Resistance to disease and pests varies markedly between subspecies and lines. It is a criterion worth considering when choosing a queen.

Where resistance comes from

Resistance comes mostly from particular behaviours:

• Hygienic behaviour: Recognising and removing infected or dead brood
• Varroa sensitive hygiene: Targeting cells in which mites have reproduced, interrupting their cycle
• Grooming: Bees removing mites from one another
• A shorter brood period: Less time for the mite to raise offspring

All of these are heritable and can be selected for.

The natural model

Apis cerana evolved alongside Varroa and Tropilaelaps over millions of years and developed these defences. It lives in balance with the mite.

The western honey bee has no such history, which is why the mites are destructive in it.

Differences between subspecies

Marked tolerance has been reported in some populations, generally groups that have lived under mite pressure and undergone natural selection.

But note: tolerance is not immunity. Monitoring and, where necessary, treatment are still required in tolerant lines.

Regional variation

A resistant line performing well in one region may not do the same in another; resistance behaviours are affected by climate and forage conditions.

A claim of resistance should therefore not be accepted without being tested in your own conditions.

Trade-offs

Resistance traits sometimes come with others:

• Some tolerant populations are more defensive
• Some swarm more often
• Some build smaller colonies

These have to be weighed in the selection.

What a beekeeper can do

• Measure hygienic behaviour and rear queens from those scoring highest
• Compare the rate of mite increase between colonies
• Leave drone comb in selected colonies
• Requeen colonies performing poorly

These four steps make a marked difference within a few years, without buying any special line.