Bob Harrison wrote:

>Bailey wrote( many years ago):
>> was wrongly attributed to the mite, which causes no overt symptoms.

No, Bob. Not many years ago. It was in "Experimental and Applied
Acarology" 25: 745–749, 2001.

He goes on to say:

The high incidence of the tracheal mite found in North America during the last
two decades of the last century have caused much concern there (Morse
and Flottum
1997). However, this concern is much influenced by the very common
misapprehension,
which arose when the mite was first discovered in Scotland about 1918
(Rennie et al. 1921), that it causes the Isle of Wight disease.

The mathematically deduced hypothesis of Royce et al. (1991), that the adoption
of modern beekeeping techniques in Britain about 1900 diminished the swarming
of bees and increased the drifting of bees between colonies to cause
"devastating
mite epizootics", is completely contrary to the actual events.
Infestation decreased
greatly and spontaneously in Britain since records began about 1920,
notwithstanding
the predominance of modern beekeeping techniques throughout the
century (Bailey and Perry 1982). Royce et al. (1993) observed that
feral bee colonies
are less infested than those of beekeepers and suggested that this is because
feral colonies swarm more. Our alternative interpretation, based on
the facts given
in this paper, is that isolated feral colonies experience less
competition, and so forage
more intensively than beekeeper's colonies, which are usually kept in close
groups.

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