The concept of the F1 hybrid variety was introduced by Shull in 1903. He observed that the methods used to create pure lines in cereals could not be applied to maize because of excessive inbreeding depression. Shull therefore proposed crossing pure lines with one another in order to reproduce an interesting genotype identically.

The heterosis effect

The heterosis effect, also known as “hybrid vigor,” results in improved performance (more precisely, the cancellation of the “defects” of pure lines) arising from the mixing of different alleles from different lines.

Heterosis refers to the particularly pronounced increase in performance of hybrid or crossbred individuals. This effect is exploited in both animal and plant breeding. Heterosis is said to occur when the F1 hybrid generation exhibits performance superior to the average performance of the parental F0 generation, which is homozygous or a pure line.

For heterosis to be expressed, at least two distinct and relatively distant varieties, breeds, or lines are required. The purity of these lines allows good control of hybrid traits and ensures their consistency.

A line is considered “pure” when it tends toward homozygosity, meaning that for each gene both alleles are identical. The advantage of a pure line is that its offspring are homogeneous and therefore predictable. Its drawback is an increased risk of expressing deleterious traits.

Pure lines are obtained by repeatedly breeding a restricted population with itself over several generations. In animals, this is referred to as inbreeding. This can lead to genetic drift and inbreeding depression, which may be alleviated through population mixing.

The heterosis effect is strongest in the first generation, decreases in subsequent generations, and the vitality of the third and fourth generations is lower than that of the two original breeds. Naturally, heterosis may also amplify traits that are undesirable from a human perspective; in bees, this notably includes aggressiveness. Trials conducted at the MONFAVET Experimental Apiary in France showed that one-year-old first-generation hybrid queens (F1) produced higher yields than control queens (F0). Brood development was also superior in hybrids (Jean Verlaine, 2016).

To monitor honey yield in hybrids over successive backcross generations with the parent (F0), four lines were created. The results reveal very high variability among lines, tending to mask differences between generations. Nevertheless, the F1 of the best line is significantly superior to the control (F0), whereas F3 is generally clearly inferior. This work highlights the need for effective selection based on crossbreeding value and the advantage of replacing hybrid queens before the F3 generation (J. M. Cornuet, J. Fresnaye, J. Blanc, R. Paris, 1979).

First axiom

Station queens (hereafter F0) are reserved for breeding, whereas first-generation hybrids (F1) are used for production. Whenever possible, second-generation hybrids (F2) should be avoided.

Second axiom

Breeding stations should be used in accordance with their regulations, with at least ten nucleus colonies to allow effective selection. Bringing only two nuclei to a breeding station is a waste of time and energy. A station queen is not automatically a good breeding queen whose brood can be grafted to obtain high-performing offspring.

The daughters of a good breeding queen should show homogeneous traits. This homogeneity is difficult to assess, and when it can be measured, the mother queen is often no longer present. In any case, the daughters will systematically be distributed into: a few very good ones (those sought after), some good ones, many average ones, and the remainder.

If the apiary size does not allow such a scale (ten nuclei), beekeepers should contact the regional breeding supervisor, who can provide selected F0 queen brood for grafting.

From ten potential queens, losses due to mating, introduction, overwintering, and culling for aggressiveness, swarming tendency, lack of vitality, or low production reduce the number to only two or three queens.

Third axiom

Grafting should be performed using brood from a two- or preferably three-year-old F0 queen (1st year in a nucleus, 2nd year in production, 3rd year assigned to breeding after selection) originating from a certified breeding supervisor. It is not permitted to use one’s own grafting material at a mating station. This is advantageous for the beekeeper, since grafting from an individual within one’s own apiary—even an exceptional one—is highly uncertain. In breeding, it is essential to consider the quality of all sisters and to select only homogeneous, high-quality lines. By grafting from a breeding supervisor, one benefits from this groundwork and from an adequately low level of inbreeding.

For those who do not wish to use mating stations but perform F1 mating within their apiary, observable evaluation criteria include gentleness, vitality, low swarming tendency, brood quality and regularity, and high productivity. Health status and disease resistance are more difficult for an isolated beekeeper to assess and are better managed by breeding supervisors.

Queens older than four years should be avoided for breeding, as egg quality declines with age.

Fourth axiom

For production, F1 queens should preferably be chosen. The heterosis effect, or hybrid vigor (enhancement of positive traits), disappears in subsequent generations. For further details, consult Wikipedia or specialized sources.

Thus, in general, F1 queens are scientifically the best choice for production compared with F0 or F2 queens. This does not preclude the possibility that, in a given apiary, an F0 queen may prove to be the most productive.

Fifth axiom

F2 queens should be used only as a last resort when F1 queens are lacking. A good F2 queen can satisfactorily replace an aggressive F1 queen or rescue a queenless colony.

Sixth axiom

Systematically, both the queen that has swarmed and the new queen of the colony remaining in the apiary should be replaced. The propensity to swarm is genetically dominant and should therefore be eliminated from the apiary. Retaining such queens creates additional problems for F1 mating at the apiary, as the swarming trait may spread in subsequent years through mating with drones from these swarming colonies.