Landscape configurations of refuge areas that delay the evolution of resistance to Bt sugarcane: an agent based modeling approach

Although transgenic crops expressing genes from the bacterium Bacillus thuringiensis (Bt) are considered to be an effective pest control method, reckless usage adds environmental pressure on a pest population to develop resistance to the protein over time. The use of small portions of non-Bt crop (refuge areas) limits the rate of resistance development. Strains of Bt sugarcane for the South African market are being developed, and a prerequisite to releasing such a product on the market is a recommendation on the size and layout of the refuge areas. In this article, an agent-based simulation model is used to test the effectiveness of different landscape configurations of refuge areas in Bt sugarcane against resistance development occurring in an associated lepidopteran pest population. Individual insects are modeled as agents on an underlying sugarcane field that can either be Bt or refugium. The model is applied to 2 hypothetical case studies, each focusing on a specific aspect of refugia planning. The first focuses on the size and distribution of refuge, and the second on the shape of the refuge. A conservative general recommendation of 30% per farm, planted in large blocks on farms, is made based on simulation results and what is currently known about the target pest species, to provide regulatory bodies as well as growers with a starting point on how to regulate and plan refuge areas in South African Bt sugarcane.