It shouldn't surprise anyone that selection of bees for tracheal mite
   resistance, in its detail, is not as simple as indicated by a summary.
 
   However, it doesn't take much detailed monitoring of ( 20 to 50)  hives
   of a variety of origins, to be convinced that a range of susceptibility
   to tracheal mites exists (and this, including it's inheiritability, has
   been amply demonstrated with, among others,  Page and Gary's
   publications in 1989).
 
   The ranking of test lines, by introducing newly emerged bees of known
   origin into an infested hive, measures one aspect of resistance which
   can be thought of as "attractiveness" of a bee to mites (its actual
   mechanism may be something else).
 
        Here's some possible mechanism's to think about (maybe someone will
   test them). Young bees of a particular line may not become infested
   because they "smell" more like old bees, or they start to smell like old
   bees, at a younger age than other lines. 2. Newly emerged bees of a
   "susceptible" line may move from the brood nest (surounded by young
   bees, with no migrating mites) out to the "forager" area of the hive, at
   an earlier age, 3. Resistant bees may groom their nestmates more
   frequently and thereby reduce the mite's reproductive success (this
   trait would be a characteristic of the host colony, rather than the
   introduced test bees, so might not be selected in the test we used.
   However, if resistant bees also groom themselves more, it could be
   reflected in what we might think of as "reduced attractiveness").
 
   I've worked in cooperation with the British Columbia Bee Breeders'
   Association since 1989, in a project to select from within existing bees
   in Canada, lines with resistance to tracheal mites which also have
   superior beekeeping qualities.
 
   We did several generations of selection (using the new bee mark and
   retrieve method) and crossing in isolated yards, then tested the results
   on a whole colony basis. (The simultaneous introduction controls to a
   great extent, for Jerry Bromenshenk's concern about variation in time of
   year: the host colony is what it is, for all lines. Ranking indicates a
   difference in the line's susceptibility). That was an important test.
   The mites in the host colony had a great choice in bees to infest, a
   real smorgasbord. If a particular line was slightly unattractive, it
   might be ignored (suggesting high resistance). In an individual colony,
   however, mites don't have such a choice. (You might never eat mutton and
   brussels sprouts at a smorgasbord, but you wouldn't go hungry if they
   were all you had.. OK you get the point. I lost my appetite too).
   Our observations of the correlation of "resistant" ranking of marked
   bees, and relatively low mite populations in colonies, indicated that it
   was a good measure. (Medhat Nasr did a larger test in Ontario and found
   the same thing).
 
   We haven't had the problem of great variability of tracheal mite
   populations mentioned by Dr. Bromenshenk. Generally mite counts in
   specific colonies changed on a trend which could be measured (and
   distinguished bewteen colonies) by 50 bee samples on a 2 month interval.
   We first used 1 month intervals, but cut back to 2 (or sometimes longer)
   to reduce cost. This was adequate to distinguish differences between
   groups (lines) but may not have been suitable for precise distinction of
   small differences between individual colonies, which Jerry might
   require.
 
   In 1993 and 1994, lines of the selected B.C. stock were compared to
   lines of Buckfast stock imported directly from Europe by Guelph
   University, and to unselected lines from Ontario and B.C. The comparison
   was duplicated in B.C. and Ontario (2 projects with coordinated
   protocol) and involved 144 hives. The hives were started at about 15 %
   of bees infested, and monitored for 2 year. The analysis did become a
   bag of snakes in some ways (variable conditions, small sample size after
   2 years) but it was clear that in relatively unfavorable conditions
   tracheal mites increased substantially more (beyond 50 % of bees
   infested) in the unselected and Buckfast stock, than in the selected
   B.C. stock (below 20 %). In good conditions (crops above 200 lb per
   hive) the resistance differences appeared to be not biologically
   significant (all less than 20 %).
 
   The conclusion?
   Tracheal mite resistance is available to be selected in the bees in
   North America.
 
    Natural selection will eventually cause the North American bee
   population to become resistant. A selection program based on new bee
   marking and retrieval can speed the process (artificial insemination
   too, although we didn't use it). Too radical a selction might unduly
   reduce the beneficial variation in stocks, so I wouldn't advocate
   everyone getting or even aiming at, one best stock.
 
   Of course there will be deceptive advertising, and also honest mistakes.
 
 
   Kerry Clark, Apiculture Specialist
   B.C. Ministry of Agriculture
   1201 103 Ave
   Dawson Creek B.C.
        V1G 4J2  CANADA          Tel (604) 784-2225     fax (604) 784-2299
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