Hi all
Regarding mite sampling, any one of them is going to be useful. The main thing is to be consistent and have a clear aim. For example, the following are excerpted from the Coloss Beebook:

4.2. Measuring colony infestation rate  

4.2.1. Acaricide treatment 
Use an effective acaricide > 95% product as per manufacturer recommendation. Beware of resistance of mites to this product. 

1. A protected bottom board should be used to prevent bees removing the fallen mites. The protection is typically a wire screen with 34 mm holes covering the whole surface of the board, leaving no access for bees to the fallen mites. 
2. Ant protection should be put in place to prevent their access to the hives and predation on fallen mites and therefore biasing the number of mites counted.
3. Given the rapid action of efficient acaricides and to ease counting, mite fall should be assessed daily. See sections 4.2.4. ‘Natural mite fall’ and 4.2.5. ‘Subsampling mites’, to count mites on a bottom board 

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. 

4.2.3. Measuring the infestation rate of brood and adult bees 
4.2.3.1.2.1. Powdered sugar 
4.2.3.1.2.2. Ether wash 
4.2.3.1.2.3. Warm/soapy water or ethanol (75%) 

1. Collect 200–250 bees from both sides of at least 3 unsealed brood combs. 
2. Kill the bees in a container filled with alcohol 
3. Stir the container for 10 min. 
4. Separate the bees from the mites by pouring the alcohol over a sieve with a mesh size of approximately 2–3 mm.  
None of these three methods is distinctly superior to the other and they can all be considered as reliable given that mite separation is done in a standardised manner  

4.2.4. Natural mite fall 
This method is based on the quantification of naturally dead mites. … Various studies gave contradictory conclusions regarding the accuracy of the natural fall method to determine total infestation rate since natural mite fall is largely determined by the amount of emerging infested brood (Lobb and Martin, 1997), but it is in general considered as a good indicator of colony infestation (see Branco et al., 2006). 

Pros: nondestructive/ noninvasive, fast, no need to open the hive depending on design; reliable for noncollapsing colonies with brood; this is a method providing relative quantification that can be used for comparison between colonies within an experiment, not across studies. 

Cons: sometimes unreliable, death rate may vary according to colony status, season, bee race, climate (regional variations possible), amount of brood; little is known on the influence of these factors on mite death; specific equipment necessary.  

http://www.coloss.org/beebook/II/varroa/4/2

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