Bees are much more robust than bumblebees

Clothianidin, an insecticide, affects different species of bees in different ways. Although this has no obvious negative effect on honeybees, it disrupts the growth of bumblebees and threatens the survival of whole colonies. However, the insecticide does not make either species more susceptible to diseases and pathogens, as shown by a large field study conducted in Sweden. The international team, composed of scientists from Martin Luther University Halle-Wittenberg (MLU) and the Swedish University of Agricultural Sciences, presents its latest findings in a reputable journal. Nature Communications.

The data from this study come from a unique research project in southern Sweden. In 2013, 96 honeybee colonies were established in oilseed rape fields where the seeds of the plants had already been treated or not treated with clothianidin. The researchers closely observed the development of the colonies, looked for typical pathogens and analyzed the pollen collected by the bees. A year later, the experiment was repeated with a subset of the first year's honeybees colonies. "Most of the previous studies examining the negative effects of neonicotinoids on bees had been conducted in the laboratory.The objective of this project was to determine if laboratory results could be confirmed in the field," says Julia Osterman, first author of the study. who is doing his doctorate at the MLU Biology Institute and at the Helmholtz Center for Environmental Research (UFZ). The large-scale project was led by Dr. Maj Rundlöf of Lund University in Sweden.

In 2015, the research team made a splash when its first article was published in the journal. Nature. The paper describes how the insecticide had a negative impact on wild bees. In the new study, the team has completed its previous discoveries with new details. One of the goals of the new study and a parallel study on drones, even if it only lasts one year, was to determine whether pesticides make bees more vulnerable to disease. The researchers have found no evidence of this. Instead, colonies near the treated sites acquired fewer pathogens over time, whereas the pollen they collected contained considerable amounts of clothianidin, whereas pollen from control colonies was virtually free from neonicotinoid.

The size of the honeybee colonies also remained constant. "Because of their size, honeybee colonies can offset the negative effects on bees much better than solitary bees or drones," says Osterman. But the situation was different for the bumblebees: if they were placed near fields treated with clothianidin, their offspring would not only be much smaller, but the colonies would produce far fewer queens and male drones. "Since only newborn bumble bee queens survive in the winter, the negative influence on their numbers is of particular concern," says Dimitry Wintermantel of the French Institute of Agricultural Sciences INRA, who also played a key role in the new study.

The new findings not only confirm the analyzes of the initial field study, but, according to the researchers, they also show the importance of testing wild bees in the pesticide approval process. At the same time, the study suggests that it can be difficult to transfer the results of laboratory tests under real field conditions. Both could mean that the risk assessment of pesticides may need to be modified. In 2018, the European Union banned the outdoor use of three out of five neonicotinoids, including clothianidin, because of their harmful effects on bees. This forced farmers to resort to alternative pesticides. "However, the impact of this ban on bees and the way mass crops, such as rapeseed, are changing in Europe, is still uncertain," Osterman concludes.

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Martin Luther University Halle-Wittenberg