Genetic Selection and Evaluation

Genetic selection is the work of separating the heritable share from the observed performance of bee colonies and propagating only genetically superior queens and drone sources. This is the essence of breeding; queen rearing and mating control are the ways this decision is put into practice. The honey bee's multiple mating and the drone's having no father make selection different from that in other animals.

What is genetic selection?

Every trait you see in a colony (the phenotype) comes from two sources: genetic make-up and environment. A colony that makes a lot of honey may have good genes; but it may also have made a lot of honey because it stands in a good position, did not swarm, or built up early that year. Only the genetic share passes to the next generation.

The aim of genetic selection is to separate these two shares. There are three basic tools for this: testing colonies under the same conditions, measuring the same trait repeatedly, and evaluating the results of relatives (sisters, mother, daughters) together.

What is heritability and how does it affect selection?

Heritability (h²) shows how much of the variation in a trait comes from genetics. Traits with high heritability respond quickly to selection; in those with low heritability, environmental noise dominates and progress is slow.

Expected progress is roughly summarised by this relationship: response to selection = heritability × selection differential. The selection differential is how much better the colonies you select as breeders are than the apiary average. If selection is made only on the queen side, without selecting the paternal side, only about half of this gain is achieved.

That is why starting breeding with behavioural traits gives faster results; productivity is improved patiently, with several years of records.

Why is selection different in the honey bee?

The drone has no father

A drone develops from an unfertilised egg and carries a single set of chromosomes. All the sperm cells a drone produces are genetically identical. A drone is therefore a vehicle "carrying" the genes of his mother, the queen; selecting the paternal side means selecting the queens that produce the drones.

The queen mates with many drones

A queen usually mates with 10–20 drones. In the colony a separate subfamily forms from each father. Workers from the same father are very closely related; those from different fathers are like half-sisters. This diversity makes the colony more resilient to diseases and changing conditions, but it also makes the colony's behaviour the joint product of many fathers.

The unit evaluated is the colony

Honey yield, defensiveness and hygiene are measured in the colony, not in a single bee. A colony's performance depends both on the queen effect (laying capacity, pheromones) and on the worker effect (foraging, defence, cleaning). Modern breeding value calculations estimate these two effects separately.

What is a breeding value and how is it calculated?

A breeding value is an estimate of the genetic superiority a queen is expected to pass on to her offspring. Rather than the score of a single colony, the results of sisters, the mother and, if available, daughters are used together. Differences between apiaries, years and testers are corrected statistically.

Large breeding programmes do this calculation with statistical models also used in livestock breeding (BLUP). In some systems the result is published as a percentage, with the population average set at 100; above 100 means better than average. Even if a small-scale beekeeper does not do this calculation, they can use the same logic: look not at a single colony but at the average of the sister group.

What selection methods are there?

• Tandem selection: Selecting for one trait only until it reaches a sufficient level, then moving on to the next. It is simple but slow; the other traits may slip back in the meantime.
• Independent culling levels: Setting a minimum for each trait (e.g. gentleness at least 3, hygiene at least 90%) and culling those below it. This is the most useful method in practical beekeeping.
• Selection index: Weighting traits according to their importance to create a single total score. It advances several traits in a balanced way; it needs good records.

How do you balance selection intensity and inbreeding?

The fewer colonies you breed from, that is, the stricter the selection, the faster the progress. But narrowing down to a single line increases the risk of inbreeding. Because sex in the honey bee depends on a single gene region, as inbreeding increases sterile diploid drone larvae are produced; the workers remove them and the brood area looks spotty.

• In each generation, breed from several unrelated breeder queens.
• Choose the breeder you take larvae from and your drone colonies from different lines.
• Keep pedigree records; at intervals bring in a new line from a reliable source.
• Keep the generation interval reasonable: a breeder is used only after being tested for at least a year, which means a generation interval of about two years.

What are DNA tests and race identification for?

Today, DNA markers can be used to determine racial origin, the degree of hybridisation and relatedness. Wing vein measurement (morphometry) is a common, cheap method for estimating race and ecotype. Genomic selection, that is, estimating breeding values by looking directly at DNA, is still under development in the honey bee. These tools do not replace performance testing; they complement it.

What are realistic expectations from genetic selection?

Breeding is slow but cumulative work: what is gained in each generation is kept and built upon. In behavioural traits a clear difference is seen within one or two generations; in traits such as productivity and resistance, progress is spread over years. Even breeding from the best colonies and regularly requeening the worst raises the apiary average within a few years.