Allen Dick said...
 
" On one hand some people say that it just happens over time and that after
a while it will kill colonies if nothing is done.  Others say that 'wham' it
hit us out of nowhere and colonies were dead before we realized it was here.
 
Why is this?"
 
For what it's worth this is my experience...
I had the (near) sudden death experience last spring. This is what I believe
happened.
 
I treated as usual in the autumn with Bayverol, the bees (as far as I knew)
went into the winter clean. Next spring they came crawling out during the
first spell of good warm weather.
 
Turned out my neighbour, 2 blocks away from me, lost his last colony
sometime during that winter. He said they had still been there at the end of
the summer but had disappeared by spring. This was the last of 3 colonies he
had had and not treated or attended to for 5-6 years, since developing an
allergy to bee venom.
 
I assume these bees absconded to my hives, or my hives robbed them out, or
both. The varroa had been building up somehow during the winter (despite
assumptions that queens stop laying and therefore varroa production should
stop too).
 
It was a sorry sight, deformed and crawling bees, and it was the first time
I had to treat both spring and summer. They revived rapidly after treatment
though, but had I not picked up on this I would have lost them before the
season had gone very far.
 
Latest theories in UK are that we see are seeing a cyclical pattern here.
 
1)  First of all there is a slow build up of varroa in feral and beekeeper's
colonies, then the collapse begins.
2)  Feral colonies and 'let alone' bees start to die out, get robbed, varroa
and absconding bees move into the 'cared for' colonies.
3)  Those colonies now come under severe stress and beekeepers need to be
aware of signs of reinfestation (possibly even just after you took out those
varroa strips).
4)  Feral colonies and let alone bees are now gone. Beekeepers breathe sigh
of relief. Infestation rates/numbers drop significantly.
5)  Colonies set about swarming and filling up all those lovely empty trees
and roofs, with there mothy wax and all.
6)  We all go back to 'square one', first of all there is a slow build up of
varroa in feral and beekeepers bees, then the collapse begins...
 
Knowing where you are in the cycle (your area not just you) may well be a
part of diagnosis too.
 
Lastly, at the time you are observing the bees there are a few things to
remember. In really heavily infested colonies you will see the varroa on the
backs of the bees quite clearly during a routine inspection. But what you
see doesn't necessarily tell you all of what is going on. If there is no, or
little brood, the varroa will all be on the bees themselves. If there is
lots of brood most of those same varroa will have got themselves in to the
cells and will be out of sight. So seeing no signs is not necessarily a
reassurance. When those young bees come out there will be a population
explosion of both bees and varroa. The more varroa go in, the more come out,
and the more badly affected the young bees will be when they emerge and you
could be on the downward spiral.
(Bit simplistic but I hope you get the drift)
 
Its all relative as they say.
 
Which reminds me of something I read yesterday by Chuang Tzu (an ancient
Taoist):
 
"Everything is useful from some position or other and there are some
positions from which even the most useful thing is useless."
 
Good luck to all in the forthcoming season.
Madeleine Pym, London, UK