Resistance to disease and pests differs considerably between subspecies and between lines. It is a criterion worth weighing when choosing a queen.

Where resistance comes from

Resistance rests largely on specific behaviours:

• Hygienic behaviour: Detecting and removing infected or dead brood
• Varroa-sensitive hygiene: Targeting cells in which mites have reproduced, interrupting their cycle
• Grooming behaviour: Bees removing mites from one another
• A shorter capped stage: 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 and developed these defences. It lives in balance with the mite.

The western honey bee has no such history, which is precisely why the mites are devastating to it.

Tolerance is not immunity

Clear tolerance has been described in some populations, usually groups that lived under mite pressure and underwent natural selection.

But tolerance is not immunity. Even with tolerant lines, monitoring and treating when necessary remain essential.

Regional differences

A resistant line that performs well in one region does not necessarily do so in another; resistance behaviours are influenced by climate and forage conditions.

A resistance claim should therefore not be accepted without testing 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

What a beekeeper can do

• Measure hygienic behaviour and rear from the highest-scoring colonies
• Compare mite growth between colonies under equal conditions
• Leave drone comb in selected colonies
• Requeen poorly performing colonies

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