Thanks so much for all the suggestions and advice.  Luckily the
inspector was able to pinpoint the cause, which actually had not been
suggested here yet: small hive beetle.

He said that mine and some neighboring counties have been experiencing
a huge spike in absconds due to SHB, which he attributes to the warm
winter and early swarms that left a lot of hives with more honey and
fewer bees than usual for this time of year.  The high temps actually
helped keep them under control for a while, but two weeks ago when the
temps dropped and the humidity went way up he starting getting calls
from all over the county with descriptions like mine.  He said he
often sees SHB in neglected or shaded hives, but has not seen levels
like this in strong hives in 30 years.  Hives that fail and are not
emptied of comb quickly become SHB incubators that increase the
pressure on remaining hives.  In some cases, so many SHB invade at
once that the colony absconds before the SHB eggs actually hatch, so
that on first discovering the deadout the combs may not even be slimed
or crawling with larvae yet.

The robbing actually occurred after the abscond, as local colonies
cleaned out what my colony left behind.  The punctured but not sunken
cappings were the result of SHB pushing their ovipositors into capped
cells to deposit eggs on the pupae. The popped out brood were also
related to the abscond, but weren't caused by starvation....he pointed
out that the abdomens of these pupae had been emptied by SHB larvae
for the protein in their body fluids.  Interesting to learn that SHB
larvae eat bee eggs and pupae as well as honey and pollen.

He also confirmed no sign of brood diseases, and tested two surviving
hives in the yard for varroa and found 0 per 300 bees in both cases.
Good to know and I'm grateful to know that this was not a result of
disease or poor queen selection.  Now to install beetle traps in the
rest of my hives...

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