[bjelkeman-again]

Could it be that the colony is less able to handle pressure from varroa because of other stresses, like pesticides? We use several methods in combination to deal with the varroa.

If a colony has too much after the winter we treat with ApiGuard, and the honey produced during the period is marked for winter feed. We do drone larvae cutting (not sure that is the terminology used) and treat with oxalic acid before the winter. We let them winter on at least 50% honey.

We have lost one colony in the last four winters, that was wintering on sugars alone. We overwinter three four colonies normally. So we are just hobbyists and our methods may not scale.

[raxxorrax]

Some have argued that taking honey and replacing it with sugared water is bad for the bees immune system and general health. There was a very small scale study if you even can call it that, but I cannot find the article about it anymore.

Since taking honey hasn't been this deadly before, some form of infection seems plausible and the mites would fit here. As far as I know they are primarily feeding on fat reservoirs of bees. Are there any signs of varroa on the dead colonies?

[ghostoftiber]

I am also a hobby beekeeper. My sample size is "2" - I always have two hives. I also had both hives die out last year after 3 years of not needing really any help at all. The one colony didn't really have any signs of mites to speak of. There were just a bunch of dead bees in the bottom of the box. The other colony absconded or was overrun. They had a decent-ish amount of stores they left out, but no bees whatsoever.

It's not just CCD that kills bees, other things happen which are very difficult to diagnose. That latter behavior also is what makes this really difficult, if there's no bodies to look at, it's really difficult to figure out what happened.

[nicoburns]

> Some have argued that taking honey and replacing it with sugared water is bad for the bees immune system and general health

It'd be pretty hard to believe that it wasn't bad for the bees health.

[Nasrudith]

The real question is how different is it from true nectar. They produce honey by preserving nectar in the first place. Of course even if they were given true nectar as a replacement directly (an ironic subversion of their job) it could theoretically cause issues from not being properly "preprocessed" or lacking the lead time to make a batch for their own consumption.

Just because sugar water isn't a good basis for humans doesn't neccessarily apply to bees - giving a cat a salad is not healthy for them and they will probably not be happy.

[bjelkeman-again]

Honey contains lactic acid bacteria [1], which has proven to work as an antibiotic agent in scientific test[2]. Suger do not have that. Honey contains many other things, like pollen, that suger doesn’t.

[1] https://www.sciencedirect.com/science/article/pii/S094450131...

[2] (In Swedish) https://kurera.se/mjolksyrabakterier-i-farsk-honung-kanske-m...