W2B-029 Bees-0.txt
Focus on Research By Michael Clancy

Prologue

Some years ago I visited Australia, and in the course of my travels from Perth in Western Australia right around to Rockhampton in Queensland I met many beekeepers, all of whom were most hospitable and friendly. On a visit to apiaries north of Perth, I was amazed at the size of the worker bees - "fat" bees my Australian host called them. These bees were on pollen collection at the time - early August, The beginning of the Australian Spring. Later at Garton Agricultural College - now a College of Queensland University - I met Graham Kleinschmidt who told me about his work on the importance of protein in the life of the honeybees. I was reminded of this work recently, when I read in an issue of the Australasian Beekeeper about the threatened closure of the internationally renowned Garton College Bee Research Centre. This, then, prompted me to write about the importance of pollen for honeybees. In doing so I must acknowledge how influential Australian research has been on this topic.
Honeybees and Pollen
Introduction
The honeybee, like all other creatures, requires a balanced diet consisting of proteins, carbohydrates, lipids, minerals and vitamins. The honeybee, however, is unusual in two respects, viz: (a) it's two major nutrients, carbohydrates and proteins, are obtained from two different immediate sources, nectar and pollen respectively, and (b) it has a two-phasic system of digestion. Carbohydrates, in the form of simple sugars, are provided by nectar and honey, and are the honeybee's main source of energy. Nectar and honey also contain very small quantities of proteins, lipids, minerals and growth factors. Pollen is the honeybee's main source of protein, lipids, minerals and vitamins. Honey and pollen together provide all the nutrients, which are essential for the growth and development of the hypopharyngeal glands and the fat bodies of the winter bee
(1) Like all living creatures, honeybees also require water.

(to be continued) Focus on Research by Michael Clancy Honeybees and Pollen (Continued)

Ingestion and Digestion

In view of the availability of both natural and substitute foods, it is worth recalling how the honeybee ingests and digests both sugars and proteins. Honeybees have two different feeding behaviour patterns, which are related both to the type of food and to their nutritional requirements.

Honeybees, who require sugars feed on honey which they imbibe in liquid form through their extended proboscis. If they food contains more than 50% sugars, the honeybee dilutes it with saliva from the salivary glands of it's head and thorax so that it will readily pass up the food canal. Dry sugar is first dissolved and diluted in the same way.

When honeybees feed on pollen - mostly from stored material or bee bread - their behaviour is quite different. The proboscis remains folded back under the head and the mandibles are used to scoop pollen from the honeycomb cell and to pass it directly into the mouth. Honeybees feeding on dry pollen exhibit the same behaviour. It has also been observed that when bees were given a mixture of dry sugar and pollen grains, some selected the pollen grains from the mixture with their mandibles, while other bees applied the tips of the proboscis to the sugar, imbibed the liquefied sugar and neglected the pollen.

Ingested food is stored in the honeycrop. The two main foods, sugars and protein are separated both during storage and digestion. This separation is made in the proventriculus, which has three main functions: (a) it regulates the movement of sugars back to the ventriculus, (b) it acts as a one-way valve to prevent the movement of liquid from the ventriculus forward to the crop, and (c) to remove pollen grains from the crop so that the crop contents become a clear liquid of about 40% sugars. These sugars are digested in the crop by enzymes secreted by the salivary glands, and which have been mixed with the food as it is ingested.

As pollen is filtered out of the honeycrop by the proventriculus, it accumulates in the proventricular pouches, and as each pouch is filled, the pollen grains are forced back into the ventriculus, where they are enclosed in peritrophic membranes as discrete packages. The pollen is thus stored and digested over a period of several hours. In this way pollen digestion is separated from sugar digestion (1).

The Importance of Pollen

The importance of pollen lies in the fact that it is the honeybee's main and natural source of protein. Protein influences the rate of breeding and longevity, making pollen the single most important factor in colony development and honey production.

Honeybees in collecting pollen mix it with nectar or honey and saliva. They add micro-organisms to start a fermentation. On return to the hive this mixture is deposited in honeycomb cells, where it is layered over with honey and continues to ferment in a manner rather analogous to the ensilage of herbage. This product is called bee bread and in recent times over 200 microbes had been identified in it (10). Bee bread and honey are the two items of the honeybees'stored food. This hoarded food enables the honeybee colony to generate heat, rear brood and survive periods when food is not available from plants.

Protein from pollen is required to (a) feed larvae, (b) allow full development of young bees, and (c) repair tissue in older bees. While the high protein dietary requirement for young bees and breeding is well known, the large amount used by older bees, particularly the wax producers on a heavy flow, is usually not considered and this can be a major factor in colony rundown. For example the demand for protein by colonies storing quality protein. Consequently, not only breeding, but the harvesting of a heavy honey flow can require a high protein input (2).

Estimates of the amount of pollen a honeybee may require vary considerably. The amount required to rear one kg of brood varies from half a kg to one kg (3). Studies in South West Queensland indicated that colonies used about 400 g pollen per week during Winter (Australian) and over 600 g per week in September (mid Australian Spring)(2). No doubt these variations are confounded by variations in the quality of the pollen proteins, and because of difference in climate it would be difficult to relate these Australian observations to the Irish situation. Nonetheless, it would appear that pollen requirements are greater than hitherto realised.

Honeybee longevity depends on the protein content of it's body. When the protein content exceeded 40%, honeybees lived for 46-50 days, whereas bees below 40% protein lived for 20-26 days, and the lower it's its body protein level it took disproportionally longer for a honeybee to regain it's body protein with good quality pollen (4).

In the absence of sufficient food protein, the honeybee while active will use it's own body protein. During death periods the honeybee minimises it's body protein depletion by reducing it's activity, breeding, foraging etc. Insufficient protein during queen production can reduce queen quality and drones exposed to low protein diets can have reduced sperm counts (2).

Susceptibility to infectious and non-infectious diseases is another consequence of inadequate protein levels. Nosema infection is a typical outcome of such poor conditions (5).
To be continued
Focus on Research by Michael Clancy

Honeybees and Pollen (Continued)

Pollen Variation

There are wide variations in the protein content (7 - 35%) of the different types of pollen and also in their biological or food values. Variety in pollen types collected by the honeybee can ensure that their food requirements are met. However, pollens with less than 20% protein cannot satisfy colony requirements for optimum production (2).

Moreover, proteins do vary very much in their food, or biological, value depending on the amount of essential amino a acids, which they contain. All proteins are formed from amino acids and there are eight to ten of these amino acids, which are regarded as determining the biological value of proteins. They are called essential, because as a general rule, most organisms cannot synthesise them and they must, therefore, form part of the diet. The essential amino acids required by the honeybee are arginine, histidine, lysine, tryptophan, phenylalanine, methionine, threanine, leucine, isoleucing and valine. Three others (glycine, proline and serine) which are not essential for growth, exert a stimulating effect on suboptimal growth (3).

The absence of any one of the ten essential amino acids will have a direct effect on the development of brood, and young bee, and also on the longevity of the adult honeybee. Thus, both the amount and quality of dietary protein are of the utmost importance in the optimum performance of the honeybee.

The honeybee does not appear to be able to distinguish between the nutritive values of various pollens and in times of pollen scarcity has been known to collect fungal spores and other non-pollens indiscriminately (6).

Pollen Substitutes

In view of the importance of protein in the diet of the honeybee it is not surprising that there have been many attempts to develop a pollen substitute. Regretfully, research to date has not been successful and it appears that some pollen is required in artificial diets to stimulate the development of the pharyngeal glands, which secrete the protein rich "bee milk" (7).

In the introduction above, the heterogeneous nature of protein digestion is described, from with it appears that honeybee digestion favours insoluble proteins. Lack of success in substitute pollens may be due to the use of soluble proteins. Certainly, the value of feeding soluble amino acids, in the absence of insoluble protein, can be legitimately questioned.

Research to-date indicates that there is no satisfactory substitute for pollen. Current thinking favours the harvesting and preservation of pollen for later bee feeding. Fresh pollen is a very perishable material and it should either be carefully dried or frozen. Drying must be carried out at temperatures under 45 ̊ C, with a gradual removal of moisture. It can then be milled to a fine powder and used as required either directly or incorporated in syrup of honey (7). Alternatively, fresh pollen can be deep-frozen and is an excellent option.

The spread of disease, e.g. American foulbrood, is a very real possibility when feeding honeybees and particularly so in the case of pollen feeding. protection afforded by irradiating the pollen and beekeepers should check that any pollen powder or pellets they purchase is sterilised by irradiation. The irradiation itself has no significant effect on the nutritional quality of the pollen - neither is irradiated pollen radioactive (7).

Irish Pollens

Pollen from Irish flora is likely to be of differing nutritional value to the honeybee. Unfortunately, no work has been done on Irish pollen from this point of view. However, there is some indication that wind-pollinated plants produce pollen of low nutritive value, while most insect-pollinated plants produce pollen which is of high value to the honeybee (1). Provided that the honeybee gathers from a variety of sources there is little likelihood that pollen quality will be poor. Rather, it is amount of pollen, especially in Autumn, which may be the limiting factor in colony development if not survival. For this reason it would be good honeybee husbandry to set up pollen traps when pollen is plentiful. The British black bee is an inveterate pollen gatherer and clogs its brood with pollen (8). This behaviour leads to swarming, but this can be prevented by the use of pollen traps (9).
