Drone Pheromone
In comparison to the other pheromones drone phermone has not been the subject of much research.

It is suggested that a drone-produced attractive odour substance may be involved in the formation of drone congregation areas. It may also be possibile that virgin queens use the same cue when orienting toward drone congregations areas.

A paper was published in 1985 entitled "Pheromonal activity and fine structure of the mandibular glands of honeybee drones (Apis mellifera L.) (Insecta, Hymenoptera, Apidae)" by Y Lensky et al. The paper described the examination of the drone mandibular gland. The abstract reads:

"Experiments were conducted to determine the role of drone mandibular gland secretions in attracting flying drones and the effect of age on the secretory activity. Extracts of mandibular glands and of cephalic tissues were applied to cotton lures which were attached below balloons tethered at 8–12 m above the ground. Most flying drones were attracted to extracts of mandibular glands but a few were drawn to other cephalic tissues or to solvent controls. Histological and electron microscope studies showed that the structure of the tiny (0.12 mm long) mandibular gland varied according to age. Its secretory activity in 0–3-day old drones was evident from the abundant rough endoplasmic reticulum. At 7-days the glands were fully developed. After 9 days the glands were no longer active and showed an autolytic process; the product was stored in the gland lumen for further emission during drone mating flights."

It appears strange that by the time a drone becomes fully mature at 14 days the mandibular glands are no longer active. Perhaps the secretions persist.

Another paper was published in the Journal of Experimental Biology in 2014 which confirmed that single drones are attracted to a larger group of drones ( See left). This study also confirmed that the drones were attracted to pure 9-oxo-2-decenoic acid (9-ODA) but not to the mated queen's queen mandibular pheromone (QMP) of which 9-ODA is a component.

in 2017 further research appears support the findings above and also to prove that virgin queens are attracted towards drones. The abstract reasds :

"Although the honeybee is a crucial agricultural agent and a prominent scientific model organism, crucial aspects of its reproductive behaviour are still unknown. During the mating season, honeybee males, the drones, gather in congregations 10-40 m above ground. Converging evidence suggests that drones emit a pheromone that can attract other drones, thereby increasing the size of the congregation. Virgin queens join the vicinity of the congregation after it has formed, and mate with as many as 20 males in mid-air. It is still unclear which sensory cues help virgin queens find drone congregations in the first place. Beside visual cues for long-range orientation, queens may use olfactory cues. We thus tested virgin queens' olfactory orientation on a walking simulator in which they have full control over odour stimulation. We show that sexually-mature virgin queens are attracted to the odour bouquet from a group of living drones. They are not attracted to the bouquet from a group of workers. In addition, non-sexually receptive females (workers) of the same age are not attracted to the drone odour bouquet. Interpreted in the context of mating, these results may suggest that virgin queens use volatile olfactory cues from the drones to find the congregations. Virgin queen attraction toward males in honey bees." Virgin queen attraction toward males in honey bees" Bastin F et al. 2017

Several theories have been put forward as to how guard worker bees recognise returning drones. In 1994, KiKirchner W.H, Gadagkar R. Discrimination of nestmate workers and drones in honey bees. Insect Soc. 1994;41(3):335–38, observed that returning drones received the same interrogation as worker bees returning to the hive. they postulated that it was some sort of recognition system based on a cuticular pheromone signal.

Research printed in 2018 ( Evaluating the Role of Drone-Produced Chemical Signals in Mediating Social Interactions in Honey Bees (Apis mellifera). Villar G et al.) stated that "Drone mandibular glands primarily produce a blend of saturated, unsaturated and methyl branched fatty acids ranging in chain length from nonanoic to docosanoic acids, and both gland extracts and synthetic blends of these chemicals serve to attract drones outside of the hive, but do not attract workers inside the hive."

This gives us a little more information into the mysterious world of drone pheromones.
Scientific Beekeeping
Chemical Communication in the Honey Bee Society.
Honeybee drones are attracted by groups of consexuals in a walking simulator. Lensky et al, 2014.
Pheromonal activity and fine structure of the mandibular glands of honeybee drones (Apis mellifera L.) Abstract only
Virgin queen attraction toward males in honey bees. Bastin et al 2017. Abstract only
Evaluating the Role of Drone-Produced Chemical Signals in Mediating Social Interactions in Honey Bees (Apis mellifera). Villar et al, 2018 Abstract only