Thanks Pete for the great historical finds!

We have a similar situation in California as does Bill in Maine--our
late-season honeydews do not make good winter feed.  Bill brought up the
mineral "ash" content, but there is also the issue of complex sugars in
honeydews that bees are not able to digest themselves.  Some of these
sugars, such as mannitol and inositol, are well known to be "toxic" to
bees.  In addition, there are other poly- and oligo-saccharides in
honeydew.  Of interest is that some of these complex sugars appear to be
produced by the sap-sucking insects themselves:

>Most studies detected little or no sucrose in the honeydew, but found
oligo- and polysaccharides in considerable quantities. The insects seem to
convert sucrose—or its monosaccharide derivatives— into oligosaccharides of
different sizes. A possible explanation for this is the need to avoid
dehydration, since the osmotic pressure in the diet is higher than that of
the haemolymph.... There is evidence that the chemical rearrangement of
sucrose and its derivatives for the synthesis of oligosaccharides is
carried out by the bacterial symbionts of the aphids and whiteflies. (Wool,
et al (2006) Seasonal variation in honeydew sugar content of galling aphids
(Aphidoidea: Pemphigidae: Fordinae) feeding on Pistacia: Host ecology and
aphid physiology. Basic and Applied Ecology 7: 141—151).

It's not that these sugars are necessarily directly poisonous to bees, but
rather that since they are not directly digestible, they wind up in the
hindgut, where they may be digested by the gut microbiota.  Some of the
degradation products may be toxic to bees (Lee, et al (2014) Saccharide
breakdown and fermentation by the honey bee gut microbiome.  Environmental
Microbiology  doi:10.1111/1462-2920.12526).

Something that I'm curious about is why I often observe live yeast cells in
fecal samples from bees with dysentery.  As far as I can tell, yeasts are
able to enzymatically digest simple sugars and sucrose, but not more
complex sugars.  So I'm not clear as to how the bacteria and yeasts in the
bee hindgut  interact with the indigestible complex sugars of honeydews.

-- 
Randy Oliver
Grass Valley, CA
www.ScientificBeekeeping.com

             ***********************************************
The BEE-L mailing list is powered by L-Soft's renowned
LISTSERV(R) list management software.  For more information, go to:
http://www.lsoft.com/LISTSERV-powered.html