> I checked mite levels again in early October, after the autumn honey
> had been removed, and found that mites were high again, or my formic
> treatment had failed. I used Apivar(first chemical strips used since
> 1999) and lost only one hive that I can blame on varroa(strong hive,
> great production, found dead early winter). This year, with late
> spring(last frost May 28), I find almost no varroa, so will forgo
> formic acid mitewipes unless my next varroa count, late next week,
> indicates otherwise. I use oxalic in early December.
Something to remember is that formic treatments reduce risk of tracheal
mite problems, even when applied for varroa. In fact, formic is quite
effective for acarine even though much less reliable for varroa.
The TM load or susceptibility of a yard of bees to TM is relatively
difficult to assess. Acarine resistance and prevalence are variable
from low to high across North America. TM resistance is not a dominant
trait and yards that were never bothered by TM may become susceptible
after queens change either naturally or by requeening with outside stock.
Whether Apivar has a significant effect on TM or not is a question I
have not seen clearly decided. My impression from keeping my ear to the
ground is that it does, and the widespread use of Amitraz in the US may
account for the lack of reports of TM kills recently although recent
reports from ARS seems to indicate that TM resistance in US stocks is as
variable as when surveyed a decade previously.
Another explanation is that people see what they expect to see and that
TM is as bad as ever. Could it be that many 'varroa' kills, especially
with low varroa loads, were actually hastened by an undetected
co-infestation with TM.
Pulling bees apart to detect TM is laborious and although it was de
rigeur before varroa, I don't know if anyone does it anymore.
Nonetheless, TM is still here and still doing the same harm it always
did - AFAIK, but is masked by other concerns.
In the talk of resistance to amitraz and fluvalinate evolving, an
important point that slips below the radar came up in this post made ten
years ago:
http://community.lsoft.com/scripts/wa-LSOFTDONATIONS.exe?A2=BEE-L;PWMGnQ;200310180744440600C
and AFAIK, has been largely ignored.
A treatment does not have to kill mites to be effective if stunned mites
drop to where they cannot get back on a bee.
Although the instructions that come with strips like Apistan and Apivar
do not mention additional considerations which might increase efficacy,
smart beekeepers have found that treatments made in shoulder seasons
when the bees are up off the floor and nights can be cool require fewer
strips and are far more effective, although I have never seen this
documented. Using open bottoms or screens during strip treatments could
improve efficacy considerably where partial resistance is a factor.
My impression is that Apivar (Amitraz) is a safer chemical than Apistan
(fluvalinate-tau) for bees, beekeeper and hive products, but I don't
have any conclusive data on this. Maybe our researchers can comment.
It seems clear that Apivar works really well and that even after many
years of use, it continues to be the best synthetic available. As for
Apistan, it may be working again, especially if used for knock-down and
not expected to kill without a mite trap (oil) or an open bottom below.
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