The Bawden Assay: A Better Method for VSH Breeding Selection and Varroa Sampling
- Trevor Bawden
- 22 hours ago
- 5 min read
Lloyd Street Bees has big news for all the beekeepers! There is a new varroa sampling and mite resistant breeding tool in town and we created it.
The journey of creating the Bawden assay
Monitoring for varroa has been a critical task for beekeepers since its arrival to North America in 1987. The three most common forms of varroa sampling are the alcohol wash, screened bottom board and the sugar roll - the most frequently used being the alcohol wash. The first stage of development of the alcohol wash used today was produced in 1976 by honey bee researcher, Stolbov. This method was refined to use simple alcohol by De Jong et al, 1982. The version we are likely most familiar with is the simplified method made popular by Randy Oliver. Not much has changed in this process since those developments. However, we have learned that the worker brood will almost always contain more mites than the phoretic mite sample found using the alcohol wash. To get a true sample of the colonies varroa load, we must search inside the capped brood - which the alcohol wash cannot do.
This brings us to the work of Harbo et al, 1997. While work on better understanding mite reproduction had occurred already, it was the work of Dr. Harbo that focused on identifying a mechanism for mite resistance using varroa detection in the brood. Later known as the VSH assay. This produced a high level of confidence for the user, as they would know what the true varroa load is inside the colony. But there are glaring drawbacks to this method. It is extremely time consuming, requires extensive training/practice and there is a high barrier to entry due to the equipment required.
I spent my beekeeping career trapped between these two methods. I saw the merits of both, the simplicity of the alcohol wash and the accuracy of the VSH assay for better sampling and a tool in queen breeding. After having done thousands of alcohol washes and hundreds of VSH assays, I started to think about how we could simplify this process and combine the best abilities of both these sampling methods. What if we had a sampling method that was quick, cost effect and highly reliable? Even better, it can be used a queen breeding tool to select for mite resistance and works at any time of the field season! It was this point that the Bawden assay was created.
I spent my beekeeping career trapped between these two methods. I saw the merits of both, the simplicity of the alcohol wash and the accuracy of the VSH assay for better sampling and a tool in queen breeding.
The Bawden assay
The Bawden assay was developed by Trevor Bawden, owner of Lloyd Street Bees, and provides an extremely quick, cost effective and easy method for accurate varroa and mite resistance sampling that requires very little training. This novel assay utilizes the varroa infestation in capped brood as a key detection tool for varroa resistant queen breeders. The Bawden assay was field trialed on 50 colonies. This was done alongside the traditional mite wash, the Harbo VSH assay and the uncap/recap assay on all 50 colonies used in the experiment. In this article, we will briefly show how the Bawden assay stacks up against the competition with the field data Trevor and his team collected. Trevor Bawden currently has a paper under review in collaboration with Zac Nelson, Edward Hsieh and Dr. Elizabeth Walsh. Because this publication is currently under review, we will not be able to share every detail of data yet. Once the paper is published, you will be able to read a copy here on the Lloyd Street Bees website.
Before continuing to read this article, we encourage everyone to read the protocol first to be able to better understand what is being said moving forward. This is a current copy of the protocol which has been sumbitted and is under review.
Why the Bawden assay?
The most prolifically used mite sampling method implmented by beekeepers is the traditional alcohol wash. The issue with this method is that it only samples the phoretic mites on the bees, not mites developing in the capped brood. It is well known that varroa prefer to stay within a brood cell and multiply instead of being vulnerable on a bee. Because of this, the traditional alcohol wash underrepresents the varroa load in the colony. Using the Bawden assay, we sample approximately 200 capped brood cells in the purple-eye-tan-body stage or older, using a faster new novel protocol. This allows the beekeeper to surmise exactly what the current varroa load is in the colony accurately. When compared to the traditional alcohol wash, the Bawden assay found a significant difference in the amount of mites collected per sample. Beekeepers can use the Bawden assay as a tool to accurately monitor their varroa loads and also determine the efficacy of their mite treatments much more reliably. One further benefit to the Bawden assay is that the chances of the beekeeper killing their queen during the assay are greatly diminished, since all the bees must be removed first before the assay can take place.
Using the Bawden assay as a VSH queen breeding tool for mite resistance
The Harbo VSH assay relies on sampling 200 capped brood cells of purple eye tan body or older pupae and inspecting for varroa. The Bawden assay follows this same process, but removes the costliest and time-consuming parts. Those being the individually opening of all the cells individually, cost of equipment and also the extensive training it takes to perform the Harbo VSH assay correctly. To summarize, the Bawden assay does the same thing, but 5 times faster and with very little cost or training involved. We found no statistical difference between the accuracy of the Harbo VSH assay and the Bawden when sampling for mites and predicting their breeding potential. Simply put, the Bawden assay is just as accurate as the Harbo VSH assay for assessing varroa counts in the capped brood.
The Bawden assay can be used to screen a yard of 50 colonies for their levels of VSH mite resistance in an afternoon compared to the days it would take using the Harbo VSH assay. We recommend that users of the Bawden assay use this tool as a prescreening for breeder queen selection in their yards. Once this screening is complete, the user can choose to conduct the more time-consuming Harbo VSH assay on the top 10% of the colonies that scored the highest marks. We consider the Harbo VSH assay the gold standard of breeding tools still, but the Bawden assay is a highly streamlined process for first screening and identifying colonies with mite resistant breeding potential.
What’s next for the Bawden assay
We have lots of data to share with everyone in the near future once the paper has been published. Please check back with us and keep an eye out for the announcement of more details via our newsletter.
Citation
Stolbov, N. M., Vasikov, N. A. 1976. An apparatus for discovering the varroa mite. Pchelovodstvo (8): 17 (In Russian)
De Jong, David, Roger A. Morse, and George C. Eickwort. "Mite pests of honey bees." Annu. Rev. Entomol 27.1 (1982): 229-252.
Harbo, J. R., R. A. Hoopingarner, and J. W. Harris. "Evaluating honey bees for resistance to varroa mites: procedures and results." (1997): 223-224.