The honeybee comb serves as the primary site for all essential colony activities, and its structural and functional integrity plays a crucial role in colony development. As combs age through successive brood-rearing cycles, their physicochemical properties undergo significant changes, which can negatively affect colony health and productivity. This review synthesizes the current knowledge on the biological functions of combs, the aging process, and the negative impacts of old combs on cell structure, worker morphology, colony strength, and bee product quality. Additionally, it examines the adaptive strategies employed by honeybees and the recommended beekeeping management practices to mitigate these effects. Specifically, old combs undergo structural changes in cell dimensions and reduced spatial capacity, leading to the growth of smaller bees with diminished foraging and productivity. Furthermore, bee products, such as honey and beeswax, collected from old combs demonstrate compromised quality and higher levels of environmental contaminants. To counteract these challenges, colonies engage in hygienic behaviors, such as cell cleaning and comb rebuilding, while their enhanced immune and detoxification systems help mitigate comb-derived stressors. This review demonstrates that the systematic replacement of old brood combs is a critical management strategy to optimize bee health and ensure sustainable apiculture.

Heavy metal pollution has emerged as a major challenge in global environmental science in the 21st century because of its extensive distribution, long-term environmental persistence, and non-degradability. As indispensable pollinators in ecosystems, honey bees have undergone marked population declines, a trend closely associated with multiple environmental stressors, including heavy metal contamination. Notably, lead (Pb), a widespread legacy toxic metal pollutant, is released into the environment through industrial emissions, vehicle exhaust, and other anthropogenic sources, contributing to long-term environmental contamination. Moreover, Pb can be transferred to honey bees through contaminated pollen and nectar. This exposure route may pose a risk to honey bee health, particularly under chronic or repeated exposure. This review synthesizes current evidence on Pb exposure routes, bioaccumulation, sublethal toxicity, and physiological responses in honey bees, while highlighting major uncertainties in colony-level risk assessment. Pb-associated physiological effects may impair individual bee health, but their long-term implications for colony health require further study.

The accumulation of cocoons within brood cells of old combs is a key factor causing a series of negative impacts on bee colonies. Previous studies did not sufficiently address this dynamic nature as the core microenvironment for preimaginal bee development. During this accumulation, the enrichment of potentially harmful microorganisms and chemical substances may pose a latent threat to colony health. This study combined microbiome and metabolomics analyses to systematically investigate the potential colony health risks posed by multi-generational accumulation of cocoons in Apis mellifera combs. The results demonstrated that with the growing number of brood rearing generations, the microbial diversity within the cocoons underwent significant shifts. For the bacterial community within multiple-generation cocoons, the Simpson index exhibited a significant increase, whereas indices including Sobs, Ace, and Chao showed significant decreases (p < 0.05). In the fungal community, the Shannon and Pielou_e indices significantly increased, while the Simpson and Faith_pd indices significantly declined (p < 0.05). Potential pathogens such as Melissococcus and the mycotoxin-producing fungus Wallemia became significantly enriched, reaching alarming relative abundances of 42.70% and 13.52%, respectively, in the multiple-generation cocoons. Metabolomic analysis further revealed the enrichment of 685 differential metabolites, including persistent exogenous pesticides such as cyanazine and pymetrozine, etc. Correlation analysis uncovered a significant positive relationship (r > 0.8) between these pesticide residues and pathogen abundance, indicating interactions between pollutants and pathogens that may exacerbate risks. This study reveals the aggravation of microecological imbalance and chemical pollution load within the cocoons of old combs and therefore provides strong scientific support for risk assessment of comb age in colony health management and offers practical guidance for the sustainable development of beekeeping.