This is a very interesting discussion Pete.  Nutrition, as far as colony
growth is concerned, centers around pollen income.  When there is fresh
pollen coming in, the nurses are well fed, and can lavish all other bees in
the hive with jelly.  At other times, the nurses immediately restrict
broodrearing.

Let me float an idea—that it is the presence of fresh incoming pollen that
is the key trigger for nurse behavior, jelly production and sharing,
epigenetic regulation, and physiological responses.  I emphasize “fresh,”
rather than beebread reserves.  When there is little or no incoming fresh
pollen, the colony immediately adjusts.

It occurs to me that there is likely no single mechanism for the colony to
deal with a dearth of fresh pollen.  But in any scenario, it would be to
its advantage to prepare workers for longer-term survival.  Off the top of
my head, I can think of three main potential scenarios taking place:

Scenario 1:  A moderate pollen income dwindles slowly. This scenario would
be typical in my area in late summer.  In this case, the colony lives
“hand-to-mouth,” consuming each day’s pollen income, and is unable to store
reserves of beebread.  The nurses restrict broodrearing and jelly
production to match pollen income, in some cases feeding less than the
optimal amount of jelly to the larvae.  Those larvae would then up- or
downregulate genes to make them “survivors.”  But they would not be Vg-rich
diutinus bees, due to lack of pollen resources.  A colony consisting of
such bees fares very poorly during the winter (personal observations).

Scenario 2: Pollen income is cut off suddenly during a major pollen flow,
with a great deal of brood present.  This occurs in springtime in my area
when a storm hits, or when major pollen sources suddenly stop flowering.
In this scenario, the nurses consume remaining beebread stores, and then
restrict the amount of jelly given to larvae, the queen, and other
workers.  Within a day they start cannibalizing first the eggs, then young
larvae, then older larvae—leaving only sealed brood.  Some late-stage
larvae go into early pupation. The well-fed workers that subsequently
emerge from the already-sealed brood would not detect the odor of either
fresh pollen or young larval pheromone, and as a result become diutinus
bees by consuming the remaining larvae—thus allowing them to build their
fat bodies for diutinus survival.

Scenario 3:  A heavy pollen flow dwindles and then ceases.  The colony
contains large reserves of beebread.  This occurs, for example, following
an intense fall pollen flow.  In this case, the lack of fresh incoming
pollen would cause the nurses to cease feeding young larvae (not from lack
of available food, since there is plenty of beebread, but due to lack of
fresh incoming pollen).  The last emerging (and well-fed) workers would
then not detect either fresh pollen or young larval pheromone, and as a
result gorge on beebread and become diutinus bees, rather than short-lived
nurses.

Thoughts or observations that either support or refute the above hypotheses?

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

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