Microplastics in honey bees (Apis mellifera): from exposure pathways to mechanistic toxicity, behavioral disruption, and colony-level risks

Microplastics (MPs) have emerged as pervasive contaminants across terrestrial and atmospheric environments, yet their implications for honey bees ( Apis mellifera ) - a globally important managed pollinator - remain insufficiently synthesized. This review integrates current evidence on MP exposure pathways, physiological and cellular mechanisms, and colony-level consequences in honey bees, while critically evaluating the strength and ecological realism (qualitatively) of the underlying evidence base. Honey bees encounter MPs through multiple routes, including atmospheric deposition on floral surfaces, ingestion via contaminated nectar, pollen, and water, and adhesion to their electrostatically charged cuticle during foraging. Plastic Particles have been detected in hive matrices such as honey and beeswax, with reported concentrations reaching up to 1,280 particles kg⁻¹ in honey and approximately 32,000 microfibres kg⁻¹ in beeswax. Experimental evidence indicates that MP ingestion induces oxidative stress, disrupts gut epithelial integrity, alters metabolic regulation, and reduces gut microbial diversity. However, the mechanistic evidence is predominantly derived from polystyrene (PS) exposures, with limited data for other polymers, and these findings should not be assumed to apply uniformly across polymer types. Toxicity is strongly influenced by particle size and polymer type, with nanoscale plastics exhibiting enhanced biological reactivity and greater potential for tissue translocation. Emerging studies further suggest that MPs may impair cognitive functions such as learning and memory, potentially affecting foraging efficiency. Although these effects are well documented at the individual level, most evidence derives from short-term, single-polymer laboratory exposures, and their translation into colony-level outcomes under field-realistic conditions remains largely unresolved. Reported concentrations of MPs in hive products are heterogeneous in analytical quality and units, and should not be compared directly across studies. Additionally, the presence of MPs in hive products establishes a possible dietary exposure pathway, although no measurable human-health risk has been demonstrated, underscoring the need for integrated, evidence-graded ecological risk assessment in honey bees. Whether these individual-level effects translate into reduced pollination efficiency under field conditions remains uncertain, and any such decline should currently be regarded as a hypothesis grounded in mechanistic plausibility rather than a demonstrated ecological outcome.