The Polyandrous Queen Honey Bee: Biology and Apiculture

 Apis mellifera (2n=32), commonly known as the European honey bee or the Western honey bee, is a eusocial insect. Each honey bee colony is a composite unit of thousands of bees, with three different castes: a polyandrous reproductively active queen; thousands of workers; and a few hundred drones. The queen and the workers represent the female caste that develops from fertilized eggs, whereas the drones are male bees formed from unfertilized or fertilized eggs. In the case of the female honey bees, the phenomenon of polyphenism can be easily highlighted, which is the developmental plasticity of the same genomic contents to express differently as per environmental cues. During the queen larval developmental phase, the exclusive diet is royal jelly, which induces hyper-secretion of juvenile and ecdysone hormones that ultimately cause sequential activation of certain genetic elements, specifically after 3rd instar onward. For the worker honey bee larvae, initially, the diet includes royal jelly exclusively, followed by honey, pollen grains, and worker jelly, which collectively direct development toward the worker caste. Furthermore, for harmonious social interaction, the queen secretes certain volatile chemical bouquets including 9- ODA(2E)-9-oxodecenoic acid), 9-HDA (9-hydroxy-(E)-2-decenoic acid), 10-HDA (10-hrdroxy-2-decenoic acid), HVA (4-hydroxy-3-methoxyphenylethanol), HOB (Methyl-p-hydroxybenzoate), 10-HDAA (10-hydroxydecanoic acid), OLA (oligolactide), methyl oleate, decyl decanoate, linolenic acid, coniferyl alcohol, cetyl alcohol, etc. The concerned pheromones facilitate the regulation of workers' behavior; workers' ovarian suppression; retinue control; overall worker’s development modulation; colonial product production; swarming tendency; pseudo-queen formation suppression; mating, etc. The queen honey bee is polyandrous, as she mates with many drones during the nuptial flight in 'Drone Congregation Areas (DCA)’, within about 2 weeks of her post-emergence. This chapter provides a comprehensive review of the polyandrous queen honey bee; her synchronous developmental phases; her pheromone dominance; her regulation and coordination of colonies; her mating preference and habits; and her role in a composite hive. Subsequent chapters provide an elaborative view of different aspects of the queen honey bees' life cycle.

 In a honey bee colony, a polyandrous queen bee performs two important duties predominantly. The first is reproduction, for modulation of colonial strength; and the second is the secretion of queen pheromones for regulation of social organization, developmental specification, colonial productivity control, retinue behaviour induction, worker ovarian suppression, foraging control, swarming reduction, other queen rearing inhibition, etc. In the female caste of honey bees, reproduction is uni-righted by a polyandrous queen, which mates preferably with multiple drones of other colonies during a nuptial flight in a Drone Congregation Area(DCA) and thereafter lays fertilised or unfertilized eggs depending on in-situ and ex-situ hive ambience, whereas worker honey bees perform the remaining tasks, including hive construction, brood rearing, foraging for food and nectar, honey production, protection and general organisation of the colony, pollen grain storage, water collection for the colony, ventilation in the hive, and the removal of carcases. In other words, worker bees perform all tasks except for reproduction and colony dominance. The specific duties assigned reflect the rectitudinous behaviour of the honey bee colony. Additionally, the specific division of labour enhances the competence of all honey bee castes. The Queen's honey bee is considerably fertile due to differential genomic expression, proteomics, and developmental specification. Further, her reproducibility is influenced by different biotic and abiotic factors prevailing within and outside the hive. In this chapter, a brief description of two predominant duties of the queen, including reproduction and pheromonal secretion, is highlighted. Subsequent chapters provide elaborative views of reproduction and pheromones. 

The queen bee carries the same genetic information as worker bees. Still, the genomic expression is variable, eventually resulting in the development of an enormously sizeable female bee, with an enriched blend of pheromone possession, a comparatively long life span, better immunity, development, and physiology. Differential developmental patterns compared to the workers are due to the influence of royal jelly, ultimately inducing differential genomic expression. Furthermore, with profound pheromone secretion, the queen regulates the colony's development, differentiation, reproducibility, behaviour, communication, and task management. This chapter briefly describes honey bees' morphology, development, and reproductive system development.

Larval feeds for different castes of honey bees include exclusively royal jelly from 4–9 days of development for the queen, and for worker larvae, royal jelly and worker jelly for 4-6 and 6–9 days respectively, whereas for drone larvae, royal jelly and a blended composite mixture of honey and pollen grain for 4-6 and 6–9 days respectively. For the queen, worker, and drone larvae, larval feeds include royal jelly and worker jelly for 4-6 and 6–9 days respectively. Royal jelly is a thick, creamy substance that is produced by the hypopharyngeal and mandibular glands of worker honey bees. Its primary components include water, hydrocarbons, proteins, lipids, minerals, vitamins, and a small amount of various types of polyphenols. Because the queen eats different larvae than the worker bees, this triggers a chain reaction of biochemical reactions, which ultimately leads to a high concentration of juvenile and ecdysone hormones being released. These hormones, in turn, regulate the expression of different genes in a sequential manner. Queen larvae have a variant proteomic that promotes the healthy development of the female reproductive system, which in turn leads to profound fertility and immune protection, as well as a longer life span for the queen.

Before the 4th instar larval phase, worker larvae exhibit totipotency to develop into either female caste. In subsequent larval stages, differential expression of various genetic elements occurs under the prominent induction of royal jelly, developmental hormones, and volatile queen emission. In the honey bee female caste, anatomical reproductive disproportionality establishes due to this diversification of genomic expression. Exponential fertility and pheromonal profiling of the queen regulate colonial strength, colonial productivity, submissive behaviour, and the development of workers. Different factors prevailing within the hive or outside of the colony premises influence the queen's quality. For example, the queen's fecundity is negatively proportional to the age of the worker larva before entering the queen differentiation pathway. Further, numerous additional factors like genomic content, physiology, quality and quantity of royal jelly, colonial food storage, social environment, queen pheromones, etc. influence queen reproductive potential.

Further, queens have differential immune protective characteristics for different pathogens and parasites. This chapter highlights influencing factors for nonsynchronous ovarian development and variant immune-protective measures in female honey bees. The subsequent chapters elucidate the details of workers' ovarian programmed cell death under the regulation of multiple factors.

The queen and worker caste of the honey bee exemplified the polyphenism phenomenon. In specific female caste, diversification of the same genomic (2n=32) expression ultimately induces plasticity in development, morphology, physiology, reproduction, division of labour, immunity, and life span. Physiological plasticity is remarkably highlighted through glandular secretion variation in female castes, as pheromonal queen glands ensure her reproductive monopoly and dominant hierarchy in the colony. In contrast, in workers, pheromonal profiling facilitates foraging, nursing, alarming, colony protection, pseudo-queen formation inhibition, and other social interactions. Queen's volatile bouquet emission contains biochemicals like 9-ODA, OLA, HVA, 9-HDA, 10-HDA, HOB, 10-HDAA, cetyl alcohol, coniferyl alcohol, linolenic acid, methyl oleate, and decyl decanoate. In contrast, workers' pheromones include predominantly; isopentyl acetate (IPA), butyl acetate, 1-hexanol, n-butanol, 1- octanol, hexyl acetate, octyl acetate, n-pentyl acetate, and 2-nonanol, (Z)-11-eicosenol, 2-heptanone, geraniol, geranial, geranic acid, (E)-citral, nerolic acid, etc. Queen and workers secrete different pheromones following their role in the colony. This chapter provides insights into differential pheromonal secretion in queen and worker caste within the honey bee colony. The biochemical synthesis of pheromonal contents in both castes is elaborated on in the next chapter

Queen Mandibular Pheromones (QMP) include (E)-9-oxo-2-decanoic acid(9-ODA), (R)-and (S)-(E)-9-hydroxy-2-decanoic acid(9-HDA), methyl 4- hydroxybenzoate(HOB), 10-hydroxy-decanoic acid (10-HDAA), 4-hydroxy- -methoxyphenyl ethanol (HVA), and10-hydroxy-2 (E)-decanoic acid (10-HDA), whereas worker honey bees mandibular gland pheromones include mainly 10-hydrox- -2 (E)-decanoic acid (10-HDA),10-hydroxydecanoic acid (10-HDAA), and 2- mainly 2-heptanone (2-H), traces of 9-hydroxy-2 (E)-decanoic acid (9-HDA) and 9-ODA. Biochemical modifications of stearic acid occur through hydroxylation of stearic acid at ω or ω-1 positions in worker honey bee and queen, synthesizing the primary pheromones listed above. 9-ODA pheromone influences alcohol dehydrogenase gene expression, and the specific enzyme is essential for converting 9-HDA to 9-ODA in worker honey bees. Further, the differential synthesis process is influenced by the gene expression of various cytochromes. QMPs impose differential influence on various developmental, functional, and behavioural regulations on nest mates, which include retinue behaviour, suppression of the development of worker honey bee ovaries, wax secretion, drone attraction, swarming, queen dominance regulation, general regulation, mating, and reproduction, juvenile hormone secretion in workers, foraging behaviour and the different submissive response of workers in the presence of the queen. 

Different queen pheromones attract colonial workers who respond by forming a surrounding group around the stationary queen. This specific behaviour is considered retinue behaviour. Workers lick, groom, and antennate the queen to get pheromones which influence workers' behaviour, physiology, development, hormones, reproduction, etc. Various pheromonal glands like the Mandibular gland components, the Tergal gland, Dufour's gland, etc., influence the retinue. Primary pheromones which influence the retinue process include (E)-9-oxo-2-decanoic acid(9-ODA), methyl 4-hydroxybenzoate(HOB), (R)-and (S)-(E)-9-hydroxy-2-decanoic acid(9-HDA), 4- hydroxy3-methoxyphenylethanol (HVA), 10-hydroxy-decanoic acid (10-HDAA) and10-hydroxy-2 (E)-decanoic acid (10-HDA), methyl oleate, coniferyl alcohol, palmityl alcohol, and linolenic acid. Furthermore, queen ester includes palmitates, oleates, ethyl stearate, ethyl, and methyl palmitoleate. Additionally, specific volatiles influence swarming, drone attraction, and general organization of the colony. This chapter comprehensively describes the retinue behaviour of workers, responsible elements, and the significance of retinue.

Queen honey bee imposes her reproductive dominance through the secretion of volatile chemicals, especially from the mandibular gland, tergal and defour glands. Further, queen pheromones and different larval diets; aggregately control the differential expression of specific genetic elements. The altered transcriptomic activity resulted in Programmed Cell Death (PCD) in the ovaries of worker honey bees. Furthermore, after the hatching of workers, the specific degenerative process remains continuous for a brief period, destroying numerous ovarioles. As a result, few facultative functional ovarioles remain active in worker honey bees' ovaries. Available literature also witnesses the formation of pseudo-queens or egg-laying workers.

This chapter provides insight into responsible queen pheromones for induction of programmed cell death in worker honey bees' ovaries. The next chapter focuses on the genetic elements for queen pheromones's-induced ovarian PCD in workers. 

Variant genomic expression and proteomics ultimately induce plasticity in honey bees' ovarian development. The expression of the same genomic content in female castes is influenced by; the compositional difference between royal jelly and workers jelly, queen pheromones, hormones associated with metamorphosis and environmental cues. Various concerned genetic elements with diversified transcriptomics include Kr-h1,hsp, Cut-like protein gene, Ftz-F1, anti-apoptotic buffy, Incov, oat, Apaf-1, ark, Incov2, MAPK, FoxO, mTOR, Hedgehog, TGF-β, Wnt, Hippo, Toll, Imd, H3K4me3, H3K27ac, H3K36me3, etc. The specific genetic elements are responsible for the structural and functional activation of the queen ovary. In workers, the same genetic factors act as the primary criterion for induction Programme Cell Death (PCD). This chapter attributes to enlisting concerned genetic elements which serve as an inducer for divergent ovarian development. The next chapter describes the details of PCD in workers' ovaries. 

Drone honey bees develop from haploid/unfertilized/diploid eggs produced by parthenogenesis or from fertilized eggs having identical sex alleles, formed after sexual reproduction, with more probability when the queen mates with drones of the same hives. Nurse bees generally remove diploid drone larvae due to cannibalism hormones secreted by developing larvae. Further, the development of drones is influenced by colony temperature, hence can be completed within 24-25 days. Queen attracts drone honey bees toward herself with pheromones9-ODA,9-HAD and 10 HDA. Drone number depends upon the colony's environmental conditions and available food to the colony. The specific chapter provides deep insight into the development of drones, the biology of drones, the reproductive system and the mating behaviour of particular castes. 

Queen honey bee is polyandrous, per her mating tendency with multiple drones of other colonies in the drone congregation area. Post-hatching, the virgin queen takes a few short flights near the colony, and eventually, within two weeks of her posthatching, she takes 1-2 nuptial flights for mating. During mating, the queen receives ample sperm storage for her entire life. Virgin queen attracts drones through her characteristic pheromonal profiling, especially by mandibular gland pheromones. After mating, drones die, and the queen returns to the native hive to perpetuate the species. The queen can regulate the fertilization of eggs; therefore, a colony is the composite aggregation of bees of different patriline inheritance. Queens can lay two types of eggs, fertilized and unfertilized, which tend to develop into female and male castes. Therefore, the queen can potentially regulate the overall strength of the colony and caste ratio to direct the colony in a specific direction.

The reproductive swarms usually include queens, young worker bees and drones, leaving the native hive to explore the pre-selected site and construct a hive there. Various factors which accelerate swarming events include congestion in the colony, reduced queen pheromones, limited available food resource, different ecological conditions, genetic possession of the colony, etc. Swarming is a significant event for a honey bee colony but drastically affects beekeeping. Therefore apiarists generally take specific measures to control packing events, including proper management of the colony, clipping of queen honey bee's wings, destruction of a queen cell, maintenance of adequate strength of the colony, re-queening of the colony and use of swarm resistance honey bees.

Polyandrous queen honey bee plays a crucial role in regulating colony strength, sex ratio, colony productivity, social communication, pheromonal regulation of colonial events and developmental controls. On the other hand, a honey bee colony without a queen fails to perpetuate. Therefore for profitable beekeeping, apiarists try to inoculate a colony with a queen with considerable fertility and strong pheromonal profiling. The present chapter highlights the importance of requeening and its method .