and obligate hostassociation (Boxaspen 2006); this means that local environmental conditions, sea currents, and population densities are important ecological and demographic conditions to facilitate or impede infestation (Boxaspen 2006;Jackson et al 2012;Salama et al 2013).…”