Jim asks some excellent questions.

Over the years, I've seen plenty of AFB, and have burned hundreds of hives'
worth of frames.  As I learned how to control the disease, I've been able
to give up my former practice of prophylactic treatment with antibiotics.

I've seen how easily the symptoms of AFB disease spread via robbing or the
transfer of infected combs.  I'm also aware that the spores are ubiquitous,
and that it is difficult to initiate the disease via a small inoculum, such
as of that on a hive tool.

>
> >If a beekeeper choses to use antibiotics for AFB, why are only the hives
> on either side dusted?
>

Sorry for not being clear--I meant the hives for several feet in any
direction, not just the the two immediately adjacent.



> >If the hive was badly-enough infected to prompt burning, wouldn't there
> be a
> very good chance that the entire yard had already started robbing it at
> some
> low, hard to perceive level, and thus be infected at some level, prompting
> yard-wide treatment?
>

Sorry for leading you to a misassumption.  I never said that the hives that
I burn were "badly" infected, nor on the verge of being robbed--IMHO, a
good beekeeper rarely allows a colony to reach that point of infection.  I
burn a colony if I find even a single infected larva.  I've experimented in
tracking colonies to see whether those with a single infected larva can
"clean themselves up."  I've been sorely disappointed in the results.
Symptoms may temporarily disappear, but nearly always resurface.  Since I
do a fair amount of comb transfer, and the selling of nucs, I do not wish
to spread spores.  Since I started my zero tolerance policy some years ago,
AFB has been a non issue for me.

>
> >If the rationale is "because of drift", there are a number of studies that
> show that bees would only rarely drift to the adjacent hives
>

Odd to me that you would use the term "rarely."  In the paper by Goodwin
that you cited, he found that:
"An average of 5.72% of the marked bees were in the neighbouring colony
after two days"

That works out to 3% of the bees drifting to the adjacent hive every single
day.  That hardly qualifies as a rare event in my book!

The other point is that of Stan--some of us simply move the infected hive
out of the yard during our visit, leaving the field force to return to
adjacent hives.



> >So, if an antibiotic is used to
> protect hives where bees might drift, why only treat the adjacent ones in
> the same row?  Wouldn't wider use be a "safer wager"?
>

Certainly, we are now speaking of risk management, and back to prophylactic
treatment.  If I had suspected that robbing had taken place, of course I
would treat the entire yard.  Ditto if I had found more than one infected
hive in the yard.

>
> >But the entire concern about drift seems misplaced - drifting bees
> (returning foragers) don't spread much AFB at all according to several
> studies
>

Nonsense!  Of course drifting spreads spores of the causative
bacterium Paenibacillus
larvae.  One cannot spread a "disease."  Disease happens only if a colony
is unable to control the bacterium with its immune defenses.

And the above point brings us to the interesting part of this discussion.
Virtually every honey bee colony contains causative organisms with the
potential to cause disease.  Yet we generally do not observe the symptoms
of disease unless the colony becomes stressed, either by environmental or
nutritional causes, or due to infection by another pathogen (especially
viruses).

If one breeds for strongly hygienic bees, one can easily observe that AFB
symptoms can come and go concurrent with stress factors.

This brings us back to Pete's question of whether nosema is the proximate
cause of colony morbidity, or whether a high infection level is indicative
that the colony was already stressed, which allowed an opportunistic
parasite (nosema) to propagate extensively.  Could this also be the case
with AFB?  Goodwin's (and others') research indicates that it takes an
inoculation with a heckuva lot of spores to bring about symptoms of AFB
disease.  Clearly, colonies normally keep that parasite in check, despite
exposure to spores.

As I run large-scale field trials, I invariably observe the "proximity
effect" of colony morbidity and mortality.  At the end of the trial,
deadouts and dinks will nearly always be in small clusters--hives next to
each other, and often back to back.  vanEngelsdorp found the same--being on
the same pallet with a sick hive increases a colony's relative risk of
getting sick.  In practical experience, we can often watch an epidemic of
collapsing colonies slowly spread across a yard, one hive at a time.  This
would not be the result of robbing, but more likely due to drift (I am well
aware that AFB spores are effectively spread by robbing).

By my way of reasoning, any colony that comes down with AFB symptoms was
likely a stressed hive.  This suggests that adjacent hives were also likely
stressed.  The fact that I often observe colonies to collapse like dominoes
leads me to pay the most attention to those hives near to a sick hive.

In practice, I find that this appears to work.  I have not found benefit to
treating the entire apiary if I find only one weakly-infected AFB hive.
But I have found benefit in giving a bit of TLC to hives on either side of
one that came down with any sort of illness.


--
Randy Oliver
Grass Valley, CA
www.ScientificBeekeeping.com

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