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Some insects, when subjected to high insecticide pressure, develop the ability to survive these toxins. This adaptive phenomenon called insecticide resistance is an example of microevolution. Through the study of various biological models I have addressed questions concerning (i) the types of resistance mechanisms and their importance in the development of field management strategies; (ii) the anticipation and study of resistance to biocontrol products in order to increase their sustainability; and (iii) the genetic basis of resistance. Studies conducted on two lepidopteran pests: Grapholita molesta (Tortricidae) and Ostrinia nubilalis (Pyralidae) highlight complex and variable resistance mechanisms between populations, based on panels of combinations of increased activity of detoxification enzymes and mutation in the molecular target of the insecticide. Research on the pre-existence of resistance to two natural plant extracts (3,5-dicaffeoyl quinic acid and dicaffeoyl tartaric acid) with aphicidal properties in several aphid species showed (i) small differences in susceptibility between clones or populations of Myzus persicae (Aphididae) possibly related to the size of the individuals (ii) insensitivity of one clone of Aphis craccivora (Aphididae). No cross-resistance between synthetic insecticides and these natural extracts was detected. Research on the cost of resistance in Cydia pomonella (Tortricidae) to Cydia pomonella GranuloVirus isolate M (CpGV-M), a widely used biopesticide, showed a low cost limiting the possibilities of managing this resistance. Finally, the genomic study of the genetic basis of resistance in C. pomonella to deltamethrin, thiachloprid, phosmet and CpGV-M shows that the CYP6B2 gene is responsible for cross-resistance between two synthetic molecules and that the major determinant of resistance to the virus is located in the 53,600,000 bp area on chromosome 1.The complexity of resistance mechanisms complicates their management in the field. The use of knowledge and techniques acquired in the study of resistance to synthetic insecticides is relevant and advisable to improve the sustainability of naturally occurring insecticides. The study of the genetic basis using genomic techniques confirms the existence of gene convergence, with resistance mechanisms often comparable between species, and opens up numerous research prospects., Certains insectes lorsqu’ils sont soumis à de fortes pressions insecticides développent la capacité à survivre à ces toxiques. Ce phénomène adaptatif appelé résistance aux insecticides est un exemple de microévolution. Grâce à l’étude de divers modèles biologiques j’ai abordé des questions concernant (i) les types de mécanismes de résistance et leur importance dans élaboration de stratégies de gestion sur le terrain ; (ii) l’anticipation et l’étude de résistances à des produits de biocontrôle pour augmenter leur durabilité; et (iii) les bases génétiques des résistances. Les études menées sur deux lépidoptères ravageurs : Grapholita molesta (Tortricidae) et Ostrinia nubilalis (Pyralidae) mettent en avant des mécanismes de résistances complexes et variables entre populations, basés sur des panels de combinaisons d’augmentation d’activité d’enzymes de détoxication et de mutation de la cible moléculaire de l’insecticide. Les recherches sur la préexistence de résistance à deux extraits naturels de plantes (l’acide 3,5-dicaféoyl quinique et l’acide dicafféoyl tartrique) avec des propriétés aphicides chez plusieurs espèces de pucerons ont montré (i) de faibles différences de sensibilités entre clones ou populations de Myzus persicae (Aphididae) possiblement en lien avec la taille des individus (ii) une insensibilité d’un clone d’Aphis craccivora (Aphididae). Aucune résistance croisée entre insecticides de synthèse et ces extraits naturels n’a été détectée. Les recherches sur le coût de la résistance de Cydia pomonella (Tortricidae) à l’isolat M de Cydia pomonella GranuloVirus (CpGV-M), un biopesticide largement utilisé, ont montré un faible coût limitant les possibilités de gestion de cette résistance. Enfin, l’étude génomique des bases génétiques des résistances de C. pomonella à la deltaméthrine, au thiaclopride, au phosmet et au CpGV-M montre que le gène CYP6B2 est responsable de résistances croisées entre deux molécules de synthèse et que le déterminant majeur de la résistance au virus est situé dans la zone des 53 600 000 pb sur le chromosome 1.La complexité des mécanismes de résistance complique leur gestion sur le terrain. L’utilisation des connaissances et des techniques acquises dans l’étude des résistances aux insecticides de synthèse est pertinente et souhaitable pour améliorer la durabilité des insecticides d’origine naturelle. L’étude des bases génétiques par des techniques de génomique confirme l’existence de convergences géniques, les mécanismes de résistance étant souvent comparables entre espèces et ouvre de nombreuses perspectives de recherche.

Tuberculosis remains currently one of the top ten causes of death worldwide. As a matter of fact, Mycobacterium tuberculosis (M.tb), which is the pathogen responsible for this disease, spreads easily and quickly through saliva droplets in air [1]. Moreover, this mycobacterium is becoming more and more multidrug-resistant [2]. Hence, new therapeutic targets need to be found in order to design new efficient drugs against M.tb.Multiple previous experiments in our research group focus on M.tb phosphoserine phosphatase (SerB2) as new perfect therapeutic target, for three main reasons. Firstly, the enzyme is vital for the pathogen: SerB2 inhibition stops the biosynthetic pathway of L-serine and leads to bacterial death [3]. In addition, SerB2 possesses an intrinsic pathogenic effect and expedites the infection [4]. Finally, the primary sequence of phosphoserine phosphatase is highly conserved among pathogens. The study of its inhibition could therefore lead to the design of a drug, used as panacea, especially against tuberculosis.As a result of our research, some efficient inhibitors have been discovered, thanks to the screening of NAMEDIC’s chemo-library [5]. However, the precise mechanism of action of the aforementioned inhibitors remains unclear because the crystallographic structure of SerB2 was never obtained. The main goal of this research project is the study of the closest counterpart of SerB2 (83.7% of identity) that can be crystallized: the Mycobacterium avium phosphoserine phosphatase (SerB) [6]. Indeed, this enzyme can easily be overexpressed, and crystallized after an optimized purification. First results show that SerB2 inhibitors follow similar enzymatic kinetics and remain effective against SerB. As a final outcome of this research work, crystallographic assays of SerB complexed with the inhibitors will be performed in order to provide more information about the structure and the inhibition of SerB2.[1] Global tuberculosis report 2018, World Health Organization: Geneva, 2018.[2] T.M. Walker et al., Lancet Infectious Diseases, 18, 2018, 431-440.[3] G.A. Grant, Biochemistry, 56, 2017, 6481-6490.[4] G.P. Yadav et al., PLoS ONE, 9, 2014, 1-24.[5] E. Pierson, Master’s thesis, UNamur: Namur, 2017.[6] G. Arora et al., Journal of Biological Chemistry, 289, 2014, 25149-25165.

A rapid and sensitive heterologous enzyme-linked immunosorbent assay (ELISA) was developed to measure rainbow trout maturational gonadotropin. Purified salmon maturational gonadotropin (sGtH II) was used as reference hormone. Optimization of the procedure was performed by using an anti-beta sGtH serum. Two procedures were developed: an equilibrium assay (which did not involve a preincubation step) which lasted for 8 hr and a nonequilibrium assay (which involved a preincubation step) which lasted for 26 hr. The nonequilibrium assay gave the best sensitivity (70 pg/ml sample). GtH II measurements on in vivo and in vitro samples from GnRH analogs or sGnRH experiments showed that the ELISA procedure could be used over a wide range of concentrations. The method was validated by comparing GtH II concentrations measured by both RIA and ELISA.