Qingxin Meng

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.

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.

Honey bees transform nectar into honey through a combination of physical and chemical processes, with the physical process primarily involving the evaporation of excess water to concentrate the nectar. However, the factors affecting evaporation efficiency, such as evaporation duration, cell type, and bee species, remain incompletely understood. This study aimed to examine how these factors affect nectar evaporation efficiency during honey production. We measured the sucrose content in solutions subjected to combined active and passive evaporation, as well as passive evaporation alone. The results showed that eastern honey bee (EHB; Apis cerana) colonies were more efficient at concentrating sucrose solutions in worker cells than in drone cells under both combined active and passive evaporation conditions, as well as passive evaporation alone. Conversely, western honey bee (WHB; Apis mellifera) colonies exhibited greater efficiency in drone cells. Additionally, EHB colonies were more effective than WHB colonies in converting sucrose into fructose and glucose. Under passive evaporation, EHB colonies required at least 48 h to significantly concentrate the sucrose solution, while WHB colonies achieved similar concentrations in just 24 h. Sucrose content increased with the duration of passive evaporation. These findings provide insights into how honey bee colonies can efficiently produce mature honey during periods of abundant nectar flow.

Glyphosate (GY) is the most widely used herbicide in agriculture worldwide. Lead is a common heavy metal in the natural environment. Honeybees, as pollinators, are exposed to these pollutants. So far, few reports have evaluated the toxic effects of GY mixed with heavy metals on honeybees (Apis cerana cerana). This study found that the acute toxicity of lead (LC50 = 1083 mg/L) is much greater than that of GY (LC50 = 4764 mg/L) at 96 h. The acute toxicities of the mixed substances were as follows: LC50 = 621 mg/L of lead and LC50 = 946 mg/L of GY. The combination of lead and GY was more toxic than either of the individual substances alone. Compared to the individual toxicity, combined treatment significantly affected the bees’ learning and cognitive abilities and changed the relative expression of genes related to immune defense and detoxification metabolism in A. c. cerana. The combination of lead and GY seriously affected the behavior and physiology of the studied honeybees. This study provides basic data for further research on the combined effects of GY and heavy metals on bee health. It also serves as a reference for effective colony protection.

Honey bees play a critical role as pollinators. However, their reproduction success and survival face severe threats due to the deterioration of their living environment. Notably, environmental conditions during their preimaginal stage inside brood cells can influence their immune capabilities and overall health after emergence. During the in-cell developmental stage, workers are in close contact with cocoons, which can become a source of stress due to accumulated metals. To investigate this potential threat, experiments were conducted to examine the impact of cocoons in brood cells used to rear different generations on the metal content and detoxification gene expression levels in Apis cerana cerana. Our findings indicated significant differences in the layers, weight, base thickness, and metal contents like Cr, Cd, Pb, Mn, Ni, and As of cocoons in multi-generation brood cells compared to single-generation brood cells. These increases led to significant elevations in metal levels and upregulations of the four CYP450 detoxification genes in both six-day-old larvae and newly emerged workers. In conclusion, this study highlights the negative impact of cocoons in multi-generation brood cells on bee health and provides evidence supporting the development of rational apiculture management strategies for ecosystem stability.

The cell orientation characteristics of the natural combs of honey bees have received much research attention. Although natural combs have been shown to be composed of cells with three orientations—vertical, intermediate (oblique), and horizontal—the proportion of comb cells in these three orientations varies. Knowledge of the comb-building preferences of honey bees is essential for the installation of wax comb foundations, and clarification of the cell orientation characteristics of natural honey bee combs is important for beekeeping. The purpose of this study was to determine the cell orientation characteristics of natural combs of Eastern honey bees (Apis cerana cerana) and Western honey bees (Apis mellifera ligustica). Newly built combs were used to measure the orientation of hexagonal cells and calculate the proportion of cells in different orientations relative to the total number of cells. The number of eggs laid by queens in the cells of different orientations was also determined. The orientation of cells in the natural combs of Eastern and Western honey bees was determined based on the value of the minimum included angle between the pair of parallel cell walls and a vertical line connecting the top and bottom bars of the movable frame in the geometric plane of the comb: 0°≤θ≤10°, 10°<θ≤20°, and 20°<θ≤30° for vertical, intermediate, and horizontal orientations, respectively. Natural combs were composed of cells with at least one orientation (vertical or horizontal), two orientations (vertical + intermediate (oblique) or vertical + horizontal), or three orientations (vertical + intermediate + horizontal), and the proportions of combs with the three aforementioned configurations differed. Both Eastern honey bees and Western honey bees preferred building combs with cells in a vertical orientation. Queens showed no clear preference for laying eggs in cells of specific orientations. The results of this study provide new insight that could aid the production and cutting of wax comb foundations of Eastern and Western honey bees. Our study highlights the importance of installing wax comb foundations compatible with the comb-building preferences of bees.