Monday, May 13, 2013

Honey and Bee Nutrition

It might seem intuitive that feeding bees honey rather than a sugar-syrup substitute would be better for their health.  However, it has become a common practice to feed sugar syrup to bees, and let them get their other required nutrients through pollen.  (That trend is mainly due to a 1978 paper in Apodologie that showed bees could survive as long on corn syrup as on honey, and slightly longer on a syrup of sucrose, or table sugar.  Then, due to the magic of international trade, beekeepers figured out they could sell their honey for much more than an equivalent amount of sugar syrup cost.  The paper can be found here--it's the third in the list, by Barker and Lehner).  So, if honey bees can get most of their nutritional needs from pollen, and only really need honey as a carbohydrate source, what is actually the advantage of feeding honey?  A paper in Proceedings of the National Academy of Sciences from a couple weeks ago has provided some new insight on the topic.

It seems that the honey acts as a sort of extracting medium, which results in bees getting some constituents of pollen and propolis from the honey.  (Propolis is the tree resin-based material bees use to polish honeycomb, seal cracks in the hive, and glue frames to hive boxes.)  These extracted constituents in turn stimulate the bees' immune systems, allowing them to metabolize pesticide residues and resist pathogens.

Some of the compounds extracted into honey from pollen and propolis, except coumaphos (upper left), which is a chemical commonly used to fight varroa mites.  p-coumaric acid (upper right) comes from pollen and was the most universal activator of the bee immune system.  The bottom three come from propolis; pinobanksin (middle bottom) wasn't as helpful as the other two.

As researchers are trying to figure out how the pieces of colony collapse disorder (CCD) fit together, this paper demonstrates how several of the suspected factors might interact to make honeybees susceptible.  (...which is why it was able to be published in such a prestigious journal!)  Beekeepers commonly treat their hives with coumaphos to combat varroa mites, which have become an ubiquitous pest over the last couple decades.  (Coumaphos itself may or may not be a contributing factor to CCD.)  If, at the same time, bees are eating sugar syrup instead of honey, their immune systems aren't sufficiently activated to metabolize the coumaphos (and other pesticides the bees encounter in the field), which ends up stressing the bees in addition to killing the mites.  A corollary is that if the bees' immune systems are not sufficiently activated, they are also less able to fend off other pathogenic bacteria.  If this situation goes on for long enough, the worker bees run out of vacation days, and then sick days.  And once the worker bees run out of sick days, they have no choice but to call in 'dead.'

A varroa destructor mite.  'Varroa destructor' would be a good name for a band (or maybe a professional wrestler), but as a honey bee parasite it should just go extinct.  Someone should discover the anti-varroa equivalent and name it varroa self-destructor.  Photo credit: Wikipedia.

The authors showed that they could get the same immune system stimulation by adding p-coumaric acid to 'bee candy,' a mixture of powdered sugar and sucrose syrup. Then, in an example of how to shoot a good arrow yet miss a target completely, the authors propose that based on this finding, toxicity indices of certain pesticides, which are typically tested on bees eating sugar syrup instead of honey, may need to be re-evaluated. (Because if the bees are eating honey instead of sugar syrup, they can probably handle a higher pesticide load than we're giving them credit for.)  Fortunately, the authors come around to imply that feeding bees sugar syrup laced with p-coumarin is better than unlaced sugar syrup, but is only a good option when real honey isn't available.

Of course, beekeepers can minimize the pesticide load on their bees by invoking natural beekeeping practices.  The Walden Effect has had a few discussions on the topic (e.g., here and here), and there is a growing body of science and experience of how to keep bees without adding synthetic chemicals.

Have you had good luck with keeping your bees healthy?  Have you been able to do it naturally?  Other thoughts on this research paper?  Tell us about it in the comments section below!

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