Old combs: risks for brood, bees and beeswax

1. The essentials in brief

An old comb is not merely dark : its cells shrink and accumulate cocoons, residues and contaminants.
Several studies on Apis mellifera associate old combs with less brood, smaller workers and reduced productivity.
Wax acts as a reservoir for lipophilic substances : acaricides, pesticides, certain veterinary drug residues and pollutants can accumulate in it.
Findings on Apis cerana show a natural mechanism of gnawing and rebuilding old combs, but this behaviour cannot be transferred directly to the European honey bee.
At the apiary, the practical message remains simple : renew frames regularly, remove black combs from the wax cycle and monitor the origin of recycled wax.

2. What the study shows

This chapter summarises how comb ageing alters the space available for brood development, the biological quality of the bees and the contaminant load of the wax.

Question. Janine Kievits’ article starts from a recent review by Meng and colleagues on old combs and raises a very practical question : what happens when a frame remains too long in the colony ? The comb is not merely a support structure. It serves brood rearing, the storage of honey and pollen, the transmission of vibrations during dance communication, and it also retains odours that contribute to the colony’s chemical identity (Kievits, 2025 ; Meng et al., 2025).

Method. The main study used here is a synthesis review, not a statistical meta-analysis. It brings together work on the physical and chemical ageing of combs, its effects on bee development, colony performance and the quality of bee products. The complementary article by Meng et al. (2024) provides experimental data on old-comb gnawing in Apis cerana cerana in Yunnan, China.

Results. With successive generations of brood, cells accumulate cocoons, larval faeces and other residues. Cell walls thicken, internal volume decreases and cell shape changes. In a study cited by Meng et al. (2025), the weight of an Apis mellifera carnica comb increases from 0.26 g/cm² to 1.32 g/cm² over seven years, while the diameter of worker cells decreases from 6.00 to 4.86 mm and their volume from 0.31 to 0.18 ml.

These changes are not only geometric. Several studies associate old combs with smaller or lighter workers, with less developed hypopharyngeal and wax glands, shorter appendages, reduced longevity and a decline in certain indicators of colony performance (Elnabawy et al., 2020 ; Taha et al., 2021 ; Meng et al., 2025). Micro-computed tomography analyses also confirm that old combs may contain dense deposits at the bottom of cells, reducing the space available for the pupa (Sipos et al., 2023).

Ageing is also chemical. Beeswax is rich in lipid compounds and readily absorbs lipophilic molecules. Old combs can therefore concentrate residues of acaricides, pesticides, biocides, metals and other persistent contaminants. Depending on the substances, this contamination can then migrate to bee bread, brood and, to a lesser extent, honey (Wu et al., 2011 ; Morales et al., 2019 ; Alkassab et al., 2022 ; Meng et al., 2025).

Interpretation. The central message is robust : combs age biologically with the colony. They become heavier, darker, less favourable for brood development and more likely to concentrate contaminants. This does not mean that every old frame immediately causes measurable harm, but that the gradual accumulation of old combs increases a sanitary, zootechnical and quality-related risk. For Swiss or European beekeeping, the practical relevance therefore lies in regular, reasoned and traceable comb renewal.

3. Critical appraisal

This chapter distinguishes what can be concluded fairly solidly, what remains context-dependent and what should not be extrapolated too quickly to Swiss apiaries.

Strengths. The convergence of the work is substantial : several experimental studies on Apis mellifera link comb age to reduced cell volume, a reduction in certain body dimensions of workers and lower colony performance (Elnabawy et al., 2020 ; Al-Fattah et al., 2021 ; Taha et al., 2021). The mechanism is biologically plausible : less space in the cell, more residues, more constraints during development.

Limitations. The review by Meng et al. (2025) synthesises the literature, but does not itself produce new experimental data. The cited studies come from very diverse contexts : Egypt, Saudi Arabia, Hungary, China, Venezuela, Belgium, Switzerland and the United States. The observed effects may depend on climate, bee subspecies, hive type, the actual duration of frame use, varroa levels, treatment practices and the agricultural environment.

Possible biases and confounding factors. An old frame is not only an aged frame : it may also be a frame more frequently used for brood, more exposed to treatments, more loaded with cocoons and more contaminated by the environment. It is therefore difficult to isolate perfectly the effect of comb age from the effect of chemical residues, sanitary pressure or colony strength. The results are coherent, but the mechanisms may be cumulative.

Caution with Apis cerana. The studies on comb gnawing in Apis cerana cerana are highly interesting because they show a natural strategy for renewing old cells. But this Asian honey bee is not the bee kept in Switzerland. In Apis mellifera, one should not expect comparable spontaneous rejuvenation of old combs. The safe transposition is therefore indirect : cell ageing matters, but in the European honey bee it is mainly the beekeeper who must organise comb renewal (Meng et al., 2024 ; Meng et al., 2025).

What cannot be concluded. A universal schedule valid for all apiaries cannot be inferred. Replacing too few frames increases the risk of old-comb accumulation ; replacing too many too abruptly can disrupt colony management, especially if the nectar flow, weather or colony strength do not allow good rebuilding. Good practice is therefore progressive renewal, planned and adapted to the season.

4. What other closely related studies show

This chapter places the main study in perspective with genuinely related work : direct effects of old combs, cellular mechanisms, wax contaminants and management practices.

Replications and directly related studies. Several studies on Apis mellifera confirm that colonies kept on young combs generally have more brood, more workers, more pollen or honey stores and better productivity than colonies established on older combs (Taha & Al-Kahtani, 2019 ; Elnabawy et al., 2020 ; Al-Fattah et al., 2021 ; Taha et al., 2021 ; Krim & Rashed, 2025). The recommendation recurring in these studies is not to allow brood combs to age indefinitely, with a practical threshold often situated around three years for Apis mellifera.

Mechanistic support. Morphological and micro-computed tomography analyses reinforce the proposed mechanism. Old combs have thicker walls, cell bases partly filled by cocoons and reduced internal volume. Sipos et al. (2023) show that this reduction can translate into a smaller pupal space. Meng et al. (2025) bring these results together and link them to reduced birth weight, body dimensions and certain functional organs of workers.

Contaminants and the wax cycle. The literature on residues shows that wax functions as a long-lasting reservoir. Swiss monitoring studies have documented the multi-year persistence of lipophilic residues in commercial Swiss beeswax, in particular certain acaricides used against varroa and paradichlorobenzene when it was used to protect stored frames (Bogdanov et al., 1998 ; Kast et al., 2021). Other studies show that residues present in wax can migrate to bee bread, brood and sometimes honey, with possible sublethal effects on worker development and longevity (Wu et al., 2011 ; Morales et al., 2019 ; Alkassab et al., 2022).

This issue is particularly important for apiaries undergoing organic conversion or already certified organic. In Switzerland, the regulations require wax to be replaced during the conversion period and stipulate that wax used for new frames should, in principle, come from organic units, with possible authorisations when such wax is not available. In practice, the issue is therefore not only to renew the frames, but also to be able to document the origin and the wax cycle of the wax being used.

Recent additions. Very recent work on cocoon accumulation in old combs associates brood-comb ageing, microbial enrichment, pesticides and metabolic disturbances, reinforcing the idea that old combs are not only a mechanical problem but also a complex biological and chemical compartment (Meng et al., 2026). These results are interesting, but they still need to be placed in European field contexts.

Frame management. Trials precisely comparing several renewal schedules remain rare. However, studies on best practices show that active comb management is among the levers associated with better colony health. Kulhanek et al. (2021) and Steinhauer et al. (2021) suggest that removing old frames, exercising caution when reusing frames from dead colonies and sanitising frames before reuse can help reduce losses or sanitary pressure. This does not replace varroa monitoring, but complements general apiary hygiene.

5. What should be taken from this at the apiary ?

This chapter translates the findings into cautious actions for Swiss or European apiaries, without turning a scientific review into a single recipe.

Organise regular rotation of brood box frames. As a practical reference point, ApiService recommends renewing at least one third of the frames in the brood box each year. Old black, heavy, deformed or hard-to-read frames should be removed from the brood nest first.
Avoid reintroducing very black wax into the cycle for new foundation. It can concentrate biological and chemical residues accumulated over several years.
Date or mark frames to keep track of their age. Regular rotation is more reliable than occasional sorting once combs are already very old.
Take care with the storage of removed frames. Poorly stored frames favour wax moths, moulds and secondary contamination, especially when they have contained brood.
For comb honey or very old super frames, the origin and age of the wax deserve particular attention, because the wax is then more directly associated with the product consumed.
Very dark wax should not be reintroduced into the cycle for new foundation sheets. It can concentrate biological and chemical residues accumulated over several years. For apiaries undergoing organic conversion or already organically certified, the origin of the wax and the traceability of the wax cycle deserve particular attention.

In practice, comb renewal is therefore not an aesthetic detail. It improves the readability of inspections, limits the accumulation of old brood combs, reduces the risk of recycling contaminants and supports better development conditions for young bees. The rule must nevertheless remain adapted to the equipment, colony strength, season, availability of clean wax and Swiss sanitary recommendations.

Read the original study

Kievits, J. (2025). Quand les rayons vieillissent : impacts sur les abeilles et la qualité du miel. La Santé de l’Abeille, n° 330, 25–34.
Meng, Q., Huang, R., Yang, S., Jiang, W., Tian, Y., & Dong, K. (2025). An Overview of the Adverse Impacts of Old Combs on Honeybee Colonies and Recommended Beekeeping Management Strategies. Insects, 16, 351.
Meng, Q., Huang, R., Li, H., Gong, X., Yue, D., Jiang, W., Tian, Y., & Dong, K. (2024). Analysis of comb-gnawing behavior in Apis cerana cerana. Journal of Insect Science, 24(1), 19.

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When honeycombs age: impacts on bees and honey quality

1. The essentials in brief

2. What the study shows

3. Critical appraisal

4. What other closely related studies show

5. What should be taken from this at the apiary ?

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