>I'm wonder what finally wore them down and what was, if anything, connected
to the artificial diet.

Hi Grant,

Nurse bees will dig into their body reserves to supply critical nutrients to
the brood.  This is especially true for sterols, esp 24-methylene
cholesterol.  Research has shown that their reserves are good for a couples
of brood cycles (can't cite off the top of my head).

My guess, and it's only a guess, is that the colonies ran out of a critical
nutrient, that was supplied by the beebread that cured the problem.bread.

Randy Oliver

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