Effects of trace metals on Bombus terrestris (Hymenoptera: Apidae) microcolony and excretion during larval...

Trace metal pollution is an increasing threat to wildlife, driven by the growing demand for these elements in technologies. Because metals contaminate floral resources, they represent a major but poorly understood risk for bee communities, including social species such as bumble bees (Hymenoptera: Apidae). In particular, the sublethal consequences of metal exposure for bumble bee colony development remain scarcely documented, and the associated metal excretion process occurring at the larva-pupa interface in these holometabolous insects is still unclear. Here, we exposed queenless microcolonies of the buff-tailed bumble bee Bombus terrestris (L.) to field-realistic concentrations of copper (692 µM) or cadmium (7.38 µM), and assessed their effects on sucrose syrup consumption, worker survival, egg-laying event and brood development. We also quantified metal concentrations in larval and prepupal tissues to investigate potential metal excretion during development. Copper, but not cadmium, had detrimental effects on microcolony performance, as shown by reduced worker survival, delayed egg laying and impaired brood development. Workers exposed to copper also reduced their consumption of contaminated sucrose syrup, suggesting a possible behavioral avoidance to mitigate toxicity. In addition, metals were found at higher concentrations in larval than in prepupal tissues, indicating that metal excretion likely occurs at the larval-pupal interface. Overall, our study strengthens current knowledge on the effects of trace metals in social bees and provides evidence for a potentially important excretion process occurring during larval development.