Honeybee breeding is an extremely technical and difficult procedure as compared to the breeding of other varieties of livestock, such as sheep and cattle. For a start, you are not assessing the performance of an individual but an entire colony made up of many individuals. As a queen bee can mate with up to 25 drone bees, the individuals in the colonies have complex family dynamics, with full sister, half sister and super sister relationships all playing out in the genetic mix.
Honeybees also have a very unusual way of determining sex and have diploid drones. This means inbreeding is fatal to honeybees as it results in the queen producing haploid drones, that are detected and disposed of by the workers when they are larvae. Therefore if the number of haploid drones gets too high there is a drop in brood viability to a point were the hive will collapse.
These strategies have been very successful for honeybees and have resulted in a large amount of genetic diversity. However, it does cause problems when we want to breed a line of honeybees with desirable traits for commercial purposes. If we apply selection to colonies and breed using free mating it makes it impossible to compare the queens. We do not know if the behaviours and traits we are comparing between colonies are due to the genetics of the queen or the drones. If they are due to the drones, is it one of the drones the queen has mated with or more than one. This means it becomes a matter of luck if we can transmit these traits from one generation to the next and we are very likely to lose desirable traits.
To get around this we need to maintain a closed population using Instrumental Insemination.
Closed Population Breeding
In closed population breeding we maintain a population of bees that has a closed gene pool. We control the mating with instrumental insemination. The following is an outline of how we do this.
- We have 25 breeder queens, each heading a colony.
- From the top 20 breeder queens we raise about 200 virgin queens that are confined to their hives, so they cannot fly and mate naturally. These colonies are the evaluation colonies.
- We instrumentally inseminate these virgin queens with semen from the 25 breeder colonies in 1 above. This semen is homogenised so all the virgin queens are getting the same mix of semen from the 25 breeder colonies. This means that any difference we see between the evaluation colonies is due to queens alone, as all the evaluation colonies have the same drone fathers.
- We evaluate these colonies over a year using a set of selection criteria and the best 25 colonies become the breeders and we start again.
By running a closed population breeding programme we are able to effectively select the traits we want and breed out the traits we don’t want. We are also able to maintain these traits within the population. Without a closed population to maintain these traits they would be lost or significantly diluted within 2 to 3 generations of open free mating.
Issues with closed populations
However, because of the way honeybees determine sex, closed population can quickly result in inbreeding due to the loss of the alleles that determine sex, known as the CSD allele. Traditionally, this has meant you need to run very large breeding programmes with a minimum of 50 breeder colonies to give the programme some longevity, which is very expensive. You also needed to introduce a lot of new genetic material to introduce CSD alleles that have been lost or were never present. This could also affect what you are trying to achieve in the programme as undesirable traits could be introduced.
By working with Genetics Otago at the University of Otago we have developed a solution to this inbreeding problem. Genetics Otago developed a molecular test that allows us to screen our colonies to see which CSD alleles we have within the closed population. This means we can manage the CSD alleles and ensure we do not lose any of them.
The result of this is that we can:
- Run the breeding programme with far fewer hives and breeders, thus reducing costs.
- The programme should be able to last indefinitely as we avoid inbreeding by managing the CSD alleles.
- When we introduce any new genetic material, from queens or semen, we can see if this will be worthwhile in introducing CSD alleles that we don’t have in our closed population.
Our goal is to breed the best commercial Italian honeybee. To achieve this we use a number of measurable selection criteria including:
- Honey production
- Brood viability
- Hygienic behaviour
- Absence of brood disease
- Spring build up
- Varroa Sensitive Hygiene (See VSH).
All these traits are scientifically assessed and scored. The scores are collated and used to rank each queen's performance. The 25 best performing queens are then selected as breeders.
Introduction of New Genetic Material
From time to time we introduce new genetic material to the closed population. We may do this to:
- Introduce a new CSD allele.
- Introduce a desirable trait.
- Boost a desirable trait.
- Increase vigour.
However, introducing new genetic material may have unforeseen negative impacts on the population. To minimise the possibility of negative impacts we fully asses all stock prior to introduction. This assessment may take 1 to 2 years and includes.
- Conducting an initial assessment. If the queen passes this assessment and we believe she may have something to offer we go to the next step.
- We raise a number of daughter queens from this queen and instrumentally inseminate them with pooled semen from our breeding line.
- These daughter queens are evaluated thoughout a season alongside our breeding programme. If any of the queens score highly enough we would then introduces that daughter queen into our breeding programme.