Monitoring of Sesamia nonagrioides resistance to MON 810 maize in the European Union: lessons from a long‐term harmonized plan

BACKGROUND MON 810 maize, which expresses the insecticidal protein Cry1Ab, is a highly effective method to control Sesamia nonagrioides (Lefebvre), a key maize pest in Mediterranean countries. Monitoring programs to assess the potential development of resistance of target pests to Bt maize are mandatory in the European Union (EU). Here we report the results of the S. nonagrioides resistance monitoring plan implemented for MON 810 maize in the EU between 2004–2015 and reassess the different components of this long-term harmonized plan. RESULTS No major shifts in the susceptibility of S. nonagrioides to the Cry1Ab protein have occurred over time. The reassessment of this long-term program has identified some practical and technical constraints, allowing us to provide specific recommendations for improvement: (1) use reference strains instead of susceptibility baselines as comparators for field-collected populations; (2) shift from dose–response bioassays to diagnostic concentrations; and (3) focus monitoring on areas with high adoption rates, such as the Ebro basin in Spain. CONCLUSION There are no signs of field resistance of S. nonagrioides to the Cry1Ab protein of MON 810 maize. Specific recommendations for improvement are provided, based on the knowledge and experience accumulated through the implementation of this unique EU-wide harmonized plan.