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Hi,
The following message was recently forwarded -
<snip>
> I have been viewing recent postings to this group and saw one on the
> number of mites in a hive and when to treat accordingly.
>
> Go to http://www.furnessbeekeepers.fsnet.co.uk and link to 'varroa
> calulator'.
>
> This gives an estimated total number of mites in the hive from the
> actual number dropped in a 24 hour period.
>
> The table is based on the MAFF calulator distribtued to UK beekeepers.
>
> HTH
>
> Jonty
The research undertaken by Dr. Martin is interesting and no
doubt adds to the knowledge base. As a paid-up member of
the cynics-club I suspect that the Varroa Calculator was a
way of justifying the cost of the research (paid for by beekeepers in
the UK).
I also believe that the Varroa Calculator has no practical
use for the beekeeper whatsoever.
When Varroa arrived in this part of the world the
recommendation was that if you had Varroa - treat for it.
As a consequence, within a couple of years, beekeepers
reported being hardly able to find a mite and 'beekeeping
life' returned to normal. Of course the mites were still
there but in relatively low numbers.
Dr. Martin's Varroa Calculator held out the promise that one only
had to treat once infestation levels rose above the 'economic
threshold'. Actually I don't know if Dr. M. actually used that
particular expression but the phrase has often been used by the
Varroa Calculator adherents.
Although Dr. Martin's conclusions were propped by a raft of
earlier results his work used no more than 30-40 colonies.
I'm afraid I no-longer have the exact figures because his
paper along with the Calculator were consigned to land-fill
many months ago.
DARG (Devon Apicultural Research Group) undertook a project to
evaluate the efficacy of an essential oil based Varroacide some
years ago. The point here is not the results of the trial (which are
still on the www somewhere if anyone is interested) but the data
which was collected. The trial required a pre-application
measurement of 'natural mortality' for 7 or more days, some
beekeepers undertook daily counts for several months prior to the
trial (Spring to Autumn/Fall), and a measurement of 'total'
infestation after the application of Bayverol/Apistan at the end of
the season. Of course the 'total' was an estimate based on the
efficiency of pyrethroid treatments (then apparently 98-99%).
I still have the data on floppy disk somewhere (I hope!) and
have spent many an hour looking at them in the light of the
Varroa Calculator. My conclusions are:
Natural mortality (especially when averaged over just a few days) is
an extremely poor predictor of colony infestation, varying by a
factor of 1:10. In other words, two colonies might both show a
daily drop from natural mortality of 1, yet one colony might have an
infestation level of 100 mites and the second 1000.
Natural mortality can vary by a factor of 3 from one week to
another. The Varroa calculator is calibrated in months. In
other words a colony might show a drop of say 2 per day
averaged over 7 days yet the next week might show a drop of
6 per day the very next week (within the same month).
Either of these two factors alone would suggest that the
Varroa Calculator is well nigh useless.
Because of the data collected by DARG members (over 250,000
mites were counted) it is possible to apply the Varroa
Calculator retrospectively. The results confirm my previous
points.
Joe Hemmens
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