Abstract   
    Several strategies involving refuge have been proposed for delaying insect resistance to Bt crops. The report was focused on the unstructured ‘natural’ refuges that contain plants naturally presented as part of the cropping system in the form of non-Bt plants that differ from Bt plant species, or wild host plants of the target pests. The cases of natural refuges applied in different countries were analyzed, and the factors that favor their success are discussed. The results indicate that the effectiveness of a natural refuge strategy depends on the biological characteristics of the target pest, the spatial and temporal distribution and abundance of the host plants in the agricultural system and the quality of the host plants for the pest species.