Good questions, Christina.

>sugar production is driven by respiration

Isn't sugar produced via the process of photosynthesis as a way to store
energy?  Then in the process of respiration that energy is then extracted
to create ATP and NADH.  The energy needed to concentrate sugar in the
nectar would then be from respiration, but the actual production of sugar
would be from photosynthesis.

Re nectar flows from plants, I must suspect climatic factors.  Many
beekeepers have spoken of the tulip tree flows that used to be consistent,
now being nonexistent.

Here in California, due to shifting climatic zones, a number of traditional
natural forage areas no longer produce nectar.

And even in those plants that do, the nectar secretion is tremendously
influenced by the timing of the season, winter chill, rainfall, soil
moisture, and temperature.

Red and white clover, as well as vetch, in my area, do not raise the level
of nectar high enough in the corolla tubes for the honey bee tongue to
reach except when there is high soil moisture.

Manzanita produces a watery nectar when there's lots of soil moisture, and
a drier nectar otherwise.

Yellow star thistle only produces if there was adequate moisture in winter,
then very hot days during bloom in July and August.  Some other plants seem
to produce more nectar when heat stressed.

And the blackberry brambles in my area have barely produced nectar for the
past three years, despite rainfall just prior to bloom.  I'm guessing that
it has something to do with deeper soil moisture earlier in the season, but
not sure.  The plants grow beautifully, produce plenty of pollen and fruit,
but little nectar.

And then we have a number of bee-attractive plants that produce no nectar
at all.  The bees work them solely for the pollen.  Nectar production by
plants simply makes a flower more attractive to a pollinator that requires
an energy source other than pollen.

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

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