What determines the characteristics of a honey bee colony?

Each beekeeper has a favorite bee colony that has a specific set of characteristics. For one beekeeper, colony productivity (quantity of honey and other beekeeping products obtained) is essential, for another - the colony's calmness, to make working in the apiary enjoyable, and for a third - low swarming tendency. The external characteristics or phenotype of a bee colony, which includes the amount of honey production, hygienic behavior, wintering ability, swarming behavior, aggression, disease resistance, etc., directly and indirectly are affected by the genetic diversity of bee colonies, individual interactions, genotype, and external environmental conditions.

A. Genetic level - genotype. Inherited genes directly affect the physiology and behavior of each individual organism. Thanks to gene sequencing, which is also performed on honey bees, it is possible to determine the location of genes that determine body size, sex, hygienic behavior, as well as the age of worker bees' specialization in different tasks, etc. Many traits are determined by several genes and their states (dominant - expressed/recessive - suppressed), and there may be a gene that can affect several traits (pleiotropy), resulting in genetic correlation or interdependence between traits. It is positive that many desirable bee traits have average to high heritability coefficients (the coefficient is expressed in values from 0 to 1 or 0-100% and determines how much of the manifestation of a trait is attributable to genetic changes, not external environmental factors), for example, the genetic influence on high honey production rates is 15-54%, good hygiene behavior is 18-65%, and colony defense capabilities are 30-57%. Other significant heritable traits include wax production, spring development intensity, synthesis of substances intended for pathogens, and the development time of worker bees.

B. Individual level - organism. Three different organisms are found in a bee colony - the queen bee, worker bees, and drones. The male and female sexes are determined by the sex gene, while the development difference of female bees (worker bees and queen bees) is determined by the food given to the larva. The body structure and viability of each organism are adapted to their intended roles. Drones do not determine the characteristics of a bee colony by themselves but indirectly affect the colony's reproductive efficiency. The more successful the drones are in mating with other queen bees, the more genes are transmitted to future generations in other colonies. The strength of a bee colony depends on the quality of its queen bee, who determines the laying capacity of the colony. The queen bee uses pheromones to communicate and regulate the behavior of worker bees, their maturation, and to suppress the rearing of other queen bees in the colony. Throughout their lifespan, worker bees sequentially specialize in various tasks, starting with caring for larvae, then building honeycombs, cleaning cells, protecting the colony, and finally, carrying and storing water, pollen, and honey. The age of specialization for these tasks is determined not only by the genotype but also by the number of worker bees that perform specific tasks at a given time. Physiological changes in the bee's body can affect previous levels, such as the expression of a particular gene. These changes are more related to the endocrine and exocrine gland activity of the bee's body - regulatory system, which synthesizes specific substances to ensure the body's functions. One example is the development and function of the worker bee's glands. Initially, the glands secrete royal jelly, then wax is produced, and later on, the venomous amount in the bee's venom sac increases. When worker bees become foragers from nurse bees, they begin to secrete pheromones that inhibit the development of nurse bees, thus ensuring that a certain ratio of nurse and forager bees is maintained in the colony. Foragers are genetically predisposed to collect either water, pollen, or nectar. It turns out that each worker bee has its own threshold of sensitivity to sucrose. If the threshold is lower, the bee will collect water; if it is higher, pollen will be collected, and if it is even higher, nectar will be collected. If there are many foragers in the colony, the pheromones they secrete decrease the sensitivity threshold to sucrose, ensuring that more bees will choose to collect pollen. Therefore, it can be concluded that the behavior of the organism is determined not only by genes but also by the interaction of the organisms themselves.

C. Subfamily level (patriline) - a group of organisms. The queen bee passes on 50% of her genes to the next generation. Since the queen mates with multiple drones, the worker bees in a colony can share 25% of their genes (known as half-sisters), 75% of their genes (full sisters), or more if the drones were related to the queen. Groups of worker bees that have genes from a single drone are called subfamilies. When the queen bee mates with multiple drones, the colony is provided with greater genetic diversity. Such genetically diverse colonies regulate temperature more effectively, have better disease resistance, exhibit better yield rates, and provide an increase in the strength of the colony. Improvements in the common properties of bee colonies are influenced by genetic differences between subfamilies that perform different types of tasks in the bee colony. Subfamilies of worker bees also interact with each other through pheromones. Each subfamily has its own sensitivity threshold to various stimuli, so one subfamily may specialize in certain tasks while another specializes in others, thus ensuring a stable overall response of the colony to stimuli. The number of these subfamilies in a colony, as well as their proportion, directly affects the properties of the entire colony.

D. The level of the colony. The properties of the colony level are those that a beekeeper can evaluate and are also important for commercial purposes. Typical phenotype characteristics of the colony are the amount of honey production, hygiene behavior, overwintering ability, tendency to swarm, aggressiveness, disease resistance, etc. All of these properties depend on what happens at the levels described above. Some of these characteristics are positively or negatively correlated with each other (referred to as correlations), so when a beekeeper selects a colony based on one characteristic, it is possible to improve or eliminate another characteristic. For example, a positive correlation has been observed in the hygiene behavior of bees. Bee colonies that successfully recognize damaged brood by the beekeeper (experimentally frozen or punctured) are also equally successful at recognizing the presence of disease-causing agents in damaged brood. This allows the beekeeper to evaluate this characteristic fairly accurately. On the other hand, a negative correlation is observed in the collection of nectar and pollen. Colonies that collect more pollen will produce much less nectar, and vice versa, because worker bees can only specialize in collecting one type of food at a time.

Figure 1. Biological levels of organization and their interaction. A. Genes - characteristic gene interaction (dominance, suppression, pleiotropy, genetic correlations), externally manifested as gene expression (manifestation), mutations, genetic diversity. B. Organism level - characteristic different castes (worker bees, drones, queen bees), interaction of worker bees, queen-worker bee interaction, external interaction occurs with pheromones and communication, different functions for each individual, different sensitivity thresholds for different stimuli for worker bees. C. Subfamilies - characteristic mutual interaction of subfamilies, each subfamily has different sensitivity thresholds to stimuli, subfamily proportion in the colony differs, stable response to stimuli is externally observable, genetic diversity, task specialization. D. Bee colony - a unified group of organisms (superfamily) with externally observable characteristics, such as a large supply of nectar, hygienic behavior, aggression, etc. E. External environment - resource availability, climate, pesticides, diseases. 1. Inherited genes directly affect the physiology and behavior of the organism. 2. If the bee queen mates with multiple drones, genetically diverse worker bees are born in the colony. Worker bees with genes from the same drone have similar behavioral traits and specialize in tasks, forming a subfamily with similar behavioral manifestations. 3. The number and proportion of subfamilies affect the intensity of the overall colony's characteristics. 4. External environmental factors, such as weather, affect the availability of pollen and nectar for bee families, the start of breeding in the spring, the opportunities for the queen to mate, the spread of diseases, etc. 5. Physiological changes in the organism's function affect the expression of another gene, for example, the sequential changes in the glandular function of worker bees (royal jelly, wax, bee venom).

Regardless of the complex structure of the bee colony and the interactions at various levels and their impact on the colony's characteristics, a beekeeper can evaluate, select, and cultivate desired traits. It should be noted that the colony's characteristics are directly affected by external environmental conditions (resource availability, climate, pesticides, diseases), which may differ from region to region. Often, when importing good, selected bee queens, their colony's characteristics may not be as good as expected due to external environmental factors. For this reason, to reduce the impact of external environmental factors on the colony's characteristics, it is necessary to conduct selection work at the local level to achieve the best possible results.

The next article will discuss how to create a bee colony trait evaluation system for selection purposes.

References:

• Oldroyd, B. P., & Thompson, G. J. (2006). Behavioural genetics of the honey bee Apis mellifera. Advances in insect physiology, 33, 1-49.
• Oxley, P. R., & Oldroyd, B. P. (2010). The genetic architecture of honeybee breeding. Advances in Insect Physiology, 39, 83-118.

Published in the journal "Biškopis", the 6th issue of 2021, published by the Latvian Beekeeping Association.