Date: Tue, 28 Jan 1997 08:29:02 -0800 (PST)
From: "Kerry Clark of AGF 784-2225 fax (604) 784 2299"
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Subject: Re: Surviving Varroa
Survival with varroa and without treatment is not necessarily an
indication of resistant bees. In some situations, survival of a
colony can result from the type of varroa, rather than some
characteristic of the bees.
Buchler 1994, in Bee World 75 (2): 54 - 70 (this good review of
varroa tolerance is available at the IBRA website) mentions an
isolated apiary in Austria where colonies have been maintained with
varroa and without treatment for 8 years. One explanation might be
that resistance or tolerance has been selected in the bees.
However, when unselected bee stock is brought (without varroa) into
the area, it too becomes only moderately infested and does not
require treatment. The key difference seems to be that 50 to 60 %
of these varroa in worker brood are infertile.
de Guzman's work in detecting 2 different types of varroa in North
America might be a step along the way toward benefiting from this
type of observation. I think this was reported at ABRC, but I
wasn't there. Can anyone who attended, add a comment?
Selection of "less pathogenic" tracheal mites might also be
happening throughout North America, at the same time as
"resistance" may be building in bee stock.
By the way, although many of these discussions use "tolerance" and
"resistance" (to varroa) interchangeabley, it seems to me that
tolerance implies no effect on the (former) harmful agent, while
resistance would include (but maybe not be limited to) mechanisms
that inhibit the source of the harm. eg. a bee stock that is
tolerant of tracheal mites, might show no lower infestation than
other stocks, but would do better in spite of it. A bee stock that
is resistant to tracheal mites would show consistently lower
infestations (with the same tracheal mite population).
Is this distinction consistent with usage of these terms in
parasitology?
If so, it seems to me we should be referring to varroa being
selected showing "tolerance" to fluvalinate, rather than
"resistance": Where varroa have been selected and are no longer
controlled by fluvalinate, I don't imagine that there is any less
fluvalinate in the hive environment, the mites are just tolerating
it more.
Regards
Kerry Clark, Apiculture Specialist
B.C. Ministry of Agriculture, Fisheries and Food
1201 103 Ave
Dawson Creek B.C.
V1G 4J2 CANADA Tel (250) 784-2231 fax (250) 784-2299
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