The Bees' Needs - (part 1)
We gardeners play a huge role in the continued survival (or otherwise) of bees so I thought I would do a series of blogs about honeybees and their knees – oops, I meant needs! But why just honeybees? Well, that’s what I know most about: some (but not all) of the information will apply to other bees too, though.
So, what do bees need? Like every other living creature on our planet, bees need food and water. Water is water whatever and wherever you are, but food is a different story entirely. Humans are omnivores, living happily on an extremely varied diet. Some creatures are herbivores, eating only plant-based food, others are carnivores, eating only meat. Bees are herbivores and their food, and the source of all their nutrition, is specialized, consisting of only two items: pollen and nectar. So, let’s find out a bit about them.
Bees need plants
Bees and flowers are interdependent: they rely on one another for their very existence. The bee/flower relationship has evolved over millions of years with flowers in particular adapting to attract pollinating insects. Bees are active from early spring, usually late February or March, until the first frosts which often occur in October but sometimes isn’t until November, or even later, especially in towns and cities where the temperature is often 2-3°C - and can be as much as 6°C - higher than in the countryside. (This is a recognised phenomenon known as the ‘Urban Heat Island Effect’, first described as long ago as the early 1800s.) This period of bee activity corresponds with the main growing and flowering season of plants which isn’t merely a coincidence since bees require a substantial amount of food in the form of pollen and nectar from flowers to survive.
Let’s look at pollen first – I’ll cover nectar and water in subsequent posts.
Bees need pollen
A quick secondary school biology recap coming up: pollen is produced by the male sex organs of the plant and in order for the plant to reproduce the pollen must be transferred from the stamen to the stigma, the receptive female organs. The most efficient way for the plant to bring this about is either to be self-fertile or to use an agent, either in the form of the wind or by means of an insect. Many plants have evolved to take advantage of wind pollination (particularly grasses) but the vast majority rely on insects, and particularly bees, to get the job done.
Pollen equals protein
Pollen provides bees with an essential foodstuff that all living creatures need in their diet for the growth and repair of body tissue, namely protein. Amazingly, the protein content of different pollen can vary considerably - some has as little as 2% yet it can be as much as 28%.
There are three particular reasons why honeybees need the protein found in pollen.
First, pollen is a vital component of the food that is fed to worker bees from the third day of their lives as larvae. (During the first two days they are fed a special ‘brood food’ or royal jelly, a secretion from the nurse bees, which is in some ways the equivalent to colostrum that mammal babies receive from their mothers.) They are then fed a mixture of royal jelly, pollen and honey until the cell is sealed and they start to pupate. Drone larvae receive a slightly different combination of food, and for slightly longer than the worker larvae, and a queen larva is fed exclusively on royal jelly.
Second, it’s vital for the sound development of the hypopharyngeal gland. Without getting too technical, this is a gland situated in the head of the worker bee which is crucial for the production of brood food that is fed to larvae during the first two days. The hypopharyngeal gland is also responsible for the secretion of wax with which to build comb, and for the conversion of nectar into honey. Pollen which is fed to young bees within the first 5 to 6 days after they have emerged from the cell ensures that the hypopharyngeal gland grows properly.
Third, the proper development of bees’ fat bodies, or fat cells, depends on adequate protein intake. Fat bodies, which store not only fat, but also protein and glycogen (‘stored’ glucose) can be found in the abdomen of the bee. These fat bodies are particularly important in honeybees which must over-winter: not only must they survive the winter, but they must also be fit enough to be able to provide food for the brood, or baby bees, early the following season.
How much pollen do honeybees need?
It has been calculated that about 100mg of pollen is needed to rear one worker bee so, if during the summer a colony rears about 100,000 bees, approximately 10kg of pollen is required. Bear in mind, however, that a typical pollen load weighs between 10mg and 30mg, then up to a million pollen forages must be made.
Not all forager bees collect pollen, however - this work is left to a maximum of 25% of the foraging population. Pollen foragers will generally fly from one flower to another of the same species until that resource is exhausted (although between 1% and 10% of pollen samples have been found to contain pollen from more than one species). This behaviour is called constancy. Constancy is important for successful pollination as the flower must have pollen from the same species in order to be fertilized. It also reduces the distance that bees have to fly to collect a full load. Although individual bees will remain constant to one pollen or nectar source, collectively they will visit a range of sources within the foraging zone. Pollen colour varies, too. The majority of pollen is a shade of yellow or orange, but it can range from a clotted cream colour to dark purple, almost black, and most shades and hues in between. Have a look at the pictures, and you’ll see what I mean: the picture of the honey comb shows pale-yellow pollen from rape, and burgundy-red pollen is from red dead nettle; the second picture shows a honeybee collecting pollen from a Scabiosa columbaria.
Another important factor to note is that plants allow pollen to be released at different times of the day and over varying periods of time during their flowering season. For example, pollen from individual florets on the head of Taraxacum officinale (dandelion) will be made available for about ten minutes, mainly during the morning; whereas pollen from Rubus fruticosus (bramble) can be collected from individual flowers for up to four days, throughout the day. Although forager bees tend to stay loyal to one species until the food source has run out, this behaviour has been known to change if different supplies are available at different times of day; for example, a bee will collect from Papaver rhoeas (field poppy) in the morning and broad bean in the afternoon because this is when each flower releases its respective pollen.
What happens to pollen in the hive?
When pollen is brought back to the hive it is packed into cells to exclude air, and a little regurgitated honey, hypopharyngeal secretions and enzymes are mixed in with it so that it doesn’t decompose and ferment, and to aid initial digestion. This pollen with ‘additives’ is known as ‘bee bread’. This is stored in cells close to the brood cells so that it’s readily available to the nurse bees feeding the larvae and to the newly emerged adult bees.
So that's pollen! Look out for my posts on nectar and water.
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