In early June, at a Bay of Plenty branch field day to discuss
the then recent varroa outbreak in New Zealand, Dr Denis
Anderson of the CSIRO spoke to us with some optimism regarding
the long term future for varroa control.  *My* understanding of
what he had to say was that it would be related to the discovery
of the 'trigger' that initiated reproductive behaviour within
the cell by the mite.  He was a bit cagey and loathe to provide
too much detail due to the untested aspects of what he was
implying.  I'm including below my notes from his talk on that
day, as it is an interesting overview of varroa in general...

Dr Denis Anderson

From CSIRO (Commonwealth Scientific and Industrial Research Organisation), Australia.

Returned to Australia 11 years ago after working as bee pathologist in NZ.  At that time,
varroa was just on Australia’s doorstep, in Papau New Guinea.  Recent work has indicated
that there is in fact a new name for the varroa we know on Apis mellifera, Varroa destructor.
Various ramifications to that finding that he’ll discuss in the talk.

Varroa was not originally on our honey bee, Apis mellifera.  It is on Apis cerana throughout
Southeast Asia, and exhibits similar behaviour.

Varroa was originally found in Java in the early part of this century by a man named Jacobson.
It was described by Odemanns, and it was in fact a new genus.  There are not other varroa like
mites - it is the only one in that genus.

About 50-60 years ago, varroa appears to have ‘jumped hosts’ to our honey bee.  There are in
fact three species of varroa already named: jacobsoni, underwoodi and rinderera.

When Denis first started working in Irian Jaya/Papua New Guinea, he found amazing
behaviour.  The mites in PNG (which would have come originally from Java) were not
reproducing on Apis mellifera!  Other researchers around the world had taken own direction,
and didn’t seem especially interested in the finding, or had other explanations of their own.
Published this in 1994 in Apidolgie.  Only researcher who took interest was a German bee
scientist, so Denis worked with him over the next few years.

Considered that the failure to breed was in some way related to either:
* resistant bees
* genetically different mites
* some environmental factors

Bred 40 sister queens in Australia and sent 20 to Germany (where there was varroa present)
and put 20 in PNG.  The colonies in Germany were soon killed completely by varroa, but the
PNG colonies remained.

Took DNA out of the mites in the two places and compared it.  Found 6.7% difference in
mtDNA on chromosomes which should not have been much different at all - this was a *big*
difference.  Published this in 1998 in the Journal of Apicultural Research.

Decided at this stage to go back to look at varroa on its natural host, Apis cerana.  Did DNA
sequencing from the varroa found on cerana throughout SE Asia, with very wide geographical
sampling.  For the mites all considered to be 'jacobsoni', found in fact about 6 species.  Very
tidily geographically confined - jacobsoni was confined for the most part to Indonesia and
Malaysia.  Another species (which is now being called destructor) found mostly in mainland
Asia.  Some others, others unresolved (which will perhaps lead ultimately to other new
species) from both Philippines and Sri Lanka.

Destructor is significantly larger body size than jacobsoni, and not so round.  The two cannot
interbreed.

Did more extensive testing on the COIII gene.  Again, the distribution turned out the same, with
differences from mainland Asia to the Indonesian groupings, and still the unresolved
differences in Philippines and Sri Lanka.

Then did survey for varroa found in 32 countries on Apis mellifera.  Found that there had been
two types of the mite that had in fact changed over to mellifera from cerana - now called the
Korean and Japan/Thailand types).  Korean most widely distributed, even where cerana is
present.  It is this one that is present in Europe, US, etc.

The Japan/Thailand type present and now spreading out of Brazil, explained by the fact that
honey bees were taken to Brazil from Japan in 1972.  This type now spreading into US from
the south.

Published this all in Journal of Experimental and Applied Acarology.  Easier to read review
now available from Apidologie.

Ramifications of this all.  There is a name change to contend with, from Varroa jacobsoni to
Varroa destructor.  Said that after presenting the paper in Canada, beekeeper said the
change in name shouldn't be too hard for them.  They'd only just gotten used to saying "My
bees have VJ", so the change would be interesting...

Impacts on bee trade and quarantine issues, with two species involved.  Bee management
and control methods may well be impacted.  Even destructor is not especially good at
breeding on mellifera - does not manage the necessary 'signal' to initiate reproduction, so the
development is not especially good (though obviously good enough to kill!).  This weakness
could lead to some form of permanent control method, if the signal could be disrupted or
changed in some way.  Finally, all previous research needs to be reviewed in terms of the fact
that there are two different species involved.

Denis wanted to make a special acknowledgement to the ACIAR (Australian Centre for
International Agricultural Research) who has been far-sighted enough to continue to fund his
work, along with CSIRO his direct employer.

Denis then moved into a detailed description of the varroa lifecycle.  Varroa enters the cell in
the pre-capping stage and buries itself upside down in the brood food.  Once the larva has
eaten most all the food and turns around preparing to pupate, mite moves onto position on
abdomen.  Moves from there to sit on the wall of the cell for a time.  Once the larva has
finished pupating, mite rejoins and begins to feed.  About 70 hours later, lays first egg.  First is
male, then generally about 5 females.  They develop in the cell before the bee emerges.  Male
mates with his sisters then dies.  Females come out of the cell with the bee to continue the
process.  Eventually re-enter a cell to repeat the cycle.  Goal is to develop some means of
moving the signal 'out of the range' so that mite will fail to reproduce.

Future control mechanisms for varroa were discussed.  European methods appear to be
moving from straight chemical control, to use of such things as organic acids.  Spring often
mechanical controls (variations on drone brood trapping of the mites to keep their number
down).  Later, uses of organic acids (such as formic acid, as spot treatment or longer).
Autumn treatment with chemicals as required.  Avoids continuous treatment.  Goal is to reduce
mite numbers through the winter period - if you can't do this, numbers rise too quickly in the
main part of the season.

Question about Russian queens sold in US for resistance.  Rinderer took bees from Russia,
near area of original changeover to mellifera, and bred them.  Being released to beekeepers
as unmated queens.  Possible resistance, but not clearly shown yet.

Denis was confident that some form of final control method could be found.  Expected it could
take about 3 years to identify the 'signal' that he referred to (as he has a fair idea of what it is
already).  From then, should be relatively easy to develop some means of delivery.

Discussed finds of Apis cerana (from PNG) in Australia, one of which did have jacobsoni.
Difficulty in explaining to beekeepers that they didn't have to worry, as even if it *did* get out
into the mellifera population, it would not breed.


  (\      Nick Wallingford
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  (/      NZ Beekeeping http://www.beekeeping.co.nz

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