How to Sample Bees for a Varroa Mite Count

Contributed by Dewey Caron

Mite monitoring is good bee stewardship. It lets you know precisely how the bees are doing and how successful everything you may have done for mite management so far this season has helped the bees. Monitoring means taking the pulse of the colony – are they holding their own or are the mites getting to harmfully high levels?

Mite monitoring can be done in a number of ways. Looking for phoretic mites on adult bodies or percent of drone brood cells with developing mites is highly intrusive as we have to open the hive but it also is not very accurate – it says the hive has mites but not how many mites? Using a sticky board is less disruptive, especially if you have a screen bottom board or bottom that has a built-in sticky board for monitoring, but is tedious in counting the mites, takes two visits (to put the boards in and then remove them) and, for some, difficult to count, especially with lots of hive debris. It is a measure of colony mite load.

( Editor’s Note: Randy Oliver compared natural mite drop monitoring versus using a wash. His conclusion? “Practical application:  I’ve lost faith in the natural mite drop as a means of monitoring mite levels.  It is handy when used to determine whether a miticide gives a quick knock down, but not so much to indicate the biologically relevant level of mite infestation.  If one does use stickyboards as their only monitoring method, might I suggest that you take counts over a period of time.”

Also: Many in the research community have gone to using the alcohol wash of 300 bees from the broodnest as their standard method of mite assessment. The suitability of the alcohol wash is supported by extensive sampling and statistical analysis by Katie Lee for her doctoral research (Lee, KV, RD Moon, EC Burkness, WD Hutchison and M. Spivak (2010) Practical sampling plans for Varroa destructor (Acari: Varroidae) in Apis mellifera(Hymenoptera: Apidae) colonies and apiaries. Journal Of Economic Entomology 103(4):1039-1050.

Washing adult bees of mites is a measure of colony mite intensity. It does necessitate entering the colony as we prefer to take a sample of 300 adult bees from 1-2 brood frames. It is however the best measure of how your bees and you are doing in resisting/tolerating mites. [for a review of mite sampling and what numbers mean, I suggest looking at my HONEY BEE BIOLOGY AND BEEKEEPING, revised edition, Chapter 19, pages 315-317.

Here in summary is the best way to take an adult bee sample and determine colony mite intensity: (Editor’s Note: There is a photo essay of this sampling technique on ScientificBeekeeping – Mite Monitoring Methods under Taking the Sample.)

1. Remove ~300 adult bees from brood comb into a mason jar (to the 1⁄2 cup mark) in which you have replaced the lid with an 8-mesh screen, fit snugly into the ring closure. Do this by moving wide-mouthed jar down the comb so bees “fall into” the jar. Alternately shake 2-3 brood frames into a bucket and then scoop out 1⁄2 cup bees into a jar with solid lid replaced by 8-mesh screen.  Make very sure that the queen is not on the frame before collecting bees. It is not essential to use a frame with brood on it according to Randy Oliver).

2. Place modified screen lid on jar; tap jar to settle bees on bottom.

3. Add rubbing alcohol through the screen top to kill the bees. Alternately, place 2 tablespoons of powdered sugar onto bees (through screening).

4. Close jar and shake/roll bees for 20–‐30 seconds. Set aside for 30 seconds so sugar ends up coating bees (you do not need to do this if you use alcohol]. Re-shake vigorously another 20-30 seconds.

5. Set the jar in the sun for a few minutes if you are using powdered sugar (the ‘bake’). This has been shown to increase the accuracy of the count using the sugar shake.

6. Invert and shake sugar and mites from jar onto white collecting paper or pan [if using alcohol pour liquid into a white pan]. Put a little water into the pan or mist spray to dissolve sugar if you used sugar.

Shaking mites out from an alcohol wash for counting.

Shaking mites out from an alcohol wash for counting. (Courtesy Dana Rose)

7. Count the number of mites and calculate the percent infestation of adult workers: (# mites/#bees divided by 100]. If unsure you have a thorough count, repeat with more sugar/alcohol.

8. If infestation is over 2% (i.e more than 6 mites, assuming 300 adult bees] consider the hive at risk and if mite number is approaching or over 5% (10-15 mites) consider immediately using a mite reduction management chemical (Apivar, Apiguard, ApiLife Var, MAQs, Hopguard II] or dividing the colony into several smaller units [brood break]. Follow up with another sample at end of recommended treatment period. (Apivar treatment takes 42-56 days).

The Honey Bee Health Coalition has developed a great video on sampling for mites. Check out their site for more great information on managing varroa.