What is the Anhardt gland?
What is the Anhardt gland?
- Gland secreting an orientation or recall pheromone, particularly in the absence of the queen.
- Gland secreting a short-lived repellent marker pheromone.
- Gland secreting an imprint pheromone at the hive entrance that allows a young queen to find the hive again after her nuptial flight.
- Gland secreting an imprint pheromone marking the presence of the queen in the hive. This prevents workers from building queen cells.
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Correct answer: 3 + 4
This gland (sometimes spelled “Arnhart”) is located in the fifth tarsal segment of the six legs of all three bee castes, just before the pair of claws and the adhesive pad (arolium). It produces an oily secretion that increases leg adhesion and enables bees to cling to very smooth surfaces.
The gland also secretes a marking pheromone (footprint pheromone). This secretion is 10–15 times more abundant in the queen than in workers, although the chemical composition of this pheromone is almost identical in these two castes (in contrast to males, whose composition is very different). As the queen walks over the frames, she deposits this pheromone which, when associated with mandibular pheromone deposition, prevents workers from building queen cells. In the queen, the development of the Anhardt glands and secretion of the marking pheromone follow the (seasonal) egg-laying rate and decline with the queen’s age. When the area of capped brood is very large and empty cells are lacking, slowing egg laying, and when the large number of workers pushes the queen to wander over the upper part of the frames, swarm cells appear at their lower edge. The same phenomenon is observed if the beekeeper “cuts the brood in two” by inserting a foundation sheet. The part of the frame less visited by the queen will soon contain an undesirable queen cell.
The same tarsal secretion allows foragers to signal the presence of food in foraging areas. Moreover, this marking pheromone deposited at the hive entrance enables a young queen to find her colony again after her nuptial flight and helps foragers orient themselves and reduce drifting. This marking secretion also stimulates bees to activate their Nasonov gland to perform the recall signal at the hive entrance (observed, for example, when hiving a swarm).
In males, the role of this gland is not yet well understood.
For further reading:
► Pheromones, true semiochemical communication
► Pheromones as drivers of behavioral plasticity
► A Closer Look: Tarsal Glands / Footprint Pheromone