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Plodia interpunctella Hübner (Lepidoptera, Pyralidae), también conocida como la polilla de la fruta seca, es un insecto cosmopolita que ocasiona importantes daños en frutas secas, granos, harinas y productos manufacturados derivados. El control de este insecto plaga se realiza tradicionalmente a través de insecticidas de síntesis orgánica. Sin embargo, el uso intensivo de estos productos ha generado varios problemas, entre los que se pueden citar: el desarrollo de resistencia, la contaminación ambiental, daños en la salud humana y la eliminación de potenciales controladores biológicos. Estas circunstancias han llevado a replantear las estrategias de manejo de este insecto y a buscar nuevas metodologías de control, que sean menos perjudiciales para el ambiente y la salud humana. En este contexto, este trabajo propone desarrollar nuevas nanoformulaciones basadas en aceites esenciales (AE) con actividad insecticida en P. interpunctella y evaluar los efectos ecotoxicológicos de estos productos en organismos no blanco tales como Tenebrio molitor y Artemia salina y en células de mamíferos del tipo osteoblástico. En consecuencia, se evaluó la actividad insecticida de los AE de Citrus bergamia Risso (Sapindales, Rutaceae) (Bergamota), Lavandula angustifolia Mill. (Lamiales, Lamiaceae) (Lavanda), Mentha piperita L. (Lamiales, Lamiaceae) (Menta), Geranium maculatum L. (Geraniales, Geraniaceae) (Geranio), Cymbopogon martinii (Roxb.) Wats (Poales, Poaceae) (Palmarosa) y Eucalyptus globulus Labill. (Myrtales, Myrtaceae) (Eucalipto) en larvas del IV estadio y adultos de P. interpunctella. Se utilizaron dos metodologías: exposición a superficies tratadas y aplicación tópica. Los AE de geranio, menta y palmarosa tuvieron los valores de CL50 más bajos en adultos de P. interpunctella para el ensayo de toxicidad por exposición a superficies tratadas. Sin embargo, para el caso de las larvas del IV estadio tanto en el ensayo por exposición a superficies tratadas como en el ensayo por vía tópica, ningún AE mostró una mortalidad mayor al 20%, incluso a las máximas dosis. Finalmente y en el caso particular de los adultos de P. interpunctella que se trataron por vía tópica se observó que la variabilidad de los resultados obtenidos fue muy grande. Por esta razón se descartó para el resto de la tesis este tipo de ensayos en adultos. En base a los datos obtenidos en el ensayo por exposición a superficies tratadas en adultos de P. interpunctella se procedió a seleccionar a los AE de geranio, menta y palmarosa para ser nanoformulados. En lo que respecta a la obtención de nanopartículas (NP) poliméricas, se eligió al PEG-6000 como sustrato matricial y mediante el método de fusión-dispersión se obtuvieron las NP de PEG-6000 cargadas con AE (NPAE). Las NPAE de palmarosa tuvieron un tamaño de 191 nm, mientras que las de geranio de 259 nm. Ambas NP mostraron una eficiencia de cargado (EC) cercana al 90% y fueron monodispersas. Por su parte, las NP de menta tuvieron un tamaño de 380 nm, fueron polidispersas y su EC fue del 72%. Una vez obtenidas las NPAE se probaron mediante ensayos de exposición a superficies tratadas y por exposición a vapores en larvas del IV estadio y adultos de P. interpunctella. Además se estudió, en ambos ensayos, el efecto de la temperatura de post-aplicación a 17, 24 y 31 °C. Uno de los resultados más destacables es que a todas las temperaturas, las NPAE potenciaron el efecto insecticida por exposición a superficies tratadas en adultos P. interpunctella, en relación con los AE libres, entre 1,54 y 3,54 veces. Por otra parte, en el caso del ensayo por exposición a vapores, solo las NPAE de palmarosa y menta incrementaron el efecto insecticida de los AE, entre 1,26 y 4,45 veces. Sin embargo, es para destacar que el AE de palmarosa fue el que mostró el mayor efecto insecticida y su temperatura óptima de post aplicación fue de 17 °C. A su vez, sus NPAE también presentaron a esta temperatura la mayor actividad insecticida convirtiéndose así en las más efectivas de este estudio. Finalmente, se demostró que la temperatura tuvo un efecto significativo sobre la actividad insecticida de los AE y de sus NP cuando estos productos se usaron en el ensayo por exposición a superficies tratadas sobre adultos de P. interpunctella. No se registró efecto alguno de la temperatura post-aplicación cuando las NPAE se emplearon en los ensayos por exposición a vapores. Los AE de geranio, menta y palmarosa también se formularon como nanoemulsiones (NEs) utilizando Tween 80 como surfactante y la técnica de ultrasonido. Para la elaboración de las NEs las condiciones optimizadas de la sonda ultrasonido fueron: 65 W de potencia, ciclos de 30 “on”/ 20 “off”, tiempo total de sonicación de 2 min y distancia óptima de la sonda ultrasónica de 3,7 cm. En lo que respecta a estas formulaciones, las NEs de geranio elaboradas con una relación AE:Tween 80 de 1:2 tuvieron tamaños de gota de ≈14 nm, fueron monodispersas, de aspecto transparente y comenzaron a perder su estabilidad a los 120 días. En cuanto a las NEs de menta formuladas con una relación AE:Tween 80 de 1:2 mostraron tamaños de gota ≈33 nm, fueron polidispersas y de aspecto macroscópico transparente. En cuanto a la estabilidad de estas NEs, se observó un proceso de separación de fases a los 60 dias de haber sido formuladas. Finalmente los nanosistemas elaborados con el AE de palmarosa no fueron estables ni translúcidos con la relación AE: Tween 80 de 1:2. Es por esto que para no modificar las condiciones de ultrasonido, se procedió a enriquecer la mezcla con acetato de linalilo (AL). Cuando este componente enriqueció al AE de palmarosa en un 50%, se obtuvieron NEs con tamaños de gota de ≈14 nm, monodispersas, de aspecto macroscópico transparente y estables durante 120 días. En relación a la actividad insecticida de estos productos, los resultados mostraron que las NEs combinadas con β-cipermetrina potenciaron el efecto tóxico, con respecto al piretroide solo y a este combinado con los AE en larvas del IV de P. interpuctella. Por otra parte se estudiaron aspectos ecotoxicológicos de las NAPAE y NEs a través de ensayos con distintos organismos no blanco y en células de mamíferos. Con respecto a las NPAE y a las NEs se observó que estas nanoformulaciones no generaron efectos tóxicos a las dosis ensayadas en larvas de Tenebrio molitor L. Coleoptera, Tenebrionidae). En cuanto a los estudios de las nanoformulaciones en Artemia salina L. (Anostraca, Artemiidae) los resultados fueron heterogéneos. Por un lado, las NPAE del AE de geranio resultaron ser inocuas, mientras que las NEs de este AE tuvieron una alta toxicidad en este crustáceo, incluso a bajas dosis. El caso contrario fue el de las NPAE de menta y palmarosa que resultaron ser tóxicas a bajas dosis (< 25ppm). Sin embargo, las NEs de menta y palmarosa + AL mostraron valores de CL50 muchos más altos que los encontrados en el ensayo con Cx. p. pipiens, demostrando una toxicidad diferencial. Con respecto a los estudios relacionados con las células de mamíferos de tipo osteoblástico, luego de 24 h, las NEs de menta y palmarosa + AL redujeron la viabilidad celular levemente, siendo este efecto aún más pronunciado con las NEs de geranio. Luego de 72 h, las células expuestas a Tween 80 y a las NEs de menta y palmarosa + AL, exhibieron un aumento significativo en la viabilidad celular en comparación con las células del control. Por otra parte, las NEs de geranio redujeron significativamente la viabilidad celular. Finalmente a las 168 h, solo las NEs de geranio redujeron significativamente la viabilidad celular. A estos tiempos de exposición no se hallaron diferencias significativas entre el resto de los tratamientos y los controles. En el marco del desarrolloo de nuevas estrategias de manejo de insectos plaga, las nanoformulaciones basadas en AE han incrementado su importancia como nuevos insecticidas bioracionales. Según los resultados obtenidos las NPAE y NEs, elaboradas en el marco de esta tesis, son practicamente atóxicas para organismos no blanco, como A. salina y T. molitor y podrían considerarse bioinsecticidas potenciales para el manejo integrado de P. interpuctella. / The Indian meal moth, Plodia interpunctella Hübner (Lepidoptera, Pyralidae) is a cosmopolitan major economic insect pest of stored products. The larvae prefers to feed on broken grains and especially on milled products such as flour, breakfast foods, stored cereal products, dried vegetables and fruits, processed foods and meals. Generally, the control of this insect pest in storage systems depends on synthetic insecticides. However, their indiscriminate application contributed to environmental contamination and pest resistance and affected nontarget organisms. Essential oils (EO) appear as new ecofriendly insecticides, which show good biological activity against insect pest. Consequently, they become a complementary method for integrated pest management strategies (IPM). The overall objective was to develop new bioinsecticides nanoformulations that can be used for a safer management of P. interpunctella as well as an improvement in the knowledge of the econanotoxicological field. This study evaluated the chemical constituents and bioactivity of six essential oils namely Citrus bergamia Risso (Sapindales, Rutaceae) (Bergamot), Lavandula angustifolia Mill. (Lamiales, Lamiaceae) (Lavender), Mentha piperita L. (Lamiales, Lamiaceae) (Peppermint), Geranium maculatum L. (Geraniales, Geraniaceae) (Geranium), Cymbopogon martinii (Roxb.) Wats (Poales, Poaceae) (Palmarosa) and Eucalyptus globulus Labill. (Myrtales, Myrtaceae) (Eucalyptus) against larvae IV and adults of P. interpunctella. The EO were topically applied or were evaluated in contact toxicity bioassays. The contact toxicity order was palmarosa > geranium > peppermint > lavender > bergamot > eucalyptus in adults of P. interpuctella. However, when EO were topically applied or were evaluated in contact toxicity bioassays against larvae IV, the EO showed less than 20% of mortality even at the highest doses. In topically assays with P. interpunctella adults, the results were variable. In this sense, topically assays with P. interpunctella adults were not performed in the thesis. Based on these results, geranium, peppermint and palmarosa oils were further evaluated for essential oils polymeric nanoparticles (EOPN) and nanoemulsion (NEs) elaboration. EOPN were elaborated by the melt-dispersion method using polyethylene glycol 6000 (PEG 6000) as matrix system in PEG 6000: EO ratio 10: 1. The first step of the study was the characterization of the EOPN. The EOPN sizes from palmarosa were 191 nm, followed by geranium (259 nm) and peppermint EOPN (381 nm). Palmarosa and geranium EOPN were monodisperse and the loading efficiency (LE) showed values close to 90%. On the other hand, peppermint EOPN were polydisperse and the LE was > 70%. The aim of second chapter was to evaluate the insecticidal activity of EO and EOPN on P. interpunctella adults at different environmental temperatures (17, 24 and 31 °C). In the contact toxicity bioassay, all EOPN significantly increase the insecticidal activity of the bioactive compounds from 1.54 to 3.54 times. In the case of fumigant assays, just palmarosa and peppermint potentiated the biological activity from 1.26 to 4.45 times. It has been found that palmarosa EO and EOPN presented the highest insecticidal activity and the optimal post application temperature was 17 °C. It was also observed that the temperature had a significant effect on the insecticidal activity of the EO and EOPN when applied by contact. However, this effect could not observe in fumigant bioassay. Geranium, peppermint and palmarosa EO were also formulated as nanoemulsions (NEs) using Tween 80 (surfactant) and ultrasound. For NEs elaboration, the ultrasound parameters were optimized: ultrasound power = 65 W, sonication time = 2 min, cycles = 30 on/20 off and ultrasonic probe distance = 3.7 cm. Transparent NEs of geranium EO were achieved using 1:2 oil-surfactant ratios. These nanosystems measured 13.58 nm, were monodisperse and stable for 60 days. Moreover, after 120 days of storage, NEs began to lose stability. In case of peppermint EO, transparent NEs were formulated using a 1:2 peppermint EO/Tween 80 ratio. These NEs showed sizes of 33.97 ± 33.16 nm and the PDI value of 0.424 ± 0.008, and were stable after 30 days. The NEs lost stability after 60 days. It is important to point out that the palmarosa EO alone at the highest Tween 80 ratio (1:2) was unable to produce stable and transparent NEs. The addition of linalyl acetate (LA) to the coarse emulsion made the NEs production possible with the same ultrasound parameters. When the ratio of LA was 50%, the palmarosa + LA NEs were transparent. Moreover, the NEs measured 14.73 nm and were monodisperse. According to bioassays, the NEs combine with β-cypermethrin enhance the toxicity of EO against larvae IV of P. interpunctella. Finally, it was also evaluated the potential influence of EOPN and NEs on the non target aquatic model Artemia salina, L. (Anostraca: Artemiidae), and on the terrestrial model Tenebrio molitor L. (Coleoptera: Tenebrionidae). The results from the ecotoxicology assay in T. molitor indicated that EOPN and NEs did not have toxic effect on this terrestrial model. However, the ecotoxicology assay in A. salina showed different results. On the one hand, geranium EOPN were not harmful for A. salina; on the other hand, NEs were toxic even at the lowest doses. Nevertheless, peppermint and palmarosa EOPN were toxic even at the lowest doses, though their NEs showed CL50 values higher than the values found in Cx. p. pipiens assay. In the context of the biosafety evaluation of these novel nanofomulations, the viability of cell culture exposed to NEs was also evaluated. After 24 h, the treated cells with peppermint and palmarosa + AL NEs showed a significant slowdown on the cell viability rate. The geranium NEs had a stronger effect in this variable. Nevertheless, after 72 h, cells exposed to Tween 80 and NEs exhibited a significant increase in the cell viability rate compared with control. However, geranium NEs showed a higher reduction in the cell viability rate. After 168 h, the NEs did not have a significant effect on the cell viability when compared with control and control + Tween 80. Though, the geranium NEs showed similar results as 72 h assay. The potential uses of nanoformulations based on EOs as novel bioinsecticides responds to the new socioproductive conditions and fulfill the demands of new ecofriendly pest management tools. In this sense, this work shows that the EOPN and NEs are relatively safe for nontarget organisms, such as A. salina and T. molitor and could be act as a new bioinsecticides for the management of P. interpunctella.

Semiochemicals are chemicals used to communicate. Animals tend to use these e.g. to locate food sources or to find a suitable mate. In this study, the sex pheromone of the Indian meal moth, Plodia interpunctella, was analysed. Since this is an economically important species, it is mass-reared in labs and science centers worldwide for experimental purposes. A culture of these moths was brought into the lab at Lund University for studies and has after that served as a model species demonstrating up-wind pheromone-mediated male flight in different courses held by the university. As years went by, the culture got less successful in up-wind flights, most probably because of inbreeding and bottleneck effects, and therefore, a new culture was taken in. This study focuses on using various experiments to see if there was a behavioral and/or physiological difference between the two cultures. Results show a significant difference in behavioral traits (frequency of calling behavior in females and in male up-wind flights) but not in physiological traits (female pheromone production or male antennal response). This study discusses some effects of mass-reared lab cultures.

Commercialisées depuis 1996, les plantes génétiquement modifiées produisant une toxine insecticide (toxine Cry) dérivée de Bacillus thuringiensis et appelées plantes Bt ciblent certains Lépidoptères ou Coléoptères ravageurs. Au fil des ans, les surfaces cultivées en plantes Bt sont de plus en plus importantes et contrôlent de larges populations d'insectes. Pour limiter le risque de développement de populations résistantes, une stratégie agricole appelée 'Haute Dose / Zone Refuge' est actuellement recommandée aux Etats-Unis par l'Environmental Protection Agency. Cette stratégie préventive nécessite la plantation d'une 'zone refuge' composée de plantes non-Bt utilisables par le ravageur ciblé et plantée à proximité de la 'zone Bt' qui synthétise une haute dose de toxine Cry. Mon projet de recherche s’inscrit dans le cadre de l’évaluation de l'efficacité de cette stratégie et s’articule en deux phases : une phase expérimentale et une phase théorique. La première se concentre sur la caractérisation en laboratoire de l'impact des toxines Cry sur la biologie d'un ravageur. Cette phase constitue un support au volet théorique : la mise au point d’un modèle mathématique évaluant l'efficacité de la stratégie HD/R. L'originalité de ce projet repose entre autre sur l'interactivité entre ces deux volets. Volet expérimental. Impact des toxines Cry sur la biologie de Plodia interpunctella. Nous évaluons séparément l'impact d'une gamme de concentrations de deux toxines Cry (CryXX et CryYY) sur une série de paramètres comportementaux et biologiques d'un insecte commun des denrées stockées: Plodia interpunctella (Hübner) (Lepidoptera : Pyralidae). Ces paramètres sont sélectionnés car leur variation pourrait avoir un impact sur l'efficacité de la stratégie HD/R dans le contrôle de la résistance. Il est donc pertinent de les quantifier pour intégrer dans le modèle des ordres de grandeur réalistes et générer des résultats qui ne sont pas uniquement basés sur des spéculations théoriques. Volet théorique A. Efficacité de la stratégie HD/R pour des plantes Bt synthétisant une ou deux toxines simultanément. La stratégie 'HD/R' a été développée pour prévenir la résistance envers les plantes Bt synthétisant une seule toxine. Or, depuis 2003, de nouvelles variétés de coton Bt synthétisant simultanément deux toxines Cry sont commercialisées (BollgardII® et WidestrikeTM). Nous évaluons, grâce au modèle que nous avons développé, l'efficacité de cette stratégie lors d'une utilisation exclusive de plantes Bt synthétisant une ou deux toxines. Volet théorique B. Impact du ralentissement du développement des insectes sur les plantes Bt sur l'efficacité de la stratégie HD/R. Le volet expérimental met en évidence un allongement de la durée du développement des larves se nourrissant sur une diète contaminée en toxine Cry. Ce ralentissement induit une séparation temporelle entre l'émergence des adultes de la zone Bt et de la zone refuge et perturbe une hypothèse principale de la stratégie HD/R: le croisement aléatoire entre adultes, indépendamment du génotype et de la zone d'origine. Dans ce troisième chapitre, nous étudions l'impact de la perturbation du croisement aléatoire sur l'efficacité de la stratégie HD/R. Nous testons également deux options pour optimiser la stratégie en cas d'asynchronie: l'utilisation de plantes Bt synthétisant une faible concentration en toxine (atténuant le décalage entre l'émergence des adultes) ou l'augmentation de la taille de la zone refuge (favorisant la survie des individus porteurs d'allèle de sensibilité et donc optimisant la dilution de la résistance à la génération suivante). Ce travail s'intègre dans une problématique actuelle et utilise des outils de biologie théorique (théories de la dynamique et de la génétique des populations) ainsi que le développement d'un modèle mathématique. Il apporte des éléments de réponse et de réflexion sur l'optimisation de la gestion de la résistance des insectes mais c'est aussi une illustration de la complémentarité entre la biologie expérimentale et théorique. / On the market since 1996, genetically modified plants synthesizing an insecticidal toxin (Cry toxin) stemmed from Bacillus thuringiensis, called Bt plants, target several insect pests (Lepidoptera or Coleoptera). Bt crops cover increasingly larger areas and control important pest populations The Insect Resistance Management Strategy (IRM) strategy currently recommended in the U.S.A. to limit the development of resistant populations is the High Dose / Refuge zone (HD/R) strategy. This pre-emptive strategy requires a refuge zone composed by non-Bt plants, usable by the target insect and in close proximity of the Bt zone synthesizing a high toxin concentration. My research project contributes to the effectiveness assessment of this HD/R strategy. It is structured on two main parts: an experimental, and a theoretical section. The first part characterizes the impact of Cry toxins on the biology of an insect pest. It is the basis of the theoretical part: the implementation of a mathematical model, which evaluates the effectiveness of the HD/R strategy. The originality of this project is based on the interactivity of these two components. Experimental section. Impact of the Cry toxins on the biology of Plodia interpunctella. We assess the impact of a range of concentrations of two Cry toxins (CryXX et CryYY) on several behavioural and biological parameters of a common pest of stored products: Plodia interpunctella (Hübner) (Lepidoptera : Pyralidae). These parameters are selected because their variation could influence the effectiveness of a HD/R strategy. So, it is important to quantify these parameters so that realistic values can be integrated in our model. The results of the model are thus not based on theoretical assumptions alone. Theoretical section A. Effectiveness of a HD/R strategy with Bt plants synthesizing one or two toxins. Initially, the HD/R strategy has been developed to limit the resistance towards Bt plants synthesizing one toxin. However, since 2003, new Bt cotton varieties synthesize two toxins simultaneously (BollgardII® et WidestrikeTM). We assess, with our model, the effectiveness of this strategy for Bt plants synthesizing one or two toxins. Theoretical section B. Impact of the slowing down of the insect development reared on Bt plants on the effectiveness of the HD/R strategy. The experimental part demonstrates that larvae reared on a Bt diet have a protracted development duration. The consequence of this is a temporal separation between adult emergence in the two zones (Bt zone and refuge zone). This could affect the main assumption of the HD/R strategy, i. e. random mating independently of the genotype and of the native zone. In this third chapter, we study the impact of random mating disruption on the effectiveness of a HD/R strategy. We test two options to optimise the strategy in case of asynchrony: the use of Bt plants synthesizing a lower toxin concentration (limiting emergence asynchrony) or increasing the refuge zone size (favouring the survival of insect carrying one or two susceptible allele and thus optimising the dilution of resistance at the next generation). This work is applied to a current issue. It uses some of the tools of theoretical biology (theories of population dynamics and population genetics) and develops a mathematical model. It provides some responses and some elements of thought about insect resistance management. It is also an illustration of the complementarity between experimental and theoretical biology.

This project predominantly investigated the implications of spatial heterogeneity in the ecological processes of competition and infection. Empirical analysis of spatial heterogeneity was carried out using the lepidopteran species Plodia interpunctella. Using differently viscous food media, it was possible to alter the movement rate of larvae. Soft Foods allow the movement rate of larvae to be high, so that individuals can disperse through the environment and avoid physical encounters with conspecifics. Harder foods lower the movement rate of larvae, restricting the ability of individuals to disperse away from birth sites and avoid conspecifics encounters. Increasing food viscosity and lowering movement rate therefore has the effect of making uniform distributed larval populations more aggregated and patchy. Different spatial structures changed the nature of intraspecific competition, with patchy populations characterised by individuals experiencing lower growth rates and greater mortality because of the reduced food and space available within densely packed aggregations. At the population scale, the increased competition for food individuals experience in aggregations emerges as longer generational cycles and reduced population densities. Aggregating individuals also altered the outcome of interspecific competition between Plodia and Ephestia cautella. In food media that allowed high movement rates, Plodia had a greater survival rate than Ephestia because the larger movement rate of Plodia allowed it to more effectively avoid intraspecific competition. Also the faster growth rate, and so larger size, of Plodia allowed it to dominate interspecific encounters by either predating or interfering with the feeding of Ephestia. In food that restricts movement, the resulting aggregations cause Plodia to experience more intraspecific encounters relative to interspecific, reducing its competitive advantage and levelling the survival of the two species. Spatial structure also affected the dynamics of a Plodia-granulosis virus interaction and the evolution of virus infectivity. Larval aggregation forced transmission to become limited to within host patches, making the overall prevalence of the virus low. However potentially high rates of cannibalism and multiple infections within overcrowded host aggregations caused virus-induced mortality to be high, as indicated by the low host population density when virus is presented. Also aggregated host populations cause the evolution of lower virus infectivity, where less infective virus strains maintain more susceptible hosts within the aggregation and so possess a greater transmission rate. The pattern of variation in resistance of Plodia interpunctella towards its granulosis virus was found using two forms of graphical analysis. There was a bimodal pattern of variation, with most individuals exhibiting either low or high levels of resistance. This pattern was related to a resistance mechanism that is decreasingly costly to host fitness.

Commercialisées depuis 1996, les plantes génétiquement modifiées produisant une toxine insecticide (toxine Cry) dérivée de Bacillus thuringiensis et appelées plantes Bt ciblent certains Lépidoptères ou Coléoptères ravageurs. Au fil des ans, les surfaces cultivées en plantes Bt sont de plus en plus importantes et contrôlent de larges populations d'insectes. Pour limiter le risque de développement de populations résistantes, une stratégie agricole appelée 'Haute Dose / Zone Refuge' est actuellement recommandée aux Etats-Unis par l'Environmental Protection Agency. Cette stratégie préventive nécessite la plantation d'une 'zone refuge' composée de plantes non-Bt utilisables par le ravageur ciblé et plantée à proximité de la 'zone Bt' qui synthétise une haute dose de toxine Cry. <p><p>Mon projet de recherche s’inscrit dans le cadre de l’évaluation de l'efficacité de cette stratégie et s’articule en deux phases :une phase expérimentale et une phase théorique. La première se concentre sur la caractérisation en laboratoire de l'impact des toxines Cry sur la biologie d'un ravageur. Cette phase constitue un support au volet théorique :la mise au point d’un modèle mathématique évaluant l'efficacité de la stratégie HD/R. L'originalité de ce projet repose entre autre sur l'interactivité entre ces deux volets.<p><p>Volet expérimental. Impact des toxines Cry sur la biologie de Plodia interpunctella. Nous évaluons séparément l'impact d'une gamme de concentrations de deux toxines Cry (CryXX et CryYY) sur une série de paramètres comportementaux et biologiques d'un insecte commun des denrées stockées: Plodia interpunctella (Hübner) (Lepidoptera :Pyralidae). Ces paramètres sont sélectionnés car leur variation pourrait avoir un impact sur l'efficacité de la stratégie HD/R dans le contrôle de la résistance. Il est donc pertinent de les quantifier pour intégrer dans le modèle des ordres de grandeur réalistes et générer des résultats qui ne sont pas uniquement basés sur des spéculations théoriques.<p><p>Volet théorique A. Efficacité de la stratégie HD/R pour des plantes Bt synthétisant une ou deux toxines simultanément. La stratégie 'HD/R' a été développée pour prévenir la résistance envers les plantes Bt synthétisant une seule toxine. Or, depuis 2003, de nouvelles variétés de coton Bt synthétisant simultanément deux toxines Cry sont commercialisées (BollgardII® et WidestrikeTM). Nous évaluons, grâce au modèle que nous avons développé, l'efficacité de cette stratégie lors d'une utilisation exclusive de plantes Bt synthétisant une ou deux toxines.<p><p>Volet théorique B. Impact du ralentissement du développement des insectes sur les plantes Bt sur l'efficacité de la stratégie HD/R. Le volet expérimental met en évidence un allongement de la durée du développement des larves se nourrissant sur une diète contaminée en toxine Cry. Ce ralentissement induit une séparation temporelle entre l'émergence des adultes de la zone Bt et de la zone refuge et perturbe une hypothèse principale de la stratégie HD/R: le croisement aléatoire entre adultes, indépendamment du génotype et de la zone d'origine. Dans ce troisième chapitre, nous étudions l'impact de la perturbation du croisement aléatoire sur l'efficacité de la stratégie HD/R. Nous testons également deux options pour optimiser la stratégie en cas d'asynchronie: l'utilisation de plantes Bt synthétisant une faible concentration en toxine (atténuant le décalage entre l'émergence des adultes) ou l'augmentation de la taille de la zone refuge (favorisant la survie des individus porteurs d'allèle de sensibilité et donc optimisant la dilution de la résistance à la génération suivante). <p><p>Ce travail s'intègre dans une problématique actuelle et utilise des outils de biologie théorique (théories de la dynamique et de la génétique des populations) ainsi que le développement d'un modèle mathématique. Il apporte des éléments de réponse et de réflexion sur l'optimisation de la gestion de la résistance des insectes mais c'est aussi une illustration de la complémentarité entre la biologie expérimentale et théorique.<p><p><p>/<p><p>On the market since 1996, genetically modified plants synthesizing an insecticidal toxin (Cry toxin) stemmed from Bacillus thuringiensis, called Bt plants, target several insect pests (Lepidoptera or Coleoptera). Bt crops cover increasingly larger areas and control important pest populations The Insect Resistance Management Strategy (IRM) strategy currently recommended in the U.S.A. to limit the development of resistant populations is the High Dose / Refuge zone (HD/R) strategy. This pre-emptive strategy requires a refuge zone composed by non-Bt plants, usable by the target insect and in close proximity of the Bt zone synthesizing a high toxin concentration.<p><p>My research project contributes to the effectiveness assessment of this HD/R strategy. It is structured on two main parts: an experimental, and a theoretical section. The first part characterizes the impact of Cry toxins on the biology of an insect pest. It is the basis of the theoretical part: the implementation of a mathematical model, which evaluates the effectiveness of the HD/R strategy.<p>The originality of this project is based on the interactivity of these two components.<p><p>Experimental section. Impact of the Cry toxins on the biology of Plodia interpunctella. We assess the impact of a range of concentrations of two Cry toxins (CryXX et CryYY) on several behavioural and biological parameters of a common pest of stored products: Plodia interpunctella (Hübner) (Lepidoptera :Pyralidae). These parameters are selected because their variation could influence the effectiveness of a HD/R strategy. So, it is important to quantify these parameters so that realistic values can be integrated in our model. The results of the model are thus not based on theoretical assumptions alone.<p> <p>Theoretical section A. Effectiveness of a HD/R strategy with Bt plants synthesizing one or two toxins. Initially, the HD/R strategy has been developed to limit the resistance towards Bt plants synthesizing one toxin. However, since 2003, new Bt cotton varieties synthesize two toxins simultaneously (BollgardII® et WidestrikeTM). We assess, with our model, the effectiveness of this strategy for Bt plants synthesizing one or two toxins.<p><p>Theoretical section B. Impact of the slowing down of the insect development reared on Bt plants on the effectiveness of the HD/R strategy. The experimental part demonstrates that larvae reared on a Bt diet have a protracted development duration. The consequence of this is a temporal separation between adult emergence in the two zones (Bt zone and refuge zone). This could affect the main assumption of the HD/R strategy, i. e. random mating independently of the genotype and of the native zone. In this third chapter, we study the impact of random mating disruption on the effectiveness of a HD/R strategy. We test two options to optimise the strategy in case of asynchrony: the use of Bt plants synthesizing a lower toxin concentration (limiting emergence asynchrony) or increasing the refuge zone size (favouring the survival of insect carrying one or two susceptible allele and thus optimising the dilution of resistance at the next generation). <p><p>This work is applied to a current issue. It uses some of the tools of theoretical biology (theories of population dynamics and population genetics) and develops a mathematical model. It provides some responses and some elements of thought about insect resistance management. It is also an illustration of the complementarity between experimental and theoretical biology.<p> / Doctorat en Sciences / info:eu-repo/semantics/nonPublished