Hive Death

It looks like your frame of honey there is actually foundationless, so you could also just use a sharp, thin knife to take it in one big slab, provided it's all or mostly capped honey on the other side, too.

I was really hoping to be able to save all the comb for next year's hive as a jump start so that's great news I can save it. How can I prevent them in the future?

Mostly, I know it's mite waste because it's November, OP is an American, and literally everything else about this situation fits the profile for a deadout caused by parasitic mite syndrome. It would literally be appropriate for a textbook.

But if you want me to do a differential diagnosis, then I guess I can oblige you.

It's theoretically possible that this was a pesticide kill, if OP lives someplace where there's heavy agricultural activity for some kind of cool weather tolerant crop like spinach, certain brassica species, etc., combined with an extremely mild climate.

And even if OP is in such an area, there'd need to be something flowering near the aforesaid crops. And in November, that's basically not happening. Bees generally do not crawl around licking up moisture from non-flowering plant life. It's autumn, the last flush of stuff like goldenrod is finished, and in most parts of the USA there's no longer anything blooming. We're now in the winter dearth.

Sometimes, you also see pesticide-related kills if you live near someone who uses pesticides to control mosquito or tick populations in their yard. But again, it's November, and OP is an American. This is not the right time of year for that to make sense.

All of this militates against this deadout being pesticide-related. And there are various signs and symptoms present here that would not be normal and expected for a pesticide kill.

Looking at the pics OP has provided, we are short of any other plausible explanations. There are pollen and honey stores at hand, so it's not starvation, and it's definitely not a case of this colony having been robbed of its stores by a stronger neighbor. The comb is all intact, and after a robbing incident it's ragged and crumbled.

If it were something like foulbrood, OP would have noticed and talked about a horrific stench, and we'd have already proceeded into a discussion about how to confirm EFB/AFB infection, whom to notify, what to do about it, and so on.

It's way early for this to have been nosema; that's mostly a springtime problem (although it can happen at other times of the year). And in any case there's no indication that the bees in this colony suffered dysentery.

So having ruled out all these other things, we have a list of signs and symptoms.

1. It's September, October, or November.
2. The colony looked okay during the last inspection, which OP says is relatively recent--they had COVID, but prior to that, they thought the colony was busy and healthy.
3. There is stored honey and/or pollen.
4. There are no dead bees head-first in comb cells.
5. There are very few to no bees left.
6. There is very little brood, and most of what brood is present is capped.
7. Capped brood often shows telltale pinhole openings, which you can see if you zoom in close to the pics.
8. Capped brood often is partially uncapped. Again, easy to see if you zoom in.
9. There are emergent worker bees that died after uncapping but prior to emergence. If you look closely, some have their heads poking out, proboscises extended.
10. Some brood has been fully uncapped. You can tell that it was prematurely uncapped, because the contents of those cells are pupal worker brood that has not yet begun to darken in preparation for hatching.
11. In many cases, they are missing their heads; this is called bald brood. When you see a cell that is entirely filled in with something that is kind of a pearly white color, that's what you're looking at. This is hygienic behavior; nurse bees undertake this kind of activity when they perceive that a pupal bee is diseased or has been parasitized by varroa.
12. If you zoom in to look at the sides of the empty cells in these pics, you can see flecks of a white substance. These are guanine crystals. Mite poop is about 95% guanine.

All of these numbered points of interest are distinctive signs and symptoms of a condition known as Parasitic Mite Syndrome (PMS). It is caused by several factors in concert. All are mite-related.

• Active stress to the colony from heavy mite infestation, which depletes the vitality of both adults and brood.
• Viral infections, which are vectored into the colony by varroa infestation, and subsequently spread to epidemic levels as the mite load grows out of control. Deformed Wing Virus (DWV) is the varroa-implicated pathogen of principal interest to most beekeepers, primarily because it's one of the ones that you can diagnose without recourse to a lab assay. But there are like 20 other viral infections that have been identified as affecting honeybees, and probably there are others we don't know about yet. A large proportion of these other honeybee viral pathogens are transmitted by varroa.
  It can be difficult and expensive, and usually is pointless to identify exactly which viral pathogens have infected a colony. Often, the symptoms look the same to humans in any case, and it's not like there are effective treatments for them.
• Inadequate population of nurse bees; sick workers progress much more quickly from being nurse/cleaning/undertaker bees to service as foragers. This is a form of instinctual social distancing to try to limit the spread of disease from the infected individuals to healthy members of the colony.
• Dwindling population, as terminally sick bees abscond to die somewhere outside of the hive.
• Dwindling population, as relatively healthy bees abscond to nearby colonies (bringing their mites and diseases with them).
• Dwindling population, as inadequate nurse populations finally impede the dying colony's ability to provide adequate attendants for the queen.

What has happened to OP's colony here is EXTREMELY COMMON. This is exactly what mite infestations look like when they kill your bees. OP's is approximately the 6th such posting I have seen this fall. And if you hang around this subreddit for about a year, you'll see more next fall.