October 10, 2016

Honey Bee Brain and Nervous System

Honey bees like most insects not only have a brain in their head but several sub brains or ganglia (7 of these) spread throughout their bodies. There are 2 ganglia in the thorax and 5 in the abdomen. Ganglia function independently but can be controlled or over written by instructions from the main brain. They also send feedback to the main brain about the state of the environment in their particular area.

Most locomotion is controlled by the ganglia, not the brain and in fact a beheaded bee can move it’s legs and wings vigorously. A bee will be able to walk and sting for a while when decapitated, but not fly as its balance will be out without a head.

An adult honey bee is one of the most advanced insects and is capable of  a huge range of different complex behaviour. Honey bees are capable of learning and have short-term memory.

The actual main brain of a an adult honey bee is proportionately very large in comparison with its size. In the worker bee the brain consists mainly of the optic lobes, with the central part acting as a coordinating centre and this central part is larger than in most other insects. Nerve fibres connect the brain to the 2 ganglia in the thorax and the 5 in tha abdomen.

Each ganglion has nerve fibres which connect it to sensory receptors on the outside of the body, to bring information back from the outside environment. The antennae are of course the main sites for sensory reception in the bee.

The ganglia also each have fibres which bring information about the condition of the internal organs of the bee and those which send back regulatory information. Fibres also carry information to the muscles to control their actions.

Much is still to be learned about why the bee is capable of displaying such complex behaviour in particular its amazing ability to navigate to and from its hive, remembering and passing on detailed information about the position of  food sources.

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Honey Bee Glands

The worker honey bee has several important glands situated in her head, thorax and abdomen. Starting  just inside the bee’s mouth  are the opening points of two very large glands, these are called the hypopharyngeal glands. The  hypopharyngeal glands are crucial to the honey bee and to the survival of the colony.

These glands are made up of a number of secretory cells clustered around a central canal. When the honey bee is young, in the first few weeks of its life, these cells are round and plump and produce brood food, a form of bee milk which is used to feed bee larvae. As the bee gets older and becomes a forager at about three weeks old, these cells become smaller and much reduced in size. The hypopharyngeal glands have now switched from producing brood food to producing invertase, which as the name suggests inverts sugars. However if necessary for the needs of the colony the worker bee can switch back to producing bee food from these glands.

In addition a pair of glands in the mandibles secrete a type of preservative which is mixed with the brood food as it is secreted from the hypopharyngeal glands, this has anti bacterial qualities which prevents the food from deteriorating.

The mandibular glands also produce an alarm scent called heptanone which is used to  alert other bees to danger. This is one of the reasons that beekeepers use a smoker as the smoke masks this scent and reduces the likelihood of the bees orchestrating an attack. The mandibular glands in the queen bee produce a type of fatty acid which is called ‘queen substance’ which is used to ensure the workers are aware of her presence.

Moving down the body there are two salivary glands in the head and thorax, with openings on either side of the bee’s tongue. Their liquid secretion is used to dilute honey and dissolve sugar crystals.

On the upper side of the abdomen of the bee on the last visible segment is the Nasanov gland.  This releases a pheromone which is used to attract members of the colony who might have lost the location of their hive. Often you will notice bees at the entrance of a hive fanning with their wings to propel the airborne scent to the bees flying around, especially when the hive has been disturbed.

Worker bees also have four pairs of wax glands on the underside of the last five segments of their abdomens. Wax is secreted into pockets underneath each gland and quickly solidifies into translucent white blobs which are then removed by mouth and worked on to use to build comb as required (see How and why bees produce wax ).

Finally there are two glands associated with the bee’s stinging mechanism. There is  a long thin venom gland which produces the acidic venom which is contained in the venom sac. The second sting gland produces an alkaline solution which is thought to act as a lubricant for the stinging mechanism.

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Honey Bee Larvae Digestive System – Alimentary Canal

The alimentary canal of a bee larvae is not as complex and developed as that of  a fully grown bee (see Honey Bee Alimentary System ), but still has to function efficiently to ensure nutrients are absorbed quickly to aid the larvae’s rapid growth and ensure that it has sufficient body stores to last it through the sealed pupal stage and onto its emergence as an adult honey bee. Bee larvae have voracious appetites and are fed first larvae royal jelly, then are quickly weaned onto a mixture of honey and pollen (bee bread) by adult worker (nurse) bees. Of course if the larva is to become a  queen, royal jelly will continue to be fed to it.

The bee larva has a very short fore-gut which carries the food from its mouth to its mid-gut, in which the food is digested. Up until the end of its larval period, that is until it has finished feeding and before it is sealed up to pupate, the mid-gut has no exit to the hindgut and digested food residue remains there. This is believed to be to prevent it from fouling its food.

Once the larva is fully fed the hind-gut breaks through into the mid-gut. At the same time the Malpighian tubules which act like kidneys and have being removing nitrogenous waste from the body cavity also break through and discharge their contents, thereby adding uric acid to the feacal matter. This waste is then expelled from the larva and spread over the walls of the brood cell. It is then covered with the silken cocoon that the larva is now spinning.

On emerging from her cell as an adult, one of the first things the bee does even before eating is clean out her birth cell. Ensuring that all her waste matter is removed and the cell is ready to be reused.

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Honey Bee Digestive System – Alimentary System

The honey bee  digests its food and the nutrients extracted from that food is circulated by the bee’s blood and used for energy and to build, maintain and repair the body. The waste products as with all living things then need to be excreted from the bee’s body.The alimentary system or canal and its associated glands are where the process of digestion and excretion take place.

The bee’s alimentary canal starts with the bee’s mouth which is situated between the base of the mandibles. Inside the mouth the canal expands into a cavity which is attached by muscles to the front of the bee’s head. These muscles can expand and contract to provide some suction to move food from the proboscis which the bee uses to access (nectar) food, into the oesophagus. Muscles in the oesophagus move the nectar back into the bee’s crop which is better known as the honey stomach, where it is stored for transport back to the hive.

The honey stomach has a valve at the end of it called the proventriculus which prevents the nectar from passing further, unless the bee needs some of it for its own use. If the bee is a forager it will carry the nectar back to the hive in its honey stomach where it will regurgitate it back into its mouth and then pass it to other house bees for food or to store and turn into honey.

The proventriculus also acts as a sieve for the nectar in the honey stomach, sieving out solids, such as pollen grains and plant spores and even bacteria. This is passed through into the ventriculus or stomach. If the bee needs sugar the proventriculus opens and nectar flows through to the stomach. Enzymes work on the contents of the stomach breaking it down so that the particles are small enough to pass through the gut wall into the blood. The bee digests two types of food, protein mainly from the pollen and sugars from the nectar.

The residue of the digestive process are passed into the rectum where it is held as faeces until the bee can leave the hive and void itself. Bees never pass waste inside their hive except if they are seriously ill. The presence of waste matter inside the hive is usually an indication that the colony is not healthy.

In winter when the bee cannot get out to relieve herself her rectum can often extend the length of her abdomen. As well as faeces uric acid is produced and stored in the rectum. At the end of the stomach there are a large number of thin-walled tubes called the Malpighian tubules, these act like our kidneys and remove nitrogenous waste, in the form of uric acid, which forms as a result of protein metabolism.

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Bee Blood – Honey Bee Circulatory System

The blood, or haemolymph of a bee carries no oxygen, (that is the job of the tracheal system )  so does not contain the red pigment haemoglobin and as a result is a pale straw or amber colour.  The blood carries nutrients to the tissue and organs of the bee and the waste products from metabolism to the excretion organs, the Malpighian tubules, for elimination. The bee’s blood also contains cells for destroying bacteria, dealing with foreign bodies and other toxic substances and also wound healing.

Unlike larger animals the bee’s blood is not contained within tubes but simply fills all spaces within its body, thereby surrounding all of its organs. This is called an open circulatory system, unlike our own which is a closed circulatory system. Blood circulation in a bee is achieved through a simple heart, which is an elongated organ lying just under the roof of the abdomen. It has muscular walls and has five pairs of openings with one-way valves which allow blood to enter the heart when it dilates. When the heart contracts, the valves close and the blood is forced forwards into the aorta which extends through the thorax and into the head where it ends just behind the brain.

It is worth noting that the only blood vessels to be found in a bee are at the base of each antenna, which force the blood to circulate through them, highlighting the importance of the antennae to a bee.

The bee’s heart  pushes the blood  forward into the brain until pressure increases forcing it back through the body cavity and to all the organs and tissues. On its way from the head, the blood passes back through the thorax, nourishing the flight muscles, then into the abdominal cavity where more nourishment is picked up from the digestive system before it is drawn back into the heart again.

photo courtesy of infovisual.info

Honey Bee Respiratory System

The respiratory system of the honey bee is made up of a series of tubes called the trachea. In higher species of animals oxygen is carried throughout the body by the blood, in bees and all insects, blood is not used to transport oxygen where needed but instead the trachea are used.

The trachea are made of thickened cuticle and start large but rapidly branch and divide getting smaller until they end in single cells, in such a way as to reach every organ in the bee’s body. The trachea open to the air through holes in the cuticle called spiracles, which have opening and closing mechanisms.

Initially the trachea widen to form air sacs which are used to store air. The trachea arms widen to form air sacs that are large albeit few in number and used to store air. The small branches and tubes emerging from the sacs extend as far as the tissues. Bees can accelerate the passage of air into their bodies by contracting these sacs, which speeds up the oxygenation of the tissues.

Air is drawn into the air sacs by a telescopic movement which lengthens and shortens the abdomen and can clearly be seen when the bee is at rest.

More on the Anatomy and Physiology of the Bee

Honey Bee Exoskeleton

Bees like all insects and unlike vertebrates,  have their skeletons on the outside, exoskeletons , with the muscles attached to the inside. The exoskeleton is made up of two parts, the epidermis and the cuticle.

The epidermis is a single layer of living cells forming a complete sheet over the whole body and covering the internal organs. The epidermis also secretes a non living material which forms the hard, resistant outer covering of the insect which is the cuticle.

Bee’s Cuticle

The structure of the cuticle is built from chitin, into which a protein called sclerotin is injected. The cuticle is covered with a thin coating called the epicuticle, to make it waterproof and scratch resistant.

This dead layer or cuticle means that if an insect wishes to grow the old cuticle needs to be shed or moulted and a new one produced. This process only occurs in a honey bee during the larval and pupal stages.

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Basic Anatomy of the Honey Bee

Like all insects the body of a bee is divided into three main sections, the head, the thorax and the abdomen.

Head of a Bee

The bee’s head carries the antennae, the eyes and the mouthparts. The eyes of a bee are interesting  as they consist of two kinds; two large compound eyes which are the bees main vision organ and on top of the head three simple eyes or ocelli, which are believed to monitor light intensity. Inside the head is the bee’s brain and glands.

Bee Thorax

The thorax is divided into three parts the pro, meso and metathorax. A pair of legs is attached to each of these thorax parts and the bottom two each have a pair of wings. The thorax ends in a segment called the propodeum which although looks like part of the bee’s thorax is really the first segment of the abdomen.

Internally the thorax contains the large muscles which power the wings which are also responsible for heat production both in flight and when controlling the temperature within the hive. There is also a smaller set of muscles which control wing direction.

The Abdominal Section of the Bee

The bee’s abdomen is joined to the thorax by a narrow band or neck called the petiole. The abdomen is composed of six visible segments. internally the abdomen contains the bees heart, alimentary canal, wax glands, sting and sex organs.

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Differences in the Anatomy of a Queen Bee, Worker Bee and Drone

As far as size is concerned the queen honey bee is the longest of the three. However unlike the other two her wings only extend half way along her abdomen, which itself is pointed at the end. Her legs appear to be spider-like and her head is proportionally smaller than a worker bee or drone.

The drone on the other hand is squarely built with a stumpy squared off abdomen and is a similar weight to the queen bee. His wings are large and cover his abdomen completely. He has the longest legs but these are largely disguised by his stout body shape. The drone has a large round head and very large compound eyes which appear to meet on the top.

The worker bee is the smallest of the three and half of the weight of the queen bee or drone. Her wings although longer than the queens, do not quite cover her abdomen, which is pointed at the end and she has short legs. The head of the worker bee is proportionally large and more triangular than the others.

The workers mouth parts or mandibles are spoon-shaped which helps her mould wax and collect propolis. Her tongue is also the longest as she has to be able to forage and access nectar in flowers. Her third pair of legs are also modified with special sacs or corbiculum  to carry loads of pollen and propolis when required.

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More about the Honey Bee Colony

How and Why Honey Bees Make Wax

Honey bees use wax to build comb that forms their nest and the intricate hexagonal cells that make up that comb. These wax cells are used to house the various stages of bee young (or brood)  as they develop from egg to adulthood. In addition wax cells are used to store pollen and nectar.

Wax is produced as needed by worker bees to form and repair comb and individual cells. The wax is secreted by these worker bees, from eight special wax glands situated on the underside of their abdomens (inside the protective plates or sternites of abdominal segments 4 to 7). Worker bees produce wax most efficiently during the 10th through to the 16th days of their lives and this declines steadily from day 18 until the end of  life.

When wax is required these workers fill themselves up with honey and then hang together in clusters to contain the heat generated by the metabolism of the honey in their muscles. This resultant rise in temperature allows the wax to be secreted from the bee’s wax glands and this secreted wax then pours into special holders beneath these glands and solidifies.

The eight translucent white blobs of wax that are formed are then removed by the bee using her end pair of legs and either passed to her mouth or to the mouth of others to carry to another part of the comb. The wax is worked on and manipulated until the consistency is right and  it is then moulded into position using the bees mandibles (or mouth parts) and the comb is built up to the size required to house newly laid eggs or food stores. It is in the mastication process that salivary secretions are added to the wax to help soften it and this also accounts for its change of colour. The colour of beeswax in a comb is white at first and then darkens with age and use, especially if it is used to raise brood.

It is believed that 6-8 pounds of honey is needed to produce a pound of bees wax and it is estimated that bees fly 150,000 miles, roughly six times around the earth, to yield one pound of beeswax (530,000 km/kg).

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