Replication, effect sizes and identifying the biological impacts of pesticides on bees under field conditions

1. Honeybees have world-wide importance as crop pollinators. To ensure their persistence in agricultural systems, statistically robust field trials of plant protection products are vital. 2. We consider the implications of regulations from the European Food Safety Authority that require the detection of a 7% effect size change in bee colony sizes under field conditions. 3. Based on a power analysis, we argue that the necessary levels of replication (68 replicates) may pose practical constraints to field testing. 4. Policy implications. Regulatory studies benefit from data sources collated over a range of spatial scales, from laboratory to landscapes. Basing effect size thresholds solely on expert judgement, as has been done, may be inappropriate. Rather, definition through experimental or simulation studies that assess the biological consequences of changes in colony size for bee pop- ulations is required. This has implications for regulatory bodies outside the European Union.