Hello All

I am grateful for the responses under the subject 'Resistant mites in the
UK'. I have tried below to carry out a summary of the various points made,
and I shall be glad of additional comments.

When varroa first appears in a country it moves through the
country,resulting initially in a patchy varroa presence, largely caused by
beekeepers moving infected hives. In the varroa infected area, many feral
colonies, and colonies maintained by non-compliant beekeepers, will remain
viable for some time. These colonies generate what might be termed, a
'varroa reservoir'. This reservoir can infect beekeepers' colonies, because
the beekeepers' colonies rob out these reservoirs or the reservoirs abscond
to the beekeepers' colonies. Thus the mite presence in colonies can change
dramatically in a short space of time. This phase in the establishment of
varroa could be referred to as the 'unstable' phase. And we assume that this
varroa phase is entirely populated by mites which have no resistance to
Bayvarol/Apistan (acaricide).

During this phase, the use of Integrated Pest Management (IPM) treatments
would be most unwise since the mites generated by the varroa reservoir can
easily overwhelm IPM treatments resulting in major or total losses. Indeed
during this phase, losses will probably occur even in colonies treated by
the acaricide, since reservoir generated varroa can hit hives when the
treatments are not in the hives, and push the mite threshold into the danger
zone.

The first question that comes to mind is how do we know when the unstable
phase has come to an end and has been replaced by the stable phase? What
tests can we carry out to determine this? First it must be said that the
transition from instability to stability is not IMHO a sudden event, rather
it is a process where the level of stability can waiver backwards and
forwards for some time. Presumably when we feel that stability is
approaching, we can move to IPM and monitor mite drop very carefully. And
then we may have to occasionally use the acaricide to establish how many
mites are left on the bees by the IPM approach. If we do not like the
results here, i.e. if we see too many mites, then we may have to continue
for some time longer with the acaricide. This obviously  requires work and
commitment, not necessarily what some beekeepers have the time or
inclination for (not a criticism, just a statement of fact.)

When the 'stable' phase has arrived then the threat of re infestation from
the varroa reservoir must be diminished, and ultimately must be close to
zero. (I would imagine that most of the UK is stable, but it is probably
several years distant in Ireland due to the later detected varroa
infestation in 1998). At this stage, IPM treatments can be considered. And
it is probably at this stage that resistance by the mites to acaricide is
gaining ground, since acaricide has been in use for some years.

For IPM to be successful, a mite monitoring system is essential. Since the
IPM is not as 'sure fire' as the acaricide we must ensure that the mites are
not getting the upper hand. Thus mite fall measurement, carried out on a
regular basis and interpreted in conjunction with tables of such falls is
essential. An apparently healthy hive producing a lot of honey can suddenly
collapse in the Spring, because the beekeeper did not know that the mite
infestation had exceeded the threshold.

It would thus appear that there is a case for embarking on IPM to eliminate
the problems caused by resistance. Indeed some would suggest that there is
no case for not doing so. Even if resistance to the acaricide remained, it
would not matter, since the mite is now resistant to a product which we are
not using against it.

I would read 'resistance' as the ability of the mites to change biologically
or behaviourally, to more readily handle the counter measures which we are
hurling against them. I would speculate that if we all used open mesh
floors, and the claimed 15% of mites lost through falling were true, that
the mites over time could develop a better system for fastening themselves
to the bees. Likewise if we used the drone brood entrapment system
vigorously, presumably this could cause the mites to re appraise their
liking for drone brood and perhaps concentrate on the worker brood to defeat
us. Similarly if 4.9 cells are causing varroa to be less successful in
reproducing, they would alter some of their biology to counter this. I have
no idea as to whether varroa could ever instigate resistance to grease
patties or to treatment using powdered sugar. But I suppose that given
enough time, and if the mite is 'experiencing major losses' through any
treatment, that a response to that treatment by the mite could conceivably
be expected. But much of this is speculative, and unlikely to cause present
day beekeepers a problem.

So if we are using some or all of the above IPM treatments, and thereby
attacking the mite on several fronts at the same time, it must mean that
like an army so attacked, that any of its responses must be diluted and are
therefore less effective individually. Does this explain why the mite has
become resistant to Bayvarol/Apistan in the course of 10 years or so, since
it could concentrate its response resources in one direction only?

On the face of it at least, it would seem to me that by using the IPM
approach, we need never get to the Coumaphos level. Indeed if we do not use
the IPM approach, and we get to the Coumaphos level, all we have done is
generate super mites against which we have no acaricide defence, so that IPM
then becomes the only option. And now we have created a highly polluted hive
environment which could take a long time to eliminate, not to mention the
extra work and the writing off of wax resources, and possibly severely
compromising public confidence in hive products.

And is it not the case, that IPM gives us the breathing space we so sorely
need, to enable the final answer to varroa to be perfected? At present this
would seem to be the development of varroa resistant bees, such that this
resistance will remain in an open mating environment? Perhaps a tall order,
but there is increasing evidence that this possibility is becoming more than
just a pious hope.


Sincerely

Tom Barrett
Dublin
Ireland