Hypopharangeal and Mandibular Glands of the Honey Bee
Scientific Beekeeping
Scientific Beekeeping
info@scientificbeekeeping.co.uk
This information is based on an article that appeared in the Scottish Beekeeper Magazine in July 2017
Image 1 : Saggital Section of the Head and Thorax of a Worker Bee
Exocrine glands in all animals secrete their substances through a duct.

In the worker bee there are two paired exocrine glands in the head, the mandibular glands (MGs) and the hypopharyngeal (HPGs), which have duel functions. Each gland is made up of a number of smaller units.

They variously have two different functions;
They provide food for the larvae (brood food and royal jelly)
They provide part of a complex method of chemical communication amongst the bees.

The HPGs also have a have a part to play in the digestion of food in the worker bees later life.



MANDIBULAR GLANDS:
The MGs are located in the 'cheeks' or Gena of the bee's face.. Their secretions appear on the inner surface of the mandibles These large sac like glands produce a part of brood food/royal jelly, the white secretion. This is a fatty acid which acts as a preservative, (10 hydroxydec-2-enoic acid), This is very important as the food is piped into the cell and not covered so could easily become contaminated. Particularly important elements of the food is biopterin and pantothenic acid, essential vitamins.

As the worker bee ages the MGs stop producing brood food and start to produce 2heptanone. This is a minor alarm pheromone dispensed by biting. It is said to attract other bees to investigate the bitten object. More recently it is thought to act as an anaesthetic to partially paralyse small invertebrates such as wax moth larvae or Varroa.

The drone has a vestigial mandibular gland. The function of this gland is unknown. Possibly part of the drone assembly area attractant.

The Queen's MGs play an important part in producing part of the Queen Retinue Pheromones (see link below).


HYPOPHARAYNGEAL GLANDS
The hypopharyngeal Glands lie under the 'forehead' or frons above the brain. The individual oval bodies are white and are set either side of a central tube. If dissecting the head of the bee this glands stretched out are longer than the bee measuring about 3cm. The secretion is clear and contains protein, fats and minerals. The outlets are into ducts from the right and left HPGs onto either side of the hypopharyngeal plate where the mouth meets the pharynx.

In the young worker bee eating pollen will develop the glands into brood food producing organs. These glands produce the clear component of brood food/royal jelly.

In the older house bee, once it is involved in receiving and ripening nectar from foragers, the glands decrease in size and produce enzymes which are added to the nectar as it passes from the mouth through the oesophagus and into the crop. There are sensory receptors that trigger the secretion of these enzymes. Once the bee becomes a forager these enzymes continue to be added and are important in the inversion of sucrose to glucose and fructose. This enzyme is known as sucrase. Another enzyme is also added to the mix, glucose oxidase, which acts on glucose forming gluconic acid, one of the acids found in honey. Part of this chemical breakdown also forms hydrogen peroxide which protects the nectar from microorganisms. This is one of many reasons for using honey as a dressing. Diastase, a starch digesting enzyme, is also produced by the hypopharyngeal gland and can also be found in flower nectaries.

it is possible for the HPGs to go back to their original function if necessary.


Just to clarify, brood food and royal jelly is made up in three areas. The clear component comes from the hypopharyngeal gland, the white component from the mandibular gland and then sugar (nectar or dilute honey) and some pollen from the crop (honey stomach). The workers and queen come from a fertilised egg. What makes the difference in the two female castes is that the egg is laid in a queen cup and hangs downwards rather than the horizontal cell position of a worker cell.. This causes a change in the larval diet to a specific queen diet. She will be fed more sugar in the first three days than the worker, then the protein component is increased. The queen larva eats more in those first three days. Her queen genes are activated by secretions from the corpora allata, endocrine glands which increase the production of juvenile hormone. The result is a shorter pupal stage, no pollen basket or wax glands, a straight sting, smaller mandibles, a smaller brain and an enormous pair of ovaries. So diet is all. It seems that the diet fed to larvae is specific to each of their laval days, whether worker or queen.

Margaret Thomas NDB and Jackie Elliott BSc(hons) MSc
Further reading: Winston Biology of the Honey Bee, Understanding Bee Biology, Stell
Queen Retinue Phermones
Salivary Glands
IMPACT OF VARROA MITE INFESTATION ON THE MANDIBULAR AND HYPOPHARYNGEAL GLANDS OF HONEY BEE WORKERS
Queen Phermones
Worker Phermones