> 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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