Bases de la resistencia a preparados bioinsecticidas basados en "Bacillus thuringiensis" en diferentes especies de insectos

The use of pesticides in modern agriculture is essential for optimum productivity. Currently, there is a tendency to use bio-insecticides since the harmful effects of most conventional insecticides. The bioinsecticide preparations based in insecticidal crystal protein (Cry toxins) of “Bacillus thuringiensis” (Bt) are the leading product in the insecticide market and Bt transgenic plants are being cultivated worldwide. The usefulness of this biopesticide could be limited by the development of resistant insect populations without appropriate resistance management measures, so knowledge of insect resistance mechanisms is essential. The Cry toxins mode of action is a complex process including several steps. The main step is the binding of the cry toxins to specific receptor located in the plasmatic membrane of midgut epithelial cells. Disruption of one of them could lead to development resistant insects. Resistance to one Cry toxin can be produced by different mechanisms in diverse insect species; therefore a resistant insect strain can have a specific mechanism of resistance to one or more toxic Cry proteins. The genes responsible of resistance in several strains of the same insect species, with the same kind of resistance, can be different. Then, is really important the study both the genes implicated on the interaction with Cry toxins and the nature of the proteins codified. The objective is to know its implication for designing the right management to avoid and prevent the development of Bt resistance. In this dissertation it has been studied various phenotypes of resistance in different strains of “Plutella xylostella” (first Bt resistant pest insect in field) and “Bombyx mori” (lepidopteran genetic model insect) insect species. In each of them the genetic and biochemical bases of resistance has been studied; as well as it has been determined the genes implicated in the resistance phenotype by linkage analysis. This study will contribute to a better understanding of the resistance and how to delay, or even prevent, the resistance to Bt.