Exposure of Bombus terrestris to anthropogenic pollutants in urban and agricultural habitats and their effects

Benner, Lena; Schäffer, Andreas (Thesis advisor); Brack, Werner (Thesis advisor)

Aachen : RWTH Aachen University (2023)
Dissertation / PhD Thesis

Dissertation, RWTH Aachen University, 2023


Pollinators are important key stone species for the health of ecosystems, providing the ecosystem service of pollination for wild flowers as well as for food crops. But their numbers have been declining for years, resulting in pollinator shortages and lack of pollination. Bees are probably the most publically known pollinators. They have inspired many groups from the public to take action and call for more protection, especially in agricultural practices. In the scientific community, the Western honeybee Apis mellifera is most often used as surrogate species in research regarding pollinators. Several studies have reported, that A. mellifera is not a suitable surrogate species to cover the more than 200,000 wild living bee species, as it is highly domesticated, living in hives of several thousand individuals and can thus buffer small scale effects by sheer numbers of individuals. But so far, data on other bee species such as solitary bees, is limited to non-existent. In this study we wanted to test the native bumblebee species Bombus terrestris as model species for holistic biomonitoring projects, measuring different classes of anthropogenic pollutants. B. terrestris is covered in dense fur, has a small flight range (~800 m), is ubiquitously spread throughout Europe and can be bred commercially, making it an ideal species for small-resolution biomonitoring. The project focussed on two main questions: 1) To which anthropogenic pollutants are pollinators exposed in typical land-use scenarios and in which concentrations? 2) Do these field-realistic concentrations cause adverse effects in bumblebees? In a two-year field study, we placed commercial bumblebee hives in urban and agrarian locations around Aachen, Germany. Foragers, pupae and honey were collected, extracted using a modified QuEChERS approach and measured for 25 target pesticides. In addition, foragers were measured for 12 target metals. In total, residues of 15 different pesticides were found. The most often found pesticides were the herbicide prosulfocarb (36.4% of foragers) and the fungicide flutolanil (15.9% of all foragers). 33% of foragers carried mixtures of pesticides (>1 pesticide per insect). Often observed mixtures in foragers were prosulfocarb-difenoconazole, boscalid-azoxystrobin and azoxystrobin-difenoconazole. In general, pupae had lower pesticide concentrations than foragers with mean cumulative concentrations of 6.0 ng/individual for foragers and 3.3 ng/individual for pupae in agricultural areas. Only four active substances were detected in honey samples. Mean cumulative concentrations of 258.6 ± 65.1 mg/kg dw and 383.6 ± 59.3 mg/kg dw were measured for heavy metals and half-metals in April and July, respectively. Significant differences between the land-use types were only found for boron and cadmium. A maximum concentration of 0.94 mg/kg dw Cd (0.07 µg/bee) was measured. No land-use specific pollution profiles could be identified for either pesticides, (half-)metals or their combination. The results show that pesticides occur in all investigated location, no matter the land-use type. But they seem to be rather individual occurrences instead of mass poisonings. For the following toxicity assays we investigated three priority pollutants: cadmium, terbuthylazine and difenoconazole, all detected in bumblebees in our study. They were tested as single substances and binary mixtures in a standardised oral toxicity assay (OECD Guideline 247). Terbuthylazine and difenoconazole did not cause mortality in the tested concentration ranges (NOED ≥22 µg/bee and ≥903 μg/bee, respectively). Cadmium caused mortality with a LD50 of 6.70 µg Cd/bee and effects at ED50= 1.92 µg Cd/bee after 48 h. In the binary mixtures with pesticides, the toxicity of cadmium increased to LD50= 2.84 µg Cd/bee with terbuthylazine and 3.92 µg Cd/bee with difenoconazole (synergism). We developed a novel assay to assess mobility of individuals using a flight arena, which improved the sensitivity of the effect detection compared to oral mortality tests. Significant differences between mobility of test and control groups were measured at a dose of 0.59 µg Cd/bee. The results of the oral tests highlight that it is important to consider pollutant mixtures when assessing the adverse effects in real field situations. The results from the mobility test indicate that adverse effects on bumblebee mortality and thus colony survival could already occur at concentrations measured in the field. In conclusion, B. terrestris has proven to be a suitable species for biomonitoring approaches, as it is easy to handle, resistant to different temperatures, its handling is less laborious than honeybee beekeeping and comparatively cheap. As B. terrestris can be used to monitor field concentrations as well as assess their toxicity, direct connections between exposure and effect can be drawn without the need to extrapolate e.g. on the species level. The data gathered in this study can be used as a baseline to establish a national/global monitoring scheme. We showed that wild living pollinators are exposed to mixtures of different substances, spanning different substance categories. Effects of these mixtures cannot be reliably predicted so far. Therefore, it is important that mixture effects are integrated into current regulations and monitoring schemes.


  • Department of Biology [160000]
  • Chair of Environmental Biology and Chemodynamics [162710]