Bees actually require proteins and carbohydrates, along with lipids, vitamins, minerals and water, like most living creatures, however, the composition of the diet of a honey bee depends on the availability of food, the stage of its life cycle, and its caste or function within the colony. It is perhaps easiest to look at the dietary requirements of honey bees chronologically:
Bee eggs take about three days to hatch, and whilst in the egg, the developing larvae derive nourishment from the egg yolk. For the first three days after hatching, all bee larvae are fed royal jelly, which is a milky secretion from the hypopharyngeal gland of young workers. Royal jelly comprises approximately two-thirds water, together with proteins, sugars, lipids, vitamins and minerals. After three days, only those larvae destined to become queens continue to receive royal jelly, which they will live on exclusively for their entire lives. This is responsible for the development of a suite of striking epigenetic changes, including the production of working ovaries, larger mandibles, brood food glands, and wax glands. Queens are also much larger and have greatly enhanced longevity compared to humble workers.
Honey bees collect and store nectar and pollen, and this constitutes the bulk of their diet. Through a process of repeated regurgitation and subsequent storage, evaporation and fermentation, nectar is converted to honey, which can be kept indefinitely and is rich in carbohydrates. Pollen is also stored and fermented into ‘bee pollen’ or ‘bee bread’, which is the primary source of protein for the hive. Both nectar and pollen are seasonal resources and storage in the hive sustain the colony during winter, or when food is scarce.
Larvae other than queens are subsequently fed on honey and bee bread until they pupate. Young workers consume large amounts of pollen or bee bread in the first 5-6 days of their adult life, in order to complete development. They will initially nurse the larvae and produce royal jelly from about days 5-15, after which they will spend a few days building comb and storing pollen and nectar, and then leave the hive to forage for the remainder of their lives. At this stage, they lose the ability to produce the proteolytic enzymes required to digest pollen and instead survive entirely upon nectar and honey.
Young adult drones (male bees whose only function is to mate with the queen) are supplied with a mixture of glandular secretions, pollen and honey by young workers.
Sometimes, when there are inadequate supplies of nectar, bees may collect sweet juices from overripe fruits and plant exudates. The honeydew secreted by insects, including some aphids, may also be harvested. Similarly, plant spores may be collected when insufficient pollen is available, although this is considered to be a poor substitute.
Beekeepers may choose to offer supplementary food to their colonies during lean periods or to stimulate productivity. Protein may be provided in the form of ‘wheast’, a combination of soybean flour and brewer’s yeast. Various forms of sugars including cane or beet sugar and corn syrup can be used for the carbohydrate component of diet.
What about water? Water is also collected by honey bees, and is used to dilute thick honey, as well as being critical for maintaining appropriate temperature and humidity within the hive. Water requirements vary with prevailing weather conditions, and beekeepers may provide additional water if an appropriate natural source is not available.