Know your honey bee colonies: non-destructive testing for varroa mites

Varroa mites (Varroa destructor) were accidentally introduced into the U.S. in 1987 and rapidly became a destructive pest of honeybees. Not only do varroa mites suck the blood (haemolymph) of the bees, they transmit disease through this feeding and generally weaken colonies (Rosenkranz et al. 2010).  Low infestations of varroa mites left without mitigation can develop into a serious problem for a hive.

It is recommended you test your honey bees for varroa mites periodically throughout the season. Here in Minnesota, we test for varroa in spring (May), in late August or early September, and then after treatment has been on for the recommended time, sometime in September. It is important to understand all aspects of your colonies so you can make informed decisions about treatment/intervention, but also so you know what might be causing problems in your hives.

There are a number of things to look for that indicate a hive is VERY infested with mites.  The BIP Tech Teams pay special attention to these things when assessing colonies. They are Deformed Wing Virus (DWV) (Fig. 1) , Parasitic Mite Syndrome (PMS) (Fig.2), and very small bees.

Fig. 1 Honey bee with Deformed Wing Virus (DWV)  photo credit: Rob Snyder

Fig. 1 Honey bee with Deformed Wing Virus (DWV).  Her wings are shrunken and curled. photo credit: Robert Snyder

 

Fig. 2 Parasitic Mite Syndrome (PMS) includes sunken brood sometimes with a mite present, chewed pupae, holy pupal cappings and white mite frass on the top of frames.

Fig. 2 Parasitic Mite Syndrome (PMS) includes sunken brood sometimes with a mite present, that passes the AFB “stick test”, chewed pupae, holey pupal cappings and white mite frass on the top of cells (not visible in this photo because of angle). Photo credit: Rob Snyder

Powdered sugar tests are simple, give immediate results, and are inexpensive to administer.   The bees get coated in powdered sugar, the mites fall off because they cannot hold on to the adult bee coated in slippery powder, and then the bees are returned to their hive to be cleaned by their sisters.   Also, the test is done in the field, so you don’t have a bunch of samples to assess later, and you are able to take action right away if necessary.

Gary Reuter and Marla Spivak, at the U of MN, have a free-to-download, easy-to-follow sheet on how to administer a powder sugar test to measure mite levels. (“Powdered sugar roll for Varroa mites on Honey bees”)  A sample of ~300 bees is dislodged from a brood frame,  covered in powdered sugar,  shaken into a white container, and the number of mites per 100 bees is found (If 300 bees, divide the number of mites by 3) (Lee et al. 2010).

http://www.beelab.umn.edu/prod/groups/cfans/@pub/@cfans/@bees/documents/asset/cfans_asset_317466.pdf

 

 

 

 

The simple equipment for the powdered sugar test include:

  1. quart or pint canning jar with a ring lid (or something similar)
  2. 8×8 hardware cloth mesh circle
  3. powdered sugar
  4. a white bowl or bucket
  5. optional: a piece of metal flashing long enough to catch any bees you shake from a frame

It is important to keep good notes on your hive health, your mite numbers, and the actions you take in your colonies. You will be able to get a better picture of the health of your bees if you are able to track what is happening over time.

If a hive dies and gets robbed out, the mites (and diseases such as AFB and chalkbrood) can be transferred to robber bees which can then transfer the mites to the robbers’ colonies. Mites are also transferred through honeybee drift, where bees from one hive end up in a neighboring hive. (Frey and Rosenkranz 2014)

Consider signing up for Bee Informed Partnership’s Survey to share your results and see what’s happening with the bees through out the U.S.

Click on this icon at the top right of this page to sign up:

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References:

*Frey, E., & Rosenkranz, P. (2014). Autumn Invasion Rates of Varroa destructor (Mesostigmata: Varroidae) Into Honey Bee (Hymenoptera:  Apidae) Colonies and the Resulting Increase in Mite Populations. Journal of Economic Entomology, 107, 508–515. doi:10.1603/EC13381

*Lee, K. V, Moon, R. D., Burkness, E. C., Hutchison, W. D., & Spivak, M. (2010). Practical sampling plans for Varroa destructor (Acari: Varroidae) in Apis mellifera (Hymenoptera: Apidae) colonies and apiaries. Journal of Economic Entomology, 103, 1039–1050. doi:10.1603/EC10037

*Reuter, Gary and Marla Spivak, “Powdered sugar roll for Varroa mites on Honey bees”,  (link: http://www.beelab.umn.edu/prod/groups/cfans/@pub/@cfans/@bees/documents/asset/cfans_asset_317466.pdf)

*Rosenkranz, P., Aumeier, P., & Ziegelmann, B. (2010). Biology and control of Varroa destructor. Journal of Invertebrate Pathology, 103, S96–S119. doi:10.1016/j.jip.2009.07.016

Written By: Chris Kulhanek

Chris Kulhanek has written 3 post in this blog.

Chris has been keeping bees for 5 years and has worked for the University of Minnesota Bee Lab for the last three bee seasons. She assisted in fieldwork with Bee Informed Partnership for the last two years. She has a Bachelor of Science in Biology, with a Chemistry minor, and a Masters of Science in Entomology. She particularly enjoys sharing her adoration for insects with others and is proud she has been a "weird bug girl" for more than 20 years.

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  • Andrew Dewey

    Hi Chris,

    I’ve always been told that the sugar shake (or testing for Varroa with powdered sugar) is not all that accurate. Has something changed? The only thing I can think of is that you are looking not so much at the particular counts, but comparisons of the counts as a way of indicating trends. But this is not exactly new either.

    Please don’t get me wrong – as a practitioner of alcohol washes I would love an accurate non-destructive test.

    Would you please address this?

    Thanks,

    • Alexander Jones

      Hey Andrew, I believe there’s been studies to show that the efficacy of sugar rolls is high, somewhere close to 90% effective as Alcohol washes and I know BIP is recommending the use of sugar rolls for backyard beekeepers working on their own using the documentation provided by Marla Spivak’s UMN Bee Lab.

      Ah, here it is. Macedo (2002)
      http://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1179&context=entomologyfacpub

      • Abi molnar

        If your worried about sugar roll accuracy and your already doing alcohol rolls, do your sugar roll first. Then alcohol the bees, giving you a sugar count and an alcohol count. The two numbers, mites per sugar divided by total mites from alcohol and sugar roll,gives you an error coefficient you can multiply times future sugar rolls counts to give you the true count with out killing bees. I’ve seen this coefficient vary from 1.1-3.5 depending on the beekeeper. 10%-350%error.

      • David Durden

        Is it OK to put powdered sugar on all of the bees while bearding on the front of the box ?

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