Quantifying yield losses from Bt resilience among maize cultivars in South Africa

Genetically modified crops have provided economic and social benefits since becoming commercially available. One of the most successful and widely used applications is the integration of genes from the soil bacterium Bacillus thuringiensis for protection against damaging pests. Here, we leverage a robust dataset of 85,133 field-trial maize observations spanning all major production regions in South Africa from 1980-2018 to estimate yield gains associated with the first wave of genetically modified cultivars and explore the potential dynamic erosion of these gains since resistance was reported among first wave of single gene Bacillus thuringiensis cultivars. Leveraging the cultivars commercial release year, we find that genetically modified yield gains increased dynamically from their initial introduction in 2000, peaking at approximately 0.55 MT/ha around 2006, after which they significantly eroded to near-zero by 2014. Interestingly, this erosion was followed by a dramatic rebound in gains, reaching an in-sample high of approximately 0.75 MT/ha.