A new study recently published in Science provides no consistent results on the impact of neonicotinoid seed treatments in oilseed rape on the health of colonies of honey bees, bumble bees or solitary bees. The three-country, large-scale field study was conducted by the Centre for Ecology & Hydrology (CEH) in the UK, and sponsored by Bayer and Syngenta. The aim of the study was to examine the impact on honey bee colonies of foraging on oilseed rape treated or untreated with neonicotinoid seed treatments under realistic field conditions. A bumble bee and a solitary bee species field trial ran alongside this study.
 
The CEH did not find consistent effects across Germany, Hungary and the UK on key indicators of honey bee health such as colony strength, forager mortality, overwintering success of the colonies, behavior or disease susceptibility in honey bees.
 
In the German part of the study, the researchers found a positive correlation between hive performance and neonicotinoid seed treatment, i.e. the honey bee colony strength increased when the bees foraged on treated oilseed rape. This is in line with the observation that the colonies at the treatment sites were on average stronger at study initiation than those at the control sites.
 
In contrast, a weaker colony performance was observed in the UK and partially in Hungary. Colony mortality in the UK was too high across all treatments to support robust scientific conclusions, particularly on overwintering colony strengths. Consequently, no reliable risk conclusions can be drawn from these locations.
 
In Hungary, the average strengths of the colonies at the treatment sites were slightly lower at study initiation than at the control sites and the diversity of the surrounding landscape was not the same between the control and treatment fields.
 
As Dr. Richard Schmuck, Director of Environmental Safety at Crop Science, a division of Bayer, explains, “In order to understand such inconsistencies between the country results, it is important to consider that in the CEH study, honey bee colonies of different strengths were not equally distributed over the different treatment groups. We have recently completed a sensitivity analysis of a 20-year field study database which suggests that the development of bee colonies is highly influenced by the colony strength at study initiation.”
 
If these differences in hive size and the diversity of environmental surroundings are adequately considered, statistical analysis no longer shows the reported differences. “It is unfortunate that the reported statistical analysis was not corrected for differences in hive sizes or differences in environmental landscapes, but it does highlight the complexity of doing this sort of study on such a large scale,” Schmuck added.
 
“Therefore, we do not share the CEH’s interpretation that adverse effects of the seed treatments can be concluded from this study, and remain confident that neonicotinoids are safe when used and applied responsibly.”
 
Wild bee studies need careful analysis
 
The CEH paper also reports a highly variable and inconsistent correlation between exposure to neonicotinoid seed treatments in oilseed rape and the impact on the bumble bee, Bombus terrestris and the solitary bee, Osmia. Indeed, the only statistically significant result was on drone numbers in bumble bees, which were up in Germany in treated oilseed rape compared to the control, but down in the UK. The authors comment in the paper that neither bumble bee queen nor solitary bee egg cell production were “directly affected by the seed treatments or its interaction with country”.
 
However, there has been further statistical analysis undertaken by the authors which suggests that queen production in Bombus and reproductive cells in Osmia may be affected by exposure to neonicotinoids. However, this analysis was carried out on pooled data, i.e. when the results from all three countries are aggregated, and such correlations would not be observed if the data were analyzed separately for each country.
 
Conclusion
 
This study is one of a number of landscape studies carried out recently. The results of the CEH study are inconsistent and therefore inconclusive with variability of effects over both the bee species and the countries in which they were studied. We believe that had environmental factors (colony strength and landscape effects) other than exposure to treated oilseed rape been appropriately taken into account in the analysis, the results would have been similar to, for example, recent landscape studies conducted with clothianidin in Mecklenburg-West Pomerania, a state in northern Germany which demonstrated the safety of clothianidin seed treatments in oilseed rape for bee pollinators under realistic conditions.
 
Farmers need to control pests in arable crops such as oilseed rape if they are to provide the safe, high-quality, affordable food that European consumers demand. Bayer remains convinced that neonicotinoid seed treatments for oilseed rape have no short- or long-term negative effects on bees and that these seed treatments are a useful and effective tool for farmers.