Allen and the rest of the list :
 
Allen.  I am continually impressed by the way you think.  I think your ideas
are interesting and concisely expressed.  I look forward to sitting down and
talking with you again.  But back to these ideas on Varroa resistance :
 
At 10:12 AM 7/1/97 -0600, you wrote:
 
>Yes, you have very clearly outlined my thinking on this.  As far as I can
>see, either mechanism (elimination of virtually all individuals except
>those with a previously existing trait, or recent mutation) is a
>reasonable explanation.  As far as which is more likely, I really don't
>know.  And of course the question is which actually occured here.
>In effect, one in a million chance is as good as a 100% chance if the
>number comes up.  I doubt we will ever know which happened.
 
I think there are several areas of investigation which would help us
understand how Varroa adapts to selective pressures imposed on their
populations [be the pressures a pesticide like apistan, mineral oil, or
wintergreen oil, or resistant characters (e.g. quicker larval development,
worker hygenic behavior, smaller cell sizes) among their hosts].  Studies of
Varroa mating systems and population gentics and the way Varroa populations
respond to intense selective pressures would help resolve matters.  Also, it
would be useful to know how fast Varroa populations not exposed to intense
selection will respond to intense selective pressures by evolving
resistance.  I don't think this is a necessarily safe experiment to conduct,
but it would be interesting to see how fast resistance to Apistan occurs
under different levels of treatment, at different levels of infestation,
etc..  (perhaps the risks of conducting such an experiment would be smaller
in areas where fluvalenate resistance is already endemic (e.g. Northern
Italy) although I would not bet the house on that).  Alternatively it might
be interesting to see how costly resistance is to mites, and see how quickly
a resistant mite population reverts to being suseptible after treatments are
relaxed.
 
>An aside: Of interest is that their host (our honeybee is also -- fairly
>uniquely among cold blooded critters -- fluvalinate resistant) and I will
>introduce a third -- and some will say preposterous -- suggestion, and
>that is that the mite got it's fluvalinate resistance from the bee.  I
>remember reading in Discover magazine some time back that DNA had been
>proven to have been carried from on host to another by a common parasite
>and that somehow, a characteristic from the first host had been
>'transplanted' by the parasite and subsequently became established in the
>second host.
 
Oh yah, good idea.  Somebody in the states conducted an experiment that
demonstrated that mites of fruit flies are either able to vector genes
between fly populations or incorporate genes from the flies into their own
genomes (I can't remember which). I think in honeybees such a pheomonon may
be difficult to demonstrate since we know very little about the honey bee
genome compared to fruit flies (this is a wild guess.  Maybe it would be
easy to design an experiment to demonstrate this.. I do not know).
 
>Anyhow, what we do know is that there are many different subvarieties of
>varroa, and the varroa one person has may not be the same as the varroa
>that is found a few states -- or a few miles -- away.  This has not been
>the case with other bee pests that we are used to, like AFB,  EFB and
>chalkbrood as far as we know (excepting of course, the known
>recent emergence of Tetracycline resistant AFB in South America).
>
>With the other diseases, we could assume AFB is AFB, and not worry if we
>got an exotic variety, because as far as we could tell there weren't any.
 
Does anyone know, apart from resistance to antibiotics which does not seem
to vary, do any of the brood diseases vary in virulence (or other characters
that might indicate the evolution of disease subpopulations or demes) ?
 
>With varroa, each time we bring in new varroa to an outfit, we are bring
>in a new population.  The results of mixing their population with our
>own may be unpredictable, since each has a distinct genetic experience to
>contribute to a new blend. Varroa may be fast 'learners'.
 
I am not sure that Varroa populations show that much variation between
outfits.  There was some DNA work that looked for Varroa race differences
among large geographic areas (i.e. among continents), but nothing that
indicates apiary to apiary differences.  I think the kind of population
fragmentation Allen is proposing would only be posssible if mites in one
apiary could not breed with mites in another apiary very well (i.e. gene
flow between apiaries was very very small).  When gene flow stops between
local populations, population differentiation (and even speciation) can
occur because there isn't the interbreeding to keep evening things out every
generation. Again this boils down to the question of how inbred are Varroa
populations (a question that seems more and more relevant the longer this
thread runs on).
 
>I think we are just starting to get an idea of where this can go.  Unless
>we can get a mechanism that they cannot *ever* adapt to (like
>suscepibility to oil), we are doomed to find that controls expire in
>effectiveness without warning and often.
 
Will someone explain to me why resistance to oils cannot develop ?  If I
understand the mechinism by which mineral oil is hypothesised to work (and
excuse me if I miss important details), mites die because their spiricles
get clogged up with oil.  I would not be so certain to say mites cannot
evolve resistance to mineral oil.  Resistance may not evolve as fast as does
for apistan (maybe it will - I do not think anyone knows), but I believe as
long as any treatment imposes such a heavy selective pressure on the mites,
resistance is a strong possibility (especially if the population needn't
have any previous variability for the resistant character - see Allen Dick's
mutation hypothesis).  The same goes for characters that confer Varroa
resistance in honey bee populations, if these character's significantly
reduce the fitness of Varroa, Varroa likely will evolve counterresistance.
I am afraid there are no silver bullets in Varroa management if the strategy
involves dusting mites off (more stable strategies would give Varroa a way
to reproduce without causing damage to the workforce - the apparent case
with A. cerana where Varroa spends its energy only on drone brood).
 
This thread has been very interesting to me.  I hope more people will join
in and expand these ideas further.
 
Adony
 
 
 
 
 
 
>As I mentioned before, I heard of an oil fogging machine being used to
>introduce an aerosol of an oil into beehives back when the tracheal mites
>were first becoming a problem in North America.  I don't know what
>happened to the idea. I have been unable to obtain details.
>
>Allen
>
>
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** Adony P. Melathopoulos *********
*** Center for Pest Management ****
**** Simon Fraser University ******
***** Burnaby, British Columbia ***
****** Canada, V5A-1S6 ************
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