Nectar and Pollen

One of the great advantages of being out and about in the fynbos, is that one can observe what the bees are feeding on. This varies depending on the time of day and is obviously dependent on what is currently flowering. Nectar is sucked up through the bee’s proboscis, or long tongue, and it fills its honey stomach. Back at the nest this is then passed on to the house workers and used for the production of honey and beeswax. When bees visit flowers, pollen is scattered all over their hairy bodies. The bee combs it down and packs it tightly into their pollen baskets situated on their hind legs. What is not collected together is carried to the next flower to pollinate it. The work that the bee does as a pollinator is purely involuntary, but magical. 85% of the fynbos is pollinated by honeybees!

Screen Shot 2015honeybee on Erica capensis

Looking at various aspects on nectar and pollen on the internet, I came across Susan W. Nicolson’s research paper titled: Bee food: the chemistry and nutritional value of
nectar, pollen and mixtures of the two. It can be downloaded here.

Nicolson’s paper is a review of the chemistry of the floral resources, nectar and pollen. It is a fascinating article for anyone interested in the nutritional value of both to the bees, and raises the question as to whether we, as humans, can actually digest pollen nutrients. Pollen granules are becoming ever popular in Health shops.

Following is a brief summary of Nicolson’s paper…

Bees are herbivorous, consuming nectar and pollen throughout their life cycles.

Nectar is the main source of energy for the bees, containing mostly sugars, but also may contain various minor constituents of nutritional significance.

Pollen provides bees with the protein, lipids, vitamins and minerals essential for larval rearing and development.

In honeybees, pollen consumption is highest in young adults, enabling their hypopharyngeal glands to produce royal jelly for feeding larvae. Once the bees transition to becoming foragers at around 14 days, they consume mainly carbohydrate or nectar, suggesting that foraging bees have reduced requirements for protein.

A single wild honeybee colony will harvest 120kg of nectar and 20kg of pollen annually.

There are differences in composition and nutritional value of bee-collected pollens and hand-collected pollens, as honeybees directly and indirectly begin altering pollen composition right from the first contact.

Nectar:

Energy content is directly related to its volume and sugar concentration.

Bees prefer higher concentrations of nectar which maximise their energy gains. (In arid conditions they may, however, time their foraging to maximise water gains in nectar.)

Nectars rich in sucrose (flowers of the Lamiaceae family) and hexose sugars (sunflower, canola, Eucalyptus species) are highly attractive to bees.

Other nectar components:

Amino acids, present in high concentrations in nectars of Erythrina and Aloe.

Caffeine is present in Citrus nectar which is highly attractive to bees!

Pollen:

When honeybees pack pollen into their pollen basket, the addition of nectar enables them to transport pollen grains varying in size and surface texture. More nectar and glandular secretions are added in the hive, and microbial inoculation leads to fermentation during storage, forming bee bread which has higher nutritive value than bee-collected pollen.

Protein levels in pollen vary widely. Sunflower pollen is considered to be of poor quality for bees because of its low protein content after collection by bees.

Amino acid composition determines the amount of pollen required by bees, more than its protein content. Bee-collected pollens of Eucalyptus species are deficient in some amino acids, suggesting that bees will not do well on an exclusive diet of Eucalyptus pollen.

Low lipid levels are also found in bee-collected pollen of eucalypts, whereas high levels are found in canola pollen. Higher levels of lipid are considered attractive to bees

Nicolson notes, that from an evolutionary viewpoint it makes sense for bees to be more discriminating in their choice of pollen sources: the pollen is needed on a short-term basis for larval rearing, whereas the colony requires full honey stores to survive adverse conditions. Diversity in bee diets may be necessary to avoid nutritional deficiencies and to dilute toxins, but need not involve many plant species. Pollen is usually collected from 5 – 9 plant species at a time, with mixed pollens being better than single pollens for maintaining honeybee immune systems.

It seems that much more research on pollen and nectar sources still needs to be done in South Africa. Hopefully with our observations in the fynbos, we can make a small contribution, too, to the preferred bee forage.

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