Following a request by the European Commission, the European Food Safety Authority (EFSA) assessed the scientific information in the publication by Trtikova et al. (2015), as well as the relevance of their findings for the risk assessment of maize MON 810 and other Cry1Ab-expressing Bt-maize events for which the EFSA GMO Panel has issued a scientific opinion.

Trtikova et al. (2015) studied cry1Ab transgene expression and levels of the newly expressed Bt Cry1Ab protein in the leaves of two maize MON 810 varieties grown under optimal and stressful (cold/wet and hot/dry) environmental conditions. Based on their experiments with plants grown in controlled environments (climate chambers, greenhouse), the authors claimed that genetic background and environmental conditions, especially abiotic environments, could affect cry1Ab transgene expression and Bt Cry1Ab protein levels in maize MON 810. Regarding Bt Cry1Ab protein levels in particular, Trtikova et al. (2015) concluded that these factors could alter the expression variability of this protein. The authors extrapolated their findings to field-grown maize MON 810 and postulated that the Bt Cry1Ab protein concentration in relevant plant tissues of maize MON 810 might not always be sufficiently high to kill a high proportion of heterozygous resistant genotypes to maintain any resistance allele in the target insect pest population functionally recessive. The authors considered that this may have implications on insect resistance management (IRM) measures, which aim at delaying insect resistance evolution to Bt proteins in the target insect pest populations such as the European corn borer and Mediterranean corn borer.

The EFSA GMO Panel has already considered that there can be variability in Bt protein levels of genetically modified (GM) plants. This aspect is already well known and extensively reported in the peer-reviewed literature. Moreover, Bt Cry1Ab protein content variability in maize MON 810 and other Cry1Ab-expressing maize Bt-events is clearly indicated by the data in GM plant market registration applications. Reported Bt Cry1Ab protein levels in these applications are derived from plants grown in field trials carried out in different seasons and across several locations, thereby accounting for diverse environmental conditions.

Regarding possible implications on IRM measures due to insufficient levels of Bt Cry1Ab protein in relevant tissues of maize MON 810 as hypothesised by Trtikova et al. (2015), EFSA considers that this aspect would be relevant only for GM plant market registration applications for cultivation. However, the Bt Cry1Ab protein levels reported in Trtikova et al. (2015) for the two maize MON 810 varieties grown under optimal or stressful conditions are well within the range of values determined for maize MON 810 and Bt11 in the GM plant market registration applications for cultivation for which the EFSA GMO Panel has issued a scientific opinion. Moreover, at present, EFSA is not aware of early warning signs indicating increases in tolerance to Cry1Ab-expressing Bt maize in field populations of the European corn borer and Mediterranean corn borer.

Taken together, the findings reported by Trtikova et al. (2015) present no new scientific information that would invalidate the EFSA GMO Panel’s previous risk assessment conclusions and recommendations on risk management of maize MON 810 or any other Cry1Ab-expressing Bt-maize events for which it has issued a scientific opinion. Therefore, EFSA is of the opinion that the previous risk assessment conclusions and risk management recommendations on all Cry1Ab-expressing Bt-maize events so far, including maize MON 810, remain valid and applicable.