>
> >If it is true that mites enter cells randomly, why does drone trapping of
> varroa work?  Or does it?


Good question Larry.  There are a apparently a few factors involved that
increases the probability of a mite entering a drone cell.  The best
experimental data that I've seen on this subject is by Fuchs (his thesis,
and papers in 1990 and 1995).

Due to the drone cell's larger size, and the greater amount of feeding
visits required by a drone larva, there is more chance of a mite-carrying
nurse bee sticking her head into a drone cell than into a worker cell.
Couple that with the observation that there is a longer "open" period for
invasion of drone cells than for worker cells.  And finally, the kairomonal
cue of a drone pupa to trigger a mite to climb off her ride is much
stronger from a drone than from a worker prepupa.

The end result is that any drone cell has a greater probability of being
entered than a corresponding worker cell.

If a colony is experimentally set up with ONLY drone brood (as Fuchs did),
nearly all the mites can be trapped pretty quickly.  But if there is
competing worker brood, then only a proportion of the mites will enter the
drone brood.

So it's important to take into account the *percentage* of precapping-age
drone pupa at any given time relative to the percentage of 8-day worker
brood.  For example, at a realistic ratio of 5% drone brood, Fuchs found
around 35% of the mites entering drone brood.

>Could we just remove any brood at random and achieve the same reduction in
mite population?

Yes, but you'd need to remove a greater percentage of worker brood to
remove the same number of mites.  It generally makes more sense to remove
drone brood.

What I discovered when modeling mite population dynamics is that the
percentage of drone brood in a colony theoretically makes a big difference
in the rate of mite buildup.  That said, we run a drone frame in each of
our hives, and remove those frames (with the trapped mites) from all our
hives (other than selected drone mother hives) when we split our hives
after almonds.  When I've previously checked, I often could not find a mite
in that drone brood.

Tell you what, we are in the process of making splits for the next few
weeks, and will be pulling out nearly a thousand drone trap frames.  I'll
check some to see how prevalent mites are in the drone frames.

--
Randy Oliver
Grass Valley, CA
www.ScientificBeekeeping.com

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