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A mariposa Plutella xylostella (L., 1758) (Lepidoptera, Plutellidae), conhecida popularmente como traça das crucíferas, é uma importante praga da cultura das brássicas no Brasil e em diversos países. Seu controle normalmente é realizado com aplicações freqüentes de inseticidas convencionais, porém esse controle tem se mostrado ineficiente, além dos problemas ambientais, econômicos e de resistência de insetos que pode causar. A quimioesterilização apresenta-se como uma alternativa para o manejo desta praga, utilizando inseticidas modernos, mais seletivos aos inimigos naturais e de menor impacto ambiental. O objetivo deste trabalho foi estudar o emprego de alguns inseticidas com propriedades esterilizantes sobre a fase adulta de Plutella xylostella determinando as dosagens adequadas que atuaram sobre sua reprodução. Os produtos foram fornecidos às mariposas em forma de iscas que consistiram em: solução do produto + melaço 10%. Os inseticidas utilizados e suas respectivas dosagens foram abamectina (0,0025 g i.a./L calda), diflubenzurom (0,005 g i.a./L calda), lufenurom (0,005 g i.a./L calda) e piriproxifem (0,01 g i.a./L calda), além da testemunha. Apenas o tratamento com abamectina afetou a fecundidade de Plutella xylostella, apresentando 10,23 ± 4,41 ovos em média, enquanto na testemunha obteve-se 64,54 ± 15,11 ovos, porém a fertilidade foi afetada por todos os produtos. A viabilidade média dos ovos dos tratamentos com abamectina, diflubenzurom, lufenurom e piriproxifem foi, respectivamente 3,35%; 46,69%; 9,31% e 12,47%; todos diferiram estatisticamente da testemunha que apresentou viabilidade de 83,89%. A longevidade dos insetos tratados com os produtos não diferiu dos não tratados, com exceção dos indivíduos tratados com abamectina que apresentaram uma redução no tempo de vida. Quando os produtos testados foram oferecidos isoladamente para machos e fêmeas, a ação esterilizante apenas pode ser observada em fêmeas desta espécie, os machos não apresentaram nenhuma diferença com relação à testemunha quando alimentados com as iscas esterilizantes. / Plutella xylostella (L., 1758) (Lepidoptera, Plutellidae), commonly known as diamondback moth, is an important pest of Brassicaceae in Brazil and several other countries. Its control is usually done with frequent applications of conventional insecticides. However, this approach is sometimes ineffective, besides some drawbacks such as environmental contamination, the high cost of application and the development of insecticides resistance. Chemosterilization using modern insecticides presents an alternative for this pest management. The aim of this study was to evaluate a range of insecticides with sterilizing properties on the adult reproduction of Plutella xylostella. Pesticides were provided to moths in baits, diluted in 10% molasses water solution. The insecticides used and respective doses were: abamectin (0.0025 g a.i./L), diflubenzuron (0.005 g a.i./L), lufenuron (0.005 g a.i./L) and pyriproxyfen (0.01 g a.i./L). A 10% molasses solution was used as a control treatment. Only abamectin affected the fecundity of Plutella xylostella, with a reduction from 64.54 ± 15.11 eggs/moth obtained in the control treatment to 10.23 ± 4.41 eggs/moth, when adults were fed this pesticide. However, fertility was affected by all pesticides. Egg viability when adults were feed abamectin (3.35%), diflubenzuron (46.69%), lufenuron (9.31%) and pyriproxyfen (12.47%) were reduced when compared to the control (83.89%). Only adults that were abamectin fed had their longevity reduced as compared to all other treatments. When the tested pesticides were offered isolated to males or females, their sterilizing activity was observed only when females had access to treated baits.

A mariposa Plutella xylostella (L., 1758) (Lepidoptera, Plutellidae), conhecida popularmente como traça das crucíferas, é uma importante praga da cultura das brássicas no Brasil e em diversos países. Seu controle normalmente é realizado com aplicações freqüentes de inseticidas convencionais, porém esse controle tem se mostrado ineficiente, além dos problemas ambientais, econômicos e de resistência de insetos que pode causar. A quimioesterilização apresenta-se como uma alternativa para o manejo desta praga, utilizando inseticidas modernos, mais seletivos aos inimigos naturais e de menor impacto ambiental. O objetivo deste trabalho foi estudar o emprego de alguns inseticidas com propriedades esterilizantes sobre a fase adulta de Plutella xylostella determinando as dosagens adequadas que atuaram sobre sua reprodução. Os produtos foram fornecidos às mariposas em forma de iscas que consistiram em: solução do produto + melaço 10%. Os inseticidas utilizados e suas respectivas dosagens foram abamectina (0,0025 g i.a./L calda), diflubenzurom (0,005 g i.a./L calda), lufenurom (0,005 g i.a./L calda) e piriproxifem (0,01 g i.a./L calda), além da testemunha. Apenas o tratamento com abamectina afetou a fecundidade de Plutella xylostella, apresentando 10,23 ± 4,41 ovos em média, enquanto na testemunha obteve-se 64,54 ± 15,11 ovos, porém a fertilidade foi afetada por todos os produtos. A viabilidade média dos ovos dos tratamentos com abamectina, diflubenzurom, lufenurom e piriproxifem foi, respectivamente 3,35%; 46,69%; 9,31% e 12,47%; todos diferiram estatisticamente da testemunha que apresentou viabilidade de 83,89%. A longevidade dos insetos tratados com os produtos não diferiu dos não tratados, com exceção dos indivíduos tratados com abamectina que apresentaram uma redução no tempo de vida. Quando os produtos testados foram oferecidos isoladamente para machos e fêmeas, a ação esterilizante apenas pode ser observada em fêmeas desta espécie, os machos não apresentaram nenhuma diferença com relação à testemunha quando alimentados com as iscas esterilizantes. / Plutella xylostella (L., 1758) (Lepidoptera, Plutellidae), commonly known as diamondback moth, is an important pest of Brassicaceae in Brazil and several other countries. Its control is usually done with frequent applications of conventional insecticides. However, this approach is sometimes ineffective, besides some drawbacks such as environmental contamination, the high cost of application and the development of insecticides resistance. Chemosterilization using modern insecticides presents an alternative for this pest management. The aim of this study was to evaluate a range of insecticides with sterilizing properties on the adult reproduction of Plutella xylostella. Pesticides were provided to moths in baits, diluted in 10% molasses water solution. The insecticides used and respective doses were: abamectin (0.0025 g a.i./L), diflubenzuron (0.005 g a.i./L), lufenuron (0.005 g a.i./L) and pyriproxyfen (0.01 g a.i./L). A 10% molasses solution was used as a control treatment. Only abamectin affected the fecundity of Plutella xylostella, with a reduction from 64.54 ± 15.11 eggs/moth obtained in the control treatment to 10.23 ± 4.41 eggs/moth, when adults were fed this pesticide. However, fertility was affected by all pesticides. Egg viability when adults were feed abamectin (3.35%), diflubenzuron (46.69%), lufenuron (9.31%) and pyriproxyfen (12.47%) were reduced when compared to the control (83.89%). Only adults that were abamectin fed had their longevity reduced as compared to all other treatments. When the tested pesticides were offered isolated to males or females, their sterilizing activity was observed only when females had access to treated baits.

A ivermectina é uma lactona macrocíclica usada como agente antiparasitário de amplo espectro de ação contra nematelmintos e artrópodes. É empregada, principalmente, no controle de infecções parasitárias de animais domésticos, e recentemente vem sendo utilizada em seres humanos para o tratamento da oncocercose, escabiose e pediculose. Em mamíferos, diversas evidências indicam que as lactonas macrocíclicas interagem com canais de cloro mediados pelo ácido gama-aminobutírico (GABA). Sabe-se que o sistema GABAérgico está envolvido com a manifestação do comportamento sexual e estudo prévios mostraram que a ivermectina prejudicou o comportamento sexual de ratos machos e fêmeas. Assim, considerando que a ivermectina pode interferir na esfera sexual, este trabalho avaliou os efeitos temporais da exposição à ivermectina (0,2 e 1,0 mg/kg, por via subcutânea) em parâmetros reprodutivos e hormonais de ratos e de coelhos. Em ratos avaliou-se peso relativo dos órgãos de machos e fêmeas, o índice gonadossomático de machos, os achados histopatológicos; o receptor de andrógeno em testículos por imunohistoquímica; concentração sérica de testosterona, FSH e LH; expressão relativa de enzimas da via esteroidogênica por reação em cadeia da polimerase em tempo real (PCR-RT); ciclo estral, desempenho reprodutivo e concentração de estradiol nas fezes de ratas. Em coelhos machos avaliou-se a concentração, a motilidade e a morfologia de espermatozoides; a integridade das membranas plasmáticas, acrossomal e mitocondrial de espermatozoides; o peso relativo dos órgãos e o índice gonadossomático; a concentração sérica testosterona; os achados histopatológicos; e a análise hematológica e bioquímica sérica. Os resultados mostraram que a administração de ivermectina em ratos: não alterou o peso relativo dos testículos, epidídimos, próstata e vesícula seminal; não modificou o índice gonadossomático; promoveu prejuízo nas células germinativas do epitélio seminífero dos testículos, achado sugestivo de prejuízo na espermatogênese e na espermiogênese de machos; não interferiu na expressão de receptor andrógeno dos testículos, bem como a expressão relativa de enzimas da via esteroidogênica; não interferiu na concentração sérica de testosterona e FSH, porém diminuiu a concentração sérica de LH; não interferiu no ciclo estral, no desempenho reprodutivo e na concentração de estradiol nas fezes de ratas. Os resultados de ratos e ratas foram discutidos considerando a interferência da ivermectina na neurotransmissão GABAérgica, bem como na via de produção dos hormônios hipofisários-gonadais. Em coelhos, não foram observadas alterações nos parâmetros da fertilidade de machos, avaliada pela concentração, motilidade e morfologia de espermatozoides, e nem no potencial de fertilização, avaliado pela integridade das membranas plasmática, acrossomal e mitocondrial dos espermatozoides; não houve interferência nos níveis séricos de testosterona, na bioquímica sérica e em parâmetros do hemograma. Esses resultados em conjunto são indicativos de que a ivermectina causa poucos efeitos prejudiciais em aspectos reprodutivos de ratos e coelhos. / Ivermectin is a macrocyclic lactone used as a broad spectrum antiparasitic agent against nematelmints and arthropods. It is mainly used in the control of parasitic infections of domestic animals, and recently has been used in humans to treat onchocerciasis, scabies and pediculosis. In mammals, various evidences indicate that macrocyclic lactones interact with gamma-aminobutyric acid (GABA)-mediated chloride channels. It is known that the GABAergic system is involved in the manifestation of sexual behavior and previous studies have shown that ivermectin impaired sexual behavior in male and female rats. Thus, considering ivermectin may interfere with the sexual sphere, this study evaluated the temporal effects of exposure to ivermectin (0.2 and 1.0 mg/kg, administered subcutaneously) on reproductive and hormonal parameters of rats and rabbits. In rats it was evaluated organ weights of male and female, the gonadossomatic index of males, histopathological findings; the immunohistochemical of the androgen receptor in the testes; serum LH, FSH and testosterone concentrations; relative expression of steroidogenic pathway enzymes by real-time polymerase chain reaction (RT-PCR); estrous cycle, reproductive performance and estradiol concentration in the feces of female rats. In male rabbits it was evaluated the spermatozoa concentration, motility and morphology; the integrity of the membranes plasmatic, acrosomal and mitochondrial of the spermatozoa; the organ weights, the gonadosomatic index; serum testosterone concentrations; histopathological findings; and hematological and serum biochemical analysis. The results showed that ivermectin administration in rats: not alter the relative weights of the testes, epididymis, prostate and seminal vesicle; not modified gonadosomatic index; caused damage in the germinal cells of the seminiferous epithelium of the testes, finding suggestive of impairment in spermatogenesis and male spermiogenesis; did not interfere with the androgen receptor expression of the testes, as well as the relative expression of enzymes of the steroidogenic pathway; did not interfere in the serum testosterone and FSH concentrations, but it decreased the serum LH concentration; did not interfere in the estrous cycle, reproductive performance and estradiol concentration in the feces of female rats. The results of male and female rats were discussed considering the interference of ivermectin in GABAergic neurotransmission as well as in the production pathway of pituitary-gonadal hormones. In rabbits, no changes were observed in male fertility parameters evaluated by spermatozoa concentration, motility and morphology, nor the potential for fertilization evaluated by the integrity of the membranes plasmatic, acrosomal and mitochondrial of the spermatozoa; there was no interference in serum testosterone concentration, serum biochemistry and hematological parameters. These results together are indicative that ivermectin causes few adverse effects on reproductive aspects of rats and rabbits.

A ivermectina é uma lactona macrocíclica usada como agente antiparasitário de amplo espectro de ação contra nematelmintos e artrópodes. É empregada, principalmente, no controle de infecções parasitárias de animais domésticos, e recentemente vem sendo utilizada em seres humanos para o tratamento da oncocercose, escabiose e pediculose. Em mamíferos, diversas evidências indicam que as lactonas macrocíclicas interagem com canais de cloro mediados pelo ácido gama-aminobutírico (GABA). Sabe-se que o sistema GABAérgico está envolvido com a manifestação do comportamento sexual e estudo prévios mostraram que a ivermectina prejudicou o comportamento sexual de ratos machos e fêmeas. Assim, considerando que a ivermectina pode interferir na esfera sexual, este trabalho avaliou os efeitos temporais da exposição à ivermectina (0,2 e 1,0 mg/kg, por via subcutânea) em parâmetros reprodutivos e hormonais de ratos e de coelhos. Em ratos avaliou-se peso relativo dos órgãos de machos e fêmeas, o índice gonadossomático de machos, os achados histopatológicos; o receptor de andrógeno em testículos por imunohistoquímica; concentração sérica de testosterona, FSH e LH; expressão relativa de enzimas da via esteroidogênica por reação em cadeia da polimerase em tempo real (PCR-RT); ciclo estral, desempenho reprodutivo e concentração de estradiol nas fezes de ratas. Em coelhos machos avaliou-se a concentração, a motilidade e a morfologia de espermatozoides; a integridade das membranas plasmáticas, acrossomal e mitocondrial de espermatozoides; o peso relativo dos órgãos e o índice gonadossomático; a concentração sérica testosterona; os achados histopatológicos; e a análise hematológica e bioquímica sérica. Os resultados mostraram que a administração de ivermectina em ratos: não alterou o peso relativo dos testículos, epidídimos, próstata e vesícula seminal; não modificou o índice gonadossomático; promoveu prejuízo nas células germinativas do epitélio seminífero dos testículos, achado sugestivo de prejuízo na espermatogênese e na espermiogênese de machos; não interferiu na expressão de receptor andrógeno dos testículos, bem como a expressão relativa de enzimas da via esteroidogênica; não interferiu na concentração sérica de testosterona e FSH, porém diminuiu a concentração sérica de LH; não interferiu no ciclo estral, no desempenho reprodutivo e na concentração de estradiol nas fezes de ratas. Os resultados de ratos e ratas foram discutidos considerando a interferência da ivermectina na neurotransmissão GABAérgica, bem como na via de produção dos hormônios hipofisários-gonadais. Em coelhos, não foram observadas alterações nos parâmetros da fertilidade de machos, avaliada pela concentração, motilidade e morfologia de espermatozoides, e nem no potencial de fertilização, avaliado pela integridade das membranas plasmática, acrossomal e mitocondrial dos espermatozoides; não houve interferência nos níveis séricos de testosterona, na bioquímica sérica e em parâmetros do hemograma. Esses resultados em conjunto são indicativos de que a ivermectina causa poucos efeitos prejudiciais em aspectos reprodutivos de ratos e coelhos. / Ivermectin is a macrocyclic lactone used as a broad spectrum antiparasitic agent against nematelmints and arthropods. It is mainly used in the control of parasitic infections of domestic animals, and recently has been used in humans to treat onchocerciasis, scabies and pediculosis. In mammals, various evidences indicate that macrocyclic lactones interact with gamma-aminobutyric acid (GABA)-mediated chloride channels. It is known that the GABAergic system is involved in the manifestation of sexual behavior and previous studies have shown that ivermectin impaired sexual behavior in male and female rats. Thus, considering ivermectin may interfere with the sexual sphere, this study evaluated the temporal effects of exposure to ivermectin (0.2 and 1.0 mg/kg, administered subcutaneously) on reproductive and hormonal parameters of rats and rabbits. In rats it was evaluated organ weights of male and female, the gonadossomatic index of males, histopathological findings; the immunohistochemical of the androgen receptor in the testes; serum LH, FSH and testosterone concentrations; relative expression of steroidogenic pathway enzymes by real-time polymerase chain reaction (RT-PCR); estrous cycle, reproductive performance and estradiol concentration in the feces of female rats. In male rabbits it was evaluated the spermatozoa concentration, motility and morphology; the integrity of the membranes plasmatic, acrosomal and mitochondrial of the spermatozoa; the organ weights, the gonadosomatic index; serum testosterone concentrations; histopathological findings; and hematological and serum biochemical analysis. The results showed that ivermectin administration in rats: not alter the relative weights of the testes, epididymis, prostate and seminal vesicle; not modified gonadosomatic index; caused damage in the germinal cells of the seminiferous epithelium of the testes, finding suggestive of impairment in spermatogenesis and male spermiogenesis; did not interfere with the androgen receptor expression of the testes, as well as the relative expression of enzymes of the steroidogenic pathway; did not interfere in the serum testosterone and FSH concentrations, but it decreased the serum LH concentration; did not interfere in the estrous cycle, reproductive performance and estradiol concentration in the feces of female rats. The results of male and female rats were discussed considering the interference of ivermectin in GABAergic neurotransmission as well as in the production pathway of pituitary-gonadal hormones. In rabbits, no changes were observed in male fertility parameters evaluated by spermatozoa concentration, motility and morphology, nor the potential for fertilization evaluated by the integrity of the membranes plasmatic, acrosomal and mitochondrial of the spermatozoa; there was no interference in serum testosterone concentration, serum biochemistry and hematological parameters. These results together are indicative that ivermectin causes few adverse effects on reproductive aspects of rats and rabbits.

Caligid copepods, also called sea lice, are ectoparasites of marine fish, with Lepeophtheirus salmonis (Krøyer, 1837) emerging as a problem for mariculture of Atlantic salmon (Salmo salar Linnaeus, 1758) in the northern hemisphere. Annual costs of sea lice to global salmon farming was estimated to be in excess of €300 million in 2006, with the majority of this accounted for through expenses accrued from chemical treatments. Only a limited range of anti-sea louse drugs are available and licensed for the treatment of fish, and the continued use of only a few compounds creates a situation potentially favouring the development of drug resistance. Emamectin benzoate (EMB) is currently used as a salmon delousing agent, being employed as a 0.2 % in-feed pre-mix (SLICE®). Atlantic salmon farmers have reported increased incidence of reduced L. salmonis sensitivity to SLICE®, which has highlighted the requirement for further research into the molecular mechanisms controlling salmon louse resistance to EMB. Genomic and transcriptomic research concerning L. salmonis drug resistance mechanisms has not often been reported, with previous transcriptomic studies using candidate gene approaches and genetic studies focussing on population genetics. Drug resistance in ecdysozoan invertebrates is associated with a variety of molecular mechanisms including target site mutations and changes in the expression of components in drug detoxification pathways. The research reported in this thesis was aimed at the exploration of mechanisms employed by L. salmonis to reduce the toxicity of EMB exposure, following a transcriptomic approach that utilised custom oligonucleotide (oligo) microarrays and a genetic approach that utilised Restriction-site associated DNA sequencing (RAD-seq) to identify Single Nucleotide Polymorphism (SNP) markers. An EMB-resistant (PT) and drug-susceptible (S) L. salmonis laboratory-maintained strain were to be used as a model for this research, as these two strains differ in EMB susceptibility (~ 7-fold) and show stable susceptibility profiles through multiple generations, suggesting that this drug resistance phenotype may be a heritable trait. Sequence resources available for salmon lice are limited as an annotated L. salmonis genome is currently under construction. Therefore, a significant amount of this study involved creating new resources to facilitate the analysis of EMB susceptibility. Suppression subtractive hybridisation (SSH) was used to enrich for transcripts that were differentially expressed between strains PT and S, which provided sufficient target sequence for the development of 15K oligo microarrays when combined with sequences assembled from existing L. salmonis ESTs. Additionally, transcripts were generated through sequencing a pooled sample representing key developmental stages of the L. salmonis life cycle, which were later used in the construction of a 44K oligo microarray. The toxicity of EMB and other avermectins (AVMs) against ecdysozoan invertebrates is reported to be based mainly on their interaction with ligand-gated ion channels (LGIC), specifically glutamate-gated chloride channels (GluCl). However, -aminobutyric acid (GABA)-gated chloride channels (GABA-Cls) are also believed to be targeted by AVMs and neuronal acetylcholine receptors (nAChRs) can be allosterically modulated by the AVM compound ivermectin. Transcriptional responses in PT and S salmon lice were investigated using custom 15K L. salmonis oligo microarrays. In the absence of EMB exposure, 359 targets differed in transcript abundance between the two strains. GABA-Cl and nAChR subunits showed significantly lower transcript levels in PT compared to S lice, which was estimated at ~1.4-fold for GABA-Cl and ~2.8-fold for nAChR using RT-qPCR, suggesting their involvement in AVM toxicity in caligids. Although, salmon lice from the PT strain showed few transcriptional responses following acute exposure (1 or 3 h) to 200 µg L-1 of EMB, a drug concentration tolerated by PT lice, but toxic for S lice. RAD-seq analysis of both genders from L. salmonis strains S and PT identified 15 RAD-markers that show complete association with salmon louse strain, although these preliminary results will need further analysis to confirm marker association with reduced EMB susceptibility. Additionally, RAD marker Lsa101901 showed complete association with sex for all individuals analysed, being heterozygous in females and homozygous in males. Using an allele-specific PCR assay, this SNP association pattern was further confirmed for three unrelated salmon louse strains. Marker Lsa101901 was located in the coding region of the prohibitin-2 gene, which showed a sex-dependent differential expression, with mRNA levels determined by RT-qPCR about 1.8-fold higher in adult female than adult male salmon lice. In conclusion, the identification of decreased transcript abundances for LGIC subunits in EMB-resistant salmon lice, and polymorphic SNP markers showing complete association with L. salmonis strains S or PT, provides suitable candidates for further investigation into their association with reduced EMB susceptibility. Further analysis will also be required to confirm whether EMB-induced mechanisms are not associated with reduced EMB susceptibility in L. salmonis. Additionally, the identification of sex-linked SNP Lsa101901 suggests that sex determination in the salmon louse is genetic and follows a female heterozygous system, with marker Lsa101901 providing a tool to determine the genetic sex of salmon lice. Improved knowledge of L. salmonis biology and the mechanisms potentially involved in EMB resistance, obtained during this study, may provide molecular markers that contribute to successful monitoring and management of this commercially important parasite of Atlantic salmon.

Efficient control of sea lice is a major challenge for the sustainable production of farmed Atlantic salmon (Salmo salar (Linnaeus, 1758)). These marine ectoparasites feed on mucus, skin and blood of their hosts, thereby reducing the salmon’s growth rate and overall health. In the northern hemisphere, the most prevalent species is Lepeophtheirus salmonis (Krøyer, 1837). In 2006, global costs of sea lice infections are estimated to have exceeded €300 million, with the majority spent on a limited number of chemical delousing agents. Emamectin benzoate (EMB; SLICE®), an avermectin, has been widely used since its introduction in 2000, due to its convenient administration as an in-feed medication and its high efficacy against all parasitic stages of L. salmonis. However, over-reliance on a single or limited range of medicines favours the emergence of drug resistance and, as a result, the efficacy of this compound in treating L. salmonis has decreased in recent years, as reported from e.g. Chile, Norway, Scotland and Canada. Declining efficacy underlines the need for an improved understanding of the molecular mechanisms underlying EMB drug resistance in L. salmonis. Elucidation of these mechanisms would allow for improved monitoring tools, earlier detection of developing resistance, extended usability of current delousing agents and development of new parasiticides. The work described in this thesis sets out to examine the molecular mechanisms underlying EMB resistance in L. salmonis. In earlier studies, research in nematodes and arthropods has linked drug efflux transporters belonging to the family of ATP-binding cassette (ABC) transporters to ivermectin (IVM) resistance, a parasiticide with high chemical similarity to EMB. ABC transporters such as permeability glycoprotein (P-gp), transport a wide range of substrates, including drugs, and have been suggested to provide a potential molecular mechanism through which EMB resistance might be mediated in sea lice. As an example of such mechanisms, increased expression of P-gp is one of the causative factors for drug resistance in human cancer cells and avermectin resistance in nematode parasites such as Caenorhabditis elegans or Haemonchus contortus. Initial research involved screening for novel salmon lice P-gps that might contribute to EMB resistance. A novel P-gp, SL-PGY1, was discovered using a combined bioinformatic and molecular biological approach. The expression was compared in two well-characterised L. salmonis strains differing in their susceptibility to EMB (S = susceptible, R = resistant). Prior to EMB exposure, mRNA levels did not differ from each other, while, after 24 h exposure, a 2.9-fold increase in SL-PGY1 mRNA expression was observed in the R strain. SL-PGY1 appears not to be a major factor contributing to reduced EMB susceptibility, although it could play a role, as expression levels increased upon exposure to EMB. A further four additional drug transporters (ABC C subfamily) were also discovered showing high homology to multidrug-resistance proteins (MRP). The relative expression levels of each MRP was compared in the strains S and R, before and after exposure to EMB. No significant changes were found in their expression patterns. If ABC drug transporters mediate the efflux of EMB and thereby reduce the intracellular concentrations of the drug in exposed animals, the inhibition of those ABC drug transporters was expected to lead to higher intracellular levels of EMB. This could result in an enhanced toxic effect when EMB is co-administered with an inhibitor. Two known inhibitors of human P-gps and MRPs, cyclosporin A (CSA) and verapamil (VER), were co-administered with EMB. CSA increased the toxic effect of EMB in both tested strains, implying that the targets of CSA are expressed at comparable levels and that they may be part of the mechanism conferring EMB resistance. VER increased the toxic effect of EMB in the R strain, but had no significant effects on the S strain. This implies that the expression of factors inhibited by VER differs between the two L. salmonis strains. It is hypothesised that a number of ABC transporters with distinct, yet overlapping patterns of inhibitor specificity are affected by those inhibitors. The search for drug-resistance conferring genes was complemented with a systematic, genome-wide survey of ABC transporters in L. salmonis to find additional members of this important gene family. Next-generation high-throughput RNA sequencing (RNA-seq) was employed to assemble a reference transcriptome from pooled total RNA of salmon lice at different development stages. The transcriptome was assembled against the L. salmonis genome and annotated. Thirty-nine putative ABC transporters were found. Of further interest were transcripts of the subfamily B, C and G, as they contain drug-transporting ABC proteins. For the ABC B subfamily, one full (SL-PGY1) and three half transporter transcripts were found. Only full transporters are known to transport drugs and SL-PGY1 is apparently not a major factor contributing to EMB resistance. Fourteen ABCC sequences were found – 11 MRPs and 3 homologues to sulfonylurea receptors. Of interest are MRPs, as they contribute to drug detoxification in humans and invertebrates. Four MRPs had been identified previously and their expression ratios did not differ between S and R strain parasites. Seven sequences belonging to ABCG subfamily were found. However, none of the L. salmonis ABCG transcripts identified showed sufficient homology to known drug transporters in other species. With the currently limited understanding of the mechanisms conferring EMB resistance, monitoring the susceptibility of L. salmonis subpopulations is essential. Dose-response bioassays are currently widely used. Tests with pre-adult II or adult parasites requires relatively large numbers of parasites (~150) to conduct this type of bioassay, which may not always be available. Addressing this issue, we tested the feasibility of a single-dose bioassay (requiring fewer test animals than dose-response bioassays) to discriminate between L. salmonis strains with differing EMB susceptibility. This alternative approach uses time-course toxicity analysis, where the toxic effect of EMB is monitored over time. After clearly defining the effect criteria, we found that it is possible to discriminate between those L. salmonis strains. However, while requiring fewer test animals, time course toxicity analysis is more labour-intensive, but the alternative design can be suitable under certain circumstances. The work reported here has provided new knowledge concerning the mechanisms of EMB resistance in sea lice. Several novel putative drug transporters have been identified, an important first step toward unravelling the complex interactions of genes involved in EMB resistance in this commercially important parasite.