The terms F0, F1, F2, or Fx are frequently used in queen rearing. They are useful for describing a queen's origin and the degree of control over her offspring. However, they are not sufficient on their own to judge a queen's quality or a colony's value. A good queen depends on several factors: genetic origin, rearing quality, mating, adaptation to the environment, and the observed performance of the colony.

1. What are we talking about?

In breeding, the letter F denotes a generation resulting from a cross. In beekeeping practice, these terms are often used in a simplified way:

• F0: breeder queen, selection queen, or original queen. In beekeeping, this is usually a tested queen used to produce daughters. In classical genetic studies, F0 can also denote a highly inbred parental line, which is not the same thing.
• F1: first generation from an F0 queen or a defined cross. F1 queens are often intended for production, especially when the line combination is known and tested.
• F2: generation arising from further propagation of F1 or of F1 daughters. Traits are recombined here and generally become less predictable.
• Fx: a later or less precisely documented generation.

These terms therefore mainly describe an origin and a level of predictability. They do not constitute a direct judgement on the biological or beekeeping quality of a queen.

2. The heterosis effect

The heterosis effect, also called hybrid vigour, refers to an improvement in certain traits among offspring resulting from crossing genetically different lines. It can arise from the masking of unfavourable recessive alleles or from favourable genetic combinations. In the honey bee, this effect can concern individual traits, such as the vitality of queens or workers, but also colony traits, such as development, thermoregulation, resistance to certain stressors, or performance.

Biologically, heterosis is mainly expected when the parental lines are genetically different and relatively stable. In classical agricultural systems, for example with certain crop plants, very homogeneous parental lines are crossed in order to obtain a more uniform and often higher-performing F1 generation. In the honey bee, the situation is more complex: a colony is not merely the expression of a queen, but of an entity formed by the queen, the workers, the drones that mated with her, and the environment.

A brief biological explanation: when genetically different lines, kept stable, are combined, F1 queens, or their colonies, may benefit from heterosis effects. Unfavourable recessive traits can be partly masked, and favourable genetic combinations can promote vitality or performance. Historical crossbreeding experiments with inbred honey bee lines showed such F1 effects in laying performance and honey yield (Cale & Gowen 1956); controlled crossbreeding experiments found similar effects also in survival after bacterial challenge and in the stability of brood nest temperature (Ryals et al. 2024). More recent field studies show that certain F1 or intertype crosses can, under suitable conditions, be more productive than their parent groups (Erkan et al. 2024), even though such individual findings – for instance with Carpathian bee crosses (Kovalskyi et al. 2022) – have not yet been broadly replicated. Other long-term data, however, show that locally adapted pure stocks can outperform hybrids when the latter are less well adapted to the environmental conditions (Ostroverkhova et al. 2024). Heterosis is therefore not a guarantee of better performance, but a possible advantage of certain line combinations under certain conditions.

Two simplifications should therefore be avoided. The first would be to believe that an F1 is automatically better than an F0. The second would be to believe that an F2 is automatically poor. In reality, the generation provides information about lineage and predictability, but the actual value is always shown by the colony itself.

3. F0, F1, F2: two perspectives to distinguish

From a breeding perspective An F0 is mainly of interest as a breeder queen or as a basis for selection when she is well documented, tested, and comes from a reputable programme. For breeding, it is not enough for a colony to look good in a single year. Lineage, mating, the performance of relatives, the uniformity of daughters, and health must also be taken into account. F1 queens can be very useful as production daughters, but they do not replace selection. If propagation continues from F1 afterwards without controlling mating, traits are recombined and the offspring become less predictable.

From a production perspective For the beekeeper, an F1 from reputable breeding can be an excellent choice, especially when the line combination has already been tested. But an F1 is not automatically good simply because it is an F1. Likewise, an F2 or an Fx does not automatically need to be eliminated. If the colony is gentle, healthy, well developed, has a low tendency to swarm, is productive, and is well adapted to the apiary, it may well be suitable for production. However, it should not be used as a basis for selection without a more thorough assessment.

4. Practical reference point: breeding and production

In some breeding schemes, F0 queens are mainly used as breeder queens or selection queens, while F1 queens are intended for production. This distinction is useful, but should not be understood as an absolute biological rule. A well-tested F0 can head an excellent colony, and a poorly reared, poorly mated, or poorly adapted F1 can disappoint.

For production, F1 queens from reputable breeding can be a very good choice. Their value lies in the combination of known lineage, prior selection, and, where possible, controlled mating. In subsequent generations, traits are recombined more extensively, and results can become less consistent. This is not necessarily a loss of quality, but a loss of predictability.

The decision to keep or replace a queen should therefore be based on actual observation of the colony: gentleness, behaviour on the comb, regularity of the brood pattern, development, health status, swarming behaviour, overwintering, and performance.

5. Mating station or open mating at the apiary?

Mating at a mating station allows better control over drone origin and thus increases the predictability of the offspring. It is particularly important when the goal is selection or the production of queens intended for breeding. On its own, however, it does not guarantee a good queen: the quality of the mother, larval rearing, mating conditions, and subsequent assessment remain decisive.

Mating at a station with only a very small number of nucs strongly limits the possibilities for selection. After losses due to mating, introduction, overwintering, and trait assessment, often only a small number of genuinely interesting queens remain. When the size of the apiary does not allow for this work, it is often more effective to turn to a breeding adviser or a recognised breeding organisation.

Open mating at the apiary remains possible for producing production queens. It is, however, less predictable, since the origin of the drones is unknown or only partially known. This does not mean that the resulting queens will be poor, but that their offspring should be observed carefully before being used more widely.

6. Choosing a breeder queen for grafting

Grafting should start from a queen whose performance has been observed over a sufficient period. A queen used as a breeder mother should ideally have shown good production results, good health, a low tendency to swarm, a gentle colony, and a regular brood pattern.

It is preferable not to rely solely on an exceptional individual case. In selection, it is important also to consider sisters, daughters, and the consistency of traits within the family. A very high-performing colony may be the result of a favourable context, a good year, or an accidental combination. To produce more predictable daughters, one should look for lines or families that consistently perform well.

Criteria observable by the beekeeper include, among others, gentleness, vitality, the quality and regularity of the brood pattern, strength of development, low tendency to swarm, apparent health, overwintering, and production. More complex health-related traits, such as certain forms of resistance or tolerance to diseases and parasites, often require structured testing and comparison between colonies.

The age of the breeder queen must also be taken into account. A very young queen has not yet been sufficiently tested. A queen that is too old may be less reliable for breeding, or may no longer be available by the time her daughters are assessed. In practice, queens assessed over two seasons often provide a more solid basis than queens judged only on their first year.

7. What to do with F2 or Fx?

F2 or Fx queens should not be used as a basis for selection without control or assessment. Their paternal origin is often unknown, and the traits inherited from F1 can recombine in variable ways. This increases the variation in results between colonies.

However, this should not lead to the conclusion that an F2 is automatically poor. A well-developed, gentle, healthy, productive F2 colony that is well adapted to the apiary may be entirely suitable for production. Conversely, an F1 can be mediocre if it comes from poor rearing, unfavourable mating, or a line combination poorly suited to the environment.

A good rule of thumb is not to decide based on the label, but on the colony. If the colony is aggressive, weak, prone to swarming, irregular, sick, or unproductive despite correct management, replacing the queen is justified. If it performs well, its replacement should not be motivated solely by the label F2 or Fx.

8. Swarming, aggressiveness, and other traits: beware of shortcuts

Certain traits such as swarming tendency, gentleness, behaviour on the comb, or spring development have a genetic component. But they are also influenced by management practices, colony strength, available space, forage, weather, queen age, disease pressure, and the environment.

It would therefore be overly simplistic to claim that a trait such as swarming or aggressiveness is solely linked to an F1, F2, or Fx generation. Poorly controlled crosses can indeed increase variability and bring out undesirable behaviours. But these behaviours must be observed in the colony itself before a decision is made.

When a colony swarms heavily or shows persistent aggressiveness, it may be advisable to replace the queen and to avoid using that colony as a source of drones or larvae for breeding. This decision should, however, be based on several observations rather than on a single isolated event.

9. Key points

• The generation F0, F1, F2, or Fx provides information about lineage and predictability, but not on its own about quality.
• F1 queens can be very valuable for production when the line combination is known, tested, and adapted to the environment.
• Heterosis is a possible advantage, not a guarantee.
• F2 and Fx are not automatically poor, but their performance is often less predictable.
• For breeding, a known lineage, controlled mating, and performance assessment are needed.
• For production, it is the colony that must prove itself under the real conditions of the apiary.

Key message: F0, F1, F2, and Fx are useful reference points, but they replace neither selection, nor observation, nor assessment of the colony. A queen must be judged on what her colony actually shows: gentleness, health, development, behaviour, overwintering, and performance.

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References

Büchler, R., Andonov, S., Bernstein, R., Bienefeld, K., Costa, C., Du, M., Gabel, M., Given, K., Hatjina, F., Harpur, B., Hoppe, A., Kezić, N., Kovačić, M., Kryger, P., Mondet, F., Spivak, M., Uzunov, A., Wegener, J., & Wilde, J. (2024). Standard methods for rearing and selection of Apis mellifera queens 2.0. Journal of Apicultural Research, 64, 555–611. https://doi.org/10.1080/00218839.2023.2295180

Cale, G. H. Jr., & Gowen, J. W. (1956). Heterosis in the honey bee (Apis mellifera L.). Genetics, 41, 292–303.

Erkan, C., Günbey, V. S., Günbey, B., & Cengiz, F. (2024). Comparison of pure caucasian, carniolan and native anatolian ecotype honey bee (Apis mellifera L.) colonies in the eastern anatolia region with reciprocal F1 hybrids. Bioscience Journal.

Guichard, M., Neuditschko, M., Soland, G., Fried, P., Grandjean, M., Gerster, S., Dainat, B., Bijma, P., & Brascamp, E. W. (2020). Estimates of genetic parameters for production, behaviour, and health traits in two Swiss honey bee populations. Apidologie, 51, 876–891. https://doi.org/10.1007/s13592-020-00774-5

Hoppe, A., Du, M., Bernstein, R., Tiesler, F., Kärcher, M., & Bienefeld, K. (2020). Substantial genetic progress in the international Apis mellifera carnica population since the implementation of genetic evaluation. Insects, 11, 768. https://doi.org/10.3390/insects11110768

Kovalskyi, I., Kerek, S., Fedak, V., Kovalska, L., Druzhbiak, A., Vovkun, Y., Klym, O., & Golovach, P. (2022). Influence of heterosis on honey productivity of Carpathian bees. Scientific Messenger of LNU of Veterinary Medicine and Biotechnologies.

Ostroverkhova, N. V., Rosseykina, S. A., Yaltonskaya, I. A., & Filinov, M. S. (2024). Estimates of the vitality and performances of Apis mellifera mellifera and hybrid honey bee colonies in Siberia: A 13-year study. PeerJ, 12.

Plate, M., Bernstein, R., Hoppe, A., & Bienefeld, K. (2019). The importance of controlled mating in honeybee breeding. Genetics Selection Evolution, 51, 74. https://doi.org/10.1186/s12711-019-0518-y

Ryals, D. K., Buschkoetter, A. C., Given, J. K., & Harpur, B. A. (2024). Individual and social heterosis act independently in honey bee (Apis mellifera) colonies. Journal of Heredity, 116(1), 54–61. https://doi.org/10.1093/jhered/esae043

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See also:

• F1 queen rearing
• Principles and methods of honey bee queen rearing
• Drone rearing
• Practical Guide: 4.7 Assessment and selection of colonies
• Breeding advisers