Varroa "Vectored Viruses"

Watching the neighbouring hives in the apiary over the past couple of weeks (that sounds far more passive than it actually is) I've been struck by the ongoing collapse of one of the colonies.

All 6 of our colonies have been treated the same way. This one is showing all the signs of collapsing from Varroa. There are large quantities of DWV (deformed wing virus) and K-Wing virus and since they did make attempts to swarm, the brood side of the AS has gone rapidly downhill.

Prior to the AS we'd culled drone brood, using icing sugar, monitored mite drop and uncapped drone brood with no obvious warning signs in terms of mite levels and, of course, they were treated over winter.

All of the other colonies in the apiary are doing fine.

So are there (still) colonies that are more sensitive, if that's the right description, to the viruses carried by Varroa (DWV seems to be the obvious one) than perhaps the mite itself?

Is it a combination of the two? The bees are less hygienic/able to cope with the mites and/or are less immune to the viruses.

Are we just crap beekeepers who missed the obvious signs in 20% of our colonies? (not discounting this one either).

All things are possible. A surge of mites coming from someone's bees with a mite problem would show the pattern of drifting or absconding or robbing that is taking them there. But yes, variation in the ability of your colonies to deal with them and variation in sensitivity to viruses could be part of it too.

I saw DWV on a drone last time I looked in at mine. It was the colony on the end. That position is usually where I see worse mites even though the colonies changed places when they came back from the heather last autumn.

It shouldn't be drifting as it's the middle of three.

The rapidity with which it seems to suffering is also quite dramatic. It's gone from no obvious problems to a few dwv bees to severe within the space of a few weeks while the surrounding bees trot on seemingly unaffected.

That some colonies might be more susceptible to the associated viruses seems not unreasonable to me but I acknowledge that might be taking a simplistic view and/or missing the wood for the trees.