Blane White wrote:

> Varroa mites resistant to Apistan are also resistant to Bayvarol.  In
> fact, this cross resistance it one of the strongest indicators in the
> field apart from actual bioassy that
> you are in fact dealing with resistance not just a bad batch of control
> strips.  You will need to use something else with a different mechanism
> of action to control such
> varroa.  Options include formic acid and other organic acids such as
> oxalic acid and thymol as well as the coumaphos which you mentioned.  As
> for where the
> resistance came from - much speculation of course but likely the varroa
> population that was introduced to UK already had a fair amount of
> resistance to pyrethoids.  The
> most likely source of mites of course is the mainland where such
> resistance seems to be pretty widespread now.
>


Medwin Bew, head of the CSL National Bee Unit has asked me to post the
following comments in response:

> 1. My laboratory is dealing with the resistance case in the UK. The most
> likely cause is through local misuse of Apistan and not natural spread
> of resistant mites. The Channel provides a natural barrier to mite
> migration either from natural or human movement of bees and makes this
> route much less likely.
>
> 2. We have been using pyrethroids in the UK since 1992. Mites may become
> resistant to any chemical used routinely against them. Of course, misuse of active
> ingredients of treatments or the treatment themselves rapidly
> accelerates resistance onset.
>
> 3. The first case of pyrethroid resistance in the UK was found by
> apiculture staff of my laboratory through a routine field screening
> programme that includes both spot checks and targeting of sites where
> treatment misuse is suspected. More information may be found on our
> website (http://www.csl.gov.uk). The resistance problem was entirely
> predictable and why we set up routine screening in the first place. It
> is likely that other pockets of resistance will come to light as field
> tests by ourselves and beekeeper organisations coninue.
>
> 4. Most areas of England and Wales we have tested have shown mite
> numbers too low to provide valid tests or mites that are showing normal
> pyrethroid susceptibility. Either way controls are working over the
> majority of the country so far. The message to beekeepers outside the
> resistant area is carry on using pyrethroids if that is your normal
> control method, but test colonies routinely for resistance (we provide
> methods to do this) and keep an eye on information coming from our
> website or via our press releases that go to the beekeeping
> associations. Above all the message is follow the treatment label to the
> letter and don't be tempted or panicked into using so called treatments
> of very dubious origin that a few people are peddling around the place
> at the moment. It will only take one case of high residues in honey (we
> have routine honey surveillance under EU rules) to wipe out consumer
> confidence in the honey market.


James
--
___________________________________________________________________________
James Morton

South-Eastern Regional Bee Inspector
Central Science Laboratory
National Bee Unit
Tel/fax: 020 8571 6450
Mobile:  07719 924 418
E-mail: [log in to unmask]
CSL website: http://www.csl.gov.uk
National Bee Unit website: http://www.csl.gov.uk/prodserv/cons/bee/
___________________________________________________________________________