Bumblebees spread tire-wear particles through colonies more than plastic ones

In laboratory colonies, workers took up and passed on tire particles more often than polystyrene particles.

Editorial illustration — not from the study.

Researchers exposed buff-tailed bumblebee colonies to sugar water containing either tire-wear particles or polystyrene particles for four weeks. They then examined workers, larvae, pupae, honeypot contents and wax for particles using a microscope.

Tire-wear particles appeared more often in workers, larvae and nesting materials than polystyrene particles. The researchers suggest that the rough surfaces of tire particles may become coated with sugar water, making them harder for bees to recognize as contaminants, although this proposed explanation was not directly tested.

Where the particles went

Colonies received sugar water containing 0.4% by weight per volume of either tire-wear particles or polystyrene particles for four weeks. Tire-wear particles were significantly more frequently found in workers’ guts, transferred to larvae and incorporated into nesting materials than polystyrene particles. The study examined whole pupae as well as honeypot contents and wax for the presence of particles. The researchers suggest that a rough surface coated with sugar water could help tire-wear particles go unnoticed by the bees.

Why tire particles matter

Tire-wear particles are widespread in human-altered landscapes, especially urban environments. Because the bumblebees in this experiment took them up and transferred them within the colony more often than polystyrene particles, tire-wear particles may deserve greater attention in research on microplastic exposure in pollinators. The study also shows why results from one type of plastic particle may not apply to all environmentally relevant particles.

Evidence and caveats

This was a controlled experiment using buff-tailed bumblebee colonies exposed to particle-containing sugar water for four weeks. Researchers detected particles in bee tissues and nest materials by stereo microscopy, but the abstract does not report the quantities found or any resulting effects on bee health, behavior or survival. The work compared tire-wear particles with polystyrene particles under laboratory conditions, so it does not establish how often these transfers occur in wild colonies or whether tire-wear particles cause greater biological harm. The proposed role of surface roughness and sugar-water coating remains an explanation for further testing.

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