The main hive regulating “queen signal” is produced by the queen honey bee mandibular, tergal, tarsal, Dufour’s and Koschevnikov pheromone-producing exocrine glands (Figure 1). The queen signal, made up of primer and releaser effect pheromones, is crucial to population maintenance and worker performance. Primer and releaser effect pheromones tell workers the status of the hive and condition of the queen.

Primer pheromones: complex, long-term responses

• Suppression of queen rearing and worker ovarian development
• Stimulation of worker behavior (cleaning, building, feeding, foraging)

Releaser pheromones: temporary, short-term responses

• Retinue formation
• Swarm clustering
• Drone mating

Figure 2. Differentiation between primer and releaser pheromone functionality

The queen signal is spread throughout the hive by initial contact with the retinue who groom and palpate the queen. Her pheromones are then transferred by antennal contact among other worker bees. In overly populated hives, swarming occurs in part because the queen signal becomes lost in translation as it is passed from workers and dissipates before the whole colony receives the queen signal. Reduction or absence of queen signal results in the decline and ultimately death of the colony if not reversed. The strength of the queen signal is an indicator of the attractiveness of the queen and population of the hive.

Produced in the mandible, the queen mandibular pheromone (QMP) is the most studied pheromone involved in producing the queen signal (Figure 2). The main chemical in QMP is (E)-9-oxodec-2-enoic-acid (9-ODA). QMP effectiveness in altering the response of the receiver is due to synergistic combinations of 9-ODA and additional chemical compounds at different concentrations. QMP concentration in the queen honeybee is minimal until she is mated and increases throughout her lifetime until she can no longer sustain the population of the colony. Studies have shown that the removal of the mandibular gland in queen honeybees eliminates 9-ODA yet the queen is still able to maintain regulation of retinue formation and suppression of queen supercedure. This suggests that other glands are also responsible for producing the synergistic compounds that complement 9-ODA in QMP.

Other pheromone producing glands that aid QMP come from tergal, tarsal, Dufour’s, and Koschevnikov glands. These additional glands emit primer and releaser pheromones like the queen mandibular gland and help amplify the effects of QMP. When in conjunction with QMP, tergal glands increase the efficiency of retinue formation and suppression of queen rearing. In each tarsomere, a saclike structure called the tergal gland secretes an oily, colorless substance called the “footprint pheromone”. As the queen honeybee moves throughout the colony, the effects of QMP and the trailing footprint pheromone alerts workers of the queen’s presence and suppresses workers from queen rearing. In overpopulated colonies, inability of the queen to travel throughout the colony leads to a lack in footprint pheromone and initiates queen rearing among workers. The role of Dufour’s gland located near the sting apparatus is like the tergal glands in its ability to stimulate retinue formation but also maintains the queen’s reproductive dominance over the workers. The Koschevnikov gland located near the sting apparatus produces the alarm pheromone in worker bees, however, in the queen honey bee it contains over 28 different unique organic compounds of which the purpose is yet clearly defined. The Koschevnikov gland contributes to the QMP signal but is quick to degrade after the first year of the queen’s life.

The functional redundancy in queen honeybee glands to produce the queen signal ensures the queen’s ability to maintain population control and worker activity. A queenright colony is dependent on the strength of both primer and releaser pheromones from the queen signal. Primer pheromones are essential to maintaining the social cohesion among honeybee colonies through physiological changes that alter long term behavior. Releaser pheromones have an immediate impact on colony behavior. Future research must be done to obtain a complete grasp on the biochemical pathways and functions of all the queen pheromones that contribute to the queen signal.

References

Bortolotti L, Costa C. Chemical Communication in the Honey Bee Society. In: Mucignat-Caretta C, editor. Neurobiology of Chemical Communication. Boca Raton (FL): CRC Press/Taylor & Francis; 2014. Chapter 5. Available from: https://www.ncbi.nlm.nih.gov/books/NBK200983/