Résultat de la recherche
Consequences of the domestication of chili pepper on multitrophic interactions
La domestication des plantes vise à réduire leurs défenses et à sélectionner des variétés ayant un rendement plus élevé que leurs ancêtres sauvages. On pense que ces caractéristiques modifiées ont un impact sur les interactions plantes-insectes. Cependant, dans le cas du piment, ces effets restent peu clair. Par conséquent, cette thèse de doctorat visait à étudier les conséquences de la domestication du piment sur les interactions multitrophiques, en utilisant des variétés de piment et leur ancêtre sauvage Chiltepin comme modèles d'étude. Le premier chapitre se concentre sur l'effet des niveaux de capsaïcine dans les fruits domestiques sur la performance de l'herbivore généraliste S. latifascia et de son ectoparasitoïde E. platyhypenae. Nous avons constaté que la domestication du piment a augmenté et diminué la capsaïcine dans les fruits. Seulement à une concentration élevée de ces métabolites secondaires, la capsaïcine a eu un effet négatif sur les insectes herbivores, et leur ectoparasitoïde. Par conséquent, la réponse de la plante à l'herbivorie dépend du niveau de piquant des fruits. Le chapitre deux explore les insectes nuisibles et leur virus associé sur les piments sauvages et domestiques dans leur environnement naturel. Nos résultats montrent que la domestication du piment a altéré les défenses physiques et chimiques des feuilles. En conséquence, les piments sauvages étaient plus résistants aux insectes broyeurs et aux virus, mais pas à leurs vecteurs, les aleurodes. Le chapitre trois est consacré à l'étude de l'alimentation et de l’oviposition du charançon spécialiste du piment (A. eugenii) sur les piments sauvages et domestiques comme ornement et pour la consommation. Globalement, la domestication a modifié les caractéristiques morphologiques et chimiques (capsaïcine) des fruits avec des conséquences directes sur l'alimentation et l’oviposition du charançon du piment. Ce travail a des implications importantes pour l'agriculture durable qui repose sur une résistance accrue des plantes et une utilisation réduite des pesticides. Enfin, cette étude permet de comprendre l'impact des pressions de sélection à court terme exercées par l'homme sur nos plantes cultivées et les forces de sélection naturelle qui ont façonné les interactions plantes-insectes au cours de l'évolution. ABSTRACT Plant domestication aims to reduce plant defenses and select varieties with a higher yield than their wild ancestors. It is believed that these altered traits have an impact on plant-insect interactions. However, in the case of chili pepper, these effects remain unclear. Therefore, This Ph.D. thesis aimed to study the consequences of domestication of chili pepper on multitrophic interactions, using chili pepper varieties and their wild ancestor Chiltepin as study models. Chapter one focuses on the effect of altered levels of capsaicin in domesticated chili on the performance of the generalist herbivore S. latifascia and its ectoparasitoid E. platyhypenae. We found that chili domestication has increased and decreased capsaicinoids in fruits. Only at a high concentration of these secondary metabolites, capsaicin had a negative effect on insect herbivores, and their ectoparasitoid. Therefore, the response of the plant to herbivory depends on the pungency level in fruits. Chapter two explores the pest insects and their associated virus on wild and domesticated chili peppers in their natural environment. Our results showed chili domestication has altered physical and chemical defenses in leaves. As consequence wild chili were more resistant to chewing insect and viruses’ infection but not to their vector, whiteflies. Chapter three is devoted to studying the feeding and oviposition of the specialist pepper weevil (A. eugenii) on wild and domesticated chiles as ornamental and for consumption. Overall, domestication has altered morphological and chemical (capsaicin) traits in fruits with direct consequences for the feeding and oviposition of the pepper weevil. This work has important implications for sustainable agriculture that relies on enhanced plant resistance and reduced pesticide use. Finally, this study allows understanding the impact of short-term human-mediated selection pressures applied to our crop plants and the natural selection forces that have molded plant-insect interactions over evolutionary time.
Interpopulation variation in a larval parasitoid of bruchids, Stenocorse bruchivora (Hymenoptera : Braconidae): Host plant effects
For parasitoids of herbivores, the two most important biotic factors that will influence their fitness are the host species that they attack and the plant species that the host feeds on. Variation in these two trophic levels because of different habitat characteristics may largely drive the evolution of the interaction between parasitoids and their hosts. Through transplant experiments with three plant-insect populations in Mexico, we examined the consequences of plant variation for the interaction between a bruchid beetle, Zabrotes subfasciatus (Boheman) (Coleoptera: Bruchidae), that feeds on bean seeds of the genus Phaseolus L. (Leguminosae: Phaseolinae) and one of its main parasitoids, Stenocorse bruchivora (Crawford) (Hymenoptera: Braconidae). Results revealed great variation in performance among parasitoid populations. Both the population of origin of the parasitoid and of the host plant influenced the performance of developing parasitoids as well as adult oviposition behavior. Wasps from the Atila population were more likely to parasitize the herbivore and developed faster than wasps from the other two populations, Malinalco and Tepoztlan. The results call be explained in part by the spatial distribution of the host plant, host availability, and seed quality in this population. Variation in performance among parasitoid populations decreased when wasps were exposed to their host in cultivated seeds. This could be caused by the better and less variable quality of this novel resource, and consequently, of the bruchid host. The results from this study indicate that both host plant quality and genetic variation among populations are crucial factors in determining the nature and evolution of the interaction between parasitoids and their herbivorous hosts.
Microsatellite markers in a complex of Horismenus sp. (Hymenoptera: Eulophidae), parasitoids of bruchid beetles
Parasitoids of the genus Horismenus (Hymenoptera: Eulophidae) are the main natural enemies of bruchid beetles that feed on several species of Phaseolus beans. Samples of Horismenus depressus, H. missouriensis and H. butcheri were collected from seeds of three Phaseolus species throughout Mexico to examine the impact of plant variability on the genetic structure of parasitoid populations. For this purpose, six microsatellite loci were isolated and characterized. These loci are of great interest in understanding the taxonomy of the genus Horismenus, the most important Eulophid genus in the Neotropics.