at first it just seemed like aggressive housecleaning, but the bee bodies kept on piling up... deeper and deeper:
-- many thousands of dead bees around the hive
-- declining hive population (duh)
-- twitching, jittery bees among the dead
-- fair number of small, shiny, black, hairless bees in the hive
-- many lethargic, pale colored bees huddled in the corners of the frame top bars (nurse bees isolating themselves perhaps?)
-- some defecation in the hive
after reviewing bee diseases, I'm thinking either nosema or chronic bee paralysis virus. I'm leaning towards CPV, yet the case for nosema is also compelling, and I have no clue how to treat CPV, so I treated them for nosema.
we'll see how it goes!