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Bees’ pesticide risk is species and landscape dependent

Bees swarming around a pollen trap. Photo.
Photo: Theresia Krausl

There is newfound evidence of how bees' pesticide exposure depends on their interaction with the environment.

According to scientists from Lund University and the Swedish University of Agricultural Sciences, more agricultural land surrounding the bees increases their pesticide-related risk, but only for the solitary bee and bumble bee, species that forage over smaller areas than the honey bee. These findings support the capacity of semi-natural areas to reduce pesticide risk for wild bees.

Agricultural landscapes expose bees to pesticides as their activity coincides with pesticide use. Ecological traits, like foraging range and life cycle, determine this activity. This means that species with different foraging ranges and activity periods will likely have different pesticide exposure and risk.

– Pesticide risk assessment is evolving to capture this ecological complexity, but requires a better understanding of how exposure varies among bee species and landscape contexts. Our study uniquely describes how bees' ecology relates to their pesticide exposure and risk. We evidence this with a landscape-scale study where we measured pesticide concentrations in three bee species’ collected pollen and nectar, which was sampled across southern Sweden, says Jessica Knapp, biology researcher at Lund University.

Most pesticide-related risks came from a few insecticides. The study points to specific pesticide uses that could be changed to reduce pesticide-related risks for bees. Furthermore, pesticide risk correlated between nectar and pollen and among bee species, but was highest in honey bee-collected pollen. These results are practically relevant because, to some extent, they suggest that we can cautiously predict risk among bee species and food sources.

The results are timely as the European Commission has just revised the EU Pollinator Initiative, taking stronger and broader action to reverse the decline of pollinators, including bees, by 2030. This aligns with the European Commission's Farm to Fork Strategy, which aims to decrease pesticide use and environmental risk by 50 percent by 2030.

– To track the success of this target in reducing pesticide risk, we need studies like ours that provide information on how current agricultural practices and approved pesticide use lead to exposure levels and frequencies of, often multiple, pesticides for non-target organisms such as bees. Based on our results, we suggest that honey bee-collected pollen could form the basis for tracking bees’ pesticide-related risk in agricultural landscapes, says Maj Rundlöf, biology researcher at Lund University.

The MixToxBee project is significant for the conservation of pollinator species in agricultural landscapes by exploring their relative differences in pesticide-related risk depending on the amount of agricultural land.

– In contrast to previous work, we combine multiple aspects of pesticide exposure usually restricted to individual studies. Such as landscape contexts, pollinator species, crop types and food sources. Our findings are also practically relevant because they provide, for the first time, an assessment of pesticide mixtures in different food sources for different bees species in multiple cropping systems, concludes Jessica Knapp.

The study is published in Nature Ecology and Evolution.