Head Segment of the Honey Bee

Bee Health October 13, 2009|Print

Contents

Head

Head of the honey bee
Head of the honey bee

The head is the center of information gathering. It is here that the visual, gustatory and olfactory inputs are received and processed. Of course, food is also input from here.

Important organs on or inside the head: 1. Antennae, 2. Eyes, 3. Mouth parts, 4. Internal structures.



Antenna(e)

Honey bee antenna with its three segments labeled
Honey bee antenna with its three segments labeled

Because honey bees live inside tree cavities (natural) or hives (man-made), both of which have little light away from the entrance. Smell and touch therefore are much important for them than visual when inside the colony.

The honey bee antennae (one on each side) house thousands of sensory organs, some are specialized for touch (mechanoreceptors), some for smell (odor receptors), and others for taste (gustatory receptors). It used to be thought that honey bees couldn’t hear any airborne sound because they do not have pressure-sensitive hearing organs (like our ear-drums or similar structures on the legs of katydids). Because of this, scientists were puzzled the ways through workers can perceive the buzzing sound produced by workers during waggle dances. About 10 years ago it was discovered that bees can indeed ‘hear’ airborne sound in close range, this is through sensing the movement of air particles by the hairlike mechanoreceptors on the antennae. This discovery helped the construction of robot bees that can be directed to dance (by a computer) inside a hive and guide workers to a specific location.

Eye(s)

Honeybee eyes. A – Two compound eyes. B – Three simple eyes. From "Beekeeping in Tennessee"
Honeybee eyes. A – Two compound eyes. B – Three simple eyes. From "Beekeeping in Tennessee"

Honey bees have two compound eyes that make a large part of the head surface. Each compound eye is composed of individual cells (ommatidium, plural ommatidia). Each ommatidium is composed of many cells, usually including light focusing elements (lens and cones), and light sensing cells (retinal cells). Workers have about 4,000-6,000 ommatidia but drones have more 7,000-8,600, presumably because drones need better visual ability during mating.

As in most insects, bees eyes are not designed to see high resolution images like our eyes do, but rather they see a mosaic image but are better than us for motion detection. Bees also have three simple eyes that are called ocelli (singular: ocellus), near the top of their head. Ocelli are simple eyes that do not focus but provide information about light intensity.



Mouthparts

(c) Zachary Huang.
(c) Zachary Huang.

Honey bees have a combined mouth parts than can both chew and suck (whereas grasshoppers can chew and moth can suck, but not both). This is accomplished by having both mandibles and a proboscis.

The mandibles are the paired "teeth" that can be open and closed to chew wood, manipulate wax, cleaning other bees, and biting other workers or pests (mites). The proboscis is mainly used for sucking in liquids such as nectar, water and honey inside the hive, for exchanging food with other bees (trophallaxis), and also for removing water from nectar. The workers can put a droplet of nectar between the proboscis and the rest of the mouth parts to increase the surface area, and slowly moving the proboscis back and forth.



Internal organs

(c) Zachary Huang
(c) Zachary Huang


(c) Zachary Huang
(c) Zachary Huang


Honey bee mandibular gland. (c) Zachary Huang
Honey bee mandibular gland. (c) Zachary Huang

The main internal organs in the head are the brain and subesophageal ganglion, the main component of the nervous system, in addition to the ventral nerve cord that runs all the way through the thorax to the abdomen. Yes, the bee does have a brain, a pretty sophisticated one too. The brain has a large area for receiving inputs from the two compound eyes, called optic lobes. The next largest input are from the antenna (antenna lobes). One important region in the middle of the brain is called the "mushroom body" because the cross section resembles two mushrooms. This area is known to be involved in olfactory learning and short term memory formation, and recently shown to be also important in long term memory formation in insects.

There are also endocrine organs attached to the nerve cords, very close to the esophagus (the food canal). One is called the corpora allata (CA, in Latin it means the body beside the food canal), which is the only source of one important hormone, juvenile hormone, which is involved in both the queen-worker differentiation, and also division of labor in workers. The other one is called corpora cardiaca (CC, the body near the heart), which is a neurohemal organ and stores and releases another hormone (PTTH, prothoracicotropic hormone). PTTH can stimulate the production of ecdysteroids, by a gland located in the thorax, the prothoracic gland.

Lastly there are exocrine glands inside the head also, most notably the mandibular glands, the hypopharyngeal glands and the salivary glands. Mandibular gland is a simple sac-like structure attached to each of the mandibles. In the queen this is the source of the powerful queen pheromone. In young workers the gland produces a lipid-rich white substance that is mixed with the secretion of hypopharyngeal glands to make royal jelly or worker jelly and fed to the queen or other workers. In old workers (foragers) the gland also produces heptanone, a component of the alarm pheromone. Similarly hypopharyngeal glands produce protein-rich secretions when young (nurses), but produce invertase (an enzyme to break down sucrose into fructose and glucose) in foragers. The glands is consisted of a central duct (which is coiled between the front cuticle and the brain) with thousands of tiny grape-like spheres (acini, singular: acinus). The secretion flows to the mouth through the long duct. The glands are large in size (hypertrophied) in nurse bees but become generated in foragers. There is also a pair of head salivary glands inside the head. The glands produce saliva which is mixed with wax scales to change the physical property of wax.

Honey bee hypopharyngeal gland. (c) Zachary Huang
Honey bee hypopharyngeal gland. (c) Zachary Huang
Honey bee salivary gland. (c) Zachary Huang
Honey bee salivary gland. (c) Zachary Huang




Answers from our experts:

I am doing honeybee studies and need to dissect out the hypopharyngeal glands, salivary glands, and if possible the corporum allatum. Is there a detailed protocol (preferrably with images) of how to dissect these structures? Answer - FAQ #41477


Source:
Page text and photos(unless otherwise stated above) are authored and Copyrighted to Zachary Huang, Dept. Entomology, Michigan State University.