4.2.2. Whole colony estimate
This method requires killing the whole colony. This is necessary when the real infestation rate of a colony is needed. Indeed, the use of acaricides is under these circumstances not appropriate since their efficiency is not 100 %.
1. When all foragers are in the colony (early in the morning, late in the evening or at night) close the hive so that no bees can escape.
2. Place the whole colony in a freezer.
Depending on nutritional status and size, colony survival in a freezer will vary. To determine when the colony died, workers from the centre of the cluster can be sampled and left to thaw. If they do not wake up, the whole colony can be considered dead and used for mite counts. In case the colony is of large size, gazing with CO2 is required before freezing. This will prevent the bees thermoregulation and entering in the cells. Thermoregulation extends the duration needed to kill the colony and if bees get into the cells, they will be more difficult to collect for mite counting.
3. Refer to section 4.2.3. ‘Measuring the infestation rate of brood and adult bees’ for phoretic and brood infestation rate measurement.
If a measurement of total infestation rate is needed in summer, the colony can be made broodless by caging the queen for three weeks. When all the brood runs out (after 21 days if only worker brood was present or 24 days if drone brood was present), all mites have become phoretic. There is then no need to look for mites in the brood.
Pros: provides the exact total number of mites in a colony.
Cons: destructive, high workload, tedious.