Re: Unfortunately starting over with a step ahead
Get a bright flashlight, really bright one, or do this at noon with a clear sky. Pull that brood comb from the freezer shine the bright light into the comb, and use a magnifying glass to look carefully in the comb cells around the dead pupae. If you see small whitish flecks on the comb wall, I have been told that is mite feces.
Many of these guys told me the nucs I lost were due to mights, but just was not seeing them in sugar rolls. Was told to check my last nuc that crashed in this way and bingo. About a year of a little doubt and lots of confusion cleared suddenly with one little check.
Mites, plain and simple. And the nucs I lost went the same way as yours did. Had some hives that did the same but superceded the queen and the brood break gave the hive breathing room to recover.
Gassing them all very soon.
Started 9/13, building slowly, now @ 7 Lang hives + 2 nucs, and treatment style not decided yet