Glands

Posted by Jeff Gabric on

Glands

 

Honey bees possess numerous glands that synthesize and secrete an array of chemical compounds, many of which are pheromones. Some of these compounds are used within the bee’s body (such as hormones), some are secreted by the body (such as pheromones) and some produces substance used by the bees (such as wax).

 

Hypopharyngeal glands, located in the crown, snake through the head and empty into the mouths of worker bees. For the first few weeks of their lives these glands produce royal and worker jelly. As workers age and transition from brood care to foraging, the hypopharyngeal glands switch to producing intertase (a carbohydrate digesting enzyme that splits sucrose into glucose and fructose). If need dictates, these glands are capable of reverting to synthesizing royal and worker jelly.

 

The mandibular glands of worker honey bees, also housed in the head, secrete an antibacterial preservative (10-hydroxyl-2-deconic acid, 10-HDA), which when mixed with brood food (royal and worker jelly) prevents the latter from deteriorating. Additionally, the mandibular glands produce 2-Hepanone, which acts as alarm pheromone and temporary immobilizer. Excreted as honey bees bite hive pests such as wax moth larvae, it serves to announce the presence of the pest to other bees and allows the bee to remove the pest from the hive more easily. Drones’ mandibular glands produce a pheromone used to help establish and maintain Drone Congregation Areas (DCAs). Queens’ mandibular glands produce a powerful pheromone, Queen Mandibular Pheromone (QMP) which serves numerous, essential functions in service of colony cohesion.

 

The paired salivary glands (the post cerebral and thorax, located in the head and abdomen respectively), look like bunches of delicate champagne grapes and produce sucrose (used to break down sugar), lipase (used to digest fat) and amylase (used to digest starches). This oily substance is also used to lubricate the mouth, soften wax and dilute bee bread. The glands meet in a common tube in the head and empty into either side of the proboscis. In the larval stage of development these glands produce a pheromone which acts as an indicator of brood presence.

 

Worker honey bees boast four pairs of wax glands located within the last four sternites of the abdomen. These glands produce liquid wax (made mostly of esters of fatty acids and long-chain alcohols) which is exuded onto smooth internal plates, called wax mirrors. Here the wax hardens into flake-like sheets that the bees use to build and repair comb. Wax glands vary in size and productivity relative to the bee’s age, with the largest, most generative occurring around day twelve post-emergence.

 

Only worker bees have a Nasanov gland, located just below the intersegmental membrane of tergites six and seven. This gland produces a volatile pheromone used to announce location. You can see the upper part of the gland, looking like a slice of ripe mango, when workers extend and bend their abdomens while fanning, often at the hive entrance.

 

Darfour’s gland, formerly called the alkaline gland, is only present in female bees. Located dorsally, just below the oviduct and emptying into the vaginal wall it produces a pheromone which inhibits ovary development in workers. When secreted by queens this pheromone stimulates workers to form retinues (circles of attendants) around the queen.

 

The Koschevnikov, aka sting, gland is a tiny organ located near the sting sheath which produces a volatile pheromone released before, during and after stinging.

 

The Tergal glands are located just beneath the cuticle of the posterior edges of the abdominal tergites. Queen’s tergal glands are much larger than workers’ and produce a pheromone which elicits retinue behavior.

 

The Arnhart or Tarsal gland (composed of a unicellular layer surrounding a pouch-like reservoir) are in the 5th tarsomere (the very last section) of each leg. The colorless, oily secretion, called footprint odor, is exuded through the arolia, the footpads, as the bee walks. It is also released from the tip of the abdomen and is thus also sometimes referred to as trail pheromone. The chemical composition of this gland secretion is complex, but its general purpose seems to be to mark the locations bees have visited.

 

Female honey bees house Venom glands in the abdomens which generate acid. This acid empties into the venom sac where it mixes with other chemicals ultimately resulting in apitoxin, the compound which causes pain and inflammation upon being stung.

 

Honey bees possess three endocrine, hormone producing, glands. The protothoracic gland, only present in larvae, is a tiny structure located between thoracic segments, which produces ecdysone, a steroid hormone that controls molting. The corpora cardiaca and corpora allata are paired bulbous glands, sitting astride the esophagus, located in the head, connected to one another and the brain. It is not clear what functions the corpora cardiaca serve. The corpora allata produce juvenile hormone (JH) which plays many roles in the life of the larva, pupa, and adult bee. Juvenile hormone regulates development, via molting and growth, in larval and pupal honey bees. In adult bees it controls role changes as bees develop from nursing duties (during which time their JH titers are low) to foraging (at which point JH titers rise).

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