By: Clarence Collison
Pollen Micronutrients
Carbohydrates, proteins, lipids, vitamins and minerals available to honey bees are factors responsible for the amount of progeny produced, longevity and health of adults and for the survival and productivity of a colony. Colonies facing a limitation of an essential nutrient, such as pollen in general, or an essential amino acid or vitamin in particular, will cease brood production and may not survive if not supplied with the missing nutrient (Brodschneider and Crailsheim, 2010). There are approximately 25 vitamins and minerals (elements) that should be accounted for in a honey bee diet. Their classification is made not on the basis of chemical structure, but on their chemical activity and biological properties (Lipiński, 2018).
Sterols and Lipids
Honey bees obtain lipids exclusively from pollen, and the lipid content of pollen from various species ranges between 0.8% and 18.9% (Roulston and Cane, 2000). Lipids are mainly metabolized during the brood stage of honey bees and are regarded as an important energy source, and as precursors for further biosynthesis (Cantrill et al., 1981).
For honey bees, lipids from pollen are important sources of substances that contribute to their development and reproduction (Manning, 2001). Simple lipids, popularly called fats, are the main source of glycerol, essential fatty acids, sterols and fat-soluble vitamins (A.D.E.K.) (Lipiński, 2018).
A sterol, 24-methylenecholesterol, is common in pollen and is the major sterol source for honey bees. Nearly all insects need to obtain sterols from their diet because of their inability to synthesize them directly. Sterol is the precursor for important hormones such as the molting hormone, which regulates growth because it is required at the time of each molt. It is not clear what other lipids are required by honey bees, but most likely normal consumption of pollen provides all the lipid requirements. Pollen with low fat content is less likely to be consumed by honey bees, but can be made more attractive to bees with the addition of lipids. The total lipid concentration within a pollen supplement is recommended to be 5-8% (Huang, 2010).
The sterols of prepupal honey bees, from brood reared by workers fed chemically-defined synthetic diets containing cholesterol, campesterol, sitosterol, stigmasterol, 24-methylenecholesterol or no sterol over a 12-week period were isolated, identified and quantified. The major sterol present in each prepupal sample was 24-methylenecholesterol, but significant levels of sitosterol and isofucosterol were also present in every case, as was a very small percentage of desmosterol (usually <1%). This is the first report of isofucosterol being identified in the sterols of the honey bee. A considerably larger percentage of each dietary sterol was found in prepupae reared by workers fed that particular sterol in the diet. This was most dramatic in the case of the cholesterol diet in which case cholesterol content increased to as much as 17.2% of the prepupal sterols, whereas cholesterol had not exceeded 2.2% in samples from other diet regimens. However, stigmasterol comprised no more than 6.3% of the total sterols in any sample from prepupae fed the stigmasterol diet. The preponderance of 24-methylenecholesterol in all prepupae, regardless of the dietary sterol provided to the workers, as well as the lesser quantities of sitosterol and isofucosterol present in all samples, suggest a unique system of utilization and metabolism of these dietary sterols by the worker bees. Apparently, they make available to the brood varying amounts of unchanged dietary sterol plus considerable and fairly constant portions of 24-methylenecholesterol, sitosterol and isofucosterol drawn from their own sterol pools (Svoboda et al., 1980).
The honey bee is one of only a few species of phytophagous insects known to be unable to convert C-24 alkyl phytosterols to cholesterol. Regardless of the dietary sterols available to worker bees, the major tissue sterol of brood reared by the workers is always 24-methylenecholesterol, followed by sitosterol and isofucosterol. Normally, little or no cholesterol is present in honey bee sterols. The maintenance of high levels of certain sterols is accomplished through a selective transfer of sterols from the endogenous sterol pools of the workers to the developing larvae through the brood food material secreted from the hypopharyngeal and mandibular glands and/or the honey stomach of the workers. The selective uptake and transfer of radiolabeled C27, C28 and C29 sterols have been studied to correlate these aspects of sterol utilization with the discovery of an unusual molting hormone (ecdysteroid) in honey bee pupae as the major ecdysteroid of this stage of development. The phylogenetic implications of this selective transfer phenomenon in the honey bee and comparison with sterol metabolism in certain other hymenopteran species emphasize the diversity of steroid biochemistry in insects (Svoboda et al., 1986).
Plant pollens have distinctive fatty acid profiles; some are characteristically dominant in one or more fatty acids. Pollens with high lipid concentrations and dominated by linolenic, myristic and dodecanoic acids probably play a significant role in inhibiting the growth of the spore-forming bacteria Paenibacillus larvae larvae (American foulbrood), Melissococcus pluton (European foulbrood) and other microbes that inhabit the brood combs of beehives. Those pollens high in oleic and palmitic acids probably have a greater role in honey bee nutrition (Manning, 2001).
Honey bee colonies require adequate pollen for maintenance and growth. Pollens vary in nutritional value, and a balanced diet is achieved by mixing pollens with complementary essential nutrients. Subjective evaluation of pollens by foragers in colonies deprived of one or two essential fatty acids (eFAs), alpha-linolenic acid (omega-3) or linoleic acid (omega-6) were tested. Four pollens, two rich in omega-3 and two rich in omega-6 were used. A colony in an observation hive was allowed to forage for two to five days on a single pollen source. The following day, we repeatedly presented one of three pollens: the same pollen that the bees had been collecting the previous days, a novel pollen that was similarly deficient in omega-3 or omega-6 and a novel pollen that complemented their eFA deficiency. The rate of waggle dances, which reflects on the strength of recruitment effort, of foragers returning to the observation hive from each of the pollens were measured. Dance rates did not differ between the four pollens, but they were the highest to the “complementary” pollen and the lowest to the “same” pollen. Furthermore, this effect was greater for pollen combinations with greater eFA disparity between the same and the complementary pollens. Their findings support the ability of bees to balance colony eFA intake. Conditioning of the proboscis extension response (PER) tests showed that pollen foragers discriminated well between the four pollen odors, but the mechanisms by which bees assess pollen eFA composition remain to be elucidated. Differential dancing would recruit foragers to pollens that balance colony nutritional needs (Zarchin et al., 2017).
Vitamins
In general, the vitamin needs of a honey bee colony are satisfied as long as the beebread stores are abundant in the hive, or fresh pollen is available to bees. Also, microbiota present in the elementary canals of bees provide vitamins and other central substances which complete the diet (Standifer, 1980). Nurse bees are thought to need the following vitamin B complex for brood rearing: thiamine, riboflavin, nicotinamide, pyridoxine, pantothenic acid, folic acid and biotin. Ascorbic acid (vitamin C) also seems essential for brood rearing (Huang, 2010).
The requirements of nurse honey bees for fat soluble vitamins to support brood rearing was studied by feeding a chemically defined diet supplemented with either vitamin A, D, E or K (0.4 µg/gram diet) or with a complex of all four vitamins. Control bees were fed the basic diet without fat soluble vitamin supplementation. Bees fed diets containing vitamin A reared more bees to the sealed stage; bees fed vitamin K and ADEK diets reared the next most brood. These three diets all resulted in twice as much brood as the control diet. Bees fed diets containing vitamin D or E consumed little diet and reared minimum levels of brood to the sealed stage (Herbert and Shimanuki, 1978).
Diet in the Winter has a vital effect on the survival and condition of a honey bee colony in the Spring. The effect of supplementation of the diet with vitamin C (ascorbic acid) on the total antioxidant status (TAS), glutathione content and activity of four antioxidative enzymes: superoxide dismutase (SOD), peroxidase (POX), catalase (CAT) and glutathione transferase (GST) of honey bee brood developing in the Spring was studied. Twelve stages, from newly hatched larvae to emerging adult worker bees were studied, allowing changes in the antioxidant profile during brood development to be determined for the first time. It was shown that bees are more exposed to oxidative stress after emergence. In workers emerging in colonies after supplementation with vitamin C, higher contents of protein and glutathione, and higher activities of peroxidase, catalase and glutathione transferase were observed. Vitamin C did not alter brood weight increase, and the level of protein in emerged workers was higher than in the control group. The mean of bee losses over Winter were about 33% lower in colonies receiving vitamin C (Farjan et al., 2012).
The effect of dietary vitamin C on brood rearing of honey bees was studied using both free-flying and confined colonies. Pollen traps were placed on free-flying colonies for a three hour period and the weight of pollen and levels of vitamin C (L-ascorbic acid and dehydroascorbic acid) were determined. The amount of sealed brood in each of these colonies was also measured. Additionally, the consumption and brood rearing by caged bees fed a pollen substitute fortified with zero, 500, 1,000 or 2,000 µg L-ascorbic acid/g diet were measured. Pollen proved to be a rich but variable source of Vitamin C depending on the date of collection and floral source. There was, however, no relationship between the vitamin C level in the pollen collected and the rate of brood rearing. There were highly significant differences in the vitamin C levels in pollen depending on the date of collection. In the study using caged bees, significantly more brood was reared by bees fed either the diet supplemented with 500 µg/g or the control than by bees offered diets containing either 1,000 or 2,000 µg/g L-ascorbic acid. This study also demonstrated for the first time that bees are able to produce this vitamin since prepupae from colonies fed the diets without vitamin C had equivalent levels of ascorbic acid to those fed the enriched diets (Herbert et al., 1985).
In this investigation, the effects of different levels of vitamin C in sugar syrup on the rate of queen laying, colony population and body weight and protein in honey bees were studied. Experimental colonies had the same age queens and the same population and fed with sugar syrup (50% sugar) in three levels 2000, 4000, 6000 mg/L syrup—soluble vitamin C while the control group fed only with sugar syrup (treatment one control, treatment two, three, four respectively 2000, 4000 and 6000 mg/L vitamin C) were compared. In this experiment, feeding colonies for 60 days in May and June (the first 45 days of feeding every second day and the other without feeding-period of 15 days) were done. The highest average brood area was in treatment two with 2000 mg/L vitamin C (9049 cm2) while the lowest one was in treatment one (control) (4848 cm2), respectively. Mean colony population in treatment four was higher than control (10.41 vs 8.38 comb), respectively. The highest mean percent of protein was in treatment two (17.5%) while the lowest was in treatment three (14.18%). Worker bees in treatment four had the greater mean body weight than other groups. The results indicated that supplementing the level of vitamin C to Spring nutrition (1:1 sugar syrup) to the colonies, increases the brood area, colony population and the worker’s body weight and protein (Andi and Ahmadi, 2014).
Minerals
The mineral requirements of honey bees are poorly understood. High amounts of potassium, phosphate and magnesium are required by all other insects, and so presumably are by honey bees as well. Excessive levels of sodium, sodium chloride and calcium have been shown to be toxic to honey bees. Again, all the required minerals can be obtained from pollen, although nectar also contains minerals. Dark honey contains higher levels of minerals. The optimal ash concentration for maximum brood rearing seems to be at 0.5%–1%. Pollen with more than 2% ash inhibits brood production (Huang, 2010).
In general, pollen contains the common nutritional minerals: potassium, phosphorus, sulphur, calcium, magnesium, sodium, iron, zinc, manganese and copper (Galetto and Kevan, 2015).
References
Andi, M.A. and A. Ahmadi 2014. Influence of vitamin C in sugar syrup on brood area, colony population, body weight and protein in honey bees. Int. J. Biosci. 4: 32-36.
Brodschneider, R. and K. Crailsheim 2010. Nutrition and health in honey bees. Apidolgie 41: 278-294.
Cantrill, R.C., H.R. Hepburn and S.J. Warner 1981. Changes in lipid composition during sealed brood development of African worker honey bees. Comp. Biochem. Physiol. B 68: 351-353.
Farjan, M., M. Dmitryjuk, Z. Lipiński, E. Biernat-Ɫopieńska and K. Żóltowska 2012. Supplementation of the honey bee diet with vitamin C: the effect on the antioxidative system of Apis mellifera carnica brood at different stages. J. Apic. Res. 51:263-270.
Galetto, L. and P.G. Kevan 2015. The Production of Nectar and Pollen. In: The Hive And The Honey Bee (Ed. J.M. Graham), Dadant and Sons, Hamilton, IL, pp. 345-368.
Herbert, E.W. Jr. and H. Shimanuki 1978. Effect of fat soluble vitamins on the brood rearing capabilities of honey bees fed a synthetic diet. Ann. Entomol. Soc. Am. 71: 689-691.
Herbert, E.W. Jr., J.T. Vanderslice and D.J. Higgs 1985. Effect of dietary vitamin C levels on the rate of brood production of free-flying and confined colonies of honey bees. Apidologie 16: 385-394.
Huang, Z. 2010. Honey bee nutrition. Am. Bee J. 150: 773-776.
Lipiński, Z. 2018. Honey Bee Nutrition And Feeding. OZGraf S.A., Olsztyn, Poland, 430 pp.
Manning, R. 2001. Fatty acids in pollen: a review of their importance for honey bees. Bee Wld. 82: 60-75.
Roulston, T.H. and J.H. Cane 2000. Pollen nutritional content and digestibility for animals. Plant Syst. Evol. 222: 187-209.
Standifer, L.N. 1980. Honey bee nutrition and supplemental feeding. In: Beekeeping in the United States, Agriculture Handbook 335, pp. 39-45.
Svoboda, J.A., M.J. Thompson, E.W. Herbert Jr. and H. Shimanuki 1980. Sterol utilization in honey bees fed a synthetic diet: analysis of prepupal sterols. J. Insect Physiol. 26: 291-294.
Svoboda, J.A., E.W. Herbert Jr., and M.J. Thompson 1986. Selective sterol transfer in the honey bee: Its significance and relationship to other hymenoptera. Lipids 21: 97-101.
Zarchin, S., A. Dag, M. Salomon, H.P. Hendriksma and S. Shafir 2017. Honey bees dance faster for pollen that complements colony essential fatty acid deficiency. Behav. Ecol. Sociobiol. 71: 1-11.
Clarence Collison is an Emeritus Professor of Entomology and Department Head Emeritus of Entomology and Plant Pathology at Mississippi State University, Mississippi State, MS.
