Climate-driven pressure and landscape spillover challenge the resilience of Bt maize (MON810) against Sesamia nonagrioides in a Mediterranean hotspot (Girona, Catalonia)

Bt maize is a genetically modified crop engineered to express insecticidal proteins derived from Bacillus thuringiensis . This technology has suppressed populations of Sesamia nonagrioides , the primary pest of maize in the Mediterranean basin, by delivering a lethal toxin dose to feeding larvae. Recent anomalies in the Girona province involving the detection of larvae within Bt fields have raised concerns regarding potential field-evolved resistance. To address this, we analyzed a dataset (2013–2025) combined with spatial and climatic monitoring during recent years (2021–2023). Results indicate that Bt technology maintains functional field efficacy, as no viable pupae were recovered from Bt plants. Climatic analyses revealed significant associations between warmer autumn conditions and increased larval pressure, consistent with an extension of the pest’s seasonal activity window. Spatial analysis of the 2022 survey further identified localized areas of elevated infestation, where damage observed in Bt stands was spatially associated with high pest pressure in nearby conventional maize. This pattern is consistent with a density-dependent spillover mechanism. These findings suggest that the recent increase in damage may reflect the interaction between environmental conditions, landscape-level pest pressure, and the limits of field-level protection rather than loss of Bt efficacy per se . The durability of transgenic crops under climate change depends on plant genetics and environmental factors. This study supports the value of incorporating landscape-scale surveillance into resistance-management strategies.