>> I have not treated near like I did for AFB, have noticed it has become 
>> almost non existent and am not seeing it at all this spring.

> I'm not sure whether it is simply because I am running more hygienic 
> bees...  Any other long-time beeks out there noticing any change in AFB 
> prevalence?

I got away with going several years without treating and saw only the 
occasional cell.   I assumed that this was due to improved stock over the 
years and hoped that this condition might continue indefinitely, but I was 
also very aware of the problems of maintaining a consistent level of 
protection relying on strictly genetic resistance. (see end note)

Then, last fall and this spring, I had significant breakdown in a few hives. 
They were all directly related, being split from one another, and thus 
sharing both equipment and genetics.  Instead of rushing to treat 
immediately, I removed the worst cases and observed the progress of the 
rest.

I had some fairly hygienic stock, but also some non-hygienic stock 
intermixed and had allowed the hygienic stock to degenerate a bit as well by 
breeding indiscriminately from strong hives and by having drones which had 
been raised in all hives, both resistant and not, breeding the queens from 
the hygienic cells I obtained.

What I saw was that several hives broke down badly and had to be destroyed, 
while others did not show any overt signs, although the brood patterns 
seemed increasingly spotty in many.   Then some of the best (large, 
productive) hives started to show the odd ropey cell.  Others did not.

At that point, I figured I had seen all I needed to see and had disproved a 
lot of the malarkey I had been reading on one of the hobby boards which 
promotes fantasy beekeeping.

I began treating across the board.  (I had no concerns about timing since I 
am not producing honey).

From what I saw, I concluded that hygienic stock can withstand AFB to a 
point, but that beyond that point, an avalanche begins, moving from the 
least resistant to the most resistant.  This is unpredictable and depends on 
the source of the spores.  (Most often it is the interchange of combs when 
making up brood chambers).

The most resistant hives may remain totally unaffected, depending on the 
resistant mechanisms in that particular stock, but typically they will be 
economically burdened by the constant removal of larvae.

There are AFB years and years when AFB is less obvious.  A lot depends on 
the weather, the flows and lack of flows.  A good nectar flow suppresses 
signs of AFB, while a dearth will make AFB very obvious.

I have spent quite a bit of time looking into thousands of commercial hives 
around Alberta over the years and what I see is that some operators seem to 
be able to run thousands of hives for years without treatment and by picking 
up and destroying any diseased colonies immediately as well as putting all 
dead-outs through radiation.  Other, apparently good beekeepers seem to have 
fairly high AFB incidences. (To me anything beyond one positive in a hundred 
is high).

As a note, though, some of the first group are showing some signs of a 
build-up of background, non-clinical, infection.  Others are not.

I'm writing about areas where a background level of AFB is either in the 
neighbourhood or in the hives.  Areas where AFB is non-existent or nearly so 
are obviously different, but in North America, they are the exception and 
their status could change in a heartbeat.

My guess is that there is an element of luck in all this and that running 
without treatment requires careful and constant observation and strict 
control when AFB is found.  Breakdowns can happen fast.

For many, prophylactic treatment with antibiotics can lower the background 
level and prevent breakdowns.  Each breakdown greatly magnifies the 
infection potential and puts the other hives at risk of either breakdown or 
being burdened by the need to constantly remove larvae.

So, yes, I think that improved genetics are making a difference, but also 
that there are difficulties in relying on genetics.

For one, we cannot easily know how good a particular batch of stock is until 
it breaks down or doesn't.  (If it doesn't, we still do not know).

For another, any open-mated batch of queens is variable and vary from very 
resistant to susceptible.  A batch of 100 queens with even one or two weak 
sisters is like a picket fence with one or two board missing.  It won't keep 
the neighbour's dog out.
---

Note:  There is always variability, and the 10% of hives with the lowest 
resistance are the Achilles' heel.  In the absence of a prophylactic regime 
and when a background of spores is present, these hives slowly increase in 
levels until breakdown occurs.  If the beekeeper is on the spot, they can be 
culled, treated and re-queened or otherwise managed, but if the breakdown is 
not caught quickly, then it can spread to other hives. 

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