bee biology

The amazing genetic diversity in the best honey bee colonies

A honey bee colony has an amazing amount of genetic diversity.

Haplodiploidy makes bee genetic inheritance different from what we’re used to, but it works great for social insects.

Someone asked me why their honey bee workers were different sizes. I can’t give a concrete answer to this question, but it relates to honey bee genetic diversity.

Honey bees, like many other insects in the order Hymenoptera, have a sex-determination system known as haplodiploidy. In this system, the sex of an individual is determined by the number of chromosomes the individual has. Fertilized eggs have two sets of chromosomes and become female. Unfertilized eggs have only one set of chromosomes and become male.

A queen mates many times, expanding the genetic diversity of her offspring

In the case of honey bees, the sex of each offspring is determined by the queen. On her mating flights, which occur shortly after she matures, the queen mates with multiple drones—perhaps as many as 12 to 15. This is called polyandry, which means “many males.”

The sperm from these males is stored together in the spermatheca where it can remain viable for several years. As an egg passes through the oviduct, it may or may not be fertilized depending on the queen’s wishes.

Most sisters in the colony are only half-sisters

The point I want to make here is that even though we refer to worker bees as “sisters,” for the most part they are only “half-sisters.” If the queen has mated with 10 drones, for example, the bees in the colony have one mother and 10 fathers. This provides a colony with strong genetic diversity. It can result in distinctly different genetics between individuals and could be the reason that bees of different sizes and different colors are found in one colony.

Multiple mating of this type insures genetic variability within the colony—a phenomenon that increases the colony’s chance of survival. In our example, even if the genes of one “father” are prone to disease—and the daughters of that father do not survive—the other 90% may be strong enough to pull the colony through.

Honey bee true sisters are very similar to each other

On the downside, all the offspring of one queen and one drone (true sisters) are nearly identical. This happens because all the sperm cells produced by one drone are genetically identical to each other. This is unlike the genetic mixing that occurs when an individual has two sets of chromosomes. So in our case, the 10% of each colony that are true sisters are going to be susceptible to the same sort of environmental stressors and pathogens.

The drones in a colony—having only one set of chromosomes from the queen—are more similar to each other than the workers are to each other. For the most genetic variability, a queen needs to mate with drones from many different colonies.

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  • Hello Rusty,

    I don’t know if this is the appropriate place to post this comment/question but I’m wondering about genetic diversity and package bees. Last year I started my first hive in May and this year I am planning on starting a second hive as soon as my package of bees is available. In the interest of genetic diversity do you think it’s best to order a package from a different package supplier than I used last year? I probably have the option of splitting my hive as well but it is doing very well right now and if I did I would probably end up with another hive with similar or even identical genetics.

    Kind regards,

    • Paul,

      I don’t think it will make much difference. A package this year will have a different set of genes than last year’s package, and I don’t think the difference between producers will be much greater than the difference between packages from the same producer. Most package producers open mate their queens, so the drones have variable genetics from a large geographical area.

      If you split your colony, it will not have genetics identical to the parent hive either. The new queen (assuming they raise one) will have the genetics of the mother queen and one of the drones she mated with. Then that new queen will mate with a dozen or more drones that each introduce their own genetics. So the resulting colony will have only a portion of the genes of the parent colony. I don’t think it’s worth worrying about.

      My own preference is to split and let my bees raise their own queens because they mate with local drones, making the colony more adapted to local conditions. This works pretty well unless your locale is annually flooded with non-local packaged bees.