In message <[log in to unmask]>, Robert Brenchley
<[log in to unmask]> writes
><<The darker bees from northern Europe generally are more resistant to
>tracheal mites. >>
>
>    If this is the case, why was A. mellifera mellifera  in Britain so
>susceptible in 1920?
There are many myths in beekeeping and this was one. Read Beowulf
Cooper's The Honeybees of the British Isles BIBBA 1986 for a summary of
his findings. From memory it was more the crosses with Italians and the
Italians which were susceptible to the IOW disease. The native dark bee
is alive and well, though mongrelised somewhat, except where natural
selection kept it going (before varroa). For example in Scotland, Murray
MacGregor's Carniolan crosses which hew uses in his migratory setup
revert over the years to native and he introduces new Carniolans. Here
in West Cornwall we have little sign of acarine damage. Nosema is more
obvious and a new pocket of European Foul brood is proving difficult to
eradicate. Brother Adam is one of the main proponents of the "native bee
is dead" myth.
The IOW disease turns out to be one of the viruses which are propagated
rather well by varroa, I think it is now thought to be the Slow
Paralysis Virus which caused it. Acarine may well have been the
stimulus.
--
James Kilty