Hygienic behavior which reportedly confers some resistance to AFB is said to
be carried on recessive genes.  If this is so then there are advantages and
disadvantages.  It is difficult to eliminate a recessive gene. You cannot
identify it to destroy it until the parent, which does not display it
herself, carrying it has reproduced offspring which reveal that mum is a
bearer of the gene.  Then you have to prevent further reproduction from that
mother and all her children and seek out and destroy any that have already
done so.

That is on the presumption that a single gene is responsible when simple
Mendellian ratios will apply - heterozygote crossed with heterozygote will
produce 25 per cent homozygote dominant, 50 per cent heterozygote and 25 per
cent homozygote recessive.  It is only the Hz recessive which will be
hygienic.  If more than one gene is involved, which is more than likely, then
we are entering the realms of higher mathematics which are beyond me.  I am
sure that several of our scientific correspondents will produce formulae
which can be applied (please!).

Using the simple single gene presumption the beekeeper will have to test his
bees for hygienic behavior early in the season before drones are flying.
There are several simple ways of doing this.  With reasonable luck and a
large enough sample a quarter of the colonies will be relatively hygienic.
The rest must be culled and replacements bred from the recessives.  The loss
need not be as drastic as this seems at first sight.  All you need to kill
are selected queens and drone brood.  With careful uniting and subsequent
splitting and requeening with queens reared from the hygienic stock you could
be getting back to original numbers by the end of the season, but they will
be proportionally more hygienic than when you began.  With open mating it
will be some years before you reap the benefit of flooding the neighbourhood
with recessive drones but with perseverance it will come.
Chris Slade