Bumblebees’ nutrition influences their pesticide resistance

How susceptible bumblebees are to a common fungicide depends on the flowering plants to which it is applied on and how diverse the food supply is that is available to the insects. Monocultures can increase the insects’ sensitivity to the fungicide or generally have negative effects on health, growth and fertility. This is shown by the experiment of a research team led by Prof. Dr. Alexandra-Maria Klein, Chair of Nature Conservation and Landscape Ecology at the University of Freiburg, and Dr. Dimitry Wintermantel. They have published their results in the current issue of the journal Science of the Total Environment. They could help improve pesticide approval procedures and provide additional arguments for bringing diverse flowering habitats back into the agricultural landscape to make bumblebees and other wild bees more resistant to pesticides.

Fungicide effects solely on the flowering plant Phacelia

For their so-called semi-field experiments, the environmental scientists used 39 large flight cages in which Phacelia or buckwheat monocultures or a flower mixture was grown. In each cage, the researchers placed a colony of the buff-tailed bumblebee (Bombus terrestris), which is a wild bee. Half of the cages were treated with a common fungicide containing the active ingredient azoxystrobin. Fungicides are pesticides used to control fungal infections.

“Effects of the fungicide were seen only in Phacelia,” says Wintermantel. Although the fungicide used is classified as bee-safe, both the body weight of the bumblebees and the growth of the entire colony were reduced here. “In buckwheat, the colonies performed worse overall, but the fungicide had no effect here,” adds Wintermantel. “Only in the flowering mixture did the colonies develop well overall and there were no effects caused by the fungicide.”

A preference for high protein pollen

The pollen of Phacelia and buckwheat differ greatly. Buckwheat pollen has a low protein content, which could be one reason for the overall poor development of the insects that fed on these plants because bumblebees actually need food with a high protein content. This is provided by the pollen of Phacelia, also known as “bee’s friend”. But why it doesn’t protect wild bees from the effects of fungicide is speculative, Wintermantel says.

Perhaps the fungicide impairs the bumblebees’ ability to collect pollen that is not easily accessible or perhaps the insects need a combination of different nutrients in addition to high protein content, as offered by a flowering mixture, to develop fungicide resistance. “There is a hypothesis that a balanced nutritional offer helps bees to cope better with pesticides because they can choose the food they need.” The Freiburg researchers explain that further research is needed on the effects of fungicides and other pesticides.

Diverse habitats back into the agricultural landscape

According to Wintermantel, the results could then influence the design of trials in pesticide approval processes, such as in the selection of suitable flowering plants. “And if it is further shown that a flowering mixture contributes to pesticide resistance in bees, we should once again introduce more flowering habitats such as extensive meadows and pastures, flowering paths and hedgerows into the agricultural landscape,” Klein concludes.

Original publication
Wintermantel, D., Pereira-Peixoto, M.-H., Warth, N., Melcher, K., Faller, M., Feurer, J., Allan, M.J., Dean, R., Tamburini, G., Knauer, A.C., Schwarz, J.M., Albrecht, M., Klein, A.-M. (2022): Flowering resources modulate the sensitivity of bumblebees to a common fungicide. In: Science of the Total Environment 829, 154450. https://doi.org/10.1016/j.scitotenv.2022.154450