Bob Harrison wrote

> If A melifera and A. cerana are almost identical then Why  can varroa
> not reproduce in A. cerana worker cells?
>
> The obvious difference is size 4.7mm A.cerana 5.4mm A.melifera.

What is meant by "almost identical"?  I believe they are poles apart as has
been my experience in quarantine work.  We were looking for ways to develope
to detect cerana and kept comparing cerana to mellifera and kept coming up
against a barrier.  The classic example was with pheremones.  We tried to
use mellifera pheremone to attract cerana and it did not work.  We ended up
having to develope a pheremone just for cerana.  It could be the case that
it will only work on Apis cereana javana and not on the other subspecies but
we do not know at this stage.  So don't make the same mistake I made in
thinking that mellifera and cerana act similarly.  The only common factor,
as I see it, is that they both collect nectar and turn it into honey. Oh and
they also sting.

Varroa does enter the worker cells of cerana and can be found in worker
cells.  However there is some trigger that is not present that that cues the
female varroa to lay eggs.  Is it cell size?  Is it chemical?  Is it
pheremone related?  However, when Varroa destructor transferred over to Apis
mellifera, it received the same signal from both workers and drones but
Varroa jacobsoni does not receive the same signals.  If it was purely cell
size, why then does jacobsoni not reproduce on mellifera in larger cells?

When thinking about cell size why should it be that the size will determine
if the female varroa will lay eggs or not?  In the early stages of pupation,
the pupa does not fill out the whole of the cell so there is plenty of room
for the female varroa to lay egs.  If cell size was the criteria and did not
allow the young varroa to develop because there was not enough room then you
should be able to see dead underdeveloped varroa in the cell with the
pupating bee.  Has this ever been seen?

For the record, I would be in favour of a scientific experiment to check out
the cell size theory but at this point in time I am not convinced by the
cell size theory.  I believe it is some trigger, as outlined by Dr. Denis
Anderson, that determines if the female varroa lays eggs.  Beekeepers should
read Dr. Anderson's work as it was not until he published that we knew that
there was more than one species of varroa.  The pathogenic species attacking
mellifera was being called Varroa jacobsoni but is now called Varroa
destructor.

Trevor Weatherhead
AUSTRALIA