Modelling the spatial configuration of refuges for a sustainable control of pests: a case study of Bt cotton.

The 'high-dose-refuge' (HDR) strategy is widely recommended by the biotechnology industry and regulatory authorities to delay pest adaptation to transgenic crops that produce Bacillus thuringiensis (Bt) toxins. This involves cultivating nontoxic plants (refuges) in close proximity to crops producing a high dose of Bt toxin. The principal cost associated with this strategy is due to yield losses suffered by farmers growing unprotected, refuge plants. Using a population genetic model of selection in a spatially heterogeneous environment, we show the existence of an optimal spatial configuration of refuges that could prevent the evolution of resistance whilst reducing the use of costly refuges. In particular, the sustainable control of pests is achievable with the use of more aggregated distributions of nontransgenic plants and transgenic plants producing lower doses of toxin. The HDR strategy is thus suboptimal within the context of sustainable agricultural development.