In article <[log in to unmask]>, Alan Riach
<[log in to unmask]> writes
>Disease control by colony destruction has certain advantages since it
>will destroy "disease susceptable genes" as well as the disease itself.
We in Scotland are very fortunate to have a very low indeed incidence of
AFB, and a low rate of EFB.
I have always been under the impression that AFB and EFB are present at
low, usually non symptomatic, levels in all, or nearly all, of our
colonies. We have never had a single case of AFB in 50 years in bees,
totalling some 30,000 plus hive/seasons.
This is without burning, AND with the importation of stock from
countries where AFB is a persistent and serious problem, so we must
have, at some stage, imported some supposedly genetically susceptible
stock.
An old bee inspector and national authority who was involved in several
destruction episodes (actually he recorded several dozen over the years)
kept records going back to before the last war, up to the mid 80's. He
told me that the incidence of AFB in Scotland was little different in
his latter years than in his early years, and in the records of his
predecessor. This is despite there being considerable experimentation
undertaken in the field in the 60's and 70's from an inspector based in
Aberdeen with treatment rather than destruction. There appeared to be
not much to choose between the two strategies in terms of re-appearance
of the problem.
As the incidence of this is rare in Scotland we may actually have
several linked phenomena at work here, although I reckon environmental
factors , linked to SOME genetic predisposition to resistance, are the
main factors at play here.
The old expert I was referring to kept a map of the whole area (about
4000 square miles) on his office wall, and there were coloured pins in
it for every recorded AFB outbreak over the last 70 or so years. It was
particularly noticeable that it occurred in pockets, with large tracts
of the area with no recorded outbreaks ever, and others with 10 or more
over the period. One small area in particular, about 5 miles long in a
river valley had nearly 20 incidents in 70 years. I have heard in the
last year of yet another outbreak affecting this place.
Certainly, if genetics were the sole factor, as a result of a
destruction policy, we could (should?) have encountered AFB in our
imported stock. Yet we have not. We are not *especially* careful about
hygeine, move boxes incessantly from hive to hive, and mix colonies from
different apiaries. We have bought bees from people who have relatively
recently (in the previous 5 years) suffered from AFB somewhere in their
unit.
EFB is certainly different, and you can cause the stress that triggers
the appearance of symptoms by careless management. Having done this, and
learned from the experience, we treat our bees reasonably well and have
not seen any EFB like symptoms for several years (and never destroyed a
single colony). I am quite certain EFB at least is endemic and will only
rear its head when conditions favour it, subsiding again when the stress
is removed although some treatment may be needed to help it along. Thus
I seriously doubt if destruction for EFB has anything other than a
superficial argument for it, as it will not tackle in any way the
underlying presence of the problem.
AFB? Well, I do not really know. If I found one I would burn it (out of
fear of the problem), but in the light of the experiences of others I am
not sure if that is strictly necessary, or even if it is an effective
strategy. We have low AFB and we have a burning strategy so for the time
being I will go along with it, even if the reasons for the low AFB may
be coincidental.
--
Murray McGregor
|
