Why does a colony replace its queen?

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A colony may replace its queen for several reasons: advanced age, insufficient egg-laying, poor fertilization, injury, or general weakness. But a recent study suggests that another factor may sometimes be at play: a severe viral infection in the queen could impair her reproductive function and alter her pheromonal signal, to the point of triggering supersedure.

1. Key Points

• The central question is whether high viral infection in a queen can alter her pheromone signal to the point of prompting workers to initiate her replacement.
• Among the measured compounds of the queen's pheromone bouquet, methyl oleate is the only one showing a robust association with viral infection and with ovarian mass. [strong empirical basis]
• In a queenless colony trial, adding methyl oleate to a queen pheromone blend suppressed queen cell rearing more than the blend without this compound. [empirical basis, but in an artificial experimental setup]
• The study makes a chain plausible — high viral infection → reduced ovarian investment → altered pheromone signal → supersedure — but does not yet demonstrate this full sequence in ordinary colonies at the apiary. [theoretical, supported by several empirical findings]
• For the beekeeper, the main value is interpretive: supersedure is not necessarily just a matter of queen age or a vaguely «poor queen», but may also reflect a physiological or health problem.

2. What the Study Shows

The study combines controlled trials, field observations, and biochemical analyses to investigate a supersedure mechanism.

Research question. The authors seek to understand how high viral infection in the queen can destabilise the social organisation of the colony. Their hypothesis is that severe viral stress alters a key pheromone signal of the queen, prompting workers to initiate her replacement. The study focuses primarily on infections involving Deformed Wing Virus B (DWV-B) and Black Queen Cell Virus (BQCV), with a broader interpretation in terms of total viral load.

Methods. The work comprises several components. A cage trial involved 27 young queens, divided into three groups of 9, microinjected with saline solution, live viral inoculum, or inactivated viral inoculum. A second dataset comprised 32 nucleus colonies in five-frame hives with queens of the same age; however, inoculation did not produce a clear difference between groups, and this component was ultimately analysed observationally, with 29 queens retained in the final analysis. The authors also conducted a pheromone trial on 30 queenless colonies divided into three groups of 10, as well as a comparison between 10 queens with small ovaries obtained by caging and 10 queens with large ovaries allowed to lay freely.

Results. Of the seven measured components of the queen retinue pheromone, only methyl oleate emerged robustly: it declined as viral load increased in the experimental trial, and was positively correlated with ovarian mass in the field data. In parallel, the most heavily infected queens also showed broader lipid changes, notably a decline in numerous triacylglycerols, interpreted as major energy reserves. [strong empirical basis]

Interpretation. The most noteworthy finding is that simply reducing ovarian investment experimentally — by caging and restricting laying — also reduces methyl oleate. In other words, workers probably do not react primarily to the virus as such, but rather to a deterioration in the queen's reproductive condition that the virus contributes to causing. Moreover, in the queenless colony trial, the pheromone blend containing methyl oleate inhibited queen cell rearing more than the blend without this compound. This supports the biological role of methyl oleate in maintaining queen acceptance, without on its own proving the entire causal chain under natural conditions. [theoretical, supported by several empirical findings]

A further result nuances the immunological interpretation: when ovaries are reduced without infection, the «canonical» immune proteins do not increase, even though ApoLP-III declines. A reproduction–immunity trade-off reversible in both directions is therefore not demonstrated here. This point is of greater relevance to the biological understanding of the mechanism than to immediate apiary practice.

3. Critical Assessment

The findings are coherent and well constructed, but several limitations call for cautious reading.

Strengths. A key strength is the convergence of multiple approaches: experimental infection, field observations, independent manipulation of ovarian mass, and then a functional test of a pheromone compound. This architecture strengthens the credibility of the proposed scenario, especially because it does not rest on a single correlation. The fact that only methyl oleate stands out clearly among several measured compounds also reinforces the specificity of the observed signal. [strong empirical basis]

Methodological limitations. The principal limitation is that the field component did not remain truly experimental: inoculation did not produce a difference in viral load between groups, and the authors had to treat this component as an observational dataset. This does not invalidate the results, but reduces the causal strength of this part. Furthermore, the pheromone trial was conducted on queenless colonies receiving a synthetic blend at a dose chosen by reasonable approximation; biologically this is informative, but it is not the exact equivalent of a colony with a living queen who is infected and gradually declining.

Possible biases and confounders. The study is set in a North American context, with trials in Canada and complementary analyses on queens imported from Northern California. Direct transposition to Swiss apiaries should therefore remain cautious. In addition, the authors did not test other non-viral pathogens across all experimental components, and the exact site of methyl oleate production remains unknown. Finally, lipid measurements were taken from queen heads, which is relevant for pheromones but less than ideal for assessing overall energy reserves across the organism.

What cannot be concluded. This study does not show that all supersedure is of viral origin. Nor does it demonstrate that there is a simple viral threshold at the apiary beyond which workers replace the queen, or that a beekeeper could today use methyl oleate as a practical diagnostic tool. Finally, it does not directly prove that a given varroa treatment strategy will reduce this specific type of supersedure, even if this hypothesis becomes more plausible within a virus–varroa framework. [cautious assessment]

4. Practical Takeaways for the Apiary

At the apiary, this study primarily informs the interpretation of queen replacements, rather than prescribing new practices.

• Early, repeated, or apparently «unexplained» supersedure is not necessarily due solely to queen age; it may also reflect a physiological or health problem.
• In a temperate European context, this study indirectly reinforces attention to the varroa–virus pairing, even though this lever was not tested here as a practical intervention.
• The study does not yet justify any direct change at the apiary in the form of a new diagnostic tool, a pheromone application, or a specific technical recommendation.
• Nor does it support the conclusion that requeening alone will resolve a broader health problem within the colony.
• Its main contribution is therefore interpretive: it helps to read certain apiary signals more clearly, without in itself being sufficient to change management practices.

Read the original study

► Elevated virus infection of honey bee queens

Further reading

• Queen pheromones
• Queen cells
• Renewing colonies and queens
• Deformed wing disease
• Integrated varroa management through the seasons

Bibliography

McAfee, A., Chapman, A., Alcazar Magaña, A., Marshall, K. E., Hoover, S. E., Tarpy, D. R., & Foster, L. J. (2025). Elevated virus infection of honey bee queens reduces methyl oleate production and destabilizes colony-level social structure. Proceedings of the National Academy of Sciences, 122(42), e2518975122. https://doi.org/10.1073/pnas.2518975122