Understanding Bee Nutrition (with Dr. Priyadarshini Chakrabarti Basu)

On April 1st, the Alberta Tech Transfer Program’s Hive-Side Chat webinar hosted a timely and informative presentation, “Understanding Bee Nutrition”, by Dr. Priyadarshini Chakrabarti Basu, a Research Associate at the Oregon State University Honey Bee lab. The following article is a brief summary of key points from Dr. Chakrabarti’s presentation.

Complete nutrition is crucial for a honey bee colony to maintain its health while facing multiple stressors, including pests and parasites, pathogens, environmental stressors, and modern agricultural practices. A strong and well-nourished colony is more capable of withstanding these stressors; however, if bees do not have continuous access to pollen of good quality, diversity,  abundance, or if there is an insufficient nectar flow, they may lack adequate nutrition to remain healthy.

Beekeepers are well-aware of the macronutrients (carbohydrates, protein and lipids) that bees need to stay healthy and productive. Colonies in commercial apiaries are often fed early in the season to stimulate brood rearing and build well-populated hives in time for crop pollination or honey production. Beekeepers provide supplemental feed to colonies by adding sugar syrup, protein, and nutritional supplements designed to promote colony health when carbohydrates (nectar, pollen) or protein and major lipids (pollen) are not available from natural sources. But are these dietary supplements providing all the nutrients bees need? Dr. Chakrabarti’s team took a deep dive into the research that has been completed on bee nutrition and found that while macronutrients have been well studied and the main research focus for decades, micronutrients have been severely understudied.

What are micronutrients?

Micronutrients are important nutrients that bees need in smaller quantities (hence the name ‘micro’), such as phytochemicals, vitamins, minerals, and phytosterols, which are all mainly sourced from pollen (but also found in nectar).

One micronutrient in particular drew the attention of Dr. Chakrabarti, the sterol 24-methylenecholesterol (24MC). What is so special about sterols and 24MC? Sterols are key nutrients for bees and required for numerous physiological processes. However, bees are not able to synthesize sterols and must get them from pollen, the only natural source of sterols for bees. Sterol requirements differ between insect species, and even bee species, but 24MC is the only sterol that honey bees can effectively utilize and metabolize (Herbert et al. 1980). Therefore, the next step for Dr. Chakrabarti’s team was to set out lab studies to determine answers to two questions: 1) Which concentration of the sterol 24MC would provide the maximum benefit, if any, to bees? And, 2) In what ways would it be beneficial? To summarize the study findings, Dr. Chakrabarti said that with higher concentrations of “sterols in the diet their (the bees) consumption (of the artificial diet) increased, their survival was better, and important physiological markers were also better. And most of these changes we found from a diet of 0.5% of sterol in the artificial diet.”

The next questions Dr. Chakrabarti wanted to answer were how is the sterol moving across the honey bee body over time? And how can it help improve colony health? The first question was answered by placing a marker in 24MC molecules to track the pathway of the sterol through a bee’s head, thorax, and abdomen over a 4-week period. In short, they found that “the accumulation of 24MC in the 3 different body sections (head, thorax, and abdomen) was comparable with honey bee life history traits”. To answer the second question and to better understand how the sterol 24MC might influence bee health on the colony level, colony structure, and queen health, studies have now moved to a semi-field scenario using flight cages, each housing a nucleus colony being fed an artificial diet containing one of several different concentrations of 24MC. Over a period of eight weeks the research team will track the health of the colonies. Stay tuned!

How do we know which plant has sterol and how much of each sterol? And do we know the sterol profile of the different pollen sources that are available for bees?

Information on plant micronutrient profiles for North America is currently in short supply, which makes it difficult to know if a particular flower is actually providing good nutrition for a particular species of bee. By teaming up with researchers in the O.S.U. Mass Spectrometry Centre, Dr. Chakrabarti is building a database of information on bee nutrition that will answer these two questions, as well as looking into metabolites, phytochemicals, amino acids, and different flavonoids as part of the bee nutrition database. Additionally, a comprehensive range of bee diet sources will also be analysed – commercially available pollen, corbicular pollen (trapped), vegetable oils, commercially available supplements – as well as honey bee tissues (to know which sterols bees are assimilating). To ensure the bee nutrition database includes a wide variety of pollens from as many crop and non-crop plants as possible, Dr. Chakrabarti is asking beekeepers to submit pollen samples as part of a “citizen-science” project. A database of nutritional profiles for commercially pollinated crops, non-crop forage, and commercial dietary supplements that is accessible to growers, beekeepers, and researchers will be a valuable resource. It will provide comprehensive information on which micronutrients bee diets may be lacking and give users the ability to take a range of targeted actions to provide the missing nutrients.

Dr. Chakrabarti also provided a few general recommendations for beekeepers regarding bee nutrition during spring/early summer:

  • Feed 1:1 sugar syrup (one part sugar, one part water). This type of syrup mimics nectar and will stimulate brood production. If 2:1 syrup (fall feed) is used the bees may process and store the thicker syrup as they would honey
  • Syrup should be fed once it is warm enough for bees to break cluster and fly (10°C).
  • If it is too cold for syrup, then solid sugar candy works well
  • Feeding protein patties in the spring stimulates brood production, however, once protein feeding is started it should be continued until abundant natural pollen sources are available
  • It is best to feed protein when natural pollen will be available very soon
  • “If you are adding commercial diets (commercial protein supplements) to the hives, adding borage oil may help to maximize 24MC in the patties. Of the three oils we tested, borage had higher concentrations of 24MC”
  • “If you are thinking of planting forage for bees, please ensure what your local guidelines for plantings are. Some plants we see having high 24MC concentrations include clovers, borage, mustards, phacelia etc. The idea is to be able to provide a staggered bloom and sustained forage all through early fall if you can. Please be careful of the local regulations before you decide to plant these supplemental forages”

The TTP would like to ask beekeepers some questions to help us better understand bee feeding practices in Alberta (please reply to ttp@albertabeekeepers.ca):

  1. Do you add any vegetable oils to commercial protein patties or supplements to increase the sterol content?
  2. Do you add any ingredients to commercial protein patties or supplements? Why?
  3. If you make your own patties, which type of oil(s) do you put in them?

To view the full presentation of “Understanding Bee Nutrition”, please visit the TTP youtube channel. Further information and links to Dr. Chakrabarti’s research can be found at www.priyadarshinichakrabarti.com, as well as contact details to learn about her citizen-science pollen project.

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