What are Queen Pheromones?

Queen Pheromones

The honey bee queen’s important role in regulating colony functions is achieved through primer pheromones. These pheromones, collectively known as the “queen signal,” are produced by various glands and induce physiological and behavioral changes in worker bees.

The queen signal maintains the social hierarchy, upholds the queen’s reproductive dominance, and ensures the colony’s stability by coordinating worker activities. It plays a crucial role in maintaining worker cohesion and regulating their behavior. The queen signal suppresses queen rearing and inhibits worker reproduction. In addition, it stimulates various activities like cleaning, building, guarding, foraging, and brood feeding.

When the queen is old, sick, or dies, workers sense a low pheromonal signal and start to rear new queens within 12-24 hours. Without young brood, the colony’s decline is rapid. The workers lay unfertilized eggs that develop into drones. The colony becomes disorganized, dirty, and susceptible to diseases and predators, leading to depopulation and ultimate demise. This shows that the queen is vital in regulating colony behavior and maintaining a healthy and thriving colony.

The queen signal also exerts an attractive releaser effect in addition to its primer effect. This summons worker around the queen into an entourage that stimulates them to feed and groom her. In young virgin queens it serves as an attractant for drones during their mating flights. When a swarm occurs, the queen signal plays a significant role in keeping the swarm intact.

Where are Queen Pheromones produced?

The Queen Mandibular Pheromone

The queen mandibular pheromone (QMP) is the most extensively researched and prominent chemical signal in honey bees. It contains chemical compounds that all work in synergy and is released from the queen mandibular glands. These are situated inside the head atop the base of the mandible. The pheromones are secreted through a brief duct that travels along a deeper channel encircled by hairs.

Various studies about the evolvement of the QMP components from queen emergence to full dominant status ended in differing results. Although all studies concluded that the amount of volatiles increased with age, findings about the different compounds and their relative amounts were inconsistent.

Until now, the individual QMP components of the queen signal are not fully understood. It is also possible that there are undiscovered compounds in fertilized queens’ mandibular glands.

Queen Pheromones to Attract her Entourage

Originally, researchers discovered the QMP for its ability to attract worker bees. This was observed during the formation of the queen’s entourage and the maintenance of the swarm cluster. The entourage consists of roughly 8-10 workers that surround the stationary queen, feeding, grooming and tending to her. It is the QMP that is responsible for the formation of the entourage. Changes in its pattern can affect worker attraction towards the queen.

The queen´s attractiveness varies depending on her age and mating status. Workers are not attracted to virgin queens, but this changes when the queen is fertilized and starts to lay eggs. The chemical signal of a fertilized queen is more attractive to workers than that of a virgin queen. This attractiveness further increases if the queen mated with multiple drones.

Mating plays a crucial role in the development of the queen’s chemical signal and her ability to attract workers. The attention of the entourage workers towards the queen changes depending on the queen´s  age and reproductive status. Workers display the highest level of attraction to queens aged between 5 days and 18 months.

According to research, QMP is not the sole substance responsible for this function. Scientists found that the absence of mandibular glands in queen bees does not diminish their ability to attract entourage workers. This shows that there are alternative pheromones apart from the QMP that can also attract workers.

Queen Pheromones for Swarming

Bees swarm to reproduce. The workers tend to the new queens, but only one queen becomes the new leader after she killed the others and mated. The old queen leads the swarm to a new nest. If the queen cannot fly or dies, the swarm returns to the hive. The swarm is attracted to the queen because she releases various pheromones, of which the main one is the QMP.

Scientists analyzed the impact of the queen, the QMP, and a five-component blend on swarming behavior in bees. They found that the queen had the strongest attraction, although the others also had similar effects. This suggests that other components could be responsible for a swarm cluster formation. The result is similar to the one discovered with the entourage behavior.

Queen Pheromones to Attract Drones

Virgin queens use the QMP to attract drones during mating flights. In an experiment that used queen dummies, researchers demonstrated that a specific component (9-ODA) in particular attracts drones. Further research showed that combinations of other components (9-HDA, 10-HDA, and HOB) also increased mating with the queen dummy.

At close range only, 9-HDA and 10-HDA proved to be responsible for increased mating contacts, whereas 9-ODA acted at a distance. Research comparing QMP components in virgin and mated queens revealed that 10-HDA is more abundant in virgin queens, but highly reduced in quantity in mated queens. The production of 10-HDA in large amounts by virgin queens suggests its crucial role as a sex pheromone in mating behavior.

Another study showed an increase in mating behavior frequency when Tergal gland extracts were added to 9-ODA. When various glandular sources work together, the effectiveness of the pheromonal stimulus is enhanced. This leads to a stronger response and better performance.

It proves that there are various ways to influence mating behavior beyond simple pheromonal stimulus. The implications of these findings could be significant, especially with regards to the impact on hormone function and the evolution of mating systems.

The exact contribution of different QMP components and other glands to the sex pheromone blend remains unclear and  need further research.

Suppression of Queen Rearing and Swarming

Monogynous insect societies have a single queen in each colony. Smaller species rely on physical competition to maintain queen dominance, while larger colonies use pheromonal signals for a more efficient system. In honeybee colonies the removal of the queen from an A. mellifera colony prompts worker bees to construct queen cups for rearing new queens. The exact mechanism behind this behavior remains unclear.

A colony rears new queens for two main reasons. To reproduce through swarming, or, to replace an old, weak or dead queen. The dispersion of QMP throughout the colony is crucial to stop queen replacement and swarming. Several studies explored the mechanisms of transferring QMP among workers and dispersing it within the colony. The queen´s entourage workers are the first to transfer queen hormones to other workers. The queen pheromones are transmitted through self-grooming from the mouthparts and the head to the abdomen of the workers.

QMP plays a crucial role in suppressing the initiation of queen rearing. The release of QMP to queenless colonies within 24 hours of queen loss leads to a significant reduction in the production of queen cups. However, four days later it has no impact. This shows that QMP effectively inhibits the start of queen rearing, but it does not affect the maintenance of existing cells.

Queen Pheromones to Suppress Worker Reproduction

The honey bee society has two distinct female castes: the queen, the only reproductive member, and the workers, that have ovaries but are unable to develop their oocytes due to the queen’s presence. When the colony becomes “queenless,” the workers’ ovaries can become active. They can lay haploid (unfertilized eggs) that develop into male offspring.

The presence of a queen inhibits ovarian development in workers. Scientists discovered that when egg-laying worker bees are returned to a colony with a queen, their ovaries will shrink. Conversely, when reintroduced into a queenless colony, the regression does not happen. This phenomenon suggests that the Queen’s presence exerts a hormonal influence on the worker bees that effectively inhibits their reproductive abilities. It highlights the importance of the queen bee in regulating the fertility of the worker bees within the colony.

In 2006, researchers made a significant discovery: they found that QMP can halt ovarian development in worker bees. This effect was even stronger when combined with Dufour’s gland secretion. Nonetheless, the most efficient way to regulate worker reproduction was by the presence of a live queen. It became clear that the queen multi-signal system is crucial in maintaining the harmony in the colony.

However, the process of ovary development in worker bees is more intricate than initially thought. Brood signals, particularly the compounds ethyl palmitate and methyl linoleate, also contribute to suppressing worker ovary development. Interestingly, this means queen regulation alone is not enough to control worker reproduction in colonies with brood.

Regulation of Worker Activity

Insects, like bees that live in highly organized societies have worker castes that specialize in different tasks. These tasks depend on their age (temporal polyethism). Younger workers carry out cleaning, feeding, and construction tasks, whereas older workers take on tasks outside the nest, like ventilation, guarding, and foraging.

Worker behavior is influenced by the increase of juvenile hormone in worker ´blood´ (hemolymph) as they age.  However, endogenous and environmental factors also impact task allocation to workers. They shift their developmental path to meet colony needs. For example, if older workers are lost, younger bees may become foragers sooner. Conversely, interruptions in queen egg-laying can slow down or reverse the behavioral development of foragers back into nest bees. The interplay between endogenous and environmental factors plays a crucial role in the organization and dynamics of insect societies.

Workers primarily regulate their own behavioral development. Although QMP may have some impact on division of labor among workers, it is the queen’s frequent interaction with nurse bees in the nest that results in a stronger inhibiting effect on their behavioral development. This suggests that the queen has a significant influence on the nursing phase of worker bees. This in turn impacts their ability to perform other tasks within the colony.

Foraging

QMP has the ability to stimulate foraging behavior and brood rearing. It leads to an increased number of foragers and weight of pollen loads in newly established spring colonies.

However, this does not happen in large, established colonies at their summer population peak. This suggests that QMP affects foraging behavior, but its impact can vary based on environmental factors and colony conditions.

Defensive Behavior

Honey bee colonies display defensive behavior when they identify predators. They alert other bees and utilize anti-predator tactics like threat postures, buzzing, and stinging. The regulation of this behavior seems linked to the presence of the queen. A queenless colony is more aggressive than one with a queen.

Tergal Gland Pheromones

Tergal glands, lie beneath the abdominal tergites. Their ducts open through the cuticle in the tergites’ posterior edge region. Queens have many more gland cells than workers. These differences in the number of gland cells is attributed to the different roles that queens and workers play within the colony. The queen has a crucial role in reproduction. The presence of numerous large gland cells help in her reproductive success, whereas workers carry out tasks like foraging and therefore require fewer gland cells.

Tergal glands play a vital role in producing pheromones that support QMP. Both, mandibular and tergal exocrine secretions in honey bees contribute to attract worker bees.

Like the QMP, Tergal gland pheromones have both, primer and releaser properties. QMPs are more effective than Tergal gland pheromones in forming an entourage of workers. However, the use of both pheromones together is even more efficient. This shows that the queen Tergal gland pheromone has a releaser function which evokes worker entourage behavior.

Tarsal Gland Pheromones

Honeybee queens, workers, and drones have tarsal glands in the sixth tarsomere of each leg, hence the name footprint pheromones. These glands are responsible for secreting an oily, colorless substance that gathers in a reservoir within the tarsus. The secretion is discharged through articular slit openings that lie between the arolium and fifth tarsomere as the bee walks.

Although there are variations in the chemical components of these secretions among bee castes, the significance of tarsal gland secretions remains a mystery. The secretions potentially serve for different purposes in queens, workers, and drones.

When a fertilized queen bee deposits Tarsal gland pheromones on the comb, it prevents worker bees from constructing queen cups.

Dufour’s Gland Pheromones

The Dufour’s gland is a tubular gland that is associated with the venom, sting sheath, and Koschevnikov glands. it opens into the dorsal vaginal wall and lies close to the setosa membrane. This is a hairy cuticle that surrounds the entire sting bulb and acts as a platform to release pheromones.

The Dufour’s gland unique location indicates that its secretions serve various functions. First and foremost, these functions relate to reproduction and egg-laying in queens, like producing a protective layer for the egg or marking it. In workers, the gland is responsible for defense mechanisms, like the production of a lubricant to facilitate stinging and to neutralize the remains of the acidic residue in the sting.

Dufour’s gland secretion has been researched as a potential pheromone used by the queen to mark her eggs as different from those laid by workers. This would allow workers to identify and care for queen-laid eggs while removing those laid by fellow workers through a process called worker policing.

The Dufour’s gland secretion plays a vital role in the queen signal, affecting both the behavior and reproductive functions of worker bees. By stimulating entourage behavior, the secretion acts as a releaser. Its primer effects include inhibiting ovarian development and promoting reproductive dominance and fertility. Despite its significance, there is much to uncover about the specific ways in which this secretion and QMP regulate worker behavior and physiological development. More research is needed to fully understand the intricacies of this complex system.

Koschevnikov Gland Pheromones

The Koschevnikov gland is close to the sting shaft. It is made up of glandular units that each consist of a secretory cell and a duct-cell that is connected to the epidermis.

The secretions spread onto the entire setosa membrane. From there, the bee releases the secretion and the alarm pheromones that originate from the glandular region of the sting sheaths. Bees release alarm pheromones when the honey bee worker stings to signal potential danger.

In the queen bee, the gland performs a divergent role. It contributes to the queen signal. Extracts from the queen Koschevnikov glands contain 28 different compounds. These include acids, alcohols, alkanes, and alkenes that lack in worker alarm pheromones.

Furthermore, studies suggest that application of queen gland extracts to worker bees induces a highly aggressive reaction called “balling behavior,” similar to the effect produced by high-concentration QMP treatment. However, the gland eventually degenerates after the queen is aged one year, leading to the loss of signal in old queens.