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Abstract
This study examined the efficient refuge policies for Bt cotton for three cotton growing regions in
India. This was accomplished by developing a single-pest, dual-toxin biological model simulating
bollworm resistance to the Bt toxin and synthetic pyrethroids, followed by formulating profit functions
for Bt and non-Bt cotton for a representative producer in each region. Profits received in subsequent
periods were considered in the regulatory model in order to choose a refuge constraint (static problem) or
a sequence of refuge policies (dynamic problem) for each region that maximize discounted profits
received over 15 years, subject to various economic and biological constraints. Dynamic solutions for the
regulatory problem were derived for each region using the Bellman equation. Results suggested that
South Indian farmers do not need to grow a refuge, but farmers in the North and Central regions do.
Results also suggested that planting sprayed refugia might be more profitable than planting unsprayed
refugia. Sensitivity analysis revealed that the refuge requirements were sensitive to the initial Bt
resistance level, relative proportion of CBWs in natural refuges, and proportions of heterozygous and
homozygous fitnesses in all of the three regions. Moreover, static refugia were found more profitable as
compared to dynamic refugia in the North and Central regions.