Bob H has made a good start on clarifying the issue of 'running out of
glycogen' as a putative cause of death.  As a biochemist I may be able to
clarify further.
        Glycogen is the typical storage carbohydrate in the animal kingdom,
roughly as starch is in the plant kingdom.  These are polymers of glucose,
formed from glucose and typically (as in our liver) reversibly liberating
glucose by depolymerisation at need.  The notion that some animal species
has degenerated to work in only one direction is not logically impossible,
but is highly implausible.
        V B Wigglesworth was a  -  I would suggest  the  -  the top
scientist in insect physiology.  When he says as Bob quotes, you can take
it as reliable.  If VBW said  glycogen stored in *flight muscle*  supports
flight for only 10-20 minutes, you can infer that this animal indeed
possesses the means to replenish that glycogen store several times daily
(because we know bees typically fly many trips of 10-20min daily).

        It follows that running out of glycogen in the flight muscles
cannot be the normal cause of death.

        If in response it be postulated that a bee can die from inability
to fly owing to depletion of that glycogen store while far from the hive on
a foray, I would then ask whether it can run on sugars from nectar gathered
on that very foray.  I would expect it to do so.  Has this been examined?

R

-
Robt Mann
consultant ecologist
P O Box 28878   Remuera, Auckland 1005, New Zealand
                (9) 524 2949